The Change of Climate and Ecological Environment in China 2021: Synthesis Report: Synthesis Report 9819944864, 9789819944866

Table of contents :
530049_1_En_OFC
530049_1_En_BookFrontmatter_OnlinePDF
Funded by
Editorial Board of the Series of The Change of Climate and Ecological Environment in China: 2021
Editorial Board of The Change of Climate and Ecological Environment in China 2021: Synthesis Report
Foreword by Jianguo Hou
Foreword by Guotai Zhuang
Preface I
Preface II
Introduction
Contents
530049_1_En_1_Chapter_OnlinePDF
1 Introduction
1.1 Evolution of Global Climate and Ecological Environment
1.1.1 Impact of Human Activities on the Earth’s Environment and the Livable Earth
1.1.2 Impact of Human Activities on Global Climate Change
1.1.3 Impacts and Risks of Climate Change on Natural and Human Systems
1.2 Historical Evolution of Climate, Ecological Environment and Socio-economic Development in China
1.2.1 Overview
1.2.2 Historical Changes in Climate, Ecological Environment and Socio-economic Development
1.2.3 Contemporary Changes in Climate and Ecological Environment
1.2.4 Changes in Modern Social and Economic Development
1.3 Future Changes and Transformation and Development
1.3.1 Future Changes and Risks in Climate and Ecological Environment
1.3.2 Actions to Deal with Climate Change and Protect Environment
1.3.3 Transition to Sustainable Development
1.4 Contribution of China’s Assessment Reports on Climate, Environment and Ecology
1.5 Overview of This Assessment
References
530049_1_En_2_Chapter_OnlinePDF
2 Observed Climate Change and Ecological Environment Evolution and Their Causes
2.1 Observed Facts
2.1.1 Atmosphere
2.1.2 Hydrosphere
2.1.3 Cryosphere
2.1.4 Ecosystem
2.1.5 Planetary Environment
2.2 Extreme Events
2.2.1 Extreme Temperature Events
2.2.2 Extreme Precipitation Events
2.2.3 Typhoon and Severe Convective Weather
2.2.4 Sand-Dust Storms and Haze
2.2.5 Cryospheric Events
2.2.6 Forest Fire Weather
2.2.7 Compound Extreme Events
2.2.8 Attribution of Extreme Events
2.3 Impacts of Human Activities on Climate Change in China
2.3.1 Impact of Human Activities on Atmospheric Composition and the Generated Radiative Forcing
2.3.2 Impact of Human Activities on Surface Solar Radiation and Surface Air Temperature in China
2.3.3 Impact of Human Activities on the East Asian Summer Monsoon Circulation and Precipitation in China
2.3.4 Impact of Human Activities on Extreme Climate Events in China
2.4 Large-Scale Factors Affecting Climate Change in China
2.4.1 East Asian Monsoon
2.4.2 Main Modes and Teleconnections of Atmospheric Circulations
2.4.3 Ocean Modes
2.4.4 Arctic Sea Ice and Snow Cover on the Qinghai-Tibet Plateau
2.4.5 Snow Cover in Eurasia
2.5 Impacts of Climate Change on Socio-economic Systems
2.5.1 The Impact Extent of Climate Change on Socio-economic Systems
2.5.2 Regional Differences in the Impact of Climate Change on Socio-economic Systems
References
530049_1_En_3_Chapter_OnlinePDF
3 Projections of Future Climate Change and Risks
3.1 Anthropogenic Drivers of Future Climate Change
3.2 Earth System Models and Integrated Assessment Models
3.2.1 Earth System Models
3.2.2 Regional Climate Models
3.2.3 Integrated Assessment Models
3.3 Projections of Future Climate Change
3.3.1 Temperature
3.3.2 Precipitation
3.4 Projection of Changes in Extreme Events
3.4.1 Temperature Extremes
3.4.2 Precipitation Extremes
3.4.3 Compound Extreme Events
3.5 Exposure and Vulnerability
3.5.1 Observed Exposure and Vulnerability Changes
3.5.2 Possible Changes in Socio-economic Exposure and Vulnerability to Rainstorms and Flood Disasters
3.5.3 Possible Changes in Socio-economic Exposure and Vulnerability to Droughts
3.5.4 Possible Changes in Population Health Exposure and Vulnerability to Heatwaves
3.6 Future Climate Change Risks
3.6.1 Water Resources
3.6.2 Agriculture
3.6.3 Cryosphere
3.6.4 Ecosystem
3.6.5 Human Habitat
3.6.6 Human Health
3.6.7 Major Projects
References
530049_1_En_4_Chapter_OnlinePDF
4 Adaptation and Mitigation: Measures, Actions and Effects
4.1 Climate Change Adaptation
4.1.1 Global Progress
4.1.2 Adaptation Strategies
4.1.3 Adaptation Technologies and Measure Options
4.1.4 China’s Adaptation to Climate Change: Actions and Effects
4.2 Climate Change Mitigation
4.2.1 Global Progress
4.2.2 Mitigation Technology and Measure Option
4.2.3 China’s Emission Reduction Policies and Effects
4.2.4 Emission Reduction and Effects in China
4.3 Synergized Effects of Adaptation and Mitigation
4.3.1 Adaptation, Mitigation and Their Interactions
4.3.2 China’s Synergized Adaptation and Mitigation Measures, Actions and Effects
4.3.3 Adaptation and Mitigation Strategies Under the Goals of the Paris Agreement
References
530049_1_En_5_Chapter_OnlinePDF
5 The Development Pathways with Climate Resilience
5.1 Global and China’s Carbon Emission Budgets and Implementation Pathway Under the Warming Targets of the Paris Agreement
5.1.1 Global and China’s Carbon Emission Budgets
5.1.2 Global Emission Reduction Pathways
5.1.3 China’s Emission Reduction Pathways
5.2 Addressing Climate Change and the Sustainable Development
5.2.1 The Linkage Between Addressing Climate Change and Sustainable Development Goals
5.2.2 Climate Resilience and Risk Management
5.2.3 Addressing Climate Change and Air Pollution Control
5.2.4 The Linkage Between Addressing Climate Change and Other Systems
5.2.5 Tackling Climate Change and Eradicating Poverty
5.2.6 Addressing Climate Change and Fairn Ethics
5.3 Global Climate Governance to Help Build a Community with a Shared Future for Mankind
5.3.1 Global Climate Governance System and Its Challenges
5.3.2 Sustainable Management Concept of Earth System and Scientific Assessment Support
5.3.3 Coordinate International and Domestic Efforts to Actively Tackle Climate Change
5.4 Addressing Climate Change: Our Shared Future
References

Citation preview

Dahe Qin · Yongjian Ding · Panmao Zhai · Lianchun Song · Yong Luo · Kejun Jiang

The Change of Climate and Ecological Environment in China 2021: Synthesis Report

The Change of Climate and Ecological Environment in China 2021: Synthesis Report

Dahe Qin · Yongjian Ding · Panmao Zhai · Lianchun Song · Yong Luo · Kejun Jiang

The Change of Climate and Ecological Environment in China 2021: Synthesis Report

Dahe Qin China Meteorological Administration Beijing, China Panmao Zhai Chinese Academy of Meteorological Sciences China Meteorological Administration Beijing, China Yong Luo Department of Earth System Science Tsinghua University Beijing, China

Yongjian Ding Northwest Institute of Eco-environment and Resources Chinese Academy of Sciences Lanzhou, China Lianchun Song Chinese National Climate Center China Meteorological Administration Beijing, China Kejun Jiang National Development and Reform Commission Energy Research Institute Beijing, China

ISBN 978-981-99-4486-6 ISBN 978-981-99-4487-3 (eBook) https://doi.org/10.1007/978-981-99-4487-3 Jointly published with Science Press The print edition is not for sale in China mainland. Customers from China Mainland please order the print book from: Science Press. ISBN of the Co-Publisher’s edition: 978-7-03-075985-6 © Science Press 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publishers, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publishers nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publishers remain neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

Funded by

Science and Technology Service Network Program (STS Program) of the Chinese Academy of Sciences (CAS): Climate and Ecological Environment Evolution: 2021(KFJ-STS-ZDTP-052) Special project on climate change of China Meteorological Administration Climate and Ecological Environment Evolution in China

v

Editorial Board of the Series of The Change of Climate and Ecological Environment in China: 2021

Editor-in-Chief: Dahe Qin Deputy Editors-in-Chief: Yongjian Ding (Executive), Panmao Zhai, Lianchun Song, and Kejun Jiang Members: Quan Bai, Qinghua Cai, Wenjia Cai, Qingchen Chao, Fahu Chen, Sha Chen, Shiyi Chen, Wen Chen, Xi Chen, Xianyao Chen, Yaning Chen, Ying Chen, Shenghui Cui, Chunyan Dai, Wei Deng, Yihui Ding, Hongmin Dong, Wenjie Dong, Wenjuan Dong, Debin Du, Maosheng Duan, Chuanglin Fang, Shengbo Feng, Bojie Fu, Sha Fu, Qingzhu Gao, Qingxian Gao, Rong Gao, Xiang Gao, Xuejie Gao, Yun Gao, Peng Gong, Daoyi Gong, Daming He, Cunrui Huang, Lei Huang, Yao Huang, Dabang Jiang, Tong Jiang, Hui Ju, Liping Kang, Shichang Kang, Chunlan Li, Xinrong Li, Xun Li, Yongqi Li, Yu’e Li, Zhanbin Li, Zhenyu Li, Hong Liao, Erda Lin, Guanghui Lin, Guobin Liu, Guohua Liu, Hongbin Liu, Qiyong Liu, Shaochen Liu, Lijuan Hong, Yali Luo, Yong Luo, Xunmin Ou, Xuebiao Pan, Zhihua Pan, Chen Peng, Shilong Piao, Jiawen Ren, Xuemei Shao, Changchun Song, Buda Su, Fubao Sun, Jianqi Sun, Song Sun, Ying Sun, Zhenqing Sun, Xianchun Tan, Fei Teng, Zhiyu Tian, Chenghai Wang, Chunyi Wang, Dongxiao Wang, Genxu Wang, Guofu Wang, Guoqing Wang, Jiangshan Wang, Jun Wang, Ke Wang, Wenjun Wang, Xiaoming Wang, Xuemei Wang, Zhili Wang, Jiahong Wen, Zongguo Wen, Jidong Wu, Jianguo Wu, Qingbai Wu, Shaohong Wu, Tonghua Wu, Tongwen Wu, Jun Xia, Cunde Xiao, Xinwu Xu, Ying Xu, Jianchu Xu, Denghua Yan, Xinyan Yang, Xiu Yang, Zhicong Yin, Guirui Yu, Kefu Yu, Yongqiang Yu, Zhiming Yu, Xiang Yu, Jiahai Yuan, Hua Zhang, Jianguo Zhang, Jianyun Zhang, Qiang Zhang, Renhe Zhang, Xianzhou Zhang, Xiaoye Zhang, Yinsheng Zhang, Yongchuan Zhang, Zhiqiang Zhang, Chunyu Zhao, Jingyun Zheng, Yan Zheng, Botao Zhou, Dadi Zhou, Guangsheng Zhou, Sheng Zhou, Tianjun Zhou, Jianhua Zhu, Liping Zhu, Rong Zhu, Songli Zhu, Yongguan Zhu, Guiyang Zhuang, Juncheng Zuo, and Zhiyan Zuo Secretariat: Shengxia Wang, Xinwu Xu, Yuping Yan, Chao Wei, Rong Wang, Wenhua Wang, and Shijin Wang Technical Support Unit: Rong Yu, Lanyue Zhou, Jianbin Huang, Chao Wei, Yingying Liu, Lei Zhu, and Shengxia Wang

vii

Editorial Board of The Change of Climate and Ecological Environment in China 2021: Synthesis Report

Editors-in-Chief: Dahe Qin, Yongjian Ding Deputy Editors-in-Chief: Panmao Zhai, Lianchun Song, Yong Luo, and Kejun Jiang Members: Ying Chen, Chunyan Dai, Wenjie Dong, Xuejie Gao, Yun Gao, Lei Huang, Tong Jiang, Chunlan Li, Chenyu Li, Hongbin Liu, Zhihua Pan, Shilong Piao, Fubao Sun, Jianqi Sun, Ying Sun, Guoqing Wang, Shaoping Wang, Shengxia Wang, Zhili Wang, Jidong Wu, Shaohong Wu, Cunde Xiao, Xinwu Xu, Jiao Yang, Xiu Yang, Zhicong Yin, Guirui Yu, Jianyun Zhang, Xiaoye Zhang, Botao Zhou, and Tianjun Zhou Technical Support Unit: Shengxia Wang, Xinwu Xu, Rong Yu, Shaoping Wang, Jianbin Huang, Chao Wei, and Yingying Liu

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Foreword by Jianguo Hou

The research on climate change and its impact has drawn the wide attention of the world. The global climate change assessments, especially by the Intergovernment Panel on Climate Change (IPCC), have been an important scientific basis for the international community in understanding the processes of climate change, identifying the level of its impact, and finding ways to mitigate it. Climate change is not only the change of climate itself, but also refers to the holistic changes in the five spheres of the climate system, i.e., atmosphere, hydrosphere, cryosphere, biosphere, and lithosphere (terrestrial surface layer). With a huge impact on the living environment and sustainable development of human beings, climate change is inextricably linked to society, economy, politics, diplomacy, and national security. From the perspective of science, the purpose of research on climate change is to reveal its rules, principles, and impact mechanisms, so as to provide a scientific basis for human beings to adapt to and mitigate it. Because of the complexity of the climate system, climate change covers all aspects of physical and social sciences. Carrying out studies in their own fields and from their own perspectives, researchers publish their latest research results about changes in the climate system every year. In recent ten years, an increasing number of research results on climate change have been published, showing the remarkable progress in the research of climate change. The complex climate system and the explosive growth of related literature and information keep countries and communities both concerned about how to summarize regular results of the changes in the climate system, reaching and how to formulate major consensus to guide the adaptation and mitigation of climate change. Therefore, the IPCC assessment reports on global climate, initiated by the United Nations and undertaken by the World Meteorological Organization (WMO) and United Nations Environment Program (UNEP), have attracted great attention. The scientific findings and work patterns of IPCC are also recognized widely. Located in East Asia and extending to the inland Winterland, China is affected by the monsoon climate and the westerly wind system as well as the weather and climate systems of the Qinghai-Tibet Plateau and Siberia. The weather and climate of China are also influenced by Arctic sea ice and snow cover in Eurasia. With global climate change, climate change in China shows prominent regional features. The xi

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frequent occurrence of extreme weather and climate events has led to increasing disaster losses. Therefore, according to the actual situation of China, referring to the working mode of IPCC, relying on a large number of existing research results on climate and environmental changes in China, combining the latest development trends, drawing lessons from international research norms, organizing multidisciplinary forces associated with natural science, social science, etc., and combining China’s actual needs in building a harmonious society and implementing the “Belt and Road Initiative”, it is of great scientific significance to make a comprehensive assessment of the ecological and environmental problems, regional vulnerability and suitability that China faces, and their impacts on regional social and economic development and the degree of security under the changing climate system and to form a high-level assessment report which has sufficient scientific basis and authority and is in line with international practices. The Chinese Academy of Sciences (CAS) attaches great importance to the research on climate change and has, jointly with China Meteorological Administration (CMA), organized several rounds of assessment to climate change in China. With the co-funding of CAS and CMA and the leading of CAS Academician Dahe Qin, nearly 200 scientists participated in the assessment research of the change of climate and ecological environment in China in 2021 this time. In the past three years, they have finished the following reports: (1) The Change of Climate and Ecological Environment in China: 2021 (Vol. I, Physical Basis), (2) The Change of Climate and Ecological Environment in China: 2021 (Part One of Vol. II, The Impact, Vulnerability and Adaptation of Sectors), (3) The Change of Climate and Ecological Environment in China: 2021 (Part Two of Vol. II, The Impact, Vulnerability and Adaptation of Regions), (4) The Change of Climate and Ecological Environment in China: 2021 (Vol. III, Mitigation), and (5) The Change of Climate and Ecological Environment in China: 2021 (Synthesis Report) (in Chinese and English). These assessment reports evaluate the changes of climate and ecosystem in China in the past and future, their impact, as well as adaptation and mitigation measures in a systematic way. Against the backdrop of the carbon neutrality announcement China has made, this report is scientifically vital for understanding climate change and also can provide a reference for various sectors in making carbon neutrality policies, serving as an important metric for the research capabilities of China in climate change. Here, I would like to express my heartfelt gratitude to the scientists involved in this assessment. I hope, on the basis of this assessment, the research on changes in China’s climate and ecological environment will register greater achievements. Beijing, China June 2021

Jianguo Hou Academician of Chinese Academy of Sciences President of Chinese Academy of Sciences

Foreword by Guotai Zhuang

Global warming has been an indisputable fact for nearly a century. The warming trend of the global climate system was further aggravated in 2020, with the global average temperature being about 1.2 °C above the pre-industrial level (1850–1900 average), making 2020 one of the three warmest years on record. The Global Risks Report 2021 released by the World Economic Forum, for the fifth consecutive year, listed extreme weather and the failure of mitigation and adaptation measures to climate change as the most significant environmental risks in terms of frequency and impact over the next decade. The international community has profoundly recognized that addressing climate change is the most serious challenge facing the world, and taking active measures against it has become the common will and urgent need of all countries. Complex and changeable weather and climate in China make it sensitive to global climate change. Climate change has led to more and more extreme weather and climate events, increasing meteorological disaster losses and climate risks, which pose serious threats to the security in food, water resources, ecosystem, environment, energy, major projects and economy. In September 2020, President Jinping Xi solemnly announced at the 75th session of the United Nations General Assembly that China will strive to peak CO2 emissions by 2030 and achieve carbon neutrality by 2060. This is a major strategic decision China made based on its responsibility to promote the building a community with a shared future for mankind and the inherent requirement to achieve sustainable development. In April 2021, President Xi put forward the six principles at the international leaders’ climate summit, strongly calling on the international community to shoulder its responsibilities with unprecedented ambitions and actions, work together to build a community of life for man and nature, and leave a clean and beautiful world to future generations. This not only shows China’s responsibility to promote global sustainable development vigorously, but also provides a feasible Chinese scheme for global green sustainable development. CMA, as China’s lead agency for the IPCC assessment report, is an institution specializing in climate and climate change research, operations, and services and has jointly organized and implemented the assessment of “Change of Climate and Ecological Environment in China” with CAS on two occasions. This round of xiii

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assessment brought together nearly 200 experts in the field of natural and social sciences from various sectors in China to analyze and assess the basic facts of the changing climate system, vulnerability of regional climate environment, and response to climate change in an integrated manner by focusing on the national construction programs such as ecological civilization, Belt and Road Initiative, Guangdong-Hong Kong-Macao Greater Bay Area, Yangtze River Economic Belt, and Xiong’an New Area. This assessment report summarizes and puts forward the latest research findings and viewpoints of Chinese scientists, strengthens the analysis and judgment of the situation of responding to climate change from the existing level of scientific cognition. Furthermore, it clarifies the scientific tasks of addressing climate and ecological environment changes. CMA, based on its positioning and responsibilities, has given full play to its advantages in climate change science, impact assessment and decision support, providing the whole chain of scientific support for the national response to climate change. It is expected that the next ten years will be a decade of social transformation, development, and technological change. To deal with climate change scientifically and reduce the potential risks caused by climate change at different timescales effectively, it is necessary to fully consider climate change factors in national territorial and spatial planning and construction and to promote the development of nature-based solutions (NBS) to reduce climate risks by actively adapting to climate change. In view of the impact of climate change on different regions and different ecological environments in China, it is necessary to strengthen the monitoring and assessment of environmental pollution, ecosystem degradation, biodiversity reduction, resource environment, and ecological deterioration in the context of climate change, accelerate the development of appropriate risk assessment and defense technologies, and establish an early monitoring, warning, and assessment system for climate change risks. It is of great significance to publish this book in the first year of the 14th FiveYear Plan period. This is a milestone of reference that will mean a lot to disaster prevention, mitigation and relief, climate change response, and ecological civilization construction under the carbon neutrality goal. We in CMA are willing to join hands with colleagues from all walks of life to forge ahead, pioneer, and innovate in order to achieve the established strategic goals of China’s economic and social development, making our due contributions to the well-being of all mankind and the great rejuvenation of the Chinese nation. Beijing, China April 2021

Guotai Zhuang Administrator of China Meteorological Administration

Preface I

At present, climate change, like the rising temperature, has become a major international hot topic and has attracted wide attentions from scientists, heads of governments, entrepreneurs, the general public, and other people from all walks of life. This is the result of the rapid warming of climate system caused by the massive emissions of greenhouse gases by human beings since industrial revolution and their serious consequences, which have caught humans off guard. The climate system, which involves five interdependent and interactive spheres: atmosphere, hydrosphere, cryosphere, biosphere, and lithosphere, is governed by a complex internal mechanism. Climate change research comes to all aspects of nature and humanities, and scientists in various fields of natural and social sciences are conducting extensive researches from their own perspectives. Carrying out scientific assessment of climate change is an important means for grasping the overall understanding level and research degree of climate change provided by the vast research literature. It is also critical for gaining a deeper view of climate change and its impact mechanisms, adapting to the impact of climate change by seeking advantages and avoiding disadvantages, and effectively mitigating climate change. The global climate change assessment, especially that conducted by IPCC, not only offers authoritative results in understanding global climate change, but also serves as scientific basis for international community to formulate policies to address global climate change. On this basis, the regional (European Union, EU) and national (USA, Canada, Australia, etc.) assessments of the mainly developed countries have played important scientific supporting roles in making regional and national climate policies. China’s climate and environmental assessment began in 2000 with the Research on Evolution Law of Ecological Environment and Sustainable Utilization of Water and Soil Resources in Western China, which was a major program of the Western Action Plan of CAS. The program set up the topic “Assessment of Environment Evolution in Western China” and systematically evaluated the climate and ecological changes in Western China. In 2002, the report Assessment of Environment Evolution in Western China (volumes I, II, III and comprehensive volume) was completed. Highly recognized by the scientific community, the report has played a good role in the implementation of the national strategy of the Great Development of xv

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Western China. In 2003, CAS, CMA, and the Ministry of Science and Technology of the People’s Republic of China organized the first national assessment of Climate and Environmental Evolution of China and published the report Climate and Environment Evolution of China (volumes I and II). The report laid the scientific understanding foundation for the subsequent national assessments of climate change. In 2008, CAS and CMA jointly organized the assessment “Climate and Environment Evolution in China: 2012 (the Second National Climate Assessment)”. Results of the assessment were contained in following series of books: (1) Climate and Environment Evolution in China: 2012-Physical Basis, (2) Climate and Environment Evolution in China: 2012-Impact and Vulnerability, (3) Climate and Environment Evolution in China: 2012-Mitigation and Adaptation, and (4) Climate and Environment Evolution in China: 2012-Synthesis Report, which is a summary of the core findings of the above three volumes. To sum up, based on both international practices and China’s conditions, the systematic assessment was carried out from three aspects, namely, science basis, impact and vulnerability, and adaptation and mitigation. In nearly a decade since the Second Assessment, research on climate and environment change in China developed rapidly, while sciences of climate change and environment and political situation have undergone profound changes. Therefore, it has become an urgent task to carry out another assessment. In 2018, CAS and CMA jointly launched the assessment Change of Climate and Ecological Environment in China: 2021. The program involved about 75 natural and social scientists from 45 organizations of 17 sectors, who carried out systematic evaluation of the facts, impact and vulnerability, adaptation, and mitigation of climate change. The following assessment reports have been released: (1) The Change of Climate and Ecological Environment in China: 2021 (Vol. I, Physical Basis), (2) The Change of Climate and Ecological Environment in China: 2021 (Part One of Vol. II, The Impact, Vulnerability and Adaptation of Sectors), (3) The Change of Climate and Ecological Environment in China: 2021 (Part Two of Vol. II, The Impact, Vulnerability and Adaptation of Regions), (4) The Change of Climate and Ecological Environment in China: 2021 (Vol. III, Mitigation), and (5) The Change of Climate and Ecological Environment in China: 2021 (Synthesis Report) (in Chinese and English). The reports are soon to be published. I would like to express my heartfelt gratitude to all the scientists who participated in this assessment! The assessment has been going on for nearly 20 years, during which China experienced fast socioeconomic development with booming overall scientific and technological strength. We have keenly felt the rapid progress of scientific research in China from the assessments. In the first assessment, papers on basic science were overwhelming in the literature, while those on impact, vulnerability, adaptation, and mitigation were scarce. Therefore, that report only pointed out potential problems of China in these aspects in a qualitative way based on the assessment of climate and ecosystem in other countries from foreign literature. The first National Climate Assessment (NCA) report only contained two volumes, with the first being science basis and the second covering the impact, adaptation, and mitigation. By the time of doing the second NCA in 2008, the situation was better, and there were sufficient

Preface I

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published literatures for the assessment of impact, vulnerability, adaptation, and mitigation, respectively, with the focus beginning to shift toward impact and adaptation. The 2021 assessment has seen a fundamental change, for a substantial increase has been found in the literatures on impact, vulnerability, adaptation, and mitigation, and the assessment focus has turned to the impact and adaptation. This can be seen evidently in the two volumes of the second report. The first one is on the impact, vulnerability, and adaptation assessment of fields and industries, and the second is about the impact, vulnerability, and adaptation assessment of key regions. All these are also the main concerns of all countries in the world. These assessment results of climate and ecological environment changes in China have reflected the big efforts and rich results made by Chinese scientists over the past about 20 years. China has made a solemn commitment to the world to strive to reach carbon neutrality by 2060, for which Chinese scientists are conducting broad researches to this end. I believe that carbon neutrality will be one of the key aspects in the next round of assessment. Looking back to the past 3 years’ assessment, in order to mobilize a team of about 200 experts in both natural and social sciences from different departments and sectors to efficiently carry out the work, we held eight meetings with all lead authors, three meetings with all authors and meetings with volume or chapter authors, respectively. After full discussions and three rounds of internal reviews, the report was redrafted several times before it was in a form good enough for external review, during which a total of 100 experts put forward more than 1000 suggestions for modification. In view of the review comments, we revised the chapters again and responded to the experts, forming a departmental draft, which was sent to more than ten national departments for review. Then, we received 683 comments and made revision again. On this basis, the final draft for publication was formed. The national-level departments participating in the report review include the Ministry of Science and Technology, the Ministry of Industry and Information Technology, the Ministry of Natural Resources, the Ministry of Ecology and Environment, the Ministry of Housing and Urban-Rural Development, the Ministry of Transport, the Ministry of Agriculture and Rural Affairs, the Ministry of Culture and Tourism, the National Health Commission, the Chinese Academy of Sciences, the Chinese Academy of Social Sciences, the National Energy Administration, the National Forestry and Grassland Administration, etc. Experts who participated in the review of the first volume include Rongshuo Cai, Wen Chen, Zhenghong Chen, Yongyun Hu, Zhuguo Ma, Jinming Song, Bin Wang, Kaicun Wang, Shourong Wang, Xiaofeng Xu, Zhongwei Yan, Jinhua Yu, Weidong Zhai, Chuanfeng Zhao, Zongci Zhao, Shunwu Zhou, Jiang Zhu, etc. Experts who participated in the review of the second volume include Dake Chen, Haishan Chen, Peng Cui, Xuefeng Cui, Xiuqi Fang, Guolin Feng, Shuangcheng Li, Hongyan Liu, Xiaodong Liu, Fumin Ren, Hao Wang, Naiang Wang, Zhongjing Wang, Yinlong Xu, Xiaoguang Yang, Qiang Zhang, Dawei Zheng, etc. Experts who participated in the review of the third volume include Yong Bian, Shaofeng Chen, Yiyun Cui, Xiangzheng Deng, Jinlei Feng, Yong Geng, Quansheng Huang, Yanbing Kang, Guoqing Li, Junfeng Li, Guimin Niu, Yue Qiao, Xiaohui Su, Yao Wang, He Xu, Sha Yu, Shuwei Zhang, Shengchuan Zhao, Fengqi Zhou, Nan Zhou, etc. Experts who participated in the review of the synthesis volume

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Preface I

include Yong Bian, Rongshuo Cai, Qingchen Chao, Huopo Chen, Shaofeng Chen, Xiangzheng Deng, Chuanglin Fang, Quansheng Ge, Yong Geng, Jianping Huang, Junfeng Li, Qingxiang Li, Ying Sun, Jinnan Wang, Shourong Wang, Ying Wang, Xiaofeng Xu, Shuwei Zhang, Shengchuan Zhao, Zongci Zhao, Dawei Zheng, etc. Now, I would like to sincerely thank the mentioned departments and experts for their careful reviews, constructive opinions, and suggestions! We commend the painstaking and efficient work undertaken by the secretariat, which has done well in organizing the assessment work making the completion of the report possible finally. Our special thanks go to those involved in the secretarial services: Shengxia Wang, Chao Wei, Wenhua Wang, Yuping Yan, Xinwu Xu, Rong Wang, and Shijin Wang, as well as those working in the Technical Support Unit (TSU), including Rong Yu, and Lanyue Zhou (Volume I), Jianbin Huang (Part 1 of Volume II), Chao Wei (Part 2 of Volume II), Lei Zhu and Yingying Liu (Volume III), and Shengxia Wang (Synthesis Report), for their great efforts in and great contributions to the coordination of various volumes, meeting organization, communication with experts, collection of comments, and communication with the publisher, which have ensured the successful process. As the assessment involves a wide range of natural and social fields, it is inevitable that there are some inadequacies. When the report is about to be published, I am anxiously looking forward to readers’ criticism and correction. Beijing, China April 2021

Dahe Qin Academician of Chinese Academy of Sciences

Preface II

The Change of Climate and Ecological Environment in China: 2021, an assessment research co-funded by Chinese Academy of Sciences (CAS) and China Meteorological Administration (CMA), has been completed under the leadership of Academician Dahe Qin. In the past three years, nearly 200 experts from the domains of natural science and social science in China have made great efforts for the completion of this series of assessment report, which is composed of five volumes: (1) The Change of Climate and Ecological Environment in China: 2021 (Vol. I, Physical Basis), (2) The Change of Climate and Ecological Environment in China: 2021 (Part One of Vol. II, The Impact, Vulnerability and Adaptation of Sectors), (3) The Change of Climate and Ecological Environment in China: 2021 (Part Two of Vol. II, The Impact, Vulnerability and Adaption of Regions), (4) The Change of Climate and Ecological Environment in China: 2021 (Vol. III, Mitigation), and (5) The Change of Climate and Ecological Environment in China: 2021 (Synthesis Report) (in Chinese and English). This book is the Change of Climate and Ecological Environment in China: 2021 (Synthesis Report) (hereafter referred to as the Synthesis Report), which is the output produced based on the above-mentioned first four volumes of assessment reports, and formed by reorganizing the main lines, comprehensively assessing the important research results, and integrating the relevant assessment results and key conclusions. The Synthesis Report follows the line of “climate change and impact—future projections and risks—adaptation and mitigation” by focusing on the four aspects: observed climate change and ecological environmental evolution and their causes, future climate change and risk projections, adaptation and mitigation measures and action effects, and climate-resilient development pathways. In terms of climate change facts, this volume reveals the changes having occurred in the atmosphere, hydrosphere, cryosphere, and biosphere from the perspective of climate system spheres. On this basis, the volume puts a special focus on changes in the past extreme events, explains global and regional elements affecting climate change in China by analyzing the impact of human activities on climate change and the large-scale factors that influence the climate in China, and places an emphasis on two aspects: the extent

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and the regional difference of climate change impact that have been found in social and economic systems in China. In the aspect of future risks, this volume gives core conclusions on the projections of key variables such as air temperature and precipitation, based on which regional climate models are used to simulate extreme events related to future air temperature, precipitation, temperature, and humidity. Then, the volume further analyzes the exposure and vulnerability of natural and socioeconomic systems in China in the context of climate change, with a focus on future potential changes in exposure and vulnerability under the influence of floods, drought and heatwave, etc., and comprehensively assess potential impact of climate change on the future China, including potential risks to water resources, agriculture, cryosphere, ecosystem, human habitat, people’s health, major projects, and so on. With respect to adaptation and mitigation, this volume systematically recapitulates the effects, measure options, and synergies in this aspect from both global and China’s perspectives, with a focus on adaptation and mitigation and their synergies. Finally, the volume expounds the essence and connotation of choosing a development pathway with climate resilience from the viewpoints of carbon emission pathway, sustainable development, and construction of a community with a shared future for mankind. More than 40 researchers from the research institutes affiliated to CAS, CMA, National Development of Reform Commission, Chinese Academy of Social Sciences, Ministry of Education, Ministry of Water Resources, and other nationallevel departments participated in the compilation and writing of this book. Dahe Qin and Yongjian Ding act as the editors-in-chief, with Panmao Zhai, Lianchun Song, Yong Luo, and Kejun Jiang as the deputy editors-in-chief, and Shengxia Wang and Xinwu Xu as the heads of TSU. Chapter 1 is Introduction, with Dahe Qin in overall charge and Xinwu Xu, as technical support. Evolution of Global Climate and Ecological Environment’ is authored by Panmao Zhai, Botao Zhou, and Lei Huang, Historical Evolution of Climate, Ecological Environment and Socioeconomic Development in China by Cunde Xiao and Jidong Wu, Future Change and Transformation Development by Dahe Qin and Chunlan Li, Contribution of China’s Climate and Environmental Ecological Assessment Report by Botao Zhou, and Overview by Xinwu Xu. Chapter 2 is Observed Climate Change and Ecological Environment is Evolution and Their Causes, which is charged generally by Panmao Zhai, with technical support by Rong Yu. Observed Facts is written by Panmao Zhai, Guoqing Wang, Shilong Piao, and Cunde Xiao, Weather and Climate Extreme Events by Jianqi Sun and Ying Sun, Impacts of Human Activities on Climate Change in China by Xiaoye Zhang and Zhili Wang, Large-scale Factors Affecting Climate Change in China by Botao Zhou and Zhicong Yin, Impact of Climate Change on Socio-economic Systems by Yongjian Ding, Guirui Yu, Shaoping Wang, Shengxia Wang, and Chenyu Li. Chapter 3 is Projections of Future Climate Change and Risks, chiefly charged by Yongjian Ding, with Shaoping Wang as technical support, Drivers of Human Activities for Future Climate Change is written by Tong Jiang, Earth System Models and Integrated Assessment Models by Wenjie Dong and Kejun Jiang, Projection of Future Climate Change by Tianjun Zhou and Xuejie Gao, Projection

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of Extreme Event Change by Xuejie Gao and Tianjun Zhou, Exposure and Vulnerability by Tong Jiang, Future Climate Change Risks by Shaohong Wu, and Terms for Reference by Tong Jiang, Cunde Xiao, and Jiao Yang. Chapter 4 is Adaptation and Mitigation: Measures, Actions and Effects which is led by Yong Luo, with technical support by Chao Wei and Jianbin Huang. Adaptation to Climate Change is written by Lianchun Song, Jianyun Zhang, Hongbin Liu, Fubao Sun, Lei Huang, and Zhihua Pan, Climate Change Mitigation by Kejun Jiang, Chunyan Dai, and Xiu Yang, and Synergy of Adaptation and Mitigation by Ying Chen and Kejun Jiang. Chapter 5 is The Development Pathways with Climate Resilience which is mainly charged by Kejun Jiang, with technical support by Yingying Liu. Global and China’s Carbon Emission Budget and Implementation Pathway Under the Warming Target of the Paris Agreement is written by Kejun Jiang, Addressing Climate Change and the Sustainable Development by Dahe Qin, Kejun Jiang, Ying Chen, Cunde Xiao, and Chunyan Dai, Building a Community with a Shared Future for Mankind with Global Climate Governance by Yun Gao, and “Addressing Climate Change: Our Shared Future” by Kejun Jiang. My sincere thanks to all of the experts from different departments, different units, and different fields for their tireless dedication and great efforts that went into joint discussions and iterated revisions during the assessment process. My appreciation also goes to Shengxia Wang, Xinwu Xu, Rong Yu, Shaoping Wang, Jianbin Huang, Chao Wei, and Yingying Liu for their services as the chapter secretaries and technical supporters! At a time when this book is on the verge of publishing, we are specially grateful to Dr. Shengxia Wang and Dr. Xinwu Xu, who are fully in charge of secretarial and technical support for the assessment report, for their great efforts to ensure the successful completion by chapter coordination, organization of assessment meetings, liaison with assessment experts, compilation of assessment comments, and communication on publishing matters. In addition, we would also like to thank Yuping Yan, Chao Wei, Rong Wang, Wenhua Wang, Shijin Wang, and Jie Yu for their engagement in the secretary group of the report. Finally, sincere thanks must be extended to Hua Liu, who has carefully modified and polished the English language of this English Synthesis Report. Beijing, China November 2021

Dahe Qin Academician/Research Professor Chinese Academy of Sciences (CAS) Professor of CAS University Yongjian Ding Research Professor CAS Northwest Institute of Eco-environment and Resources Professor of CAS University

Introduction

Based on the systematic assessment of the facts, impacts and vulnerabilities of climatel, and environmental changes in China and mitigation measures, this book draws out the core conclusions from four aspects: focusing on observed climate change and ecological environment evolution and their causes, projections of future climate change and risks, measures and action effectiveness in adaptation and mitigation, and development pathways with climate resilience. In terms of facts of changes, this book focuses on extreme events, impact of human activities on climate change in China, large-scale factors affecting climate change in China, impact of climate change on China’s social and economic system, etc. As for future risks, the book gives the core projection conclusions based on the key variables such as temperature and precipitation as well as changes in extreme climate events. Meanwhile, according to the exposure and vulnerability, the potential risks in water resources, agriculture, cryosphere, ecosystem, human habitat, people’s health, and major projects under the impact of climate change are analyzed comprehensively. In the aspect of adaptation and mitigation, it reviews their effectiveness, measure options, and synergies in a systematic way from both global and Chinese perspectives. Finally, the essence and connotation of choosing a climate-resilient development pathway from the views of carbon emission path, sustainable development, and construction of a community with a shared future for mankind. This book serves as a convenient access for those interested in understanding climate change and can be used as a reference for readers in related professions and fields.

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Contents

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Evolution of Global Climate and Ecological Environment . . . . . . . . 1.1.1 Impact of Human Activities on the Earth’s Environment and the Livable Earth . . . . . . . . . . . . . . . . . . . . . 1.1.2 Impact of Human Activities on Global Climate Change . . . . 1.1.3 Impacts and Risks of Climate Change on Natural and Human Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Historical Evolution of Climate, Ecological Environment and Socio-economic Development in China . . . . . . . . . . . . . . . . . . . . 1.2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.2 Historical Changes in Climate, Ecological Environment and Socio-economic Development . . . . . . . . . . 1.2.3 Contemporary Changes in Climate and Ecological Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.4 Changes in Modern Social and Economic Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Future Changes and Transformation and Development . . . . . . . . . . . 1.3.1 Future Changes and Risks in Climate and Ecological Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.2 Actions to Deal with Climate Change and Protect Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.3 Transition to Sustainable Development . . . . . . . . . . . . . . . . . . 1.4 Contribution of China’s Assessment Reports on Climate, Environment and Ecology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5 Overview of This Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Observed Climate Change and Ecological Environment Evolution and Their Causes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Observed Facts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.1 Atmosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 1 1 4 5 7 7 8 10 12 14 15 17 19 20 22 23 25 25 25

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2.1.2 Hydrosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.3 Cryosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.4 Ecosystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.5 Planetary Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Extreme Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.1 Extreme Temperature Events . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.2 Extreme Precipitation Events . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.3 Typhoon and Severe Convective Weather . . . . . . . . . . . . . . . . 2.2.4 Sand-Dust Storms and Haze . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.5 Cryospheric Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.6 Forest Fire Weather . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.7 Compound Extreme Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.8 Attribution of Extreme Events . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Impacts of Human Activities on Climate Change in China . . . . . . . . 2.3.1 Impact of Human Activities on Atmospheric Composition and the Generated Radiative Forcing . . . . . . . . 2.3.2 Impact of Human Activities on Surface Solar Radiation and Surface Air Temperature in China . . . . . . . . . . 2.3.3 Impact of Human Activities on the East Asian Summer Monsoon Circulation and Precipitation in China . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.4 Impact of Human Activities on Extreme Climate Events in China . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 Large-Scale Factors Affecting Climate Change in China . . . . . . . . . 2.4.1 East Asian Monsoon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.2 Main Modes and Teleconnections of Atmospheric Circulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.3 Ocean Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.4 Arctic Sea Ice and Snow Cover on the Qinghai-Tibet Plateau . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.5 Snow Cover in Eurasia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 Impacts of Climate Change on Socio-economic Systems . . . . . . . . . 2.5.1 The Impact Extent of Climate Change on Socio-economic Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5.2 Regional Differences in the Impact of Climate Change on Socio-economic Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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3 Projections of Future Climate Change and Risks . . . . . . . . . . . . . . . . . . 3.1 Anthropogenic Drivers of Future Climate Change . . . . . . . . . . . . . . . 3.2 Earth System Models and Integrated Assessment Models . . . . . . . . . 3.2.1 Earth System Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2 Regional Climate Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.3 Integrated Assessment Models . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Projections of Future Climate Change . . . . . . . . . . . . . . . . . . . . . . . . .

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3.3.1 Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.2 Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 Projection of Changes in Extreme Events . . . . . . . . . . . . . . . . . . . . . . 3.4.1 Temperature Extremes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.2 Precipitation Extremes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.3 Compound Extreme Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5 Exposure and Vulnerability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.1 Observed Exposure and Vulnerability Changes . . . . . . . . . . . 3.5.2 Possible Changes in Socio-economic Exposure and Vulnerability to Rainstorms and Flood Disasters . . . . . . 3.5.3 Possible Changes in Socio-economic Exposure and Vulnerability to Droughts . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.4 Possible Changes in Population Health Exposure and Vulnerability to Heatwaves . . . . . . . . . . . . . . . . . . . . . . . . 3.6 Future Climate Change Risks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6.1 Water Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6.2 Agriculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6.3 Cryosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6.4 Ecosystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6.5 Human Habitat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6.6 Human Health . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6.7 Major Projects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Adaptation and Mitigation: Measures, Actions and Effects . . . . . . . . . 4.1 Climate Change Adaptation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.1 Global Progress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.2 Adaptation Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.3 Adaptation Technologies and Measure Options . . . . . . . . . . . 4.1.4 China’s Adaptation to Climate Change: Actions and Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Climate Change Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1 Global Progress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.2 Mitigation Technology and Measure Option . . . . . . . . . . . . . 4.2.3 China’s Emission Reduction Policies and Effects . . . . . . . . . 4.2.4 Emission Reduction and Effects in China . . . . . . . . . . . . . . . . 4.3 Synergized Effects of Adaptation and Mitigation . . . . . . . . . . . . . . . . 4.3.1 Adaptation, Mitigation and Their Interactions . . . . . . . . . . . . 4.3.2 China’s Synergized Adaptation and Mitigation Measures, Actions and Effects . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.3 Adaptation and Mitigation Strategies Under the Goals of the Paris Agreement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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88 92 93 93 96 98 98 99 102 102 105 110 111 113 115 116 117 121 121 127 129 130 130 131 133 138 146 146 150 152 155 156 156 160 163 164

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5 The Development Pathways with Climate Resilience . . . . . . . . . . . . . . . 5.1 Global and China’s Carbon Emission Budgets and Implementation Pathway Under the Warming Targets of the Paris Agreement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.1 Global and China’s Carbon Emission Budgets . . . . . . . . . . . . 5.1.2 Global Emission Reduction Pathways . . . . . . . . . . . . . . . . . . . 5.1.3 China’s Emission Reduction Pathways . . . . . . . . . . . . . . . . . . 5.2 Addressing Climate Change and the Sustainable Development . . . . 5.2.1 The Linkage Between Addressing Climate Change and Sustainable Development Goals . . . . . . . . . . . . . . . . . . . . 5.2.2 Climate Resilience and Risk Management . . . . . . . . . . . . . . . 5.2.3 Addressing Climate Change and Air Pollution Control . . . . 5.2.4 The Linkage Between Addressing Climate Change and Other Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.5 Tackling Climate Change and Eradicating Poverty . . . . . . . . 5.2.6 Addressing Climate Change and Fairn Ethics . . . . . . . . . . . . 5.3 Global Climate Governance to Help Build a Community with a Shared Future for Mankind . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.1 Global Climate Governance System and Its Challenges . . . . 5.3.2 Sustainable Management Concept of Earth System and Scientific Assessment Support . . . . . . . . . . . . . . . . . . . . . . 5.3.3 Coordinate International and Domestic Efforts to Actively Tackle Climate Change . . . . . . . . . . . . . . . . . . . . . 5.4 Addressing Climate Change: Our Shared Future . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Chapter 1

Introduction

1.1 Evolution of Global Climate and Ecological Environment The Earth’s environment began its “Anthropocene”1 , in which human activities have become the main driver of global climate and ecological environment changes. The continuous interference of human activities in the future will make the Earth system lose its resilience, and hence it is urgent to identify a “safe and fair corridor” for the livable Earth.

1.1.1 Impact of Human Activities on the Earth’s Environment and the Livable Earth Since human beings appeared in the wild savannah of East Africa 3.5 million years ago, they began to influence the Earth’s environment. From hunting and farming, to industrialization in 1750 and entering Anthropocene, human beings have substantially intensified their efforts to change the Earth’s environment. In 1750, the global population was less than 1 billion, and in 2019 it reached 7.7 billion. According to the World Population Prospects 2019 released by the United Nations (UN), the global population will exceed 8.5 billion in 2030 and reach about 10 billion in 2050. Ten thousand years ago, the number of wild animals on the Earth accounted for 99%, and human being for only 1%. Now, wild animals take up only 1%, human beings 32%, and captive animals 67%. At present, two-fifth of the planet’s land surface is used to grow food for humans. Three-quarters of the world’s fresh water

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“Anthropocene” was first proposed by Nobel Prize winner Paul Crutzen in 2002, which means a new geological era dominated by human beings, and human activities have had a profound impact on the whole Earth.

© Science Press 2023 D. Qin et al., The Change of Climate and Ecological Environment in China 2021: Synthesis Report, https://doi.org/10.1007/978-981-99-4487-3_1

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is controlled by humans. Seventy-five percent of the global terrestrial ecosystem has been significantly modified by humans.2 With the rapid development of science and technology, human wealth has increased dramatically, and at the same time, human beings are living longer and healthier. In prehistoric times, the average life expectancy of humans was only 30 years. From 1950 to 1955, the life expectancy of the world population was 46 years. From 2005 to 2010, the life expectancy reached 67 years, and it will exceed 75 years in 2050. In 1900, the proportion of urban population in the world was 14%, and reached more than half in the early twenty-first century. In the meantime, human beings are faced with severe climate and ecological environment problems, such as climate warming, environmental degradation, aggravated resource depletion, ecosystem damage, and sharply diminishing biological habitats. In 2015, the UN developed the 2030 Agenda for Sustainable Development (hereinafter referred to as “2030 Agenda”, which covers 17 Sustainable Development Goals (SDGs) in poverty reduction, education, climate protection, environmental degradation, and socio-economic development. It is difficult to achieve SDGs by 2030 as the new coronal pneumonia (COVID-19) was rampant across the world in 2020 and its negative impact will last at least several years. The development and prosperity of human civilization, to a large extent, benefited from the pleasant environment of Holocene. In Holocene, the atmosphere and biogeochemical processes were relatively stable, and the Earth system could absorb and eliminate external interference through internal feedback, so that the socialecological system could be in a stable and sustainable development (Steffen et al. 2018). Since the Industrial Revolution, anthropogenic activities have become the main driver of global climate and environmental changes. The man-made mass has exceeded the Earth’s biomass, and the natural stability of the Earth system has been broken. At present, human beings are standing at the crossroads of the future of the Earth system. If human beings continue to emit greenhouse gases without control, the Earth system will lose its ability to recover and become the unstable state of “hothouse Earth” in the future. Human beings will be faced with great risks at that time (Fig. 1.1a). In 2009, an international team of scientists in the field of the Earth system and environmental science, led by Johan Rockström, Stockholm Resilience Center of Stockholm University, Sweden, put forward the theoretical framework of “planetary boundary” based on analyzing the key processes of maintaining the stability and resilience of the Earth system. It provides an important concept to analyze and quantify the safe operating space of human development in the future and prevent irreversible environmental changes caused by excessive human activities (Rockström et al. 2009). Based on the comprehensive analysis of Holocene climate and ecological environment change, Rockström et al. (2009) evaluated 10 key processes and thresholds of the Earth system, including climate change, ocean acidification, stratospheric ozone depletion, nitrogen cycle, phosphorus cycle, freshwater use, land-use 2

Future Earth. Our Future on Earth 2020. http://www.futureearth.org/publications/our-future-onearth.

1.1 Evolution of Global Climate and Ecological Environment

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Fig. 1.1 Schematic diagram of evolution track of the Earth system (a) and planetary boundary (b) (Steffen et al. 2015, 2018; Rockström et al. 2009)

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1 Introduction

change, biodiversity loss, atmospheric aerosol load, and chemical pollution. The assessment shows that climate change, biodiversity loss (specifically genetic diversity) and nitrogen cycle have crossed planetary boundaries, and phosphorus cycle and land-use change have entered high-risk areas. The assessment points out that when the key processes of the Earth system are within the planetary boundaries, the sustainable development of human beings can be guaranteed, and when there are one or more crossing the thresholds, the risk of environmental change will increase significantly (Fig. 1.1b). To strengthen the resilience management of the Earth system in Anthropocene and explore the sustainable development pathway of mankind, Future Earth, an international initiative, convened a group of outstanding scientists around the world in 2019 to establish the Earth Commission with the objective to “build a new platform in the twenty-first century that integrates environment and economy, human beings and the Earth to transform the economic system, and benefit the society and maintain the Earth’s natural system”. The development and progress of human society depend on the stability of the Earth system and the comprehensive integration of human and Earth stability. The key to integration is to scientifically define a safe and fair corridor for human development on the Earth, and make the Earth’s life support system stable and supportive of human welfare. The Earth’s natural resources, such as carbon, nutrition, water and land resources, are limited, and “safety and fairness” also embraces sharing among human beings and also between humans and nature. How to quantitatively determine the “safe and fair corridor” and put it into action? It is a long-term task facing all countries in the world, and the above requirements are even more challenging for China with a population of 1.4 billion.

1.1.2 Impact of Human Activities on Global Climate Change Since the Industrial Revolution, human activities, such as burning fossil fuels to emit greenhouse gases, aerosols and other atmospheric components, production and life to emit various chemicals, land-use and land-cover changes to alter surface characteristics, have caused changes in the climate system composed of atmosphere, hydrosphere, cryosphere, biosphere and lithosphere. Radiative forcing (RF) can quantify the impact of human activities on the climate system. According to the Sixth Assessment Report (IPCC AR6, 2021) of the Intergovernmental Panel on Climate Change (IPCC), the RF in 2019 (relative to 1750) was 2.72 W/m2 , which is 0.43 W/ m2 higher than that in 2011 given in the Fifth Assessment Report (IPCC AR5, 2013). The increase in atmospheric CO2 concentration since 1750 has become the main reason for the increase in RF. In 2019, the atmospheric CO2 concentration was 410 ppm. It is 48% higher than that before industrialization and the highest in 2 million years. Widespread and rapid changes have occurred in the atmosphere, hydrosphere, cryosphere and biosphere, and the current state of many aspects of the climate system has been unprecedented in the past few centuries or even thousands of years.

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The increase in observation data, the improvement of detection and attribution methods and techniques, and the development of climate models have further confirmed the conclusion that human activities have affected the climate system. The First Assessment Report (IPCC FAR) issued by IPCC in 1990 pointed out that the observed warming might be mainly attributed to natural variability, but the influence of human activities had been felt. The Second Assessment Report (IPCC SAR) in 1995 recognized that there was obvious evidence to have detected the impact of human activities on climate. According to the Third Assessment Report (IPCC TAR) in 2001, new and stronger evidence showed that most of the global warming observed in the past 50 years was likely (more than 66% probability) attributed to human activities. In 2007, IPCC AR4 pointed out that human activities were very likely (more than 90% probability) to be the main cause of climate warming. In 2013, IPCC AR5 indicated that it was extremely likely (more than 95% probability) that more than half of the global warming observed since the mid-twentieth century was caused by human activities. According to the IPCC Special Report on Global Warming of 1.5 °C (IPCC SR 1.5) released in 2018, human activities have caused global temperature to increase by about 1.0 °C since industrialization, which further confirmed that human activities have been the main cause of observed warming. According to the Working Group I Assessment Report of IPCC AR6 (IPCC AR6 WGI report) released in 2021, human activities caused global warming of 1.07 °C from 1850–1900 to 2010–2019, which is consistent with the observed warming of 1.06 °C. It is unequivocal that human activities have warmed the atmosphere, ocean and land.

1.1.3 Impacts and Risks of Climate Change on Natural and Human Systems IPCC AR5 pointed out that climate change has a profound impact on natural systems and human systems, and the impact of climate change has been detected in many fields such as ocean warming, water resources and water cycle, cryosphere, sea level rise, extreme events, ecosystems, food production, human health, engineering projects, regional economy, social and cultural sectors. Climate warming in the future may lead to wider impacts and risks. If global warming is 1–2 °C higher than the preindustrial level, the global risks will still be controllable. If the temperature increases by 4 °C or more, it will cause more serious consequences to the natural ecosystem and human society, and it will be difficult to recover. In 2018–2019, IPCC released three special reports, namely, Special Report on Global Warming of 1.5 °C, Special Report on Ocean and Cryosphere in a Changing Climate, and Special Report on Climate Change and Land. According to the Special Report on Global Warming of 1.5 °C, 1.5 °C warming will bring many risks and impacts on terrestrial and marine ecosystems, human health, food and water security, economic and social development, etc. The negative impact of 2 °C warming

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Fig. 1.2 Climate change risks under different warming conditions. (adapted from IPCC SR 1.5) M, H, and M-H represent medium, high, and medium–high confidences, respectively

on natural and human systems is even greater (Fig. 1.2). The Special Report on Ocean and Cryosphere in a Changing Climate projected the future changes and risks of oceans and cryosphere, and pointed out that under the background of future warming, the retreat of Arctic cryosphere will intensify, and the risks of infrastructure, culture, tourism and entertainment resources in alpine and Arctic regions will increase. The ocean will keep warming, which will aggravate acidification, reduce the net primary productivity of marine ecosystem, affect marine biodiversity, and endanger the service function of marine ecosystem and human society. Sea level rise, ocean heatwave and ocean acidification will aggravate the risks to coastal lowland communities. The Special Report on Climate Change and Land emphasized that the negative impact of climate change on land will be increasing in the future, and some sectors and regions may face higher or unprecedented risks. The IPCC AR6 WGI report pointed out that the global surface temperature will continue to increase until at least the middle of the twenty-first century under all emission scenarios considered. Unless deep reduction in greenhouse gas emissions is implemented, the global temperature increase will reach or exceed 1.5 °C in the next 20 years. Future warming will cause many changes in the climate system. In particular, the changes in ocean, ice sheet and global sea level are irreversible for centuries to millennia. Many regions are projected to experience an increase in the probability of compound events. Concurrent heatwaves and droughts, and compound flooding caused by extreme sea level events (characterized by storm surges, ocean waves and tidal floods) in combination with severe precipitation will be aggravated. The once-in-a-century extreme sea level events in current time are projected to occur at least annually in more than half of coastal areas by 2100, which, in combination with extreme precipitation, will make floods more frequent. Under the scenario of a high increase in temperature, abrupt responses and tipping points of the climate system, such as rapid melting or collapse of Antarctic ice sheet and forest dieback, cannot be ruled out. Once these low-likelihood, high-impact outcomes occur, they will be disastrous to the living environment of the Earth.

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1.2 Historical Evolution of Climate, Ecological Environment and Socio-economic Development in China Judging from China’s natural endowment and historical human-environment relationship, contemporary China bears unprecedented pressure, and its sustainable development faces prominent contradictions.

1.2.1 Overview China has a vast territory, complex terrain, and marked monsoon climate. The territory starts from the Uziberi Pass in Wuqia County of Xinjiang in the west and reaches the junction of the Heilongjiang River and Wusuli River in the east. In the south, it starts from Zengmu Shoal in the Nansha Islands and reaches the heart of the Heilongjiang River near Mohe in the north. The terrain in China is high in the west and low in the east, a three ladder-like distribution with an area of about 9.6 million km2 . The Bohai Sea, Yellow Sea, East China Sea, South China Sea, and part of the Pacific Ocean east of Taiwan Island, bordering China’s land, cover an area of about 4.7 million km2 , and the sea area claimed to be under jurisdiction covers an area of about 3.0 million km2 . Dominated by geographical zonal laws such as latitude effect, elevation effect and land-sea distribution, China’s climate is mainly characterized by monsoon climate. The water vapor in the Pacific Ocean and Indian Ocean transported by the southeast monsoon and southwest monsoon in summer brings abundant precipitation to most parts of China. In winter, northerly winds prevail, carrying dry and cold air from the middle and high latitudes of the Northern Hemisphere, affecting most areas of China with less precipitation and uneven spatial and temporal distribution. Northwest China, deep in the hinterland of Eurasia, is far away from the sea, less affected by summer monsoon, and has obvious continental climate characteristics. The Qinghai-Tibet Plateau with an average elevation of more than 4,000 m accounts for about a quarter of China’s land area. Influenced by topography, characteristics of mountain climate or highland climate are outstanding. Since China adheres to the basic national policy of resource conservation and ecological environment protection, and the concept of green development goes deep into all walks of life, the overall quality of the ecological environment in China has been continuously improved. In 2019, the county area with excellent or good ecological quality accounted for 44.7% of the national land area, with a forest area of 220 million hm2 and a forest coverage rate of 23.0%, but still lower than the world average (30.1%). The per capita forest area is only about one fourth of the world average. The grassland covers an area of nearly 400 million hm2 in China, accounting for 41.7% of the land area. It is the largest land ecosystem and ecological barrier in China. Meanwhile, China is one of the countries with the largest ecologically fragile areas in the world. The protection of fragile areas is faced with

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multiple pressures such as climate change, water shortage, grassland degradation, biodiversity loss and frequent natural disasters. In 2019, the cultivated land area of the whole country was 2.023 billion Mu3 , and the per capita cultivated land was less than half of the world average. The per capita grain possession increased from less than 250 kg at the beginning of the People’s Republic of China to 474 kg in 2019. Although the yield per unit area of grain crops has increased rapidly with technological progress, and doubled the world average or more, it is increasingly difficult to continue to increase production due to the reduction of high-quality cultivated land area and the restriction of water resources. China has become the second largest economy in the world, the largest developing country and the country with the largest population. In 2019, the total gross domestic product (GDP) reached Chinese Yuan (CNY) 99.1 trillion accounting for 16.3% of the world according to the Approach of Foreign Exchange Rate, and the proportions of secondary and tertiary industries were 39.0% and 53.9%, respectively. In 2019, the per capita GDP was CNY 70,892 (about USD 10,276), but it was still less than one sixth of that of the United States. In 2019, China’s population reached 1.400,05 billion, accounting for 18.2% of the world’s total population. The urban residents accounted for 60.6% of the total population, while the population over 65 years old reached 12.6% of the total population, and, as estimated, will reach 14.0% around 2022. Thus, China will officially enter the aging society, showing the characteristics of “getting old before getting rich” (China Development Research Foundation, 2020). China’s population and GDP are extremely uneven in distribution, mainly concentrated in the central and eastern regions. The land area of western China (12 provinces autonomous regions or municipalities directly under the central government) accounts for 71.5% of the whole country, but the proportions of population and GDP are only 27.2% and 20.7% of the whole country, respectively. The unbalanced development between the eastern and western regions constrains the climate change response and ecological environment governance of China.

1.2.2 Historical Changes in Climate, Ecological Environment and Socio-economic Development In the past 20 centuries, China was relatively warmer in the 10th to the thirteenth centuries and colder in the 15th to the nineteenth centuries. Since 1850, the temperature has shown a rising trend and its rising rate is the highest over the past 20 centuries (medium confidence) (Fig. 1.3). During the warm period, most of the dry and wet conditions in eastern China were characterized by drought in South China, flooding in the middle and lower reaches of the Yangtze River and drought again in the Yellow River and Huaihe River region (medium confidence). The change of climatic elements, including cold and warm, and wet and dry conditions, affects the evolution of natural vegetation, hydrology, 3

1 mu ≈ 666.7 m2

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cryosphere (glacier, frozen soil, snow, river and lake ice, and sea ice), desert and other geographical patterns, and also affects the development of agrarian society. Over the past 20 centuries, China has been in the stage of agricultural economy for a long time, and its population has risen in fluctuation. Before the 1580s the population was below 100 million, approaching 200 million in 1760 and exceeding 400 million in 1840 (Fig. 1.3). The main farming areas expanded from the Yellow River Basin in the early AD to the Yangtze River Basin and border areas in the sixteenth century. Moreover, the cultivated land area increased from about 500

Fig. 1.3 Changes of temperature (°C, against that in 1851–1950) (a), population (b), forest coverage rate and cultivated land area (c), flood frequency (d) and drought frequency (e) in China in the past 2000 years. The data in Fig. 1.3 d and Fig. 1.3 e began in 1470, and the gray shaded area indicates the relatively warm climate period, in which the temperature data come from Section 2.3.1 of Volume I; population data come from Li et al. (2015); the forest coverage rate data from Fan and Dong (2001); cultivated land area data from Fang et al. (2021). Flood frequency and drought frequency are expressed by the number of major cities affected in China, which comes from the Map Collection of Drought and Flood Distribution in China in Recent 500 Years (Zhang et al. 2003) and has been updated. At the same time, the data of population, forest coverage rate and cultivated land area were updated according to China Statistical Yearbook

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million Mu in the early AD to about 1 billion Mu in the late fifteenth century, and to about 2 billion Mu in the late twentieth century. Agricultural development needs to expand cultivated land to yield agricultural products. With the increase in population and cultivated land area, the forest coverage rate has decreased obviously (Fig. 1.3). The forest coverage rate decreased from about 41.0% in the year 220 to 17.0% in 1840 and then down further to 11.4% in 1949, and, meanwhile, the natural lakes in the eastern plain generally continued to shrink. Large-scale land reclamation by human beings has brought about the losses of forests and lakes. Soil erosion, desertification and other ecological and environmental problems, coupled with the large interannual and seasonal changes of precipitation, caused frequent droughts and floods (Zhang and Zhang 2019), and natural disasters frequently occurred in the southeast region after the Song Dynasty (Hao et al. 2020).

1.2.3 Contemporary Changes in Climate and Ecological Environment Under the background of global warming, the trend of climate change in China is obvious. The monsoon circulation is strengthened, the rain belt in the east tends to move northward, the annual mean precipitation intensity in the eastern region affected by monsoon is significantly enhanced, and the extreme weather and climate events are increasing with obvious regional differences. In the past hundred years, the surface temperature in China has obviously increased, and since 1900, the land temperature rise in China has ranged from 1.3 °C to 1.7 °C. From 1961 to 2018, precipitation in most parts of northwest China, especially in Xinjiang, increased significantly, but the basic climatic characteristics of arid and semi-arid regions remained unchanged. Since 1961, the frequency of extreme high temperature events in China has been increasing, especially since the twenty-first century. From 1961 to 2018, the maximum daily precipitation in most parts of China showed an increasing trend; and the annual cumulative torrential rain days with daily precipitation ≥ 50 mm in China also showed an upward trend, of which an increasing trend appeared in southern China, the Qinghai-Tibet Plateau and parts of Northwest China, but a slightly decreasing trend was seen in North China and the central part of Sichuan Province. Under the background of global warming, the sea level in China’s coastal areas has been generally rising with fluctuation, and its rising rate from 1980 to 2018 was 33 mm per decade, higher than the global average in the same period. The number of typhoons landing in China has no obvious change, but the typhoon strength has become higher since the late 1990s. From 1980 to 2015, glaciers in China showed an obvious retreat, and the permafrost area decreased obviously, but the number and extent of glacial lakes in China were significant increasing and expanding.

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In view of the fragile natural ecosystem, serious ecological damage, huge ecological gap and frequent ecological disasters in China, the Chinese government has implemented a number of major ecological protection projects since the State Council issued the National plan for Ecological Environment Construction in 1998. Sixteen major eco-environmental construction projects, including vegetation construction and preservation, soil and water conservation and desertification control were launched (Fig. 1.4), which have achieved remarkable effects in improving environmental quality, benefiting people’s livelihood and sustainable development. The eco-environmental quality has improved overall, but the situation is still grim. The 16 projects covered 6.2 million km2 of the national territorial area, with a cumulative investment of CNY 2,357.4 billion (price level in 2015) from 1978 to 2015, mobilized more than 500 million labors, and improved the ecological environment significantly. The national forest coverage rate increased from 13.9% in 1998 to 23.0% in 2019. According to the Master Plan for Major Projects of National Important Ecosystem Protection and Restoration (2021–2035), the national forest coverage rate will increase to 26.0% by 2035. Huge investment in ecological protection projects has also contributed to the realization of the 17 SDGs of the UN, especially, it has contributed to the goals of protecting, restoring and promoting the sustainable use of terrestrial ecosystems, sustainable management of forests, combating desertification, stopping and reversing land degradation, curbing the loss of biodiversity, and coping with climate change and reducing poverty and hunger (Bryan et al. 2018). Since the implementation of the Action Plan for Air Pollution Prevention and Control (referred to as “Ten Articles of Atmosphere”) in 2013, China’s regional air quality has improved, and the number of haze days has shown a downward trend since 2013. Among 337 cities at the prefecture level and above in China, the compliance rate of urban ambient air quality has increased from 21.6% in 2015 to 46.6% in 2019. However the air pollution is still heavy in autumn and winter now. China still faces ecological and environmental problems such as water and soil pollution, urban expansion and biodiversity decline. According to the 2019 Bulletin of Ecological Environment in China, although water environment and soil environment continue to improve, the problems are still outstanding. The sections of class IV and class V of groundwater in China account for 66.9% and 18.8%, respectively. Total phosphorus in inland lakes such as Taihu Lake, Chaohu Lake and Dianchi Lake exceeded the prescribed limit and caused light water pollution. The eutrophication of coastal seawater in the Bohai Sea, Yellow Sea, East China Sea and South China Sea is relatively prominent. Heavy metals are the main pollutants affecting the soil environmental quality of agricultural land in China, among which cadmium is the primary pollutant. The area of first-class to third-class cultivated land in China only accounts for 31.2% of the total. China still faces challenges in improving its eological environment such as the growth of high-energy-consumption industries in key regions, the industrial structure dominated by heavy chemical industry, the energy structure dominated by coal, and the difficulty in remediation of soil and groundwater pollution.

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Fig. 1.4 Annual investment of 16 major ecological protection projects in China from 1978 to 2015 (revised from Bryan et al. 2018)

1.2.4 Changes in Modern Social and Economic Development As the age structure of the population continues to change, the proportional relationship between the labor force population and the elderly population in Chinese mainland is changing. China is faced with social problems such as the reduction of labor resources and the aggravation of social burdens. From 1949 to 2019, the population of the mainland of China increased by nearly 1.6 times, and the average natural growth rate of population for many years was 13.7‰ (Fig. 1.5a, b). China implemented the national policy of family planning in the late 1960s. In the 1970s, the natural population growth rate began to decline. Even if the policy of “couples from one-child families may have two children” was implemented in 2011, the average annual natural population growth rate from 2011 to 2019 was only 4.8‰. The proportion of the working-age population (aged 15–64) increased from 61.5% in 1982 to 74.5% in 2010, and began to decline in 2011, reaching 70.7% in 2019. At the same time, the population over 65 years old is on the rise, reaching 176 million in 2019, and the dependency ratio of the elderly is also on the rise. According to Bulletin of the Seventh National Population Census in 2020, the proportion of the workingage population dropped to 68.6% in 2020, and the proportion of the population aged 65 and above rose to 13.5%. China will face a faster population aging period. Since 1978, China has shifted from a planned economy to a socialist market economy, allowing the economy to have entered a stage of sustained and rapid growth, thus its economic structure has undergone significant changes (Fig. 1.5c, d) The averaged GDP growth rate reached 9.4% during the period between 1978 and 2019. From the perspective of industrial structure, the declining trend of proportion

1.2 Historical Evolution of Climate, Ecological Environment … Fig. 1.5 Social and economic development and changes in China (1949–2019) (From: China Statistical Yearbook 2020)

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of the primary industry in GDP is in sharp contrast with the rising trend of proportion of the tertiary industry in GDP. According to the statistics by the World Bank, China’s manufacturing value added in 2019 accounted for 28.3% globally, making it the largest manufacturing country in the world. At the same time, the tertiary industry has surpassed the secondary industry in GDP since 2012, and the service industry has become an important force driving economic growth. Since the reform and opening-up, the foreign trade dependence and foreign investment dependence of China’s economy growth have increased at first and then decreased (Fig. 1.5e, f). In 2018, the total proportion of exports and imports to GDP was 35.7%, and China’s dependence on the international trade market decreased significantly compared with that in 2006. In 2035, China’s per capita GDP is expected to reach the level of moderately developed countries, and its economic aggregate will reach a new level. With the economic growth, the demand for energy consumption continues to increase, and the emission of greenhouse gases is greatly increased, resulting in great pressure for emission reduction (Fig. 1.5g, h). In 2019, the total energy consumption and CO2 emissions were 8.5 times and 6.9 times that in 1978 in China. Especially, since the beginning of the twenty-first century, energy consumption and CO2 emissions have increased rapidly. Viewed from the energy consumption structure, coal consumption accounted for less than 70% after 2012, and decreased to 57.7% in 2019. The proportion of clean energy (including non-fossil energy and natural gas) in the total primary energy consumption in China showed an upward trend, reaching 23.4% in 2019, among which the proportion of non-fossil energy in the total primary energy consumption increased to 15.3%. In 2019, the emission intensity of CO2 per unit GDP in China decreased by about 48.1% compared with that in 2005. However, compared with the major developed economic regions in the world, the emission and concentration of atmospheric aerosols in China are still at a relatively high level. Even if China will reach the peak of CO2 emissions by 2030, it will still have considerable pressure to achieve carbon neutrality after that, and will still face huge challenges from the opportunity of industrial restructuring and the pressure of emission reduction.

1.3 Future Changes and Transformation and Development Climate and ecological environment changes in the future will pose a major threat to the national security of China in many areas. It is necessary to transform to lowcarbon and green development, improve the level of ecological civilization, and take the lead in the construction of a community with shared future for mankind.

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1.3.1 Future Changes and Risks in Climate and Ecological Environment In the future, the global warming trend will be obvious, extreme weather events will occur frequently, and the risk of disaster losses will increase. As global climate changes, the average annual temperature and precipitation in all regions of China will likely increase in the future compared with those in 1986–2005, and will show up regional characteristics (medium confidence). Extreme warm events will keep increasing, while extreme cold events will be seen less in the future; high temperature and heatwaves events will become more; extreme precipitation will change in intensity, frequency and duration; the frequency and intensity of extreme floods and geological disasters induced by rainstorms may also increase; drought and water shortage will increase in occurrence frequency, influence scope and domain as well as disaster loss. With the change of meteorological conditions, the diffusion status of air pollutants may change too in the future. The risk of disaster losses caused by climate change is huge. Compared with the global warming of 2 °C above pre-industrial levels, the direct economic losses to result from tropical cyclones and drought disasters in China may be reduced by hundreds of billions of CNY under the global temperature rise of 1.5 °C above preindustrial levels (Otavio 2018; Su et al. 2018; UN 2019; United Nations Environment Programme (UNEP) 2019; Wen 2018), and the number of people dying from high temperature may decline by tens of thousands every year (medium confidence) (Wang et al. 2019). Future climate change will pose a major threat to water resources, cryosphere, ecological security, food security, infrastructure and people’s health, and then lead to the rise in ecological and environmental risks. With the in-depth industrialization and urbanization, the construction and development of projects (such as the Silk Road Economic Belt and ecological civilization initiative) coupled with population growth and climate change, will cause fierce contradiction between supply and demand of water resources in China in the future (medium confidence). It is predicted that by the 2030s, the vulnerable areas of medium and high levels in water resources will obviously expand, the water crisis will be prominent, and the risk of water resources security will increase sharply (high confidence). In the future, continued warming in summer may cause more glaciers in China to melt (high confidence), and the function of cryosphere in water source and in regulating water availability in wet and dry seasons will also weaken or even disappear. Moreover, regional long-term water crisis may occur in the arid areas of Northwest China (medium confidence). The frequency of cryosphere hazards has further increased (high confidence). Sea level rise will increase not only the intensity of flood disasters in coastal cities, but also the risk of flood disaster and the difficulty of flood control dispatching and command. If effective adaptation measures are not taken, the potential damage may reach 10% of the global GDP by 2100 (medium confidence). Meanwhile, the potential threats and possible economic loss of coastal

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lowlands in China will become more and more serious, which will further aggravate the imbalance of regional economic development. Future climate change will accelerate the degradation trend of ecosystems, such as desertification, soil erosion, rocky desertification and frozen soil degradation (high confidence), and the functions and services of ecosystems will show imbalanced regional characteristics (IPBES 2019). In addition, ecological disasters will increase, the vulnerability in species diversity, germplasm resources and ecosystem will also increase, and some species will even be endangered (medium confidence). Under the background of national policies such as vigorously promoting the construction of ecological civilization, returning farmland to grassland and delineating the red line of ecological protection, as well as the planning and construction of national main functional areas, the expansion rate of urban construction land at the regional scale will further slow down, and the reduction trend of natural vegetation such as forest land and grassland in China will be effectively controlled (medium confidence). The impact of climate change on agriculture in the future is complicated. On the one side, global warming will prolong the planting period of crops and alleviate most low temperature disasters, especially in high-latitude and high-altitude regions. On the other side, extreme high temperature has adverse effects on crop growth, especially in low latitudes. The increase of precipitation will intensify the risk of flood disaster in humid regions, while it is generally beneficial to arid and waterdeficient areas. But Global warming will also increase the water consumption of ecosystems and human system, which increasingly squeezes agricultural water use, and the drought and water shortage in lacking precipitation regions will become more severe. In addition, the increase in agro-meteorological disasters events and pests and the vulnerability of agricultural production system, as well as the decrease in quality of agricultural products of origin (medium confidence), will pose a serious threat to food security (medium confidence). In the future, climate change and non-climate factors will produce stronger and more complex superposition and synergistic effects, which can lead to heavy risks in the construction and operation of major infrastructure projects such as water conservancy, transportation, electric power, and oil and gas pipelines, especially in areas with unstable frozen soils (medium confidence). Climate change impacts people’s health by influencing the nature of urban underlying surface, lifeline system, microclimate and livability of residential buildings, vegetation and water around urban and rural communities (high confidence). In the future, the health risks related to high temperature will be significantly increased, and the control of infectious diseases such as dengue fever and infectious diarrhea will become more difficult (high confidence), Moreover, rapid urbanization and population aging will further aggravate the risk (high confidence). With the change of lifestyle and consumption structure in the future, the demand for resources will further increase, and potential carbon emissions and new pollutant emissions from new industries may occur, which will bring new risks to people’s health and safety, and at the same time bring even greater pressure and challenges to climate and environment.

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1.3.2 Actions to Deal with Climate Change and Protect Environment As the international community continues to deepen its scientific understanding of climate change, it has become the common aspiration and urgent action of all countries to take active measures to address climate change. The Paris Agreement reached at the UN Climate Change Conference on December 12, 2015 clearly stated to hold the increase in the global average temperature to well below 2 °C above pre-industrial levels and pursue efforts to limit the temperature increase to 1.5 °C above pre-industrial levels. This manifests that international climate governance has entered a new stage (Fig. 1.6). The range of temperature rise in the future is jointly determined by the historical accumulation and the greenhouse gases emitted in the future. Achieving the net zero carbon emissions as soon as possible will make it possible to achieve the goal of temperature rise control. The contribution of the Working Group I of IPCC AR6 has pointed out that, to control the human-induced global temperature rise at a specific level, it is necessary to limit the cumulative CO2 emissions and at least achieve net zero emissions of CO2 . In the low-emission scenario, net zero emissions are needed around 2070 to achieve the 2 °C temperature rise target, while achieving the 1.5 °C temperature rise target requires net zero emissions by around 2050, with strong carbon negative emissions after that. At the same time, other greenhouse gas emissions also need to be greatly reduced, and rapid and sustained reduction of methane and other greenhouse gases will also help improve air quality. China has made contributions in promoting and guiding the establishment of a fair, reasonable and win-win global climate governance system, and has achieved remarkable results with a series of measures such as industrial structure adjustment, energy structure optimization, energy conservation and energy efficiency improvement, carbon market establishment, and forest carbon sink increase. The carbon emission intensity in 2019 was 48.1% lower than that in 2005, exceeding the target of reducing the carbon emission intensity by 40–45% in 2020 compared with that in 2005, which reversed the rapid growth of CO2 emissions. Despite the rapid economic growth, China is still in the process of industrialization and urbanization, and the per capita GDP and social development level are still far from those of developed countries. China is still faced with a series of challenging tasks such as developing the economy, improving people’s livelihood, eliminating poverty and controlling pollution. The Report of the 19th National Congress of the Communist Party of China clearly states that China will basically realize socialist modernization by 2035, the ecological environment will be fundamentally improved, and the goal of a Beautiful China will basically be achieved. In China, it is emphasized that tackling climate change is an inherent requirement of sustainable development and is the responsibility for promoting the construction of a community with shared future for mankind. China has made new contributions to achieving the ambitious goal of a Beautiful China and the global response to climate change. For example, China has implemented the national strategy of actively responding to climate change, participated

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Fig. 1.6 Development process of the UNFCCC (this figure expanded and improved on the basis of Wen and Ma 2017)

in and led the global climate governance, supported the research and development and popularization of various low-carbon technologies, strengthened the capacity building of climate change response, controled greenhouse gas emissions, advocated a green and low-carbon lifestyle, promoted the economic transformation and the construction of ecological civilization, and coordinated environmental pollution control. China has promulgated laws and regulations such as the Action Plan for Air Pollution Prevention and Control, vigorously carried out environmental protection actions, and made positive progress in mitigating and adapting to climate change (Ministry of Ecology and Environment 2019). China will also keep the medium- and long-term environmental governance strategy in line with the strategy of coping with climate change. Before 2030, China will take environmental governance as the starting point to achieve the target of, greenhouse gas emission reduction, reduce the degree of environmental pollution and lessen the pressure of environmental governance; after 2030, China will further improve the domestic environmental quality through climate governance, and fully leverage its coordinating role in tackling climate change and environmental pollution. Pilot constructions in China, such as low-carbon cities, new energy cities, climate change-adaptive cities and sponge cities, will provide technical support and policy pathway for collaborative governance of greenhouse gas emission reduction and urban development.

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1.3.3 Transition to Sustainable Development Sustainable development requires synergy among economy, society and environment, which provides a green development path for high-quality development of society and economy and high-level protection of ecological environment. On September 22nd, 2020, President Xi solemnly announced at the general debate of 75th Session of the United Nations General Assembly that China would scale up its Nationally Determined Contributions (NDC) by adopting more vigorous policies and measures, strive to peak carbon dioxide (CO2 ) emissions by 2030 and achieve carbon neutrality by 2060. Compared with western countries, China has only 30 years to reach carbon neutrality from the peak point of CO2 emissions. The time spell to realize carbon neutrality is short and the starting point is high. Hence the transition to sustainable development is an inevitable choice to achieve carbon neutrality. The carbon dioxide emissions peaking and carbon neutrality will have a positive impact on China’s response to climate change, and they are boosters for the sustainable development. Achieving carbon neutrality requires obvious transformations in the fields of the socio-economic system, energy system and technical system. It is necessary to transform the styles of economic growth and social consumption, adjust industrial structure, promote technological innovation, save energy, improve efficiency and reduce emissions, and optimize energy structure, so as to maintain sustained economic development and ensure that CO2 emissions will not increase any more. At the same time, nature-based solutions in agriculture, forestry, land use, grassland and wetland etc. should be implemented to enhance the service function of ecosystems. Finally, on the basis of the enhanced resilience of the comprehensive social-ecological system, the ability of the whole society to cope with climate change can be enhanced, and the smooth transition to sustainable development can be realized. Knowledge Tips: Carbon Neutrality Carbon neutrality refers to achieving net zero carbon dioxide emissions by balancing anthropogenic carbon dioxide emissions with the anthropogenic carbon dioxide removal, or completely eliminating anthropogenic carbon dioxide emissions. Carbon neutrality goals can be set at different levels such as global, national, regional, city, industry, enterprise and activity. Greenhouse gases neutrality means to achieve zero climate effects of all man-made emissions of greenhouse gases through human efforts. Climate neutrality means that all human activities (man-made greenhouse gas emissions, land use changes, etc.) have zero impact on the climate system through human efforts.

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1.4 Contribution of China’s Assessment Reports on Climate, Environment and Ecology After the publication of the Assessment of Environmental Evolution in Western China in 2002, Climate and Environmental Evolution in China and Climate and Environmental Evolution in China: 2012 were published successively in 2005 and 2012, forming a unique series of scientific assessment reports on climate change and ecological environment evolution in China. Aiming at the climate system, this series of reports took the assessment of climate and environmental change under the influence of human activities as the main line and refer to the IPCC report assessment methodology to have systematically assessed the information related to China’s climate, ecological environment changes, and economy and society, which objectively and comprehensively reflects the latest research results in China’s climate and environmental evolution. The Assessment of Environmental Evolution in Western China published in 2002, for the first time, comprehensively reviewed the characteristics of climate, ecology and environment in western China, their evolution and causes, future changes, historical experience and bearing capacity, and put forward recommendations on rational utilization of water resources, ecological construction and environmental governance, etc. The bearing capacity of climate and environment has attracted more and more attention. On the basis of the Assessment of Environmental Evolution in Western China, the Climate and Environmental Evolution in China has expanded its scope to the whole country. This is the first scientific report that comprehensively reviewed the scientific facts of China’s climate and environmental evolution, projected future changes, comprehensively analyzed its socio-economic impacts, and discussed adaptation and mitigation measures. The Climate and Environmental Evolution in China: 2012 further confirmed the assessment conclusion of China’s climate change in the last hundred years with more updated research results, and human activities are the main cause of temperature rise and environmental change since the late twentieth century. It proposed that the choice of adaptation and mitigation technologies and policies is the key to China’s action against climate change, and pointed out the research priorities and direction in science, impact, adaptation and mitigation, and strategy. The assessment has promoted the continued expansion and deepening of China’s research on climate and environmental change, promoted the integration of climate change, ecological environment and socio-economic disciplines, and made contributions to the development of climate system science and Earth system science. It has also made important contributions to national decision-making process and mediumand long-term planning, preparation of IPCC assessment report, and cultivation of climate change talents (Table 1.1). The main scientific conclusions are as follows. (1) Assessment of Environmental Evolution in Western China: It was the first time to have systematically put forward the perspectives of warming and wetting

1.4 Contribution of China’s Assessment Reports on Climate, Environment …

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Table 1.1 Correspondence between assessment reports on climate and environmental evolution in China and IPCC reports

Corresponding IPCC reports

Corresponding national assessment reports Contribution to IPCC

Assessment of Environmental Evolution in Western China (starting time: 2000)

Climate and Environmental Evolution in China (starting time: 2002)

Climate and Environmental Evolution in China: 2012 (Starting time: 2008)

Third Assessment Report (IPCC TAR)

Fourth Assessment Report (IPCC AR4)

Fifth Assessment Report (IPCC AR5) (The 2021 report corresponds to the Sixth Assessment Report (IPCC AR6))

First National Assessment Report on Climate Change

Second National Assessment Report on Climate Change

(1) Ding Yihui, Qin Dahe and Zhai Panmao served as co-chairmen of IPCC Working Group I during the preparation of TAR, AR4 and AR5, and AR6, respectively (2) 16, 19, 25, and 23 authors respectively served as the coordinating lead author (CLA), lead author (LA), and review editor (RE) of the IPCC AR4, IPCC AR5 and IPCC AR6. 6, 7, and 11 authors respectively served as the CLA, LA and RE of the special reports of IPCC AR4, IPCC AR5 and IPCC AR6

trend in western China from multiple circles. It projected that cryosphere would continue to shrink, and mountain disasters and snow and ice disasters would increase in scope and frequency. It concluded that land desertification would further aggravate if no measure is in place. (2) Climate and Environmental Evolution in China: Observations and evidence confirmed the assessment conclusions of climate and environmental change in China in the past century under the background of global warming. It is confirmed that human activities have been the main cause of climate warming and environmental change in China since the late twentieth century. Climate change has had a significant impact on China’s natural environment and socioeconomic fields. Adaptation and mitigation technologies and policy options are the key to China’s actions to cope with climate change. (3) Climate and Environmental Evolution in China 2012: It further evaluated the climate and environmental change in China in the past hundred years under the background of global warming, further confirmed the conclusion that human activities are the major cause for global warming, and projected the possible climate change in the future by using CMIP5. Besides, it comprehensively assessed the impacts, manifestations and degrees of impacts of climate change on water, terrestrial ecosystem, terrestrial environment, agriculture, human habitat and health, and other sectors, pointing out that taking the road of

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green industrialization and new urbanization characterized by low carbon is an inevitable choice for sustainable development. Contributions of these assessments to national decision-making consultation process and medium- and long-term planning. (1) Assessment of Environmental Evolution in Western China: It put forward suggestions on rational utilization of water resources, ecological construction and environmental governance, and provides a scientific basis for implementing the strategy of developing the western region, scientifically utilizing and allocating western resources, and protecting the regional environment. Relevant advisory reports were submitted to the State Council. (2) Climate and Environmental Evolution in China: Aiming at the characteristics of climate and environmental problems faced by each of China’s seven major administrative regions, it put forward targeted countermeasures and suggestions, and provided scientific support for China to formulate policies to deal with climate change and adhere to the independent road of sustainable development. Relevant consultation reports were submitted to the State Council. (3) Climate and Environmental Evolution in China: 2012: It gave countermeasures and recommendations to adapt to and mitigate climate and environmental change, and provided scientific support for China’s National Climate Change Programme, National Strategy of Climate Change Adaptation, National Climate Change Plan (2014–2020), National Ecological Function Zoning, China’s National Plan on Implementing the 2030 Agenda for Sustainable Development, and ecological civilization construction. Relevant consultation reports were submitted to the State Council.

1.5 Overview of This Assessment The new scientific assessment report Change of Climate and Ecological Environment in China: 2021 is being prepared during the production of the Sixth Assessment Report (AR6) of IPCC. This report synthesizes the latest research results on climate and ecological environment change published in recent 10 years, and summarizes the new progress and consensus on climate change and its impacts in China since the publication of Climate and Environment Evolution: 2012. In particular, the assessment of ecological environment change has been enhanced, and this synthetic volume has been translated into English, with the objective of providing a scientific basis for China’s strategic decision-making in response to the changes in climate and ecological environment. This assessment research got jointly funded by the Chinese Academy of Sciences (CAS) and the China Meteorological Administration (CMA) in 2018. From then on, by drawing on the IPCC working procedures and the experience of routine work for the Climate and Environmental Change in China (in 2005) and the Climate and Environmental Change in China: 2012 (in 2012), CAS and CMA organized

References

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nationwide experts to compile and write this assessment report on the basis of extensive collection of the latest scientific research achievements. After the report drafts were initially formed, they were reviewed many times, including internal mutual review, experts’review, government department review and discussion before the final version of this assessment report The Change of Climate and Ecological Environment in China: 2021 was completed. This report has five volumes: (1) The Change of Climate and Ecological Environment in China: 2021 (Vol. I Physical Basis), (2) The Change of Climate and Ecological Environment in China: 2021 (Part One of Vol. II The Impact, Vulnerability and Adaptation of Sectors), (3) The Change of Climate and Ecological Environment in China: 2021 (Part Two of Vol. II The Impact, Vulnerability and Adaption of Regions), (4) The Change of Climate and Ecological Environment in China: 2021 (Vol. III, Mitigation), and (5) The Change of Climate and Ecological Environment in China: 2021 (Synthesis Report) (in Chinese and English). Nearly 200 experts participated in the preparation of this report. They are from different sectors, academic institutions and universities, including the Chinese Academy of Sciences, China Meteorological Administration, Ministry of Education, National Development and Reform Commission, Ministry of Water Resources, Ministry of Natural Resources, Ministry of Agriculture and Rural Affairs, and Chinese Academy of Social Sciences. Hundreds of front-line experts were invited to review the full text, and there were 16 ministries or departments involved in the review. More than 1000 comments were received, and every comment was considered or replied.

References Bryan BA, Gao L, Ye Y et al (2018) China’s response to a national land-system sustainability emergency. Nature 559:193–204 Fan B, Dong Y (2001) A discussion on China’s ancient forest coverage. J Beijing Forestry Univ 23(4):60–65 (in Chinese) Fang X, He F, Wu Z et al (2021) General characteristics of the agricultural area and fractional cropland cover changes in China for the past 2000 years. Acta Geogr Sin 76(7):1732–1746 (in Chinese) Hao Z, Wu M, Zheng J et al (2020) Patterns in data of extreme droughts/floods and harvest grades derived from historical documents in eastern China during 801–1910. Climate past 16:101–116 IPBES (2019) Global assessment report on biodiversity and ecosystem services of the intergovernmental science-policy platform on biodiversity and ecosystem services. IPBES secretariat, Bonn Li X, Jiang G, Tian H et al (2015) Human impact and climate cooling caused range contraction of large mammals in China over the past two millennia. Ecography 38:74–82 Otavio C (2018) From political to climate crisis. Nat Clim Chang 8(8):663–664 Rockström J, Steffen W, Noone K et al (2009) Planetary boundaries: exploring the safe operating space for humanity. Ecol Soc 14(2):32 Steffen W, Richardson K, Rockström J et al (2015) Planetary boundaries: guiding human development on the changing planet. Science 347(6223):1259855 Steffen W, Rockström J, Richardson K et al (2018) Trajectories of the earth system in the anthropocene. PNAS 115(33):8252–8259

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Su BD, Huang JL, Fischer T et al (2018) Drought losses in China might double between the 1.5 °C and 2.0 °C warming. Proc Nat Acad Sci 115(42):10600–10605 UN (2019) In the face of worsening climate crisis, UN Summit to deliver new pathways and practical actions to shift global response into higher gear. https://www.un.org/en/climatechange/assets/ pdf/CAS_main_release.pdf (2020-03-24) United Nations Environment Programme (UNEP) (2019) Synergizing action on the environment and climate: good practice in china and around the globe. UNEP, New York Wang YJ, Wang AQ, Zhai JQ et al (2019) Tens of thousands additional deaths annually in cities of China between 1.5 °C and 2.0 °C warming. Nat Commun 10(1):3376 Wen SS (2018) Estimation of economic losses from tropical cyclones in China at 1.5 °C and 2.0 °C warming using the regional climate model COSMO-CLM. Int J Climatol 39(4):1–14 Wen ZX, Ma ZY (2017) Process, challenge and China’s action in global governance cooperation for climate change. Environ Prot 45(15):61–67 Zhang D, Li X, Liang Y (2003) Supplement to the atlas of drought and flood distribution in China in the past 500 years (1993–2000). J Appl Meteorolog Sci 14(3):379–388 (in Chinese) Zhang S, Zhang DD (2019) Population-influenced spatiotemporal pattern of natural disaster and social crisis in China, AD1-1910. Sci China Earth Sci 62:1138–1150

Chapter 2

Observed Climate Change and Ecological Environment Evolution and Their Causes

2.1 Observed Facts Since 1900, the mean surface temperature in China has increased significantly, and the atmosphere, hydrosphere, cryosphere and ecosystem, etc., have all shown obvious but regionally different changes. Starting from Climate and Environmental Evolution in China: 2012, observational data and research evidence have become increasingly abundant, which further confirms the core conclusions of the past assessments of China’s climate and environmental change during the observed period under the background of global warming, and also further confirms that human activities are the main cause for the climate warming and environmental change in China since the mid-twentieth Century.

2.1.1 Atmosphere Compared with 1850–1900, global mean surface temperature increased by 1.09 °C in 2011–2020, and the land surface warming (1.59 °C) was much higher than that of the ocean (0.88 °C) (Fig. 2.1). The surface air temperature in China also has risen noticeably. Since 1900, the surface air temperature increase in China has been ranging from 1.3 to 1.7 °C, and the warming trend is equivalent to the change amplitude of global land surface temperature in the same period (high confidence). From 1961 to 2020, the mean surface temperature in China presented an increasing trend with considerable regional differences. The warming rates in western and northern China were higher than those in eastern and southern China, of which the Qinghai-Tibet region had the highest rate of temperature rise, with an average increase of 0.36 °C per decade; North China, Northeast China and Northwest China ranked the next, with the warming rates of 0.33 °C, 0.31 °C and 0.30 °C per decade, respectively; and in East China, the average increase was 0.25 °C per decade. Comparably, the warming rates in Central China, © Science Press 2023 D. Qin et al., The Change of Climate and Ecological Environment in China 2021: Synthesis Report, https://doi.org/10.1007/978-981-99-4487-3_2

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Fig. 2.1 Changes in global mean surface temperature (GMST), global land surface air temperature (GLSAT) and China’s mean surface air temperature (CHINA) from 1850 to 2019 (Li et al. 2020a, b)

South China and Southwest China were relatively slow, rising by 0.20 °C, 0.18 °C and 0.17 °C per decade, respectively. In response to the so-called global warming “hiatus” in the period of 1998–2012, recent studies show that previous analyses of global surface temperature observation datasets underestimated the warming trend during this period, and even that the rate of warming accelerated significantly thereafter. For China since 1998, the trend of temperature change has slowed down slightly, and the maximum temperature in summer rises faster while the increasing trend of the winter minimum temperature becomes slower. Since 1961, the observed temperature in the upper troposphere in China has also shown a significant upward trend, but that in the lower stratosphere has been decreasing (high confidence). IPCC AR6 reported that global averaged precipitation over land has likely increased since 1950 (medium confidence). In China, the number of rain days in the monsoon region of eastern China has decreased significantly since 1961, but the average precipitation intensity has been significantly enhanced (high confidence) (Fig. 2.2). The changes in precipitation in China have obvious seasonal and regional differences. The areas with increased precipitation are mainly located in the Northwest China, in the Qinghai-Tibet Plateau, and in the middle and lower reaches of the Yangtze River and to the south. Over the areas near the Hu Line (i.e., HeiheTengchong Line), precipitation decreases in southern Northeast China, North China to Southwest China. Since the 1970s, when data were available, the atmospheric water vapor content in most areas of China has shown a significant increasing trend (high confidence). The average total cloud cover in China generally shows a decreasing trend, mainly due to the decrease in high clouds. Since 1961, the total surface solar radiation over China has been in a decreasing trend as a whole, but has experienced a phased change process of “dimming first

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Fig. 2.2 Variation trends of mean surface temperature (a) and annual precipitation (b) in China from 1961 to 2020

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and then stabilizing (or brightening)” (low confidence). The mean annual sunshine duration in China has been significantly decreasing, but is obviously different at regional scales (high confidence).

2.1.2 Hydrosphere Regional water cycle in China has shown obvious changes. The measured runoff in western China exhibits an increasing tendency, while that in north presents a significant decreasing trend (high confidence). The measured runoff of the seven major rivers in China is dominated by a decreasing trend. During the period of 1956– 2018, except for the Yangtze River Basin, the measured runoff of the remaining six major rivers in China all showed different degrees of decline; the annual runoff of the upper reaches of the Yellow River and the rivers to its south did not vary apparently, whilst the measured annual runoff in the middle and lower reaches of the Yellow River and the rivers to its north experienced a notable decreasing trend. From 2001 to 2018, the measured runoff of the northern rivers decreased by more than 25%, among which the Haihe River Basin experienced the largest decline, and the Liaohe River and the Yellow River ranked the next. The Huayuankou Station of the Yellow River and the Tieling Station of the Liaohe River witnessed the decreases of 41% and 42%, respectively. In southern China, the runoff of the Pearl River Basin decreased by about 7%, and the runoffs of the Yangtze River and Huaihe River were basically no change as compared to the base period (1956–1979). However, since the 1980s, the runoffs of the Tianshan Mountains, Qilian Mountains, Altai Mountains, Kunlun Mountains and Sanjiangyuan region in China, as well as the runoff from most mountain estuaries in Northwest China, have shown a trend of increasing (high confidence). As for the causes of runoff change, in addition to climate change, there are other factors responsible for the reduction of runoff, such as the construction of water conservancy projects and human excessive water consumption, especially in northern China, where the impact of regional human activities on runoff reduction is particularly prominent (Wang et al. 2020a; b). The amount of groundwater resources across China is generally stable, but there are obvious differences in regional changes, with an obvious attenuation trend in the Haihe River region, Liaohe River region and Yellow River region. Significant changes have occurred in groundwater recharge and drainage structure, evolving from natural recharge only to coexistence or gradual development of natural and human recharge. Changes in precipitation, underlying surface conditions and human activities have led to the changes in groundwater resources (Chen et al. 2020) (Fig. 2.3). The water reserves of lakes in eastern China have decreased, but most lakes in the Qinghai-Tibet Plateau have increased considerably (medium confidence). There are 2693 natural lakes (excluding reservoirs) over the area of 1 km2 in China, with a total area of 81,415 km2 , accounting for about 0.9% of the total land area of China. From the 1960s to 2015, the total area of lakes above 1 km2 in China increased by 5858 km2 , but showed strong spatial heterogeneity: 141 new lakes were added to

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Fig. 2.3 Variation of Measured runoff at typical hydrological stations of seven major rivers in China (Zhang et al. 2020)

arid areas of western China; the lake areas in the Qinghai-Tibet Plateau and Xinjiang increased dramatically by 5677 km2 and 1417 km2 , respectively. However, in Inner Mongolia, the lake area decreased by 1224 km2 , with 333 lakes having disappeared in the eastern moist region of Inner Mongolia and the water reserves of most lakes having reduced greatly (medium confidence). Soil moisture is significantly affected by changes in precipitation, having distinct seasonal and spatial differences (high confidence). During 1980–2010, for the soil moisture in China, there existed an aridification belt from the Northeast to North China and to the Southwest. The aridification phenomenon in the Northeast and North China was particularly serious, while the soil moisture in the QinghaiTibet Plateau, southern Xinjiang, East China and parts of South China showed the characteristic of obvious humidification. The long-term changes in soil moisture are seasonally different. For example, since the 1980s, the winter humidification trend in South China has been remarkable, while there are obvious drying phenomena in summer in parts of the middle and lower reaches of the Yangtze River and the Yellow River Basin. Precipitation is an important replenishment source of soil moisture, and rising temperature can enhance the process of evapotranspiration, leading to a decrease in soil moisture. Especially in arid regions, precipitation plays a major role in the change of soil moisture. The global ocean continues to warm, and the temperature warming range in the offshore areas of China is greater than the global and Northern Hemisphere averages (high confidence). The global ocean has kept warming continuously since 1950 (high confidence). The linear trend of the 2000 m thermal content in the upper

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layer of the global ocean from 1958 to 2017 was very likely to be 0.34 ± 0.12 W/m2 . And ocean warming has accelerated greatly since the 1990s (high confidence). All the Chinese seas present a warming trend, and the average warming amplitude is greater than the global average and the Northern Hemisphere average. The warming range of the East China Sea is the largest among the four marginal seas. China’s coastal sea level has been in a wavelike rise. In the recent 30 years, China’s sea level rise rate has exceeded the global mean rate (high confidence). From 1980 to 2018, the sea level rise rate in coastal areas of China was 33 mm per decade, higher than the recent global average level (the global mean sea level rise rate from 1993 to 2018 was 3.15 ± 0.3 mm/ year with high confidence). The years from 2012 to 2018 are the seven years with the highest sea level along the coast of China since 1980. During 1992–2018, the sea level rise rate was 30–47 mm per decade in the Bohai Sea, 20–69 mm per decade in the Yellow Sea, 16–57 mm per decade in the East China Sea, and 22–60 mm per decade in the South China Sea (high confidence). The microplastic abundance in the four major sea areas of China, ranging from high to low, are the Bohai Sea, the Yellow Sea, the East China Sea and the South China Sea in order, and the microplastic abundance in the coastal waters is higher than in the offshore areas (medium confidence). In terms of the average distribution, the average abundances of microplastics in the Bohai Sea (330–5000 µm), the surface seawater of the East China Sea (mainly concentrated in the coastal waters of the Yangtze River, 333 µm) and the South China Sea (330 µm) are 0.33 ± 0.34 pieces/m3 , 0.167 ± 0.138 pieces/m3 and 0.045 ± 0.093 pieces/ m3 , respectively. Observational data on the abundances, types, and distribution of microplastics in the offshore waters of China are still scarce. Existing surveys and studies are insufficient in temporal and spatial coverage, so it is still difficult to reveal the seasonal and interannual variations of microplastics in China’s offshore waters.

2.1.3 Cryosphere The cryosphere refers to a temperature-below-zero sphere with a certain thickness and continuous distribution on the Earth’s surface. The components of the cryosphere include glaciers (including ice sheets), frozen soil (including permafrost and seasonal frozen soil), snow cover, river ice, lake ice, sea ice, ice shelves, icebergs and submarine permafrost, as well as the frozen water bodies in the troposphere and stratosphere of the atmosphere. The changes in the cryosphere not only impact the variations of global climate, sea level, surface hydrology and water resources directly, but also affect ecology, environment and human society. Under the background of climate warming, the global cryosphere as a whole is shrinking. Correspondingly, the cryosphere in China has also changed obviously (high confidence). During the period of 2006–2015, the negative mass balance of global mountain glaciers [(−490 ± 100)k g/(m2 year)] increased by 30% compared with that in 1986–2005. As compared to the global, the negative mass balance of

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high mountainous areas in Asia is relatively low [(−150 ± 110) kg/(m2 year)], but the regional differences are large. Moreover, the glaciers in the Karakoram Mountain region and the Kunlun Mountain region showed a slight positive balance after 2000 (Fig. 2.4). Since the International Polar Year (2008–2016), the annual mean temperature rise of permafrost in the China region is 7.0%, and that in the Northern Hemisphere is about 8.1%. The thicknesses of active layers in the permafrost regions in China and the Northern Hemisphere increased similarly during 2000–2018, being 27.6% and 27.9%, respectively (Biskaborn et al. 2019). In recent decades, the extent of snow cover in the Qinghai-Tibet Plateau and the Northern Hemisphere showed a decreasing trend, but the amplitude of variation was largely different, with decreases of 72.8 and 8.5% from 2007 to 2016, respectively, compared with that in 1981–1990. As far as snow water equivalent is concerned, both China and Eastern Siberia had an increasing trend, but the growth rate of Eastern Siberia was about 6 times that of China. From 1979 to 2015, the extents of Arctic sea ice and the Bohai Sea ice were reduced by 12.1% and 18.1%, respectively. From 1975 to 2012, the sea ice thickness in the Arctic Ocean decreased from 3.59 m to 1.25 m, and the decrease rate from 1993 to 2007 reached 11.7%. The annual mean sea ice thickness in the Arctic Basin decreased at a rate of −0.58 ± 0.07 per decade from 2000 to 2012. However, the thickness of sea ice in the Bohai Sea in China showed an increasing trend from 2001 to 2016, with a growth of 16.1% (Fig. 2.4).

Fig. 2.4 Comparison of changes of the major elements of the cryosphere in China with that of related elements in global typical regions (Comprehensive drawing based on the evaluation results of Chapter 6 of Volume 1)

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2.1.4 Ecosystem 1. Terrestrial Ecosystems Forest area has increased, wetland area has decreased, and land vegetation coverage has generally increased in China (high confidence). Forest inventory data show that the forest area in China has increased by 38.70% (62 million hm2 ) from 1998 to 2018. During this period, China’s forest stock has increased by 55.85% (6.293 billion m3 ). Based on the National Swamp. Map (1970) and the second national wetland resource survey, the total area of swamp wetlands with an area greater than 100 hm2 has decreased from 4444.8 × 104 hm2 to 2085.8 × 104 hm2 since the 1970s. China’s land vegetation coverage has significantly increased since the beginning of the twenty-first century. Remotesensing observations show that the leaf area of terrestrial vegetation in China has increased by about 18% (about 1.3 × 106 km2 ) from 2000 to 2017, contributing to one quarter of the global increase in leaf area and ranking first globally. According to various remote-sensing vegetation indices, the vegetation coverage in China increased faster from 2000 to 2016 than from 1982 to 1999. The increase in atmospheric CO2 concentration and the implementation of major ecological protection and restoration projects have jointly contributed to the increase in terrestrial vegetation coverage in China (Fig. 2.5). The phenological change of vegetation in China is generally characterized by the early start of the growing season and the late end of the growing season (high confidence). Remote-sensing observations show that the start of the growing season for temperate vegetation in China on average advanced by 1.3 ± 0.6 days per decade, and the end of the growing season delayed by about 1.2 days per decade during 1982–2011. Temperature rise is the major driving factor of vegetation phenology change in China. For example, the date of the leaf spreading period for temperate forests in northern China advances by 3–4 days on average with 1 °C increases in air temperature. For forests in northeastern and central China and meadows in the southeast of the Qinghai-Tibet Plateau, warming in summer and autumn is the main driving factor of the delayed date of the end of the growing season. In addition to warming, precipitation can also influence the vegetation phenology in some regions. For instance, in the arid and semi-arid parts of central and western Inner Mongolia, water condition dominates grassland phenology change. The decrease in precipitation during winter and spring can lead to water stress, which delays the start of the growing season, while the decrease in precipitation during summer and autumn can lead to the advance of the end of the growing season. The GPP and carbon storage of terrestrial ecosystems in China has significantly increased (high confidence). From 1982 to 2015, the GPP of terrestrial vegetation in China has increased by an average rate of 0.02 ± 0.002 Pg C/year (1 Pg = 1015 g). Specifically, GPP has increased in 89.5% area of China, with nearly 60% of the regions showing significantly increasing trends ranging from 0 to 4 g C /(m2 year). Since 2000, the carbon storage of China’s major ecosystems (forests, shrubs, grasslands, and croplands) has significantly increased (high confidence), which is closely

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Fig. 2.5 Variations of average leaf area index (LAI), normalized difference vegetation index (NDVI), enhanced vegetation index (EVI), near-infrared reflectance of terrestrial vegetation (NIRv), vegetation optical depth (VOD), contiguous solar-induced fluorescence (CSIF) and gross primary productivity (GPP) in the vegetation growing season (April–October) in China during 1982–2016 (Piao et al. 2020)

related to the implementation of major ecological protection and restoration projects. Based on inventory data of forest resources, from 2001 to 2010, the carbon storage of terrestrial ecosystems in the regions covered by the six major national projects including the Shelter Forest System Programme in Three-North Regions of China (Shortened as the Three-North Shelter Forest Programme), Shelter Forest System Programme in the Yangtze River and Pearl River Basin, the Natural Forest Protection Programme, the Green Food Programme, the Beijing-Tianjin Sandstorm Source Control Programme and the Project of Returning Farmland to Forest and Grasses,

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has increased by 132 TgC (1 Tg = 1012 g) per year, of which 56% (74 TgC/year) can be attributed to the implementation of the six major ecological projects. Most species in China’s terrestrial ecosystems have been migrating towards the north/ northwest, and towards higher altitudes in Western China. The resource diversity of some species has declined (high confidence). Over the past 50 years, 80–100 species of amphibians, more than 100 species of reptiles, 400–600 species of birds and 120–200 species of mammals have migrated north and west to high altitudes; 300–500 species of bryophytes, more than 20 species of ferns, more than 10 species of gymnosperms, and more than 1000 species of angiosperms have mainly extended polar-wards, with parts towards higher altitude; about 80% of woody plants in the central and eastern China have moved northward. As a result of climate change and human activities, 15 of the local livestock and poultry breeds have disappeared, 55 are endangered, and 22 are dying out. The habitats of some domestic animals have deteriorated, the distributions of some wild relatives have changed, and some species have even disappeared. 2. Marine ecosystems The nearshore seawater in China’s four major sea areas (the Bohai Sea, the Yellow Sea, the East China Sea and the South China Sea) has experienced remarkable eutrophication, with increased dissolved inorganic nitrogen in typical coastal waters one of the most prominent features (high confidence). In the central Bohai Sea, the dissolved inorganic nitrogen in the ocean bottom in summer increased from 2.5 µmol/L in the 1990s to 5.0 µmol/L in the 2000s, then to 9.5 µmol/L in 2015–2016. During 1985–2006, the dissolved inorganic nitrogen in the South Yellow Sea increased from 1.5 µmol/L to 10 µmol/L. From the 1980s to the 2010s, the concentration of inorganic nitrogen in the less salty waters (salinity < 5) in the East China Sea increased from < 60 to > 100 µmol/L. From the 1980s to the 1990s, the coastal eutrophic waters of the East China Sea were mainly distributed near the Yangtze River Estuary and Hangzhou Bay. Since 2000, the nearshore waters of Zhejiang and Fujian provinces have also become eutrophic. The main reasons for the increase of inorganic nitrogen concentration in the nearshore waters of China are the impact of human emissions from terrestrial sources, the offshore input and mixing, and atmospheric deposition. The concentration of dissolved oxygen in typical nearshore waters of the four major sea areas has all decreased, and the hypoxia phenomenon has gradually intensified, especially in summer (high confidence). From 1978 to 2006, the dissolved oxygen in the bottom of the middle cross-section of the Bohai Sea declined at a rate of −0.84 µmol/(L year). By comparison, the content of dissolved oxygen in the cross-section of the North Yellow Sea during August decreased more rapidly during 1976–2015, with a decreasing rate of −1.12 µmol/ (L year). Since the 2000s, the area of low oxygen in the Yangtze River Estuary in the East China Sea has been expanding. In August 2013, an area of 11,500 km2 of hypoxia was observed in the East China Sea. From 1990 to 2014, the dissolved oxygen in the bottom water of the Pearl River Estuary in the South China Sea gradually decreased, and the anoxic area of the Pearl River Estuary aggravated possibly due to eutrophication.

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Seasonal ocean acidification has occurred in the Bohai Sea, the Yellow Sea and the East China Sea. Nevertheless, it remains to be comprehensively observed and evaluated due to the limited data. The Bohai Sea has the longest time series of ocean acidification monitoring among the four major sea areas, with a record of about 36 years. From 1978 to 2013, the average pH values of the surface seawater in the central cross-section of the Bohai Sea increased significantly in summer, but decreased in the bottom seawater. In winter, however, the average pH values of the surface and bottom seawater in the Bohai Sea both showed a decreasing trend. During the period of 2002–2011, the pH value of the surface seawater in spring for the East China Sea presented a downward trend, but showed almost no changes in summer and autumn. Seasonal succession from diatoms to dinoflagellates has occurred in the Bohai Sea, the Yellow Sea and the East China Sea in spring and summer, with the increasing abundance ratio of dinoflagellates (high confidence). Since 2000, the succession of seasonal diatom and dinoflagellates in the coastal waters of China has become increasingly obvious. In the nearshore areas of the Bohai Sea and the Yellow Sea, diatoms evolve into dinoflagellates from spring to early summer. In typical sea areas such as the Yangtze River Estuary and Hangzhou Bay in the East China Sea, the abundance and proportion of dinoflagellates reaches the highest in spring, during which the predominance of dinoflagellates (abundance ratio) is gradually increasing (high confidence). For example, according to the net phytoplankton survey in the Bohai Sea, the phytoplankton community structure gradually changed from that dominated by diatoms to that jointly controlled by both diatoms and dinoflagellates, with the ratio of diatoms to dinoflagellates increased by nearly 3 times during 1959– 2015. The changes in the structure of the phytoplankton community in the Yellow Sea are mainly manifested in the decrease in the abundance ratio of diatoms to dinoflagellates, and the dominant species of phytoplankton has changed from diatoms to dinoflagellates coexisting with diatoms. The number of jellyfish has increased and even erupted near the offshore waters of China. The species of jellyfish and the outbreak area showed significantly interannual variations (high confidence). The number of large jellyfish in the offshore waters of China generally increased, but the number of jellyfish in the Yellow Sea and the East China Sea increased first and then decreased: it began to increase in the 1990s, but declined from 2013 to 2018. Reasons for the changes in jellyfish populations are complex, among which climate warming and human activities are directly or indirectly responsible for jellyfish outbreaks. In the sea areas with jellyfish outbreaks, there is a piece of evidence showing that climate change caused by natural variability in recent years can influence the population size of jellyfish. In addition, the leading factors for jellyfish outbreaks include the increase in extreme weather events, decrease in fish populations, destruction of benthic ecosystems, and coastal zone construction and so forth. 3. Coastal Zone Ecosystems More than 90% of coral reefs in the South China Sea have been destroyed over the past 50 years (high confidence). From 2000 to 2010, the average coral reef

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coverage rate in the South China Sea dropped from 60% to about 20% (Hughes et al. 2013). Among them, the coral reef coverage rate in the Luhuitou area of Sanya decreased from 40% in 1998–1999 to 12% in 2009, and the live coral reef coverage rate in the Yalong Bay area of the northern South China Sea declined from 76.6% in 1983 to 15.3% in 2008 (Yu 2012). The live coral reef coverage rate of Yongxing Island in the Paracel Islands dropped from 90% in 1980 to about 10% in 2009. The coral reef coverage rate in the Xuwen sea area of Guangdong Province decreased from 30%-40% in 2000 to less than 7% in 2008 (Wu and Zhang 2012). The main reasons for the decline of coral reef coverage rate are the increase in seawater temperature, the aggravation of ocean acidification and the overfishing of marine fishery resources (Wu and Zhang 2012; Hughes et al. 2017; Tkachenko et al. 2020; Yu 2012). Since 2001, the total area of mangrove forests in China has significantly increased (high confidence). China’s mangrove forests once dropped from 48,801 hm2 in 1973 to 18,702 hm2 in 2000, a loss of 60%, but by 2015, the area of China’s mangrove forests has recovered to 22,419 hm2 (Jia et al. 2018). Since 2001, the area of mangrove forests in China has increased by 1.8% per year. By the end of 2019, 67% of mangrove forests have been included in nature reserves (Wang et al. 2020a, b). The area of natural wetlands has gradually decreased, while the area of constructed wetlands has enlarged in some regions (high confidence). During the period of 1991—2016, the total wetland area in the Yellow River Delta declined by about 91.39 km2 , with the most drastic area changes occurring in 2000–2010. From 1991 to 2016, the natural wetland area decreased at the rate of 30.21 km2 /year and the constructed wetland increased at the rate of 32.77 km2 /year. For the Pearl River Delta, the area of natural wetlands decreased by 189 km2 from 1980 to 2015, while the area of constructed wetlands enlarged by 284 km2 . In the Yangtze River Delta, wetlands and cultivated lands decreased obviously during 2000–2010.

2.1.5 Planetary Environment Since the pre-industrial era, the effect of solar activity on long-term variation of radiative forcing has been small (high confidence). During the period, the most obvious impact of solar activity is the 11-year cycle, which can produce a difference of about 1W/m2 between the maximum and minimum values. According to IPCC AR5 (2013), from 1750 to 2011, the impact of long-term radiative forcing variation caused by the change of solar activity was less than 0.10 [0.05–0.10] W/m2 . The impact of cosmic radiation on climate change through radiative forcing is negligible. Some studies show that cosmic rays entering the Earth’s atmosphere from space can alter the formation of new particles in the tropospheric atmosphere and promote the formation of cloud condensation nuclei (CCN), thus directly affecting the formation of clouds. Then, changes in cloud characteristics in turn can impact the Earth’s climate. However, the latest research indicates that the effect of CCN caused by the enhancement of cosmic rays through the formation of new particles is very weak, and there is limited evidence for its influence on clouds.

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Volcanic eruptions influence the Earth’s temperature mainly on an interannual scale, having little effect on the temperature trend since the pre-industrial time. The impact of large-scale volcanic eruptions on climate is significant on the interannual scale, which can reduce the average temperature of the Northern Hemisphere by about 0.3 °C and last up to 3–5 years. Moreover, continuous volcanic activities may have a longer impact time. After the eruption of Mount Pinatubo in 1991, the temperature drop in eastern China was up to 0.6 °C. However, there were regional and seasonal differences in the cooling range, which was related to abnormal atmospheric circulation caused by the volcanic eruption (Man et al. 2014; Sun et al. 2019). In recent decades of climate change, jointly with the cooling of the tropical Eastern Pacific sea temperature (Kosaka and Xie 2013) and the negative phases of the multi-decadal oscillations in the Atlantic Ocean, small and medium-scale volcanic activities are considered to be one of the possible factors for the moderation of global warming after 1998 (Santer et al. 2014). For China, the impact of volcanic eruptions on temperature change mainly depends on the latitude and season of eruption (Sun et al. 2019).

2.2 Extreme Events The fifth assessment report of the IPCC (IPCC AR5) has documented that since 1950, many extreme weather and climate events around the world have undergone significant changes. Cold days and cold nights have obviously decreased across the world, while warm days and warm nights have become more and more, especially in most parts of Europe, Asia and Australia, where the heat waves tend to occur more frequently. The land area to have seen the increasing frequency of extreme precipitation is considerably larger than that with the decreasing frequency. Particularly in North America and Europe, the frequency and intensity of extreme precipitation have become obviously increased and enhanced. The areas with more frequent droughts are significantly larger than the areas having decreasing drought events, especially in the Mediterranean and West Africa, where the increasing trend of drought is the most outstanding. With global warming, the frequency of snowfall has declined significantly, especially in North America, Europe, South Asia and East Asia. At the same time, global glaciers continue to shrink, Arctic sea ice is rapidly melting, and the temperature of permafrost has increased greatly with visibly decreasing areas. The occurrence frequency of global tropical cyclones has not changed obviously in the past century, but super tropical cyclones in the North Atlantic region have shown a significant increase since the 1970s; and the severe convective weather, such as hail and thunderstorms, varies unevenly across the globe. Existing detection and attribution studies denote that human activities have affected the changes in most extreme events around the world, including changes in high and low temperatures and extreme precipitation, as well as the retreat of glaciers and the rapid melting of Arctic sea ice. In the context of global warming, the climate extremes over China have also experienced significant changes as described in the following.

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2.2.1 Extreme Temperature Events The number of high-temperature days in China has increased considerably, with expanding affected area and increasing duration (Fig. 2.6a). Since 1961, the average annual frequency of extreme high-temperature events in China has increased by 4.4 days per decade. The number of stations with record-breaking maximum temperatures increased after the 1990s, especially since the beginning of the twentyfirst century. The record-breaking events of the highest temperature have obvious regional characteristics: they mainly occurred in the eastern part of Northwest China and the southern part of North China in the 1990s, while in the twenty-first century, they happened mainly in South China, North China and Sichuan Basin. In addition, the widespread extreme hot events across the country have become more and more with enhanced temperature strength and enlarged influence scope. Actually, the increase in high-temperature events has posed a serious threat to human health, ecological environment and socio-economic development. The frequency of extreme low-temperature events in China has significantly reduced. Since 1961, the days of extreme cold events such as cold nights, cold days and frost in China have shown a significant decreasing trend, and the widespread extreme cold events have also declined greatly in occurrence frequency (9.9 times per decade). Previously, from the 1960s to the 1980s, many record-breaking lowtemperature events happened in China, mainly in North China and Southwest China; in the 1990s, the events became less frequent, mainly appearing in the Hetao region and southern China; after the twenty-first century, Northeast China and North China experienced very cold weather more times than other regions. The increase in greenhouse gas concentration caused by human activities is an important reason for the significant increase of extreme high-temperature events in China, and the impact of land use, such as urbanization, cannot be ignored. In addition, the internal variability of the climate system, such as the Pacific Decadal Oscillation (PDO) and the Silk Road teleconnection pattern, is also correlated to the significant increase of persistent high-temperature events in summer in eastern China. However, the rapid melting of Arctic sea ice, the frequent occurrence of Ural blocking high and the phase transition of Arctic Oscillation (AO) have resulted in the frequent appearance of low-temperature events in northern China since the twenty-first century.

2.2.2 Extreme Precipitation Events The frequency and intensity of extreme precipitation events in China have increased, and the affected area has expanded, but with obviously regional characteristics. During 1961–2018, the annual accumulative rainstorm days (daily precipitation ≥ 50 mm) at stations increased by 3.8% per decade on average across China (Fig. 2.6b). The increasing trend of rainstorm was found mainly in the southern

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Fig. 2.6 Changes in the frequency of extreme high temperature (a), number of rainstorm days (b), frequency of meteorological drought (c) and proportion of landfall typhoons (d) in China during 1961–2018, as well as changes in the frequency of sand-dust processes (e) and haze processes (f) during 2000–2020. Lines represent long-term trends (data in panels a–d are from the Climate Change Center of China Meteorological Administration (2019); data in panels e and f are from the Bulletin of Atmospheric Environment and Meteorology (2020))

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part of China, the Qinghai-Tibet Plateau and the parts of Northwest China, while there was a slight decrease in rainstorm in North China and central Sichuan Province. Over the Jianghuai and South China regions, extreme precipitation events tend to occur in the form of persistent extreme events. During 1961–2018, the maximum daily precipitation presented an increasing trend in most regions of China, with an increase of 2–10 mm per decade in regions south of the Yangtze River, the central and western parts of South China, and Hainan Province, but a decreasing trend in southeastern Inner Mongolia, Beijing-Tianjin-Hebei, northern Shanxi, northern Henan, eastern Gansu, and central Sichuan Province. In the meantime, the areas affected by regional extreme precipitation events also showed a significant increasing trend, especially in the years with large affected areas after 1995. Accordingly, the direct economic losses caused by flood disasters as the result of extreme precipitation were increasing, and the high losses were mainly concentrated in the eastern and southwestern parts of China. At the interannual and decadal scales, extreme precipitation in China is closely related to major sea-air modes, such as El Niño-Southern Oscillation (ENSO), sea surface temperature (SST) anomalies over the Indian Ocean, SST anomalies over the North Atlantic Ocean, AO, North Pacific Oscillation, and PDO. In addition, anomalies of Arctic sea ice and Eurasian snow cover, etc., also had a significant impact on extreme precipitation changes in some areas of China by regulating the local atmospheric circulation in Europe and Asia. Drought in China is characterized by high frequency, wide distribution, long duration, obvious seasonality and regionality. From 1961 to 2018, there were 178 regional meteorological drought events occurred in China, including 16 extreme droughts and 37 severe droughts. The frequency of regional drought events featured an obvious inter-decadal variation, and was more frequent from the late 1970s to the 1980s and also in the early twenty-first century (Fig. 2.6c). The total area of drought events in China is increasing at the rate of 3.72% per decade, and particularly, severe and extreme droughts, as well as prolonged droughts across seasons also increase obviously. The average precipitation in most areas of Northwest China increased significantly after the mid-1980s. Since the twenty-first century, precipitation has further increased, so the drought frequency in Northwest China has shown a decreasing trend as a whole. In Northeast and North China, however, the drought situation has continued to aggravate since the 1950s. Although precipitation in North China has shown a positive trend since 2000, the aridification in this region is still worsening. For Southwest China, the frequency and severity of persistent drought events increased significantly, and especially since the twenty-first century, this region has been in a period of the high incidence of prolonged severe drought events. In South China, the annual precipitation has been increasing, but the frequency of autumn drought events has presented an inter-decadal increase tendency. In particular, since the 1990s, extreme droughts tend to occur more frequently in autumn. Since the beginning of the twenty-first century, there has been a significant increase in concurrent events of drought and high temperature, and such concurrent events often have more serious impacts on crops.

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There are many factors affecting drought changes, including local precipitation, temperature, solar radiation, wind speed and so on, among which precipitation is the most important. In addition, the elements including ENSO, PDO, North Atlantic Oscillation (NAO), East Asian westerly jet, Arctic sea ice and snow cover on QinghaiTibet Plateau, etc., also play very important roles in influencing the changes in drought in China. The increase in persistent drought events in Southwest China since 2000 is closely related to the inter-decadal transition of the phase of AO and the anomalous warming of the tropical western Pacific and the tropical Indian Ocean.

2.2.3 Typhoon and Severe Convective Weather The proportion of landfall typhoons has increased significantly in China, and the extreme precipitation caused by typhoons has shown an increasing trend in the southeast coastal areas. From 1961 to 2018, the number of typhoons generated in the Northwest Pacific and South China Sea (central wind force ≥ Scale 8) has shown an inter-decadal declining trend. Especially since 1995, the total number of typhoons has been relatively low, but the average duration of typhoon activities has increased. During 1961–2018, there was no obvious trend in the number of typhoons that landed in China, but the proportion of landfall typhoons in China increased significantly (Fig. 2.6d), and the typhoon intensity has become stronger since the late 1990s. Since 1961, the frequency of typhoon precipitation in the summer half year has shown a distinct downward trend (4.8% per decade) in China, resulting in a decreasing trend of typhoon precipitation (1.7% per decade). Since the early of the twenty-first century, the apparent reduction of tropical cyclones in the Northwest Pacific is related to the increase in local vertical wind shear and the weakening of the relative vorticity in the lower troposphere. However, the tracks of tropical cyclones in the Northwest Pacific tend to move to the northwest, contributing to the enhancement of typhoons affecting China. The intensification of local warming in the Northwest Pacific and the abnormal distribution of La Niñatype SST in the Pacific Ocean in recent years is the dominant factors that result in the tracks of tropical cyclones moving to the northwest and the increase in strong typhoons in East Asia. The occurrence days of severe convective weather such as thunderstorms and hailstorms have shown a clear decreasing trend in China, but the number of tornadoes has increased. From 1961 to 2018, the annual thunderstorm days in North China (Beijing Observatory) decreased significantly at the rate of 1.5 days per decade. The annual thunderstorm days in Northeast China (Harbin Meteorological Station) experienced an inter-decadal variation: fewer in the 1970s, more in the mid1980s to the mid-1990s, and fewer again after that. The annual thunderstorm days in East China (Xujiahui Observatory, Shanghai) had a weak decreasing trend, but became increasing since 2015. In Southeast China (Hong Kong Observatory), the number of thunderstorm days increased significantly at a rate of 2.8 days per decade. The number of hailstorm days in China was relatively stable before the 1980s, but it

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continuously decreased after that, especially in northern China and the Qinghai-Tibet Plateau. The number of tornadoes in China showed an increasing trend from 1948 to 2012, with about 200 tornadoes occurring in the peak year. Strong tornadoes mainly took place in Jiangsu, Shanghai and northern Zhejiang along the eastern coast of China, and only a few strong tornadoes were seen in the southern coast (Guangdong) and the three provinces of Northeast China.

2.2.4 Sand-Dust Storms and Haze The number of sand-dust weather processes has been decreasing in general, and the reduction of sand-dust storms and strong sand-dust storms is particularly obvious. From 2000 to 2020, sand-dust storms and strong sand-dust storm events did not happen so frequently, showing an overall decreasing trend (Fig. 2.6e), but in some years, such as in 2000 and 2001, sand-dust storms occurred more. For strong sand-dust storms, there were 21 times during 2000–2009, and only 11 times during 2010–2019. During the period of 2000–2020, the number of haze days in China was first upward and then downward. The number of haze days began to increase from 2000, reaching a peak in 2013 (15 times), and then declined obviously (Fig. 2.6f). The variation in the strength of the East Asian monsoon, the decrease in precipitation and the decrease in wind speed are all related to the changes in the number of haze days. In most regions, the number of haze days turned from rising to falling, especially in eastern China, where the concentration of PM10 and PM2.5 decreased significantly. In short, the overall atmospheric environment in China showed a trend of deterioration in the early stage but improvement in the late stage during 2000–2020.

2.2.5 Cryospheric Events Glaciers have retreated significantly, and ice avalanches have become more frequent. From the first glacier cataloguing (1960s–1980s) to the second one (2004– 2011), the area of glaciers in western China decreased by about 18%, of which about 81% of glaciers were retreating. The melting of glaciers has obviously enhanced the occurrence frequency of ice avalanches and glacier surging. The triggering factors of ice avalanches and glacier surging are complex, and are not only controlled by external factors such as climate change and local geological conditions, but also affected by morphology, thermal conditions and flow conditions of the glaciers themselves. Glacial lakes have increased significantly, and glacial lake outburst events have increased. There are 17,300 glacial lakes with an area larger than 3600 m2 in western China, covering a total area of 1133 ± 148 km2 . Climate warming has resulted in a significant increase and expansion of glacial lakes. From 1990

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to 2010, the number and area of the glacial lakes in western China increased by 24% and 22%, respectively. The instability of glacial lake dam will lead to glacial lake outburst, which will cause flood disaster and further damage the downstream areas. At present, glacial lake outbursts mostly occur in the regions of the Himalaya Mountains, Nyenchen Tanglha Mountains and Tianshan Mountains (Fig. 2.7). Since the 1930s, glacial lake outburst events have occurred more than 40 times in China and suggested a significant increasing trend. Permafrost has degraded significantly, leading to frequent thermal melting disasters. The permafrost covers about 106 × 104 km2 in the Qinghai-Tibet Plateau. Since the 1980s, the area of permafrost has decreased by 4.3 × 104 km2 per decade in the Qinghai-Tibet Plateau. The active layer of permafrost deepened at the rate of 1.95 cm/yr along the Qinghai-Tibet Highway from 1981 to 2018. The deepening of the permafrost active layer and the melting of underground ice can cause the occurrence of thermal karst landforms such as thermal melting landslides and thermal melting lakes and ponds. The growth rate of the area of thermal thawing lakes and ponds was 0.35%/yr during 1969–1999 and 0.42%/yr during 1999–2006 in the Beiluhe region in the central part of the Qinghai-Tibet Plateau, showing an increasing trend. Half of the permafrost crossed by the Qinghai-Tibet Railway is

Fig. 2.7 Spatial distribution of observed and recorded cryospheric disasters in China and its surrounding areas (Wan and Xiao 2019)

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high-temperature permafrost (≥ 1 °C), which has a great risk of potential thermal settlement. Extreme snowfall has increased and intensified, and snow disaster shows a significantly increasing trend. During 1961–2011, snowstorm (defined by an absolute threshold) mainly occurred in Northeast China and northern Xinjiang. Snowstorm days were relatively fewer in these two regions before the mid-1980s, but slightly increased after the mid-1980s, and significantly increased after the beginning of the twenty-first century. From 1961 to 2017, the amount and days of extreme snowfall in the winter half year increased by 2.2 mm per decade and 0.25 days per decade, respectively, in the Sanjiangyuan region. The increase in extreme snowfall has led to an increasing trend of snow disasters, which are mainly distributed in the Qinghai-Tibet Plateau, northern Xinjiang, and Inner Mongolia (Fig. 2.7). During 1961–2015, the Qinghai- Tibet Plateau experienced 238 large-scale snow disasters. In general, large-scale snow disasters have a decreasing frequency, while small-scale snow disasters have an increasing frequency. From 1954 to 2018, a total of 403 snow disasters occurred in Xinjiang, of which 277 snow disasters occurred in the past 20 years (2000–2018), accounting for 69% of the total. The frequency of sea ice disasters has not changed significantly, but the disaster losses have increased. Sea ice disasters are mainly distributed in the Bohai Sea and the northern part of the Yellow Sea (Fig. 2.7), mainly affecting fishing, aquaculture and waterway transportation, and so on. From 1963 to 2016, the sea ice generally showed a downward trend in China. The frequency of sea ice disasters has not changed significantly, but the losses caused by sea ice disasters have increased, and the main affected areas were Liaoning and Shandong provinces.

2.2.6 Forest Fire Weather Forest fire weather in China has increased since 1971. Forest burning requires fire-risk weather, forest combustibles and fire sources. The occurrence and development of forest fires are affected by many factors, such as meteorological conditions and vegetation conditions, among which meteorological conditions have the most significant impact on the occurrence and development of forest fires. Sustained high temperature, reduced precipitation and dry air are all favorable meteorological components for forest fires, and wind speed and direction can significantly impact the spread speed and propagation direction of fires. In the past half century, the average temperature in the forest distribution areas of China showed an upward trend, while the annual precipitation did not change significantly. The mean temperature in the fire-risk period in all forest distribution areas increased greatly, but the precipitation only had a dramatic increase in the desert coniferous forest areas in the arid areas of the middle temperate zone. The precipitation variation in other areas was not distinct. Generally speaking, in the past 50 years, with the influence of climate change, the forest fire risk in Northeast China has increased significantly, the number of days with high forest fire risk has also increased significantly, the prone period of forest fire has

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been prolonged, and the probability of serious and extraordinarily serious fires has increased. The risk degree of forest fire in North China has also increased, but not as significant as that in Northeast China. The variation trend of forest fire in the east of Northwest China was not obvious. The forest fire risk in northern Xinjiang has shown a significant downward trend throughout the year and the fire-prone period has also become shorter (Niu and Zhai 2012). In addition, with climate warming, the structural change of forest ecosystem and the migration of vegetation belts have led to the death of some vegetation as a result of their failure to adapt to the new environment, which in turn have caused the increase of forest combustibles. At the same time, climate warming has altered forest combustibility by changing the physical and chemical properties of vegetation, leading to an increase in forest fire risk levels (Wei et al. 2020).

2.2.7 Compound Extreme Events According to the definition of IPCC AR6, compound extreme events can be classified into: preconditioned events, where a weather-driven or climate-driven precondition aggravates the impacts of a hazard; multivariate events, where multiple driving factors and/or hazards lead to an impact; temporally compound events, where a succession of hazards leads to an impact; and spatially compound events, where hazards in multiple connected locations cause an aggregated impact. The frequent compound extreme events in China mainly include high-temperature and drought, in summer and low-temperature, sleet and freezing disaster in winter, etc. From 1961 to 2018, the frequency of compound high-temperature and drought events in China tended to increase, especially in Southwest China, eastern Northwest China and southeastern coastal regions of China. The occurrence of large-scale compound high-temperature and drought events is generally accompanied by the stable maintenance of large-scale high-pressure systems. Besides, human activities may have contributed to the increase in frequency. From 1961 to 2014, the occurrence frequency of low-temperature, sleet and freezing disaster tended to decrease in China, and its affected area also decreased. The occurrence of low-temperature, sleet and freezing disaster events is often related to the composite anomalies of large-scale circulation systems caused by AO, Rossby wave train and quasi-stationary front. Human activities may lead to the reduction in its frequency. The frequency of serious landslides and debris flows in China increased during 1950–2016. The triggering mechanism of landslides and debris flows is extremely complicated. Precipitation is one of the main factors affecting their occurrence. Especially in mountainous areas with complex terrain, the occurrence of landslides and debris flows is closely related to precipitation. In the past 60 years, the frequency of extreme precipitation and persistent precipitation in China has obviously increased, resulting in a significant increase in serious landslides and debris flows, especially in the middle reaches of the Yangtze River, the Yunnan-Guizhou Plateau, the Sichuan

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Basin and its surrounding mountains. In addition, the southeastern hills, northwestern Tianshan Mountains, western Kunlun Mountains and northeastern Changbai Mountains are also prone to landslides and debris flows (Lin and Wang 2018).

2.2.8 Attribution of Extreme Events It is very likely that human activities have changed the occurrence probability of hot extremes and cold extremes in China. On the whole, the current research on the attribution of temperature extremes in China is mainly based on the newest observation and global climate model data, and some studies also use reanalysis data and regional climate model data. The methods mainly include the optimal fingerprinting method, risk probability method and stepwise attribution risk method, etc. As for heavy precipitation and extreme drought events, existing studies not only quantify the contribution from anthropogenic forcing, but also consider the impacts of atmospheric circulation, the sea surface temperature and sea ice. Due to the framing issues caused by the definition of extreme events, different temporal and spatial scales used, etc., the current attribution results still show uncertainties in anthropogenic influence on some variables. But on the whole, it is found that human activities have affected the occurrence probability of some extreme events. Among them, the anthropogenic influence on hot and cold temperature extremes is clear, while the influence on precipitation extremes is still uncertain. The attribution studies on the drought is still limited while drought can be affected by different anthropogenic and natural factors (Table 2.1).

2.3 Impacts of Human Activities on Climate Change in China 2.3.1 Impact of Human Activities on Atmospheric Composition and the Generated Radiative Forcing Evidence for the leading role of human activities in climate change is increasing in IPCC assessment reports. The major conclusion on the attribution of climate change in the IPCC AR5 is that human activities have played a leading role in climate change since the 1950s, and the credibility of this conclusion is over 95%. Human activities affect climate change mainly in the following ways: greenhouse gases (such as CO2 , CH4 , N2 O, etc.) and short-lived climate driving matters (such as black carbon, organic carbon, sulfate, nitrate, ammonium salt aerosols) emitted from fossil fuel combustion and biomass burning, significantly increase the concentrations of various atmospheric components in the atmosphere, thereby changing the radiation energy budget of the Earth’s climate system. Besides, changes in land use and land

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Table 2.1 Attribution of regional extreme events in China Extreme events

Regions and events

Contribution of human activities

High temperature and The 2013 summer heatwave in central and eastern heatwave China, the 2014 spring high temperature in northern China, the 2015 summer high temperature in western China, the July 2017 high temperature in central and eastern China, the 2018 summer high temperature in eastern China, etc.

Human activities are very likely to increase the occurrence probability of high-temperature events

Low temperature and The 2015 winter cold surge, the January 2016 super cold wave cold surge in eastern China, etc.

Human activities are very likely to decrease the occurrence probability of low temperature and cold wave

Extremely severe precipitation

The July 2012 extreme heavy precipitation in North China, the 2015 summer extreme heavy precipitation in South China, the 2016 summer extreme heavy precipitation in the middle and lower reaches of the Yangtze River, the June 2017 extreme heavy precipitation in Southeast China, the 2018 extreme heavy precipitation in central and western China, etc.

Human activities have increased or decreased the probability of extremely severe rainfall events (medium confidence)

Extreme droughts

The 2014 summer heavy drought in North China, the 2015 summer and autumn severe drought in North China and other regions, the March to July 2017 heavy drought in Northeast China, etc.

Human activities have affected the occurrence probability of extreme droughts (low confidence)

cover have altered the content of atmospheric components and the surface features as well, leading to changes in the transport of energy, momentum and water between the land and the atmosphere. With the rapid development of the global economy and the intensification of human activities, the total amount of energy consumption in the world has been growing since the 1950s. From 1980 to 2018, the total global primary energy consumption increased from 6.63 to 13.865 billion tons of oil equivalent, of which coal consumption increased from 1.80 to 3.77 billion tons of oil equivalent. The increase in energy consumption has led to a significant increase in the concentrations of global greenhouse gases, aerosols and other atmospheric components. The situation in China is even more prominent. China, with a population of 1.4 billion, is the country of the world’s second largest economic scale. The area of China is similar to that of the United States or entire Europe. However, the United States has only more than 300 million people, and Europe has about 600–700 million people. Thus, China has the largest energy consumption intensity in the world. With the sustained and

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rapid development of the national economy, the consumption of fossil fuels, mainly coal consumption, has increased significantly in China since the 1980s (Fig. 2.8). With the continuous national policies on climate change, energy conservation and emission reduction, the “Action Plan for Air Pollution Prevention and Control” (“Ten Articles of Atmosphere”) for reducing air pollution emissions was issued and implemented in 2013. Therefore, the coal consumption in China decreased during the period of 2013–2016, and it fluctuated increasing slightly after 2016, but generally it did not increase significantly after 2013. Statistically, China’s coal consumption rose by about 549% from 1981 to 2019. Actually, China had ranked first in the world in total power generation, coal output, steel output, cement output and non-ferrous metal output for many years by 2013, being a veritable “world factory”. However, with China’s response to climate change and the implementation of the “Ten Articles of Atmosphere” on the prevention and control of air pollution, the proportion of coal consumption in primary energy consumption in China dropped from about 67% in 2013 to about 59% in 2018, yet its total consumption was still high. In 2019, the global coal consumption was 157.86 × 1018 J, of which 81.67 × 1018 J of coal were consumed in China, accounting for 51.7% of the world’s total coal consumption and about 3.5 times that of the United States and Europe combined. Accordingly, the change of atmospheric composition caused by such high-intensity human activities has a significant impact on climate change in China. Driven by rapid economic growth, the global average annual CO2 emissions increased three times from the 1960s to 2008–2017. In the 1960s, the global average annual CO2 emissions were only 11.367 ± 0.073 billion tons, of which three-quarters of the emissions came from Europe and North America that had developed rapidly since the Industrial Revolution. Between 2008 and 2017, the global average annual CO2 emissions tripled to 34.467 ± 0.183 billion tons, and the increase was mainly concentrated in East Asia and South Asia. Since the twenty-first century, the rapid economic development of large developing countries such as China and India has promoted the rapid growth of energy consumption, and the growth rate of global CO2 emissions has begun to increase (Fig. 2.9). According to the data provided by

Fig. 2.8 Total coal consumption in China and its proportion in the world’s total coal consumption (the data of China’s total coal consumption in 1981–1999 are from the Compilation of Statistical Data in the 60 Years of New China, the data after 2000 from the National Bureau of Statistics, and China’s coal consumption ratio data from BP Statistical Yearbook of World Energy)

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Fig. 2.9 CO2 emissions from fossil fuel combustion and industrial production processes in major countries during 1970–2017 (unit: 100 million tons)

“Our World in Data” of Oxford University, the United States accounted for 25%, the European Union for 17.4%, and China for 13% of the global accumulated CO2 emissions from 1750 to 2019, and China’s cumulative emissions were only half that of the United States. The “Emissions Gap Report 2020” released by the UNEP also clearly pointed out that China’s current per capita greenhouse gas emissions are still lower than the average level of developed countries, close to the level of the European Union, and far lower than that of the United States and Russia. The observed concentrations of major greenhouse gases in the global atmosphere are increasing, and those of China are slightly higher than the global means (Fig. 2.10). Since the 1950s, the observed concentrations of major greenhouse gases in the global atmosphere have been increasing. As of 2019, the global atmospheric concentrations of CO2 , CH4 and N2 O had reached 410.5 ± 0.2 ppm, 1877 ± 2 ppb, and 332.0 ± 0.1 ppb (1 ppm = 1000 ppb), respectively. The atmospheric concentrations of greenhouse gases have also continued to rise in China, generally higher than global or the Northern Hemisphere levels for the same period. Observations from the Waliguan Global Atmospheric Background Station (36°17 ' N, 100°54 ' E; elevation: 3816 m), located in Qinghai Province, China, show that the CO2 , CH4 , and N2 O concentrations at this station in 2019 were 411.4 ± 0.2 ppm, 1931 ± 0.3 ppb, and 332.6 ± 0.1 ppb, respectively. From 2010 to 2019, the annual average absolute increments of CO2 , CH4 , and N2 O concentrations in China were 2.4 ppm, 7.7 ppb, and 0.95 ppb, respectively. The observed global emissions of major air pollutants have increased significantly, and the increasing rates of air pollutant emissions in China have exceeded the global average since the reform and opening-up policy. From 1990 to 2014, global NOx and ammonia emissions both increased by 23%, volatile organic compound emissions by 9%, black carbon emissions by 27% and organic carbon emissions by 26%, while SO2 emissions decreased by 22% (Hoesly et al. 2018). The increasing rates of air pollutant emissions in China are much higher than the global average growth rate. In China, NOx emissions ascended by 313%, volatile organic compound emissions by 168%, SO2 emissions by 131%, ammonia emissions by 29%, and primary PM2.5 emissions by 28% during the period of 1990–2013.

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Fig. 2.10 Variation of monthly mean atmospheric CO2 concentration at global atmospheric background stations of Waliguan, Qinghai, China and Maunaloa, Hawaii, United States, during 1990–2019 (quoted from China Greenhouse Gas Bulletin 2019)

The emission of air pollutants in China was significantly reduced five years after the implementation of the “Ten Articles of Atmosphere”, but the emission intensity was still higher than those of North America and Europe. Since the implementation of the “Ten Articles of Atmosphere” in 2013, China has achieved significant reductions in the emission of major air pollutants. In 2017, SO2 , NOx and primary PM2.5 emissions dropped by 62%, 17% and 33%, respectively, compared with 2013, and the PM2.5 concentration in the three key regions of Beijing-TianjinHebei, Yangtze River Delta and Pearl River Delta decreased by 28–40% (Zhang and Geng 2019). However, the emission intensity of the Beijing-Tianjin-Hebei region, which had the largest emission of air pollutants in China, was still 3–12 times that of the United States and 4–13 times that of Europe by the end of 2018 (assessment report of the “Ten Atmosphere Articles”). Compared with the major developed economic regions in the world, the emissions and concentrations of atmospheric aerosols in China are still at a relatively high level. Climate warming has an impact on the increasing concentration of atmospheric aerosols in China, but it does not play a leading role compared with the increasing atmospheric aerosol emissions. Adverse meteorological conditions are the necessary external conditions for the occurrence of aerosol pollution in the stable emission period. As pollutants accumulate, pollution will cause further unfavorable weather conditions, forming a significant two-way feedback effect between accumulated pollution and unfavorable meteorological conditions (medium confidence) (Fig. 2.11). The growth of aerosol concentration is closely associated with the increase in emissions of air pollutants. The inter-decadal

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variation of atmospheric aerosol pollution in China is also affected by the interdecadal climate change featured with warming, but it does not play a leading role. During the period when emissions can be regarded as basically constant, like in the winter of one year, the appearance of aerosol pollution is due to the unfavorable meteorological conditions with stable regional air mass and high condensation rate of water vapor. In the case of aerosol pollution, the boundary layer height (BLH) usually drops to about 60% of the normal level, the horizontal and vertical diffusion of aerosol is suppressed, and the aerosol concentration is constantly rising. Usually, when the aerosol concentration exceeds the threshold of 100 µg/m3 , aerosol pollution will further significantly worsen the meteorological conditions in the boundary layer, causing the BLH to further drop to about 20% of the usual. Then, the aerosol concentration will at least double in a short time, finally triggering the “two-way feedback effect” between significant unfavorable weather conditions and accumulated aerosol pollution. Note that the interannual climate change signals, including Arctic sea ice, Pacific SST, ENSO, Atlantic SST, East Asian monsoon, etc., are also correlated to the interannual variation of atmospheric aerosol concentration in China, and these signals are important indicators for the seasonal and interannual prediction of atmospheric pollution. The model analysis shows that the interannual variation of surface ozone caused by meteorological fields is greater than the impact of anthropogenic emission.

Fig. 2.11 Conceptual diagram of the impact of inter-decadal climate warming on local aerosol pollution. Climate warming can create more unfavorable local and regional weather conditions, leading to more accumulation of aerosol pollution. The accumulated pollution further aggravates unfavorable weather conditions, which in turn generate more pollution, forming a “vicious circle”

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The radiative forcing of atmospheric composition indicates the influence extent of human activities on climate change, of which the estimation results of greenhouse gas forcing are relatively certain, while the estimations of the effective direct radiative forcing of nitrate and organic carbon aerosols and the indirect radiative forcing of aerosol-cloud interactions have larger uncertainties. Radiative forcing is mainly used for quantitative comparisons of the strength of different human agents in causing climate change. According to IPCC AR6, the global average effective radiative forcing (ERF) caused by the concentration changes of CO2 , CH4 , N2 O and ozone during 1750–2019 was 2.16 W/m2 , 0.54 W/m2 , 0.21 W/ m2 and 0.47 W/m2 , respectively. The total aerosol ERF from 1750 to 2014 was –1.3 ± 0.7 W/m2 . Sulfate dominates the total ERF of anthropogenic aerosols, followed by the ERF of organic carbon and nitrate. It is particularly worth noting that the uncertainty in the research on the generation, distribution and radiation effect of secondary organic carbon is large, which brings greater uncertainty to aerosol radiation forcing. The aerosol ERF still has great uncertainty, especially those due to the interaction of aerosols and clouds. The global annual mean ERF at the top of the atmosphere caused by aerosol-cloud interaction during 1750–2014 ranged from –1.7 to –0.3 W/ m2 . The radiative forcing due to aerosol-cloud interaction is very sensitive to the physical processes of cloud and precipitation, which have an important impact on the concentration of aerosols in the atmosphere. However, compared with satellite observation, the models usually have the problem that simulated precipitation occurs too frequently, but improving this problem can lead to excessive radiation forcing from the simulated aerosol-cloud interaction. This shows that even if the simulated aerosol ERF is very reasonable in many models, the model output is usually the result of the mutual cancellation of various errors.

2.3.2 Impact of Human Activities on Surface Solar Radiation and Surface Air Temperature in China The change in atmospheric aerosol concentration may be the main reason for the superimposed effect on the surface “dimming” or “brightening” in China (medium confidence). Since the 1960s, the total surface solar radiation (SSR) in China has been decreasing, which is consistent with the variation of global total SSR, undergoing a phased change process of “dimming first and then brightening”. The annual mean SSR in China before the 1990s showed a rapid downward trend. The “dimming” weakened from 1991 to 2005, but the trend of “brightening” have dominated to a certain degree since 2005. The increased greenhouse gas emissions caused by human activities have been the main cause of the rapid surface warming in China since the mid-twentieth century (high confidence). According to IPCC AR6, the potential range of global surface air temperature rise caused by human activities from 1850 to 1900 to 2010– 2019 is 0.8–1.3 °C, of which the long-lived greenhouse gases may have contributed

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1.0–2.0 °C. China has experienced faster warming than the global average. The consensus of most studies is that the regional warming in China has been closely related to the impact of human activities in the past 100 years. Human activities, especially greenhouse gas emissions, have been the main reasons for the rapid rising of surface air temperature in China since the mid-twentieth century. From 1900 to 2018, the rise of surface air temperature averaged over China varied in the range of 1.3–1.7 °C. From 1961 to 2013, the observed surface warming in China was 1.44 °C (90% confidence interval 1.22–1.66 °C). The main contributor to this warming was the increase in greenhouse gas forcing, including CO2 . The combined contribution of anthropogenic and natural external forcing was 0.93 °C (0.61–1.24 °C), which can explain most of the warming. In terms of anthropogenic forcing, the increase of greenhouse gases including CO2 contributed 1.24 °C (0.75– 1.76 °C) to surface air temperature in China, while other anthropogenic factors, including aerosols, mainly played a cooling role with the contribution to cooling about 0.43 °C (0.24–0.63 °C). Since the implementation of the “Ten Articles of Atmosphere” in 2013, the concentrations of major air pollutants in China have dropped significantly due to the substantial reduction of pollutant emissions. The reduction of atmospheric black carbon aerosol also reduces other types of aerosols with cooling effect, and its overall effect is to contribute to the rising of surface air temperature in China.

2.3.3 Impact of Human Activities on the East Asian Summer Monsoon Circulation and Precipitation in China There is still great uncertainty about the influence of human activities on the East Asian monsoon circulation and precipitation based on the simulation results. Observational data show that the East Asian summer monsoon (EASM) circulation has undergone an inter-decadal weakening tendency since the mid-twentieth century. The observed weakening of the low-level circulation of the EASM can be partially reproduced in the Coupled Model Intercomparison Program phase 5 (CMIP5) historical simulations with all forcing (anthropogenic and natural forcing), but the response degree is far weaker than the observation. Aerosol forcing plays a major role in weakening the low-level circulation of the EASM, causing a decrease in summer precipitation in eastern China. However, greenhouse gas forcing is beneficial to the enhancement of the low-level circulation, resulting in increased precipitation in most areas south of the Yangtze River and decreased precipitation in North China. Although the monsoon circulation has a weakening trend, the historical simulations with all forcing in most models cannot reproduce the “flood in the south and drought in the north” pattern of precipitation anomalies in eastern China. Thus, it cannot be concluded that human activities play a dominant role in the precipitation pattern of “flood in the south and drought in the north” in China. At the upper level, the observed southward shift of the East Asian jet stream can also be partially reproduced in the

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all-forcing simulations. Natural forcing mainly contributes to the southward moving of the eastern part of the East Asian jet, while aerosol forcing mainly contributes to the southward moving of the western part of the East Asian jet. At present, studies on the influence of aerosols on the EASM circulation and precipitation are mostly based on model simulations. However, the climatic response of different models to aerosol forcing varies greatly, so there is still great uncertainty about the effect of aerosol forcing on the East Asian monsoon circulation based on the simulation results. The effects of different external forcing factors on the long-term variation of precipitation in China are obviously discrepant on regional scales, and there are no consensus conclusions about the impact of human activities on precipitation. As the overall mean precipitation in China has not changed significantly in the past 60 years, it is basically impossible to detect the impact of human activities on precipitation in China through the existing methods. The influence of different external forcing factors on the long-term changes of precipitation in China has obvious regional differences. Studies have shown that greenhouse gases have been the major contributors to the gradual increase of precipitation in arid and semi-arid areas since the 1970s, while the precipitation in humid and semi-humid areas has been decreasing apparently as the result of the impact of aerosols. Besides, the land use and natural external forcing factors also lead to a decrease in precipitation. However, other studies have suggested that the precipitation in eastern China has a trend from light rain to heavy precipitation, and human activity forcing plays an important role in this trend. Moreover, human activities have a detectable and attributable influence on the shift of daily precipitation distribution toward stronger daily precipitation intensity in eastern China during the past 50 years, in which the surface cooling due to the anthropogenic aerosols counteracts the enhanced water vapor transport caused by greenhouse gas forcing to some extent. Some studies indicate that the urbanization effect has a detectable influence on the changes in total precipitation and frequency of short-time heavy rainfall in cities (Yan et al. 2016). However, current researches have great uncertainties in the estimation of urbanization effects, and obvious differences have been found in the urbanization effects estimated by different methods.

2.3.4 Impact of Human Activities on Extreme Climate Events in China From the research on the attribution of long-term variation of extreme temperatures in China, the effects of anthropogenic factors can be detected in the changes of frequency, intensity, and duration of extreme temperatures (high confidence). By using the optimal fingerprinting method, some researches have detected the effects of human activities on extreme temperature changes in China, and also isolated the role of natural forcing. The influence of human activities on extreme temperature changes in eastern and western China can also be detected with this method. Greenhouse gas forcing caused by human activities may be the main contributor to the

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changes of observed temperature extremes in China since the 1960s. Greenhouse gas forcing has made the extreme warming events in China occur more frequently, with stronger intensity and longer duration. Conversely, the frequency, intensity and duration of extreme cold events have decreased in this region. Greenhouse gas forcing significantly increased the risk of extreme heatwave events in eastern China in the summer of 2013, northern China in the spring of 2014, and Northwest China in July 2015. The influence of human activities on the change of extreme precipitation in China is uncertain. The detection and attribution studies have revealed that human activities have increased the occurrence probability of some extreme heavy precipitation events, such as the severe precipitation in South China in the 2015 flood season and the extreme heavy rainfall in Southeast China in June 2017. Studies have suggested that the increased greenhouse gases have contributed measurably to the observed increase in daily extreme precipitation in China, as well as the increased frequency of heavy rain and the decreased frequency of light rain in eastern China since the 1960s. However, some studies pointed out that the significant impact of human activities on the trend of extreme precipitation cannot be detected in the whole region of China.

2.4 Large-Scale Factors Affecting Climate Change in China Within the global climate system, large-scale (continental scale, ocean basin scale, hemispherical and global scale) factors (such as monsoon circulation, climate modes and other circulation systems, sea temperature, sea ice, snow cover, etc.) can affect climate in China through triggering circulation anomalies, which mainly influenced interannual and inter-decadal variations in climate. Changes of large-scale factors are influenced by both natural fluctuations and climate warming. Interannualinterdecadal anomalous signals superimposed on the sequence of climate change can cause periodic fluctuations and even impact the periodic trends of certain climate variables (Table 2.2).

2.4.1 East Asian Monsoon China is located in East Asia, and its climate change and variability are significantly affected by the East Asian monsoon. Abnormal monsoon often causes extreme climate disasters such as droughts and floods, high-temperature heatwaves, low-temperature blizzards and so on. In the context of global warming, the East Asian summer monsoon presents significant inter-decadal variability. The East Asian summer monsoon begins with the onset of the South China Sea summer monsoon. Since 1994, the South China Sea summer monsoon has tended to occur about half a month in advance, while the

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Table 2.2 Effects of major large-scale factors on climate in China Effects on climate in China

Large-scale factors East Asian monsoon

Summer monsoon

(1) In the 1970s, summer monsoon weakened on the inter-decadal scale, and the precipitation was “floods in the south and drought in the north” (2) After the late 1990s, summer monsoon strengthened, the eastern rain belt moved northward, and the precipitation in the regions south of the Huaihe River and the Yangtze River increased

Winter monsoon

(1) In the mid-1980s, the winter monsoon weakened on the inter-decadal scale, and winter temperature in China was warmer (2) In the early twenty-first century, winter monsoon strengthened, temperature in northern China tended to be lower, and southern China had more low-temperature, rain, snow and freezing

Main modes Northern Hemisphere of atmospheric circulation

AO

(1) When AO is in a negative phase in winter, extremely low temperature will occur in northern China (2) When AO is in a positive (negative) phase in spring, there will be less (more) precipitation in the middle and lower reaches of the Yangtze River (3) After 2000, negative phase of AO continued, and drought in Southwest China was intensified

NAO

(1) When NAO is in a positive phase in winter, there will be more (less) precipitation in spring in southern (northern) China (2) When NAO is in a positive phase in summer, there will be less precipitation in summer in Xinjiang

Silk Road When the Silk Road teleconnection teleconnection pattern is in a positive phase, high temperature will appear in northern China (continued)

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Table 2.2 (continued) Effects on climate in China

Large-scale factors Southern Hemisphere

Marine modes Pacific Ocean

AAO

(1) When AAO is in a positive phase in winter, there will be less precipitation in spring in South China (2) When AAO is in a positive phase in spring, the middle and lower reaches of the Yangtze River will have excessive summer rainfall

ENSO

(1) In the summer of EP-ENSO warm phase attenuation, year, there will be more precipitation in areas south of the Yangtze River and Northwest China (2) In the year of CP-ENSO warm phase, there will be more precipitation in the Yangtze River Basin, but less precipitation in southern China (3) After the 1970s, the interannual influence of ENSO on the East Asian summer monsoon enhanced

West Pacific warm pool (WPWP)

After the end of the 1990s, WPWP became warmer, conducive to less precipitation in the Jianghuai region and more precipitation in areas south of the Yangtze River and North China in summer

PDO

After the end of the 1990s, a negative phase of PDO is conducive to less precipitation in Northeast China and an increase in (extreme) precipitation in North China in summer

North Atlantic Multi-decadal Oscillation (AMO)

(1) Positive phase of AMO is conducive to high temperature and drought in Northeast China (2) AMO negative phase/PDO positive phase, more precipitation in the Yangtze River Basin, but the Yellow River and Huaihe River basins are dry with less rainfall

Consistent warming mode of Indian Ocean Basin

When the consistent warming mode of Indian Ocean is in a warmer state, the number of typhoons generated in the Northwest Pacific is reduced (continued)

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Table 2.2 (continued) Large-scale factors

Effects on climate in China

Arctic sea ice

(1) Reduction of sea ice in autumn is prone to extreme low temperature events in winter (2) Reduction of Arctic sea ice in autumn is prone to aggravate haze pollution in eastern China (3) Reduction of Arctic sea ice in spring is prone to exacerbate the summer drought in Northeast China

Snow cover on the Qinghai-Tibet Plateau

Snow cover on the Qinghai-Tibet Plateau changed from less to abundant in the 1970s and affected the precipitation pattern in eastern China

Snow cover in Eurasia

(1) When there is less (more) snowmelt in spring, lower (high) temperature will occur in Northeast China in summer (2) When there is more snow in autumn, the haze pollution in North China will be aggravated in winter (3) When snow cover in winter, is reduced, there will be less (more) winter precipitation in southern (northwesten) China

retreat has shown a late trend from 1951 to 2016, especially after 2005. The early onset and late withdrawal of the South China Sea summer monsoon lead to the trend of its being prolonged (high confidence). The intensity of the East Asian summer monsoon weakened on an inter-decadal basis in the late 1970s, causing a shift in the precipitation pattern in eastern China, presenting the distribution characteristics of “flood in the south and drought in the north” (high confidence). Since the end of the 1990s, the intensity of the East Asian summer monsoon has increased. Corresponding to the northward shift of the rain belt in eastern China, the precipitation in the Huaihe River Basin has increased obviously, and the precipitation in the south of Yangtze River has increased somewhat (medium confidence). The summer temperature in eastern China also varies with the advance of the East Asian summer monsoon and the distribution of precipitation. The East Asian summer monsoon can also affect the precipitation in the eastern part of Northwest China. In strong summer monsoon years, it rains a lot in the flood season in the northwest affected area of the summer monsoon. The inter-decadal variation of the East Asian summer monsoon is related to the internal variability of the climate system, such as the phase changes of the PDO and the AMO, as well as the heterogeneous thermal changes of the Asian continent and the surrounding oceans (high confidence). Besides, the anthropogenic external forcing also plays a role in the inter-decadal variation (high confidence). In the late 1970s, as a consequence of global warming, the interaction between the East Asian summer monsoon and the South Asian summer monsoon did not change significantly on the inter-decadal scale, which was correlated to the inter-decadal weakening of the mid-latitude wave train in the upper troposphere over Eurasia caused by AMO changes. It was also associated with the interaction between ENSO and PDO, as well

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as the inter-decadal variation of the zonal gradient of SST over the tropical Western Pacific to the Indian Ocean (medium confidence). With global warming, the intensity, amplitude of interannual variability, and intra-seasonal variability of the East Asian winter monsoon all have obvious inter-decadal variations. After the mid-1980s, the strength and interannual variability of the East Asian winter monsoon got weakened, the inverse correlation of Siberian high in the early winter and late winter strengthened, and the cold air activity in high latitudes became weakened. The winter temperature in China was generally warmer, especially in the eastern and northern parts of China, where warm winters lasted for many years and winter precipitation increased in Northwest China. At the beginning of the twenty-first century, the strength and interannual variability of the East Asian winter monsoon increased, the inverse correlation of the Siberian high in the early winter and late winter weakened, and the cold air activity in high latitudes increased. There were more periodic cold events in winter in northern China, and more low-temperature rain and snow freezing events in southern China (high confidence). From a long-term perspective (since 1961), the intensity of the Siberian high has not shown a clear varying trend, but is characterized by obvious inter-decadal to multi-decadal oscillations (high confidence). From the 1970s to the early 1990s, the Siberian high showed a trend of weakening, and then gradually strengthened, which also led to the trend of strengthening winter monsoon and frequent cold events in China in the past decade or two (high confidence).

2.4.2 Main Modes and Teleconnections of Atmospheric Circulations Climate modes (including atmospheric teleconnections) play an important role in climate system changes and profoundly affect global and China’s regional climate changes. The cooperation of different teleconnections can also cause climate anomalies in different regions of China. At the same time, there exist inter-decadal variations in the relationship between various teleconnections and China’s climate. AO influences the abnormal changes of winter climate in China by modulating the activities of cold air near the surface in the Arctic region, the intensity of Siberian high and the jet stream. The negative AO phase often corresponds to the stronger East Asian winter monsoon. Since twenty-first century, the occurrence of extreme low temperature events in northern China has matched with the negative AO phase and the strengthening of the northern modes of the East Asian winter monsoon. The worsening of drought in Southwest China since 2000 is also associated with the inter-decadal shift of AO from positive to negative phase. AO is closely related to summer precipitation in East Asia as well. On an interannual scale, when the AO index is higher in May, the summer rainfall in the middle and lower reaches of the Yangtze River to southern Japan is less, and vice versa.

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NAO has a significant impact on climate anomalies in China. When NAO is in the positive phase in winter, precipitation is more in southern China and less in northern China in spring. In the positive phase of NAO in summer, the westerly jet in West Asia is stronger to the north, and summer rainfall in Xinjiang is less. The correlations between the summer drought and flood and NAO in three river source region has been greatly enhanced in the recent 30 years. The change of NAO phase can also cause the change of thermal difference between land and sea, which in turn affects the dry–wet variation of arid and semi-arid areas in Northwest China. The summer Silk Road teleconnection (the teleconnection in the upper troposphere over the Eurasia from the west to the east) changed from the negative phase to the positive phase in the middle and late 1990s, which was closely correlated to the growth of persistent high-temperature events in northern China, and also heavily affected the climate change in the semi-arid and arid regions of Northwest China. The inter-decadal variation of the Silk Road teleconnection pattern may be related to AMO and SST variation in the North Pacific Ocean. Antarctic Oscillation (AAO), as the main mode of climate variability in areas outside the equator of the Southern Hemisphere, not only causes anomalies in the mid- and high-latitudes of the Southern Hemisphere, but also has an obvious impact on the climate in many regions of the Northern Hemisphere. Under the background of global climate change, AAO has shown a significant positive trend since the 1950s, and this trend of change has caused the response of many regions of the world to climate change. When AAO is in a positive phase in spring, the East Asian summer monsoon gets weakened in its later period, resulting in an increase of summer precipitation in the middle and lower reaches of the Yangtze River in China. Winter AAO can affect the spring precipitation in South China, and there is a significant negative correlation between them. AAO also regulates tropical cyclone activity in the Northwest Pacific.

2.4.3 Ocean Modes The changes of SST in the Pacific, Indian and Atlantic oceans can interact with each other through atmospheric bridges and ocean channels, and can also affect the climate change and variability in China through air-sea interaction. Abnormal thermal conditions in key areas of the oceans often lead to extreme climate disasters such as droughts, floods, heatwaves, and low-temperature blizzards in China. ENSO is a significant interannual signal affecting climate change in China, and its pattern shows obvious inter-decadal variation. Since the 1980s, the warming position of ENSO events has shifted westward from the original tropical eastern Pacific to the tropical Central Pacific. That is, the frequency of warming ENSO events in the Central Pacific has increased significantly. There is a significant difference between the effects of the Central Pacific warming events (CP-ENSO warm phase) and the traditional East Pacific warming event (EP-ENSO warm phase) on the East Asian summer monsoon. In the summer of El Niño attenuation years of

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the East Pacific warming type, precipitation is more in the Yangtze River Basin and its south. The warming El Niño in the Central Pacific Ocean tends to cause more precipitation in the Jianghuai River Basin, but less precipitation in the southern part of China. The CP-ENSO warm phase is also conducive to the occurrence of more tropical cyclones in the Northwest Pacific. On the inter-decadal scale, significant inter-decadal changes exist in the interannual relationship between ENSO and the East Asian summer monsoon. Since the late 1970s, the interannual influence of ENSO on the East Asian summer monsoon has increased significantly (medium confidence). The intensity and scope of the anticyclonic circulation in the Northwest Pacific triggered by ENSO warm events have increased, leading to obvious summer precipitation anomalies over East Asia. PDO significantly modulates the relationship between ENSO and the East Asian summer monsoon. In the negative phase of PDO, the correlation between ENSO and the East Asian summer monsoon is weak, while in the positive phase of PDO, the correlation between the two is enhanced. In addition, ENSO and PDO also affect the interannual and inter-decadal changes of dryness and wetness in the Loess Plateau and its surrounding areas, respectively. When ENSO and PDO are in the warm phase, precipitation is less, and the climate is drier in the related regions. In the late 1990s, the phase transition of PDO from positive to negative led to a decrease in precipitation in Northeast China, and an increase in precipitation and extreme precipitation in North China. The thermal conditions of the West Pacific warm pool have a significant impact on the climate of East Asia. When the sea surface temperature in the tropical West Pacific is higher, the convection activity near the Philippines is strengthened, which makes the West Pacific subtropical high more northward. The summer monsoon rainfall in the Jianghuai River Basin in China is less, while the rainfall in North China and regions south of Yangtze River is more. Since the late 1990s, the sea surface temperature in the West Pacific Ocean has been warmer, and the convection has been stronger, which is conducive to the reduction of summer precipitation in the Yangtze-Huaihe Valley, but the precipitation in North China and regions south of Yangtze River has become relatively more. Northwest China was generally dry throughout the twentieth century, but the regional average precipitation changed abruptly in the mid-1980s, and the amount of precipitation increased. With the interdecadal abrupt change of drought in Northwest China after the end of the 1980s, the key area of SST affecting its precipitation changed from the tropical Indian Ocean before the end of the 1980s to the Indo-Pacific junction. The inter-decadal strengthening relationship between Indian Ocean warming and El Niño is beneficial to the strengthening of the relationship between ENSO and the East Asian summer monsoon. Since the late 1970s, the consistent warming mode of the Indian Ocean basin (IOB) has been in a good relationship with El Niño. The El Niño has made the warm SST of the Indian Ocean last from the peak period to the summer attenuation period of El Niño through the atmospheric bridge process, ocean dynamics and local air-sea interaction process. During this process, El Niño signals are stored in the Indian Ocean and affect the East Asian summer monsoon in summer (high confidence). Atmospheric Kelvin

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waves triggered by IOB warming can induce anticyclone anomalies in the Northwest Pacific, suppress local convection, and reduce the number of typhoons in the Northwest Pacific. The phase shift of AMO significantly affects the inter-decadal change of climate in China. At the end of the 1990s, AMO turned into a positive phase. The warm anomaly in the North Atlantic was conducive to stimulating the Rossby wave train that propagated eastward and the wave train that spread to East Asia through the polar regions along the great circle path. It caused anticyclonic circulation anomaly and positive anomaly of geopotential height over Northeast China, resulting in the occurrence of high temperature and drought events in Northeast China. The different phase combinations of PDO and AMO also have a significant impact on the interdecadal variation of precipitation and drought in the Yangtze-Huaihe region. When PDO is in a positive phase and AMO is in a negative phase, there is more precipitation in the Yangtze River Basin and less precipitatice between the Huaihe River and the Yellow River; when PDO and AMO are both in negative phases, the Yangtze River Basin usually receives less precipitation, which is easy to cause drought.

2.4.4 Arctic Sea Ice and Snow Cover on the Qinghai-Tibet Plateau The rapid decline of the Arctic sea ice and the rapid rise of the Arctic air temperature not only affect the Arctic climate and ecological environment, but also modulate the interannual and inter-decadal changes of the regional climate in China through complex interaction and feedback processes. The Arctic Barents Sea to Kara Sea is one of the key waters affecting the winter climate in China. If the sea ice in this sea area is less (more) in winter, the East Asian trough and Siberian high are stronger (weaker), the East Asian winter monsoon is stronger (weaker), and the cold air invading China is more (less). The less sea ice in the Arctic in summer and autumn is also closely correlated to atmospheric circulation and climate change in winter. Since the late 1980s, the Arctic sea ice has decreased in autumn, the sea temperatures in the Arctic Ocean and the North Atlantic Ocean have increased, and the temperature in northern Eurasia has shown a decreasing trend in winter, leading to frequent extreme low temperature events in Eurasia in recent years. The decrease of the Arctic sea ice in autumn can also lead to the increase of haze days in eastern China (high confidence). The warming of the Arctic and the reduction of sea ice also affect the East Asian summer monsoon and precipitation by altering the meridional pressure and temperature gradient in the Northern Hemisphere and stimulating the teleconnection wave train. Significant changes in the Arctic spring sea ice in the early 1990s may have contributed to the enhanced East Asian summer monsoon. The decrease of the Arctic sea ice in spring also exacerbated the summer drought in Northeast China by affecting the Baikal high and snow cover in Eurasia. The Arctic sea ice in early spring can significantly affect the climate conditions related

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to surface ozone in North China, and in turn show close links with summer surface ozone pollution in North China (moderate confidence) (Yin et al. 2019). The winter and spring snow cover on the Qinghai-Tibet Plateau is an important forcing affecting the inter-decadal variation of the East Asian summer monsoon. The thermodynamic forcing and dynamic effect of the Qinghai-Tibet Plateau have important effects on the East Asian monsoon and climate. Since the 1850s, the Qinghai-Tibet Plateau has presented a warming trend with the centennial warming rate from the 1850s to the 1990s being more than 0.6 °C/100 year, of which the warming trend became more rapid after 1920 with the rising about 0.9 °C in a hundred years, slightly higher than the national means for the same period. In this context, the winter snow cover over the Qinghai-Tibet Plateau changed significantly from less to abundant in the 1970s, which was well correlated with the transition of precipitation modes in eastern China. After the end of the 1990s, the winter snowfall over the Qinghai-Tibet Plateau decreased significantly, but the temperature became warming apparently. Meanwhile, the SST over the central and eastern tropical Pacific decreased, which finally made the land-sea thermal difference become increased in spring and summer, resulting in the northward advance and enhancement of the East Asian summer monsoon. However, the interaction process between the two still needs to be further studied, and the transition of the East Asian summer monsoon in the 1990s is still controversial.

2.4.5 Snow Cover in Eurasia Snow cover in Eurasia can stimulate the abnormal response of atmosphere by affecting albedo and moisture, thereby causing abnormal changes of climate in China. After the end of the 1990s, snow cover in the high latitudes of Eurasia reduced in winter (medium confidence), which led to the northeast wind anomaly in the lower troposphere of southeastern China and its surrounding waters. This situation made the warm and humid air from the tropical ocean blocked over the South China Sea and the Philippines Sea, and subsequently caused winter precipitation to be lessened in southern China and abnormal easterly winds to occur in Northwest China, finally resulting in more precipitation in the northwest. The amount of snowmelt in Eurasia also significantly affected the temperature in Northeast China. Before the end of the 1980s, the amount of spring snowmelt in middle and high latitudes in Eurasia was relatively small, corresponding to the low summer temperature in Northeast China. After the end of the 1980s, the amount of spring snowmelt was on the high side, and the summer temperature in Northeast China was on the high side as well. There was also an obvious link (moderate confidence) between the autumn snow cover over East Europe to the West Siberia region and the winter haze pollution in North China, and this link began to strengthen in the late 1990s (Yin and Wang 2018).

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2.5 Impacts of Climate Change on Socio-economic Systems Climate change has affected different fields and sectors of China’s natural and social systems to varying degrees. This section is mainly to conduct a comprehensive assessment from two aspects: the impact degree or level of climate change on China’s social and economic systems and the differences of impact level in different regions.

2.5.1 The Impact Extent of Climate Change on Socio-economic Systems Climate change has affected different industrial sectors, major projects, human habitat and people’s health at different degrees or levels in China (Fig. 2.12). With the continuous warming of climate, the affected fields and scope are expanding, and the intensity of impact is increasing. The transportation industry is one of the most prominent industries affected by climate change in China, particularly by extreme weather such as thunderstorms, severe torrential rains, blizzards, gales, typhoons, fog-haze and sanddust storms (high confidence). On the one hand, global warming has caused more frequent severe precipitation, high temperature and drought events in China and influenced the normal operations of roads, railways, and aviation, even causing traffic delays and traffic interruptions. Some ground facilities and transportation equipment

Fig. 2.12 Impacts of climate change on socio-economic systems in China

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were greatly damaged, which had a huge adverse impact on traffic. On the other hand, global warming is beneficial to activating the economic and social activities in high-altitude regions and increasing the development of travel and logistics. China is one of the countries in the world with the most tropical cyclones landing and most severe disasters caused by tropical cyclones, with an average of 7–8 tropical cyclones landing every year. Tropical cyclones destroy lifeline projects such as transportation, communication and energy, and the impacts are very severe. The increase in tropical storms can cause more frequent disruptions to roads, railways, navigation and air transportation, resulting in a large number of infrastructure failures. In the middle and late January of 2008, the large-scale freezing rain and snow disaster which was caused by the continuous low temperature in the Yangtze River Basin and the areas south of the Yangtze River was a once-in-50-year disaster. The intensity and duration of this disaster both showed extreme values in historical records, and 38 airports were shut down for short or long time successively, and the ground traffic was basically paralyzed. Climate change has had a huge impact on China’s manufacturing industry, with significant and far-reaching influences on six major industries, namely, iron and steel, non-ferrous metals, building materials, petrochemicals, chemicals and electric power (high confidence). The impact of climate change on manufacturing is very clear, which, by the middle of the twenty-first century, will result in an annual 12% reduction in the output of manufacturing industry of China if adaptive measures are not adopted to address climate change. High temperature can lead to a decline in the production efficiency of physical capital, such as reducing the lubrication performance between mechanical parts. Based on the data of 500,000 manufacturing enterprises in China from 1998 to 2007, it was found that there was an inverted U-shaped relationship between the daily average temperature (especially the high temperature of > 32 °C) and the total factor productivity (TFP) of manufacturing enterprises. In addition, in order to respond to climate change, the implementation of climate policy will inevitably lead to changes in the structure and scale of manufacturing industry. According to China’s “Action Plan for Climate Change in the Industrial Sector (2012– 2020)”, the six major industries of iron and steel, non-ferrous metals, building materials, petrochemicals, chemicals and electric power account for about 71% of the CO2 emitted by the combustion of industrial fossil energy. In addition, CO2 , NO2 , fluorine and other greenhouse gas emissions from industrial production take up more than 60% of the greenhouse gas emissions from non-fossil energy combustion in China, and CO2 emissions account for about 10% of the national CO2 emissions. In order to improve the ability to cope with climate change and achieve low-carbon development, the production capacity of steel, petrochemicals, building materials, non-ferrous metals and other industries will be further controlled and compressed. At the same time, new energy, new materials, information, energy conservation and environmental protection, life sciences and other emerging technology industries will develop rapidly. Climate change also impacts consumer demand. For example, the demand for winter goods decreases, while the demand for summer goods and energy, water, and material saving and environment-friendly products increases.

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Climate change has contributed to the increase of heat resources, the variations of the spatial distribution of precipitation, the frequent extreme weather events and the changes in hydrothermal conditions, and accelerated the rate of biological invasions to a certain extent, showing a negative impact on agriculture in China obviously (high confidence). The positive impacts of climate change on agriculture were reflected in the following aspects. (1) The increases in accumulated temperature (daily temperature ≥ 10 °C) and precipitation make the frost-free period prolonged, the growth period of warm-loving crops prolonged, the suitable planting area expanded, and the planting boundary expanded to the north and high altitude, thus changing the crop yields and planting systems. For instance, based on provincial statistics of China, the yields of single-cropping rice in China increased by 11% between 1961 and 2010 as temperatures rose. The change of precipitation increased the yields of single-cropping rice by 6.2%, and at the same time moved China’s rice planting center to the northeast by about three latitudes. (2) With the warming of the ocean, on the one hand, the warm-water fish species migrated from low latitude to high latitude, increasing the richness of fish that can be cultured in cold regions; on the other hand, the strength variations of the Taiwan island warm current and the southward cold current along the coast of China altered the stirring intensity of the seawater at the junction of the cold and warm currents, thus altering the species and composition of marine fish in the East China Sea and increasing the richness of fish caught. Climate warming has impacts on the temporal and spatial distribution of precipitation, which changes the water conditions for the growth of forage grass and crops, and promotes the fertilization effect of photosynthesis together with the increase of CO2 concentration, causing changes in grassland area and coverage, affecting the numbers of livestock in stock and slaughter, and finally changing the output of livestock products and crops. The negative impacts of climate change on agriculture are mainly manifested in the following aspects. (1) It has adverse effects on the yields of corn, potatoes, oil crops, sugar crops, fruits and vegetables. For example, climate warming will shorten the growth period of peanuts in most parts of China and decrease the yield per unit area (high confidence). So, it is estimated that after the middle of the twenty-first century, the reduction in peanut yields will rise distinctly. (2) Climate warming has caused the frequent occurrence of extreme weather events, and the growth in extreme temperature events and extreme precipitation events has reduced the yields and quality of crops and livestock products. For instance, snow disasters in China have been increasing every year in the past decade, with Inner Mongolia, Qinghai, Xinjiang and other grassland regions suffering more severely. (3) The rise in global temperature has also accelerated the rate of biological invasion to a certain extent, and the invasion of some vector insects indirectly caused the serious outbreak of crop diseases. In recent years, the Q-type Bemisia tabaci has become a dominant pest on cotton, vegetables and other crops in most provinces in China, and the tomato yellow leaf curl virus caused by it has broken out in vast areas of China, leading to extensive damage to crops. The invasion of pine wood nematode has made other harmful organisms easily infect pine trees from wounds, which indirectly causes a large area of pine trees to die. The pathogen carried by Procambarus clarkii has contributed to the cross infection of Chinese mitten crab and freshwater

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shrimp, making a large-scale loss of aquatic products. The invasion of red fire ants has increased the density of Ageratum thistle obviously, and Ageratum thistle is also an invasive plant. All these have formed a synergistic invasion of alien insects and plants, resulting in compound losses (Zhang et al. 2016; Ju et al. 2012). The warming in winter helps increase the survival rate and base number of pests, so that the occurrence of pests and diseases will be earlier, the damage period will be prolonged, and the number of reproduction generations will increase. These factors will ultimately affect food production. According to the National Bureau of Statistics, of China, the area of forest pests and diseases in China increased at a rate of 160,000 hectares per year from 2003 to 2014. Since the end of the 1990s, the incidence of diseases and insect pests has been at a high level. The incidence area of crop diseases and insect pests in China is over 300 million hectare-time every year, and from 1988 to 2012, the incidence rate increased by about 8.52 million hectare-time per year. During the period from 2006 to 2015, the corn borer showed a continuous aggravation trend. Slime worm disaster occurred lightly before 2011, but broke out in Northeast China, North China and Huanghuai (Yellow River and Huaihe River) region in 2012, and the situation became worse after 2013. In addition, the plant diseases of big leaf spot, small leaf spot and corn rust have shown an aggravating trend in recent years. The increase of extreme weather/climate events has an increasingly prominent impact on tourism (high confidence). Tourism is an industry that relies heavily on natural resources, ecological environment and climate conditions. Climate change affects China’s tourism through extreme events and changes in climate drivers. The increase in the frequency of extreme weather events, the expansion of affected areas and the extension of the impact duration have led to increased losses in the tourism industry. For example, in 1998, due to the catastrophic flood, the inbound tourism of China lost 29.9 × 104 persons; in 2008, affected by the snow disaster, the passenger flow losses in Guangdong and Jiangsu reached 11.7 × 104 persons and 5.6 × 104 persons, respectively; in 2016, the sustained severe precipitation in Wuhan, Hubei Province, caused the loss of tourism to reach 20 million Yuan (CNY), and the loss of entrance tickets alone reached 5 million Yuan (CNY) in Wuhan. In the meantime, the change of climate elements directly affects the length of the tourism season, tourism comfort, the annual variation and spatial distribution of passenger flow, and the determination of these factors depends, to a great extent, on the decision-makers’ experience of phenology in the previous year. This lag of tourism decision-makers in responding to phenological variation and climate changes indicates that people lack effective measures or means to respond to climate change in a timely manner. These lags directly lead to the failure of seasonal tourism to achieve the expected results, which not only causes the waste of tourism resources, but also affects the economic benefits of seasonal tourism. Climate change can also lead to significant changes in tourism resources and market demand. The demand for summer tourism to avoid heat increases rapidly, and the suitable time for ice and snow tourism is shortened or shifted to higher latitudes and altitudes. Climate change can also vary the natural phenology and meteorological landscape, so tourism departments must adjust the time, place and content of viewing programs in time to capture business opportunities.

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Climate change has a wide range of impacts on China’s energy system (energy development, transmission, supply and user side, etc.) (high confidence). With global warming, heating energy consumption in China tends to decrease in winter, while cooling energy consumption is expected to increase significantly in summer. Generally, the overall energy demand is going to show an upward trend. Developing renewable energy is an important measure for China to manage global climate change, in which wind power generation and solar power generation heavily depend on weather and climate conditions. China is rich in wind and solar energy resources, which far exceeds the demand in 2050 for resources in wind power and photovoltaic development in China, so the decrease of wind speed (the national average wind speed decreased by 0.13 m/s per decade from 1961 to 2017) and the reduction of total radiation (the average annual total radiation received by the land surface has decreased by 10.7 kW·h/m2 per decade) caused by climate change have little impact on the wind power and photovoltaic development in China. However, the fluctuations of wind and solar energy in different time scales and regions caused by climate change have potential impacts on electric power supply, which will also have an impact on the demand for energy reserves. Extreme weather events can also cause significant changes in the supply of wind power and photovoltaics, threatening the safe operation of the power grid. Therefore, it is necessary to strengthen the climate risk assessment and prediction of power grid security. In addition, extreme weather events can also seriously threaten the safety of energy production and transmission facilities. For example, the freezing rain disaster in early 2008 caused a large number of highvoltage towers to collapse, resulting in a large area of long-time power outages in southern China. Meanwhile, industry, construction and transportation are the major end-use energy sectors in China, thus the low-carbon transition process in response to climate change will affect the energy utilization status of these sectors as well as the energy consumption concept and lifestyle of the public. Therefore, it is necessary to combine government regulatory measures with market mechanisms to promote the implementation of the strategy to deal with climate change in the end (Tsinghua University Institute of Climate Change and Sustainable Development 2020). Climate change has a greater impact on water projects. It has continuously increased the risks of reservoir allocation, water transfer projects, and threatening of disasters to projects (medium confidence). Under the condition of climate change, the uncertainty of the increase and decrease of water inflow has put forward higher requirements for the comprehensive management of water resources in the Three Gorges Reservoir Area. The frequency and intensity of extreme weather and climate events around the reservoir area may increase in the future, and the occurrence probability of sudden debris flows, landslides and other geological disasters may be on the rise, which will adversely affect reservoir management, dam safety and flood control. The probability of simultaneous droughts in the water source area and the water-receiving area in the middle route of the South-to-North Water Diversion Project is increasing, and there is greater pressure to achieve the balance between supply and demand. Climate change is conducive to alleviating the problem of water shortage in the catchment area of the west route, and may have little overall impact on the adjustable water volume of the water diversion area; it can alter the

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ecological balance of water receiving area and project water body, and help to solve the problems of underground water pollution, land subsidence, seawater intrusion, etc.; it can cause damage to the vegetation and soil ecosystem on the surface of the construction area; it is beneficial to raise the service value of the water ecosystem in the water resources area. Generally speaking, the ecological environment of the upper and lower reaches of the Yangtze River has been affected by the South-toNorth Water Diversion Project, showing up the tendency to increase vulnerability and risks. In the past 500 years, the probability trend line of drought years in the water source area of the South-to-North Water Diversion Project was declining and then increasing. Since the twentieth century, the probability of drought years in the water source area has been at a historically high level, reaching 31.7%. The probability of water transfer in Huaihe River Basin is the highest, reaching 87.3%, while that in Tangbaihe River Basin is the lowest, being 78.4%. Since the twentieth century, the probability of simultaneous droughts in all river basins and water source areas has reached a historically high level. The probability of sustained simultaneous droughts in Hanjiang-Tangbaihe River Basins is higher than that in the HanjiangHuaihe River Basins. The autumn flood season (September–November) is the most favorable period for water transfer. The impacts of climate change on projects in permafrost areas are increasing, and the risks are increasing (high confidence). Climate change and projects have caused widespread degradation of permafrost, with a significant increase in freeze– thaw disasters, influencing the stability and safe operation of projects in frozen soil regions. For example, the frozen soil under the ordinary subgrade of the Qinghai-Tibet Railway has varied apparently, and the deformation of frozen soil subgrade has been found prominent. In the frozen soil region, with high temperature and high ice content, the subgrade with block stone structure can adapt to the influence of frozen soil change when the temperature rises by 1 °C; in the low-temperature permafrost region, it can adapt to the effect of frozen soil changes with the temperature increasing by 1.5 °C. Climate change-induced thermal thawing landslides and frozen soil landslides occur more, enhancing the risks of influencing the stability of the Qinghai-Tibet Railway engineering Project. Climate and thermal disturbance to project have had a greater impact on bridges and road-bridge transition sections. According to the investigation results of 164 bridges with a total length of 220 km, 83% of the roadbridge transition section has undergone significant settlement deformation, with an average settlement of 70 mm. The monitoring of the ground temperature of the tower feet at the natural sites in 120 permafrost areas along the Qinghai-Tibet Direct Current (DC) Networking Project showed that the annual average temperature at the 6 m depth in 114 monitoring holes is increasing, while the ground temperature in only 6 holes is decreasing. The rise rates of the maximum and mean ground temperatures are 0.22 °C and 0.06 °C each year, respectively. At the moment, the actual rate of temperature rise in the ground is clearly higher than the predicted value. Climate change and ecological projects interact with each other, and changes in precipitation play a dominant role in controlling ecological projects (high confidence). Since the implementation of a series of major forestry projects, including the Three-North Shelter Forest Programme, the National Sand Prevention

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and Control Project, the Natural Forest Protection Project, the Project of Returning Farmland to Forest and Grassland, the Loess Plateau Soil and Water Conservation Project, the Southwest Rocky Desertification Control Project and the Beijing-Tianjin Sandstorm Source Control Programme, land desertification and soil erosion have been clearly reduced, showing a good momentum of overall containment, continuous reduction, enhanced functions and obvious effectiveness. Climate change has caused changes in temperature and precipitation in the Three-North Shelter Project area. The western, central and eastern parts of the Three-North Shelter Project area have different increases in vegetation coverage. There is a significant spatial difference in the increases between vegetation coverage and precipitation, and ecological restoration activities contribute mainly to the expansion of vegetation coverage in the eastern and central regions. Various impacts of climate change on the urban living environment are constantly emerging. Extreme weather and climate events like drought, extreme high-temperature heatwaves, torrential rains, urban waterlogging, storm surges, etc., can directly affect the safe supply of urban water, electricity, gas and other living necessities as well as the safe operation of infrastructure (high confidence). Research on megacities in China showed that the intensity of heat islands has increased with the beginning of urbanization after China’s reform and opening-up. The number of high-temperature days in urban areas is more than that of suburbs and outer suburbs. After entering the twenty-first century, the urbanization process has accelerated and has experienced a transition from “single heat island” to “heat island groups” and to “multiple heat island centers”. The observation and model study of the Yangtze River Delta and Pearl River Delta metropolitan areas showed that urbanization has increased the number of heavy precipitation events (amount), decreased the number of weak precipitation events (amount), and made precipitation become polarized and extreme. The distribution of precipitation landing points in cities and surrounding areas has also been significantly changed by the urban canopy, and the intensity of the summer half-year precipitation in the urban center and its downwind area has increased. As the intensity and frequency of urban precipitation are increasing, the urban temperature is also rising. This means that when the water vapor content is constant, the saturated water vapor pressure can increase, reducing the relative humidity and surface water vapor of the urban are as, and thus it tends to be dry in the urban areas. Climate change impacts the urban climate and environmental comfort, causing deterioration of dwelling and living conditions, and thus adversely affecting the comfort and well-being of urban residents (medium confidence). Climate change will have a certain impact on the policy formulation of green town construction and on the implementation of urban planning and construction measures for mitigating and adapting to climate change. Air pollution, extreme weather, and water and food pollution associated with extreme weather are important incentives for respiratory, circulatory, urinary and other systemic diseases (high confidence), and invasive alien species also have a significant impact on people’s health (medium confidence). At present, the main air pollutants that are considered harmful to human health include particulate matter (PM2.5 , PM10 ), SO2 , NOx , ozone and CO2 . These six air quality factors are

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often used as reference indicators to evaluate environmental air quality. A metaregression analysis conducted in 272 cities across China showed that as the annual mean temperature drops in urban areas, the total daily death toll is more strongly correlated to ozone. For every 10 °C decrease in annual mean temperature in cities, the daily total mortality due to the daily increase of ozone concentration by 10 ug m–3 will rise by an additional 1.4% (95%CI: 0.02%-0.25%). Extreme weather, such as floods, droughts and typhoons, can directly cause injuries and deaths and indirectly increase the risk of water and food-borne diseases through water pollution and food shortages. Taking the period from 2013 to 2015 as an example, the most suitable average temperature in China, that is, the average temperature for the lowest nonaccidental death rate, is 22.8 °C, any lower or higher temperature than this tends to result in a rise of non-accidental mortality (Chen et al. 2018). The impacts of high temperature and low temperature on death are different. The effect of low temperature lasts longer, while that of high temperature generally lasts only 1–3 days. With the lowest mortality percentile as a reference, the population mortality in China increases by 22% at extreme low temperature (temperature lower than the 1st percentile of daily temperature) and by 11% at extreme high temperature (temperature higher than the 99th percentile of daily temperature). Studies have found that typhoons can affect the risk of respiratory infectious diseases such as measles, rubella, mumps, and chickenpox, as well as diarrhea, tuberculosis and other diseases. After a typhoon, children under the age of 5 are more likely to have infectious diarrhea. The effects of typhoons in different scales and their accompanying precipitation and wind speed on hand-foot-mouth disease (HFMD) among children under 6 years old in Guangdong Province from 2009 to 2013 were evaluated. The results showed that tropical storms can increase the risk of HFMD in children under 3 years old, especially in boys aged 3–6 years old. The rainfall of 25–49.9 mm or more than 100 mm during activities of typhoons is a risk factor for HFMD in children. The extreme wind speeds reaching 13.9–24.4 m s–1 have adverse effects on children’s health. The northward expansion of schistosomiasis hosts due to climate warming also poses a threat to human health in relevant areas. Alien biological invasion not only causes serious economic losses, but also threatens human health. For example, ragweed can produce a large amount of pollen, which is the source of complications such as allergy and asthma, so it is prone to incurring respiratory diseases among residents in some areas of China (Ju et al. 2012).

2.5.2 Regional Differences in the Impact of Climate Change on Socio-economic Systems Climate change has affected the major sectors and fields such as agriculture, transportation, tourism, human habitat, population health, energy industry manufacturing, industry, ice-snow industry, and major projects in the seven administrative regions of China (Fig. 2.13).

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Fig. 2.13 The major sectors and fields affected by climate change in different regions of China and their extent and sensitivity

In Northeast China, the sectors and fields which are highly affected by and sensitive to climate change are agriculture, ice and snow industry and energy industry (high confidence), followed by tourism (high confidence) and manufacturing (medium confidence). Population health and transportation are affected by climate change to a higher degree but less sensitive to climate change (medium confidence), while major projects are less affected by climate change but highly sensitive to climate change (high confidence). Agriculture in Northeast China is developed with grain yields ranking first in China. The cold climate makes the ice and snow resources rich, and ice-snow industry and its related tourism are well developed. There are convenient waterway, land and air transport with the developed transportation industry. Energy industry is developed with abundant coal, oil and hydropower resources which are available for development and utilization. The manufacturing industry is developed, having three industrial belts including Shenyang-Dalian, Changchun-Jilin, and Harbin-Qiqihar-Daqing. The central-south

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Liaoning urban cluster and the Harbin-Changchun urban cluster are formed, and people’s health is a concern. Shelterbelt system with coordinated development of agriculture, forestry and animal husbandry is distributed in the western part of Northeast China, accounting for about 13.9% of the total area of the three northern regions of China (i.e. Northeast China, North China and Northwest China). During the period of 1961–2018, the climate in Northeast China warmed significantly, with the average temperature rising by 0.29 °C per decade, showing a warming and drying trend. The agriculture, ice and snow industry, energy industry, tourism and manufacturing industry are the most distinctive and developed industries in Northeast China. Changes in water and heat conditions, higher temperatures in winter and summer, and reduced runoff and water resources have led to the changes in crop growth conditions, the accelerated melting of ice and snow, the degradation of wetland vegetation, the reduced heating consumption in winter, and the increased cooling consumption in summer. All of these would greatly influence the agriculture, snow and ice industry, tourism, energy industry and manufacturing industry in this region. Northeast China is more densely populated and economically developed, and its population health and transportation industry are also very sensitive to climate change. The air pollution events accompanied by extreme high temperatures are becoming more common, affecting the health of people adversely in this region. With the increase in temperature, the number of fog and strong wind days shows a decreasing trend, which is beneficial to transportation. In addition, the warming and drying climate and the regional degradation of permafrost have a certain degree of influence on the ThreeNorth Shelter Forest Programme and Sino-Russian oil pipeline projects that pass through Northeast China, and these major projects in Northeast China are even more sensitive to climate change. In North China, human habitat, population health and agriculture are highly influenced by climate change and sensitive to climate change (high confidence), followed by transportation, tourism and energy industry (high confidence), while manufacturing industry and major projects are both less affected and less sensitive to climate change (medium confidence). North China has a temperate monsoon climate with flat terrain and developed agriculture. With the world-class Beijing-Tianjin-Hebei city cluster, people’s health and living environment are of great concern. There is the largest comprehensive industrial base in the northern part of China, where the manufacturing industry is developed, sea, land and air transportation are convenient, and tourist attractions are countless. The Beijing-Tianjin-Hebei region adjacent to the Shanxi energy base has oil pipelines connecting the oil fields of Northeast and North China, so the energy industry in this region is very developed. The northern part of North China with a shelterbelt system, is mainly composed of wind-proof and sand-fixing and water conservation forests, accounting for 3.9% of the total area of the three northern regions of China. During the period from 1961 to 2018, the climate in North China warmed significantly, with the average temperature rising by 0.33 °C per decade. The risks of extreme high temperature and extreme heavy precipitation increased significantly, leading to a growth in air pollution events and flood disasters. Therefore, the key socio-economic sectors and fields in North

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China were impacted significantly, including agriculture, human habitat, population health, transportation, tourism, energy industry, and manufacturing industry. The Three-North Shelter Forest which covers a small area in North China are also affected by climate change, but they are less sensitive and less affected by climate change. In Northwest China, agriculture and tourism industry are the major sectors that are highly influenced by climate change and sensitive to climate change (high confidence), followed by transportation and major projects (high confidence). While energy and manufacturing industries are highly impacted by climate change, they are relatively less sensitive to climate change (medium confidence). Human habitat is less affected by climate change but more sensitive to it. Irrigation, agriculture and animal husbandry have been well developed in Northwest China where wind energy, solar energy, natural gas and petroleum resources are abundant, and the energy industry is developed. In addition, this region is rich in mineral resources, and has a developed manufacturing industry. Northwest China owns a vast number of cultural and natural landscape attractions, and its tourism industry is highly developed. With the famous Silk Road, Lanzhou-Xinjiang Railway and Eurasian Land Bridge all passing through this region, the transportation industry has grown up. A comprehensive shelterbelt system dominated by wind-proof and sand-fixing forests has been built, accounting for about 82% of the Three-North Shelter Forest. However, due to drought and water shortage in Northwest China, the economy is underdeveloped and the human habitat is unsatisfactory. During 1961– 2018, the average temperature in Northwest China increased by 0.30 °C per decade, and the climate became warmer and more humid than before. In general, the key social and economic fields in this region such as agriculture, tourism, transportation and major projects are all very sensitive to changes in climate, and at the same time, these sectors are also impacted by climate change greatly due to the increase and intensification of extreme hydrological events. High temperature reduces the demand for heating in winter but increases the demand for cooling in summer, which has a greater impact on the energy industry and manufacturing. Air pollution levels have also increased with increasing temperature, posing a certain impact on the human habitat. In Southwest China, agriculture and tourism are the most vulnerable and sensitive sectors to climate change (high confidence), followed by transportation and major projects (high confidence). Energy and manufacturing industries are less affected by climate change but more sensitive to it (medium confidence), while human habitat is relatively less affected by and sensitive to climate change (medium confidence). Southwest China is mainly dominated by the subtropical monsoon and plateau mountain climate with developed planting and animal husbandry. It has rich biological resources and developed tourism, as well as convenient railway, highway and air transportation under the industry of developed transportation. The major projects such as the Qinghai-Tibet Railway, the Three Gorges Reservoir and the Sanjiangyuan Ecological Construction Project, etc., are distributed in this region. In addition, Southwest China is rich in mineral resources and energy resources, having developed manufacturing and energy industries. During

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1961–2018, the average temperature in Southwest China increased by 0.16 °C per decade, and the climate showed a trend of warming and humidification. The agriculture, tourism, transportation, and major projects in this region are very sensitive to changes in hydrothermal conditions and degradation of glaciers and frozen soil, being affected greatly by them. In the Southwest, where the climate is already warm, climate warming can easily increase the cost of energy and manufacturing industries, so the energy and manufacturing industries in this region are very sensitive to climate warming. Generally speaking, Southwest China has mild climate, beautiful environment and good human habitat, less affected by regional climate change. In central China, the sectors and fields with high degree of influence and sensitivity to climate change are agriculture (high confidence), followed by manufacturing, transportation and tourism (high confidence). Major projects are moderately affected by climate change, having less sensitivity to climate change (medium confidence). Energy industry is less affected by climate change but more sensitive to it (low confidence). Human habitat is less affected by climate change and less sensitive to climate change (medium confidence). The region of central China is mainly dominated by the temperate monsoon climate and the subtropical monsoon climate. It has developed agriculture with abundant rainfall and temperature. It is rich in mineral resources and has solid industrial manufacturing bases. With convenient water, land and air transportation, it is the transportation center of China, and the transportation industry in this region is well-developed. Central China owns rich history and culture, numerous tourist attractions and a welldeveloped tourism industry. The power resources are distributed in the pattern of “north coal and south water” with a certain amount of coal, petroleum, natural gas and nuclear resources. The reserves of energy minerals, oil, coal and natural gas rank among the top in China, and the energy industry is relatively developed. Central China is the location of the core water source and canal head of the middle route of the South-to-North Water Diversion Project, which is a major national project. From 1961 to 2018, the average temperature in Central China increased by 0.19 °C per decade, and the climate showed a warming and drying trend. The agriculture, tourism, transportation and manufacturing industries in this region are very sensitive and greatly affected by high temperature, frequent droughts and floods, uneven distribution of water resources in time and space, severe grassland degradation and reduced river runoff etc. The decrease in runoff caused by climate warming has a great impact on the South-to-North Water Diversion Project, however, due to the rich water resources in Central China, the major water conservancy projects in this region are less vulnerable to climate change. In Central China, where the climate is mild, and the ecological environment is healthy, climate change has little impact on the human habitat. The energy industry is less affected by climate change, but it is more sensitive to climate change because the energy industry in Central China is relatively underdeveloped. In East China, human habitat and population health are highly affected by and sensitive to climate change (high confidence), followed by tourism and transportation (high confidence). Climate change has a relatively high degree

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of impact on agriculture and energy industry (medium confidence). Manufacturing is low in exposure but high in sensitivity to climate change (low confidence). The East China region’s economy is flourishing and its urban clusters are highly developed and densely populated; the living environment and population health have attracted much attention. The mega-urban cluster in the Yangtze River Delta plays a leading role in the economic development of the entire Yangtze River Basin indeed the whole country, with healthy conditions of natural environment and developed tourism. Due to the convenient land, sea and air transportation, and many transportation hubs, the transportation industry in this region is well developed. The light industry, machinery and electronic industry and other manufacturing industries in this region are dominant in the whole country. There are abundant rain and heat resources in this region, and the types of crops are diverse. Energy industries such as coal, coalbed methane, electric power, hydropower, solar energy, biomass energy, geothermal energy and nuclear energy have a solid foundation and have been rapidly developing. From 1961 to 2018, the average temperature in East China increased by 0.24 °C per decade, indicating a warmer and more humid climate. The intensified storm surges, sea water intrusion, coastal erosion, typhoons, floods, high-temperature heatwaves, urban heat island effect, sea level rise and air pollution have significant impacts on the human habitat, population health, tourism, transportation, agriculture and energy industries, but show a relatively weak effect on the manufacturing industry. Moreover, this region is economically developed and densely populated, and the second and third industries are the dominant industries, thus the human habitat, population health, tourism, transportation and manufacturing industry in East China are relatively more sensitive to climate change. In South China, population health, human habitat and agriculture are the sectors and fields being highly affected by and sensitive to climate change, followed by transportation (high confidence). Tourism is less sensitive to climate change (medium confidence). Manufacturing and energy industries are affected by climate change to a lower degree but highly sensitive to climate change (medium confidence). Major projects have a relatively lower degree of being influenced by climate change and are less sensitive to climate change (low confidence). South China has a tropical-subtropical climate with abundant water and heat from solar radiation, resulting in developed agriculture. It has a mega-urban cluster in the Guangdong-Hong Kong-Macao Greater Bay Area, and population health and living environment there are seriously concerned. The sea, land and air transportation in South China is well developed, which promotes tourism in this region. The energy industry in this region is well-developed because renewable resources such as hydro-energy, wind energy, solar energy and biomass energy generate a greater amount of electricity. Automobile, iron and steel, petrochemical, machinery manufacturing and other heavy and chemical industries, as well as household appliances manufacturing, metal processing, mechanical and electrical manufacturing installation and other manufacturing industries are rapidly expanding in this region. Major projects in this region are the industry base of renewable resources and the Zhanjiang Port Deep water Waterway Project, etc. During the period from 1961 to 2018, the average temperature in South China increased by 0.17 °C per decade, and the

References

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climate became warmer, more humid and more extreme than before. The superurban clusters in this region have intensified the effect of the increased temperature in summer. With the increase in temperature, humidity and high-concentration air pollution events, diseases like dengue fever and malaria have become more common. Thus, the health of the population in this region is greatly affected by and sensitive to climate change. The sea level rise and the intensity of typhoon storm surges have increased the frequency and intensity of flood disasters in South China, especially in the Greater Bay Area, which may increase coastal erosion, saltwater intrusion, landslides and other secondary natural disasters. The human habitat, transportation, agriculture and tourism in this region are greatly influenced by and highly sensitive to climate change. The increased number of extreme temperature days has also increased the cooling water consumption in the manufacturing industry. The cost of refrigeration in summer ascends but the work efficiency of workers declines. This will have a certain effect on the manufacturing industry in this region. Besides, climate warming also affects the energy industry and major engineering projects which mainly use renewable resources, and the manufacturing and energy industries are much more sensitive to climate change in this region.

References Biskaborn B, Smith S, Noetzli J et al (2019) Permafrost is warming at a global scale. Nat Commun 10(1):264 Chen F, Xu XY, Yang Y et al (2020) Investigation on the evolution trends and influencing factors of groundwater resources in China. Adv Water Sci 31(6):811–819 (in Chinese) Chen R, Yin P, Wang L et al (2018) Association between ambient temperature and mortality risk and burden: time series study in 272 main Chinese cities. British Med J 363:k4306 Climate Change Center of China Meteorological Administration. 2019. China Blue Book of Climate Change (2019). Beijing. (in Chinese) Hoesly RM, Smith SJ, Feng L et al (2018) Historical(1750–2014) anthropogenic emissions of reactive gases and aerosols from the Community Emissions Data System (CEDS). Geoscientific Model Dev 11(1):369–408 Hughes TP, Huang H, Young MAL (2013) The wicked problem of China’s disappearing coral reefs. Conserv Biol 27:261–269 Hughes TP, Kerry JT, Álvarez-Noriega M et al (2017) Global warming and recurrent mass bleaching of corals. Nature 543:373–377 Institute of Climate Change and Sustainable Development, Tsinghua University (2020) Comprehensive report on “China’s long-term low-carbon development strategy and transformation path.” China Popul Resour Environ 30(11):1–25 (in Chinese) Jia MM, Wang ZM, Zhang YZ et al (2018) Monitoring loss and recovery of mangrove forests during 42 years: the achievements of mangrove conservation in China. Int J Appl Earth Obs Geoinf 73:535–545 Ju RT, Li H, Shi ZR et al (2012) Progress of biological invasions research in China over the last decade. Biodivers Sci 20:581–611 (in Chinese) Kosaka Y, Xie SP (2013) Recent global-warming hiatus tied to equatorial Pacific surface cooling. Nature 501:403–407 Li Q, Dong W, Jones P (2020a) Continental scale surface air temperature variations: experience derived from the Chinese region. Earth Sci Rev 200:102998

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Li Q, Sun W, Huang B et al (2020b) Consistency of global warming trends strengthened since 1880s. Sci Bullet 65(20):1709–1712 Lin Q, Wang Y (2018) Spatial and temporal analysis of a fatal landslide inventory in China from 1950 to 2016. Landslides 15:2357–2372 Liu WC, Liu ZD, Huang C et al (2016) Statistics and analysis of crop yield losses caused by main diseases and insect pets in recent 10 years. Plant Prot 42:1–9 (in Chinese) Man W, Zhou T, Jungclaus JH (2014) Effects of large volcanic eruptions on global summer climate and East Asian monsoon changes during the last millennium: analysis of MPI-ESM simulations. J Clim 27(19):7394–7409 Niu R, Zhai P (2012) Study on forest fire danger over Northern China during the recent 50 years. Clim Change 111(3):723–736 Piao SL, Wang XH, Park TJ et al (2020) Characteristics, driers and feedback of global greening. Nat Rev Earth Environ 1(1):14–27 Santer BD, Bonfils C, Taylor KE et al (2014) Volcanic contribution to decadal changes in tropospheric temperature. Nat Geosci 7(3):185–189 Sun D, Zheng J, Zhang X et al (2019) The relationship between large volcanic eruptions in different latitudinal zones and spatial patterns of winter temperature anomalies over China. Clim Dyn 53(9–10):6437–6452 Tkachenko KS, Thuy D, Nguyen H (2020) Estuarine, coastal and shelf science ecological status of coral reefs in the Spratly Islands, South China Sea (East sea) and its relation to thermal anomalies. Estuar Coast Shelf Sci 238:106722 Tsinghua University Institute of Climate Change and Sustainable Development (2020) Comprehensive report on “China’s long-term low-carbon development strategy and transformation path”. China’s Population. Res Environ 30(11):1–25. (in Chinese) Wang GQ, Zhang JY, Guan XX et al (2020a) Quantifying attribution of runoff change for major rivers in China. Adv Water Sci 31(3):313–323 (in Chinese) Wang WQ, Fu HF, Lee SY et al (2020b) Can strict protection stop the decline of mangrove ecosystems in China? From rapid destruction to rampant degradation. Forests 11(1):55 Wei S, Luo S, Luo B et al (2020) Occurrence regularity of forest fire wonder the background of climate change. Forestry Sci Technol Guangdong Province 36(2):133–143 (in Chinese) Wu S, Zhang W (2012) Current status, crisis and conservation of coral reef ecosystems in China. Proc Int Acad Ecol Environ Sci 2(1):1–11 Yan ZW, Wang J, Xia JJ et al (2016) Review of recent studies of the climatic effects of urbanization in China. Adv Clim Chang Res 7(3):154–168 Yin ZC, Wang HJ, Li YY et al (2019) Links of climate variability among Arctic Sea ice, Eurasia teleconnection pattern and summer surface ozone pollution in North China. Atmos Chem Phys 19:3857–3871 Yin ZC, Wang HJ (2018) The strengthening relationship between Eurasian snow cover and December haze days in central North China after the mid-1990s. Atmos Chem Phys 18:4753– 4763 Yu KF (2012) Coral reefs in the South China Sea: their response to and records on past environmental changes. Sci China Earth Sci 55:1217–1229 Zhang J, Wang G, Jin J et al (2020) Evolution and variation characteristics of the recorded runoff for the major rivers in China during 1956–2018. South-to-North Water Transf Water Sci Technol 31(2):153–161 (in Chinese) Zhang Q, Geng G (2019) Impact of clean air action on PM2.5 pollution in China. Sci China Earth Sci 62:1845–1846 Zhang RZ, Jiang CY, Xu J (2016) Defence biological invasions: In case of invasive alien insects. Biol Secur Issues Challenges 31(4):400–404 (in Chinese)

Chapter 3

Projections of Future Climate Change and Risks

3.1 Anthropogenic Drivers of Future Climate Change The Shared Socio-economic Pathways (SSPs) and Representative Concentration Pathways (RCPs) describe how and to what extent greenhouse gases generated by future human socio-economic activities drive climate change. The coupling of the SSP and RCP pathways (SSP scenarios) forms a scientific loop for assessing the climate change science-impacts-risks-adaptation-mitigation. A scenario is a tool for describing the future development and change possibilities of the world. In line with the coherence and consistence principles of scenario planning, climate scenarios are assumptions of the relationship between the quantity of greenhouse gases produced by socioeconomic changes and key climate drivers. IPCC has a history of more than 30 years in climate change scenario development and application, starting from the SA90 simple experiment with a doubling or quadrupling of CO2 (IPCC 1990) to the six alternative scenarios of IS92 (IPCC 1992), the SRES Scenarios (IPCC 2001, 2007) taking into account 4 storylines of socio-economic development, the RCPs Scenarios of climate drivers of radiative forcing expressed in representative concentration pathways (IPCC 2013), and finally the SSPs scenarios for the Sixth International Coupling Model Comparison Program (CMIP6) which put more stress on the radiative forcing of anthropogenic greenhouse gas emissions. The SSPs are socio-economic pathways designed according to the national and regional development status and future planning, consisting of quantitative elements covering 7 major aspects: population and human resources, economic growth, lifestyle, human development, environment and natural resources, policies and institutions, and technological growth. Currently, there are five most commonly used SSPs (SSP1-SSP5), namely, sustainability pathway (SSP1), middle-of-the-road pathway (SSP2), regional rivalry pathway (SSP3), inequality pathway (SSP4), and fossilfueled development pathway (SSP5) (Zhang et al. 2013; O’Neill et al. 2014; Jiang et al. 2020a, b) (Fig. 3.1). The pathways were designed in two steps: in step one, the global mean radiative forcing (RCPs) were determined; in step two, the SSPs responsive to different radiative forcing levels were chosen. CMIP6 inherited from © Science Press 2023 D. Qin et al., The Change of Climate and Ecological Environment in China 2021: Synthesis Report, https://doi.org/10.1007/978-981-99-4487-3_3

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Fig. 3.1 SSPs scenarios: the combination of representative concentration pathways and shared socio-economic pathways (colors denoting SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0, SSP4-3.4, SSP4-6.0, and SSP5-8.5)

CMIP5 the 4 typical scenarios (RCP2.6, RCP4.5, RCP6.0, and RCP8.5) but filled up its gap with the addition of 3 new emission pathways (RCP1.9, RCP3.4, and RCP7.0). In this way, the research needs for certain scientific and policy strategy problems (such as the global warming of 2 °C or 1.5 °C) were satisfied at the same time. Model simulations cover the Tier-1 and Tier-2 tests. Presented in this chapter are the 7 scenarios of SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0, SSP4-3.4, SSP4-6.0, and SSP5-8.5. See Fig. 3.1 in this chapter for corresponding CO2 emissions for each scenario. SSP1-1.9: This is the radiative forcing scenario for extremely low anthropogenic CO2 emissions, or the “authentic” 1.5 °C pathway scenario. This scenario was designed mainly to be used for the research of the global temperature rise of 1.5 °C reached in the Paris Agreement. Global and regional demographic and economic changes in the sustainability pathway (SSP1) were put into the integrated assessment model (IAM) to obtain the quantities and trajectories of global and regional CO2 emission changes with time, with the radiative forcing to be stabilized at approximately 1.9 W/m2 in the year 2100. It is believed that global warming by 2100 is very likely (probability higher than 66%) to be kept below 1.5 °C in this scenario. This pathway reflects that world carbon emission will peak between 2020 and 2025 and reach net zero emissions by 2055. SSP1-2.6: Similar to the lowest greenhouse gas emission pathway in CMIP5, this scenario belongs to the family of radiative forcing scenarios for the lowest anthropogenic CO2 emissions. A controll experiment with the IAM driven by population and economic change data in the sustainability pathway (SSP1) is adopted to keep radiative forcing at 2.6 W/m2 or so by 2100. For its projection of instant global warming of 1.7 °C between 2020 and 2060, this pathway is considered to be a transitive scenario towards the 2.0 °C target. This pathway reflects that global carbon emission will peak between 2020 and 2025 and hit net zero emissions by 2075. SSP2-4.5: This is an updated version of RCP4.5 in CMIP5, and falls under the category of radiative forcing scenarios for medium anthropogenic CO2 emissions. Based on historical experiences of socio-economic development observed over decades, it follows the “middle-of-the-road” socio-economic trajectory (SSP2) to stabilize the

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81

control of radiative forcing at 4.5 W/m2 by 2100. Since the land use and aerosol pathways represented by SSP2 are not extreme, this scenario is a mere combination of medium socio-economic vulnerability with medium radiative forcing. This pathway suggests that global carbon emission will peak around 2030 and then drop to approximately 10 billion tons by 2100. This pathway can not lead to net zero emission within the twenty-first century. SSP3-7.0: This is a novel radiative forcing scenario in CMIP6 designed to fill up the gap of relatively high forcing scenarios in CMIP5, in which the radiative forcing is stabilized at around 7.0 W/m2 by 2100. The SSP3 pathway represents medium– high land use changes (drops in global forest cover in particular) and high radiative forcing factors (non-CO2 gases such as SO2 and methane in particular). SSP3-7.0 is a combination of high socio-economic vulnerability and relatively high anthropogenic radiative forcing. This pathway points to a continued rise in global CO2 emission in the twenty-first century which would still exceed 80 billion tons by 2100. SSP4-3.4: This is a novel CMIP6 radiative forcing scenario, falling under the category of radiative forcing scenarios for low anthropogenic CO2 emission. Demographic and economic change data in the adaptation-oriented inequality pathway (SSP4) were put into the IAM controll experiment, with radiative forcing level by 2100 to be kept to 3.4 W/m2 . It represents the combination of a high socio-economic vulnerability with medium radiative forcing. This pathway reflects that global carbon emission will peak between 2020 and 2025 and hit net zero emissions by 2085. SSP4-6.0: This is an updated version of RCP6.0 in CMIP5, filling in the range of medium radiative forcing scenario, with a forcing level to be kept to 5.4 W/m2 by 2100 and stabilized at 6.0 W/m2 after 2100. SSP4, an adaptation-oriented inequality pathway, is a combination of RCP3.4 and RCP6.0. Its objectives are for comparative studies of climate outcomes of different global radiative forcing pathways at the same socio-economic development level and for exploration of regional climate feedbacks on land use and aerosol. This pathway suggests that global carbon emission will peak around 2030 but still stay around 20 billion tons by 2100. This pathway can not lead to net zero emissions within the twenty-first century. SSP5-8.5: This is an updated version of RCP8.5 in CMIP5, and is a high radiative forcing scenario, marking the radiative forcing at the level of 8.5 W/m2 by 2100. This scenario was designed to solve scientific issues related to risk assessments in various model intercomparison projects. The CO2 radiative forcing induced by demographic and economic changes in the fossil-fueled development pathway (SSP5) could reach 8.5 W/m2 by 2100. SSP5-8.5 represents the highest economic growth and highest anthropogenic radiative forcing. This pathway points to a continued rise in CO2 emission in the twenty-first century, which would reach 120 to 130 billion tons by 2100. The SSPs scenarios are currently used in Scenario Model Intercomparison Project (ScenarioMIP) for CMIP6 and in human development, water resources, energy and economic projection researches related to future socio-economic development. SSPs scenarios have incorporated both the anthropogenic radiative forcing drivers and the socio-economic drivers (Jiang et al. 2018). Take China for instance, population might follow an increase-then-decrease pattern in all five SSPs, with respective SSP1, SSP2

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and SSP5 peaking of 1.393, 1.409 and 1.393 billion people by 2030, SSP3 peaking of 1.427 billion people by 2035 and SSP4 peaking of 1.388 billion people by 2025. By 2050, a population gap of 122 million between the highest SSP3 and lowest SSP4, would appear, so a population trap would come to the surface but later tend to alleviate upon the implementation of the three-child policy (Jiang et al. 2017). With the implementation of the universal two-child policy and three-child policy, China’s economy is expected to be on the rise in general before 2050, no matter which socio-economic development pathway is followed. The ranking of economic growth rate is SSP5 > SSP1 > SSP2 > SSP4 > SSP3 (Pan et al. 2019). The SSPs scenario analyses can offer a dynamic assessment of the impacts and risks of climate change on socio-economic development as well as the costs of the climate policies. They can also be used to reveal socio-economic development uncertainties under climate change adaptation and mitigation efforts, thus offering an effective way to measure the costs and risks related to different climate policies and socio-economic development models.

3.2 Earth System Models and Integrated Assessment Models 3.2.1 Earth System Models An Earth System Model (ESM) is a mathematical-physical model using mathematical equations (including dynamic equations and parameterization schemes) built upon the dynamic, physical, chemical and biological processes and their interactions with human activities, for the representation and identification of the traits and properties of major Earth system components (atmosphere, hydrosphere, cryosphere, lithosphere, biosphere and human activities). This model runs on computers as a large-scale integrated computational software, and its numerical solutions are able to describe the interactions between different components of the Earth System. As an early version of ESM, as well as the preliminary stage of the development of ESM, the climate system model is mainly based on geofluids and land surface processes, simulating the dynamic and physical processes and giving no or very simple considerations to the biological and chemical processes. Climate models before CMIP5 were known as the climate system models, which mainly took into account the physical processes of the climate system. Starting from CMIP5, chemical and biological processes have been extensively introduced into climate system models. Considering the carbon–nitrogen cycle and dynamic vegetation, they started to be known as the ESMs. However, neither CMIP5 nor CMIP6 has involved the solid earth processes related to the core, mantle and crust. Up to now, the ESMs still use the spatial structure and framework inherited from the climate system models. The ESM achieves the coupling between its component models through couplers and describes the correlation between subsystems. ESM component models include

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the atmospheric general circulation, oceanic general circulation, oceanic carbon cycle, sea ice, land surface process and terrestrial carbon cycle models, etc. The focus here is on CMIP6, the latest-generation ESM. CMIP6 embodies two major development trends of ESM, namely “integration” and “refinement”. “Integration” means that weather and climate, world and regions are put into consideration together to realize “seamless” simulation and forecast in temporal and spatial terms. “Refinement” means the development and maturation of model representations and subgrid-scale parameterization schemes for key processes of the Earth system based on deepening the understanding of Earth system science, in order for higher resolution and lower uncertainties in future projections and forecasts. “Integration” and “refinement” have greatly expanded and upgraded the ESM simulation capacity. On the temporal scale, the coupled model has reinforced subseasonal, seasonal, interannual and decadal climate projections, and is gradually acquiring the short-term and medium-term weather forecasting ability. On the spatial scale, ESM has improved the ability to simulate the interactions between individual, local, regional and global scales. The coupling of multiple climate economic models has enriched the ESM functions. Earth system simulations are extending from climate to weather, ecosystem, environment and also socio-economic fields, as well as from the mere passive responses of ecosystem to environmental change to the feedbacks of ecosystem processes and human activities to environmental conditions. Forty research institutes and higher education institutes in 18 countries took part in CMIP6-related tests, 8 of which are based in China, registering a total of 13 ESM/ CSM versions (Table 3.1). Among the 8 Chinese institutes are 4 former participants—the Institute of Atmospheric Physics, Chinese Academy of Sciences, National Climate Center affiliated to China Meteorological Administration, Beijing Normal University and the First Institute of Oceanography under the Ministry of Natural Resource, and 4 newcomers—Tsinghua University, Nanjing University of Information Science and Technology, Chinese Academy of Meteorological Sciences, and Academia Sinica, of Taiwan, China. The horizontal resolution of CMIP6 has got improved compared with that of CMIP5, with around 100 km for the atmospheric models and half 100 km and half 50 km for the ocean models.

3.2.2 Regional Climate Models A regional climate model (RCM) focuses the global climate model on one region so that the low-resolution simulation results of the global climate system model (CSM) and ESM can be dynamically downscaled to the target region of interest to significantly improve its resolution for higher-quality vernacular climate simulations or projection results. Dynamical downscaling refers to using physical models to downscale the response of circulations to large-scale forcing simulated by global CSM/ESMs, which can be achieved by high-resolution global circulation models (HIRGCMs), changeable resolution global circulation models (CARGCMs) and RCMs. Since the 1990s, some

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Table 3.1 Metrics of CMIP6 participating ESM/CSM from China Model names

Host institutes

BCC-CSM2-HR

Atmospheric Ocean model CMIPs participated model resolution resolution (km) (km)

BCC

50

50

CMIP, HighResMIP

BCC-CSM2-MR BCC

100

50

CMIP, C4MIP, CFMIP, DAMIP, DCPP, GMMIP, LS3MIP, ScenarioMIP

BCC-ESM1

BCC

250

50

CMIP, AerChemMIP

BNU-ESM-1–1

BNU

250

100

CMIP, C4MIP, CDRMIP, CFMIP, GMMIP, GeoMIP, OMIP, RFMIP, ScenarioMIP

CAMS-CSM1-0

CAMS

100

100

CMIP, ScenarioMIP, CFMIP, GMMIP, HighResMIP

CAS-ESM1-0

CAS

100

100

AerChemMIP, C4MIP, CFMIP, CMIP, CORDEX, DAMIP, DynVarMIP, FAFMIP, GMMIP, GeoMIP, HighResMIP, LS3MIP, LUMIP, OMIP, PMIP, SIMIP, ScenarioMIP, VIACS AB, VolMIP

CIESM

THU

100

50

CFMIP, CMIP, GMMIP, HighResMIP, OMIP, SIMIP, ScenarioMIP

FGOALS-f3-H

CAS

25

10

CMIP, HighResMIP

FGOALS-f3-L

CAS

100

100

CMIP, DCPP, GMMIP, OMIP, SIMIP, ScenarioMIP

FGOALS-g3

CAS

250

100

CMIP, DAMIP, DCPP, GMMIP, LS3MIP, OMIP, PMIP, ScenarioMIP

FIO-ESM-2–0

FIO-QLNM 100

100

CMIP, C4MIP, DCPP, GMMIP, OMIP, ScenarioMIP, SIMIP

NESM3

NUIST

250

100

CMIP, DAMIP, DCPP, GMMIP, GeoMIP, PMIP, ScenarioMIP, VolMIP

TaiESM1

AS-RCEC

100

100

AerChemMIP, CFMIP, CMIP, GMMIP, LUMIP, PMIP, ScenarioMIP

Note BCC for National Climate Center; BNU for Beijing Normal University; CAMS for Chinese Academy of Meteorological Sciences; CAS for Chinese Academy of Sciences; THU for Tsinghua University; FIO-QNLM for Laboratory for Regional Oceanography and Numerical Modeling, the First Institute of Oceanography, Ministry of Natural Resource; NUIST for Nanjing University of Information Science and Technology; and AS-RCEC for Research Center for Environmental Changes, Academia Sinica, Taipei, China

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85

progress has been made in the application of dynamical downscaling in climate researches, the application of RCMs in particular. RCMs, the most powerful tool available for simulating meso- and micro-scale climate, extreme climate events and changes, can finely depict climate outcomes of regional-scale forcings (such as aerosols, topography, inland lakes, coastlines, mesoscale convection systems, land use/land cover changes, etc.) with large-scale circulation inputs from global models or reanalysis data, and simulate the response to subgrid-scale forcing (such as complex topography and land surface heterogeneity) within the regional scope using high-resolution limited-area numerical models, so as to represent the details of circulations on finer time–space scales. Regional climate simulation was first applied to ecological and climate change evaluations in Yucca, United States in 1987. In 1989, the world’s first RCM-RegCM was formally released, which was built upon the Mesoscale Model Version 4 (MM4) and coupled with Biosphere–Atmosphere Transfer Scheme (BATS). In recent years, the horizontal resolution of the new-generation RCMs has improved from around 50 km to 10–25 km or even below10 km, with the demand for global change science and sustainable development science. Besides, a cloudresolving version has evolved, in order to simulate the impact of complex topography and mesoscale convection systems on regional climate and enhance the representation of meso- and small-scale extreme events (short-term intense precipitation, heatwaves, tropical-subtropical storms, etc.). The development of international RCMs has taken on new features: in addition to the application of the above higher resolution and convection-resolving versions, new regional ESMs will be developed in consideration of the impact of a fuller range of regional Earth system processes. In addition, ocean, sea ice, dynamic vegetation, underground and surface hydrological processes, and atmospheric chemical processes have been coupled into models such as Weather Research and Forecasting (WRF) and RegCM to build a fully coupled geophysical and biochemical simulation system. In terms of simulation, there is a tendency to use an ensemble of multiple global and regional models, in order to reduce uncertainty in regional climate projection. For instance, simulations and projections within the framework of the World Climate Research Programme (WCRP) Coordinated Regional Downscaling Experiment (CORDEX) are based mostly on multi-model ensembles. CORDEX resorts to dynamic and statistical approaches to make climate change downscaling projections across different land scales around the globe, so as to improve the resolution and confidence of regional climate simulations and projections, support regional climate change impact assessment and adaptation researches, and serve IPCC AR6. Chinese researchers have made great efforts to promote the application and development of RCMs, achieving remarkable progress in recent years. In order to improve the simulation capacity of regional climate in East Asia and the comprehensive simulation effect of the model, the parameterization schemes and the parameters have been debugged and tested under different combinations. For instance, the various convection parameterization schemes of the RegCM4-CLM were tested to find the Emanuel scheme to be better suited for regional climate simulations in China, with temperature

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and precipitation simulation efficiency being developed significantly. On this basis, long-term integration experiments on contemporary climate were conducted, and the results were compared with observational data for model verification to determine a recommended model version suited for this region. Therefore, RCMs are developing towards regional Earth system coupling models.

3.2.3 Integrated Assessment Models Integrated Assessment Model (IAM) is used for cost–benefit studies of climate change to feed decision-making on climate change actions. IAM represents the coming together of some key factors in climate change response, including emissions, impacts, adaptation, losses, etc., in order to derive an integrated cost–benefit analysis. IAM studies have rendered substantial support to the global responses to climate change. The research results of IAM support the emission pathways envisioned in IPCC reports from the FAR up to the most recent Special Report on Global Warming of 1.5 °C (SR15) and the AR6, derive emission scenarios for the year 2100 from the global cost–benefit analysis, and support the setting of the 2 °C and 1.5 °C targets and the emission reduction pathway options. IAM is able to analyze the interactions between the climate system and economy system, including mainly three modules, namely the climate module, economy module and impact module. Meanwhile, combined with the Global Climate Model (GCM) and the impacts, adaptation and vulnerability (IAV) assessment, IAMs can realize integrated assessments of climate change (Fig. 3.2). With the deepening of IAM researches, remarkable progress has been made. To better address the needs of global climate change response, the development of IAM has entered the phase of third-generation complex models. Some of the most representative models are IMAGE, GCAM, AIM, MESSAGE, ReMIND and IPAC. The first-generation IAMs emerged in the 1990s and were known as the highintegration models. They were rather simple, only taking emissions, concentrations, warming and impacts into account, such as DICE, RICE, MERGE and WITCH. These models played a vitally important role in determining whether global climate change needs to be addressed. The main conclusion was that the benefits of tackling climate change far outweigh the costs, thus promoting the international cooperation on climate change in the 1990s. The second-generation IAMs developed rapidly after 2000. Since it was hard for the first-generation IAMs to meet policy-making demands regarding emission reduction implementation stages, the second-generation IAMs came to the force. They were featured with incorporating the abundant sectoral and technological economy analyses in the energy model and land use model, and considering more energy transformation policy needs, with more detailed technical parameters and in-depth country-specific and regional researches. However, most of the climate models in IAMs were very simple. For instance, MAGGIC was a climate model focused solely

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Fig. 3.2 Relationship between IAM framework and other climate researches

on post-emission concentrations, radiative forcing and warming. The research results of the second-generation IAM were mainly used in IPCC AR3 and AR4. After 2010, the IAM development entered the third stage, in which emissions, concentrations, radiative forcing, temperature rise, impacts and adaptation were all carefully depicted in the models. The models were expanded further in scales, having the models like GCMs, atmospheric chemical models and oceanic dynamics models incorporated. In addition, regionalization and gridding were also improved, enabling these models to put out 0.25° × 0.25° gridded analysis data. Meanwhile, these models also took into account more relevant affecting factors, such as air quality, water demand, socio-economic employment rate, SDG, etc., as is shown in Fig. 3.2. For higher demand regarding the setting of global warming targets since AR4, international IAM analyses have focused on the lower warming targets such as the temperature rise of 2 °C and 1.5 °C, thus supporting the proposal of the Paris Agreement targets. Due to the large-scale and complexity of IAMs, the required parameters and the results are getting more complex, which drives the progress in IAM research towards higher model transparency. To better promote the development of IAMs, the Integrated Assessment Model Consortium (IAMC) was established in 2011 for its systematic development. Currently, IAMs resort to model intercomparison and diagnosis, databank building, and monographic study for higher confidence and transparency in model outputs. When it comes to important research issues, IAM

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groups around the world will participate. Besides, parameters in the model databank have increased from around 150 at the beginning to more than 700 to 1000 at present. As the largest emitter in the world, China is considered as a separate region in IAMs. The Chinese IAM groups often take part in the global model diagnosis to compare and analysis the China-related parameters in the global models. Because of the limited ability to participate in key global research projects, especially the urgent need for long-term funding support required for up-scaling the IAMs. China’s research teams need greater support and motivation for participating in the global and regional emission pathway researches in the future. The research orientation of IAMs may change in the future. Given the big number of current studies on the rise level and path of global warming by 1.5 °C, there are also international calls for accepting global warming of 1.5 °C as the future global mitigation target. With more and more countries committing to carbon neutrality, there are growing calls for the rise of 1.5 °C to be a possible mitigation target. Therefore, the research orientation of IAMs might need to be adjusted from the previous assessment of the target pathway to more integrated studies of factors relevant to achieving the temperature rise targets, such as food-energy-water connections, nature-based emission reduction pathways, ecosystem impacts, etc. in order to combine more with other socio-economic development factors. China’s major advances in IAM research. Chinese IAM models started to participate in global research in 2000. The IPAC model took part in the EMF24 research activities, and its global scenarios were submitted for comparative study with the international scenarios, and were then included in the contribution of Working Group III to the IPCC AR4. After that, China’s IAM researches did less on global scenarios, mainly focusing on the scenarios of China, and few teams participated in global scenario comparative studies. It was not until 2015 that research teams from THU, Beijing Institute of Technology (BIT), Sun Yat-sen University (SYSU) and Peking University (PKU) began to publish some research results on global emission scenarios. Since 2005, some Chinese models have taken part in international largescale IAM research projects, including the IPAC, THU-TIMER, NCSC-PECE, and PKU-IMED. Besides, SYSU developed a new-generation IAM coupling the Earth System Model with the climate-economy model realizing the coupling between the Earth system and the climate-economic system initially. However, IAM research requires large groups and long-term investment, which are currently lacking in China.

3.3 Projections of Future Climate Change 3.3.1 Temperature CMIP6 projects a future increase in annual mean temperature over China, with smaller increase values in the near-future period under different emission scenarios, and then the differences become more pronounced in the mid- and late

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twenty-first century under the high-forcing scenarios (high confidence). Climate change projections are subjected to the joint effects of external forcings (including greenhouse gas, aerosol, land use changes, etc.) and internal natural variability of the climate system. The latter one has a greater impact in the near-future (2021–2040) than in the middle (2041–2060) and end (2080–2099) of the twenty-first century. Figure 3.3 presents the projected annual mean temperature changes over China (land only, the same as below) during different periods of the twenty-first century, based on the historical and future climate change experiments from 19 CMIP6 models (4 from China) under four different emission scenarios, from low to high including SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5. General increases in the temperatures are found in all projections. The differences in the warming magnitude are small during the near-future period, indicating the less dependence of the change on scenarios and the large internal variability in the period. The differences among estimated results of the four scenarios gradually appear increase in the mid- and far-future period, and become more pronounced in the high-emission scenarios. The annual mean temperature will increase by 1.6–5.3 °C at the end of twentyfirst century in China (high confidence). Under the low emission scenario SSP12.6, the annuall mean temperature in China will reach 1.5 °C (0.9–2.0 °C, with the model range of 10–90%, the same below) by the mid-twenty-first century and then slowly hit 1.6 °C (0.9–2.2 °C) in the end of the twenty-first century. For the medium scenario SSP2-4.5, the values are 1.8 °C (1.2–2.3 °C) and 2.8 °C (1.8–3.7 °C), and under the high end scenario SSP5-8.5, are 2.4 °C (1.6–3.1 °C) and 5.3 °C (3.5–7.1 °C), in the middle and end of the twenty-first century respectively.

Fig. 3.3 Regional mean annual temperature (a) and precipitation (b) changes (in °C and %) in China (in relative to 1995–2014) projected by the multi-CMIP6 models for different time periods of the twenty-first century under different emission scenarios. Middle thick transverse line indicates the mean of the 19-model ensemble and the histogram indicates the model range of 10–90%

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The warming shows large spatial differences across regions, with greater magnitude found over Northeast China, Northwest China, and the QinghaiTibet Plateau. This spatial heterogeneity tends to be more pronounced in the middle and end of the twenty-first century in the projections. In the near-future, weaker and more evenly distributed warming is found (Fig. 3.4). In the middle and end of the twenty-first century, the temperature rises are more remarkable and the distributions show significant geographical differences. A latitudinal distribution, i.e. larger values in the north and smaller values in the south are found, except in the Qinghai-Tibet Plateau. For the mid-twenty-first century, the projected warming is smaller than 2 °C in most places under SSP2-4.5, and greater than 2 °C except in the regions south of the Yangtze River under SSP5-8.5 (Fig. 3.4). By the end of the twenty-first century, the temperature increase under SSP5-8.5 is greater than 5 °C over almost all of China, with greater than 5.5 °C and even in excess of 6 °C found over the Northeast, Northwest, and the Qinghai-Tibet Plateau except in southern China. It is noted that the projections presented in this chapter are based on the ensemble data of CMIP6 models. As indicated in the latest IPCC AR6, CMIP6 models show higher climate sensitivity compared with CMIP5, indicating greater warming in the CMIP6 model projections. In IPCC AR6, the constraint technique based on the observation of warming and the best estimation of the climate sensitivity are employed in constructing the global mean temperature projections. But how to apply this constraint method on the regional scale is still a problem, so further studies in this aspect are needed. Thus the uncertainties related to the high climate sensitivity of

Fig. 3.4 Annual mean temperature changes in China (in °C) projected by the multi-CMIP6 models for different time periods of the twenty-first century (in relative to 1995–2014) under different scenarios

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CMIP6 models need to be considered cautiously when the regional climate change is projected, in particular in quantitative comparisons. Lower warming is in general projected by RCMs compared with the driving GCMs, except for the greater magnitude over Qinghai-Tibet Plateau in winter (medium confidence). With higher resolutions, RCMs show better performances in reproducing present-day climate, and at the same time can project more reliable future climate change signals. Analysis of the five GCMs-driven RegCM4 ensemble projections indicates that while the RCMs preserve the large-scale magnitude and spatial distribution of the warming, which are senerally affected by GCMs’ driving fields, differences are found in the spatial distribution and values of the temperature increase (Fig. 3.5). In the medium range emission pathway RCP4.5, the mean temperature rise values over China in winter by the end of the century (2080–2099, in relative to 1986–2005) from the driving GCMs and RCMs are 3.0 °C and 2.5 °C respectively. The RCMs project smaller temperature increases in addition to the finer spatial details, and the prominent warming over the Qinghai-Tibet Plateau. The warming in summer is generally weaker and shows remarkable differences in the distribution compared with the warming in winter. The projected regional mean temperature in crements in summer by the GCM and RCM ensembles are 2.7 °C and 2.4 °C respectively.

Fig. 3.5 Mean temperature changes in winter and summer (in °C) in China as projected by the ensembles of driving GCMs and RegCM4 for the end of twenty-first century (2080–2099, in relative to 1986–2005) under the RCP4.5 scenario. Adapted from Wu and Gao (2020)

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3.3.2 Precipitation Annual mean precipitation is projected by CMIP6 models to be in a general increase trend in China (high confidence), with the increase rate in the range of 8% to 27% at the end of the twenty-first century (medium confidence). The annual mean precipitation would increase in all time periods of the twenty-first century and under all emission scenarios in China (Fig. 3.6). Under SSP2-4.5, the regional mean precipitation will increase by 6% (2%–10%) in the middle and by 11% (4%–17%) at the end of the twenty-first century. Under SSP5-8.5, the increments are 8% (2%–13%) and 17% (8%–27%) in the two periods, respectively. Precipitation changes show large differences in spatial distribution, with greater increases in North China, Inner Mongolia, the eastern part of Northwest and the Qinghai-Tibet Plateau (medium confidence). In the early twentyfirst century, precipitation has a general increase trend in China, except in Southwest China, and there is good consistency among the wodels, particularly under the highemission scenarios and in the late twenty-first century. Under SSP5-8.5, the precipitation increments are greater than 25%, in North China, Inner Mongolia, the eastern part of Northwest China and the Qinghai-Tibet Plateau in the end of the twentyfirst century, with 50% increase in some localized regions. The increase is smaller, mostly around 10%, in the areas south of the Yangtze River (Fig. 3.6). Comparative analysis for the seasonal-scale precipitation indicates that the projected annual mean

Fig. 3.6 Annual mean precipitation changes in China (%) projected by the multi-CMIP6 models for different time periods of the twenty-first century (in relative to 1995–2014) under different scenarios The dots indicate more than 75% of the models correspond to the change sign in the ensemble

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precipitation is mainly dominated by the changes of rainfall in summer, i.e. the main rainy season in China. Different from the general increase in the GCM projections, less or decreased precipitation changes in many areas are projected by the RCMs in China (medium confidence). The annual mean precipitation changes projected by the RegCM4 ensemble for the mid-twenty-first century (2041–2060) in relative to 1986– 2005 under RCP4.5 show a predominant increase in western China and the northern part of Northeast China, and the arid areas in Northwest China have 10%–25% increase in annual mean precipitation (Fig. 3.7), but under RCP8.5, more expanded areas and greater increment of precipitation increase are found. In terms of seasons, in winter, there is a common increase of precipitation more than 10% in most parts of northern China, more significant in the northwest with the maximum up to 75% found in the Tarim Basin under RCP8.5. Meanwhile, a remarkable decrease occurs over the Yunnan-Guizhou Plateau. In summer, areas with increased precipitation are located in the eastern part of the arid Northwest, the three-river source region in the eastern part of the Qinghai-Tibet Plateau, the northern part of Northeast China, and the Yellow River and Huaihe River region. The winter, summer, and annual mean precipitation changes under RCP8.5 at the end of the twenty-first century are 25%, 8% and 12%, respectively.

3.4 Projection of Changes in Extreme Events 3.4.1 Temperature Extremes There will be more extreme high-temperature events and fewer extreme cold events in the future in China (high confidence). CMIP6 projections show a general increase of the extreme indices TXx (annual maxima of daily maximum temperature) and TNn (annual minima of daily minimum temperature), with a prominent increase magnitude for the latter (Fig. 3.8). The averaged temperature increases in China for TXx and TNn by the end of the twenty-first century in relative to 1995–2014 under RCP4.5/RCP8.5 are 2.8 °C/5.2 °C and 3.5 °C/6.3 °C respectively. The increase of TXx is most significant in Northwest China, and TNn in Northeast China (high confidence). For the spatial distribution, the increase of TXx is the largest in Northwest China and smallest in Southeast China. Under RCP8.5 by the end of the twenty-first century, the magnitude of TXx increase ranges from 7 °C to 8 °C in Northwest China, and 3 °C to 4 °C in Southeast China respectively. For TNn, the largest increase (higher than 8 °C) is found in Northeast China, followed closely by the portions in the Qinghai-Tibet Plateau with a range of 7–8 °C. The large increase of the extreme high-temperature events with a 50-year return period, and the decrease of extreme cold events with a 50-year return period are projected for the future (high confidence). The projections based on CMIP6 models show consistency with those of CMIP5 models, with an increase

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Fig. 3.7 Precipitation changes (%) projected by the RegCM4 ensemble for the mid- twenty-first century (2041–2060) in relative to 1986–2005 a RCP4.5 annual mean; b RCP8.5 annual mean; c RCP4.5 winter; d RCP8.5 winter; e RCP4.5 summer; f RCP8.5 summer. Regional mean values are provided in the lower left corner of the panels. Adapted from Zhang and Gao (2020)

in both daily minimum and maximum temperatures, an increase in extreme hightemperature events and heatwaves, and a decrease in extreme cold events and frost days. Under the high-emission scenario RCP8.5, the present-day (1986–2005) 50year-return extreme high-temperature events will become one-to-two years’ return, and the extreme cold events will gradually disappear by the end of the twenty-first century. The events of warm days and warm nights with a 10-year return period at the present times will turn to normal by the end of the twenty-first century. Based on CMIP5 model projections, the increase values of TXx and TNn are 2.8 °C and 3.0 °C under RCP4.5, and 5.6 °C and 5.9 °C under RCP8.5 respectively by the end of the twenty-first century in relative to 1986–2005. The increase of TNn

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Fig. 3.8 Spatial distribution of TXx, TNn (°C) and Rx5day (%) changes projected by the multiCMIP6 models at the end of the twenty-first century (2081–2100) in relative to 1995–2014 under different gas emission scenarios. Adapted from Chen et al. (2020a, b)

is the most significant in Northeast China, the northern part of Northwest China and the southern part of Southwest China, while TXx shows the biggest increase in East China. In general, the increase of TNn is large than that of TXx. At the end of the twenty-first century, the frost days (FD, daily minimum temperature < 0 °C) and ice days (ID, daily maximum temperature < 0 °C) will decrease by 21 (43) and 17 (32) days under RCP4.5 (RCP8.5), tropical nights (TR, daily minimum temperature > 20 °C) and summer days (SU, daily maximum temperature > 25 °C) will increase by 18 (38) and 25 (44) days under RCP4.5 (RCP8.5), respectively. Projections from the RCMs show overall consistency with the results of GCMs, but have some differences in details. The RegCM4 ensemble projections

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Fig. 3.9 Regional mean a maximum daily maximum temperature (TXx; °C) and b annual maximum 5-day precipitation amount (Rx5day; %) change (in relative to 1986–2005) over China in the twenty-first century projected by the RegCM4 ensemble

indicate that in relative to 1986–2005, the regional mean TXx across China shows a trend of significant increase, and the increment can reach 2.6 °C ± 0.4 °C (5.1 °C ± 0.4 °C) by the end of the twenty-first century under RCP4.5 (RCP8.5) (Fig. 3.9a). Under RCP4.5, the temperature increase in the mid-twenty-first century (2046–2065) is mostly in the range of 1.6–2.4 °C in most parts of China, with larger values in the southeastern part of the Qinghai-Tibet Plateau, the Yellow River and Huaihe River Region and the Northeast China Plain. The increments are more evenly distributed at the end twenty-first century (2080–2099) in the range of 2.0–3.0 °C in most places (Fig. 3.10a). However, it is worth noting that extreme cold events may still occur due to the natural variability under the background of global warming. Thus special attention is needed for these events to avoid possible heavy catastrophe.

3.4.2 Precipitation Extremes Heavy precipitation events and their contribution to the total precipitation will increase in the future (high confidence). The present-day 50-year-return events are projected to become less than 10 years’ return by the end of the twentyfirst century under SSP8.5 in most of China (medium confidence). The CMIP6 projections show a general increase trend of Rx5day (maximum 5-day precipitation amount) in China (Fig. 3.8e and f). Under SSP5-8.5, regions with large-value increases in precipitation (>30%, with the largest increase up to 50% in portions) include North China, Inner Mongolia, southern Xinjiang, and the border areas of Yunnan and the Qinghai-Tibet Plateau. The regional mean increases in precipitation of Rx5day in China will rise by 16% and 29% by the end of the twenty-first century in relative to the situation in 1995–2014 under SSP2-4.5 and SSP5-8.5 respectively. The CMIP5-based analyses also suggest significant increases in precipitation index of Rx5day and R95p (annual total precipitation with the daily precipitation > 95th percentile) in China in the twenty-first century and the increased proportion of severe precipitation to the annual total. By the end of the twenty-first century under

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Fig. 3.10 Spatial distribution of future changes in TXx (a, b; °C) and Rx5day (c, d; %) projected by the RegCM4 ensemble under RCP4.5 in (a, c) mid-twenty-first century; and (b, d) the end of twenty-first century

RCP4.5 (RCP8.5), the increases in extreme rainfalls of Rx5day and R95p are 11% (21%) and 25% (60%) respectively, compared to these in 1986–2005. The increases in both R95p and Rx5day are more significant during the end of the twenty-first century compared with those in the earlier periods, being more pronounced in the Northwest China and Yangtze-Huaihe Valley, with the maximum > 20% in portions of the regions. Consecutive dry days (CDD) will decrease in the northern part of China and increase in the southern part. Moderate, heavy and torrential rainfalls are projected to occur with much higher frequencies, positively correlated to the warming at 1.5%/°C, 6.0%/°C and 27.3%/°C respectively. The present-day 50-yearreturn events will decline to 13-year and 7-year events by the end of the twenty-first century under RCP4.5 and RCP8.5 respectively. Projections from RCMs also show a general increase trend of severe precipitation events with more spatial details. The regCM4 ensemble projections show a remarkable increase in precipitation of Rx5day by 9% (21%) under RCP4.5 (RCP8.5) by the end of the twenty-first century in relative to 1986–2005 (Fig. 3.9b). Under RCP4.5, more than 20% increases of precipitation are found in the Yellow River and Huaihe River region, the Yangtze-Huaihe Valley, the northern part of Northeast China and portions of Northwest China (Fig. 3.10d). The rainfall increases of Rx5day

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under RCP8.5 are more prominent, with a greater than 20% increase found in most of China, and more than 40% in Northwest China, The large-value areas (>30%) of the increased rainfall of Rx5day are distributed in North China, Inner Mongolia, southern Xinjiang and the border areas of Yunnan Province and Tibet, with the max increased rainfall exceeding 50% in some regions.

3.4.3 Compound Extreme Events Extreme events such as compound high temperature and high humidity are projected to increase significantly in China (high confidence). Compound extreme events, like storm surge with heavy precipitation, high temperature with drought, and high temperature with high humidity events, etc. are attracting more and more attention from the research community and public. Limited studies have been conducted so far in the field, which in particular calls for future change projections using highresolution climate models. Some studies used daily maximum wet-bulb temperature to represent the compound high temperature with high humidity events, and made 3RCM ensemble projections under RCP8.5. Results show that future warming together with irrigation effects will increase the risk of heatwaves in North China Plain and other parts of eastern China. In fact the region may experience deadly heatwaves with wet-bulb temperature exceeding the threshold, thus increasing the uninhabitable for the human being in the region. The RegCM4 ensemble projections are used to investigate future changes of the thermal-comfort index “effective temperature”, which considers the aggregate effects of temperature, humidity and wind speed. It is found that even under the medium-range emission pathways, the exposure of population to heatwaves will be greatly increased by the end of the twenty-first century. For instance, the number of people with no “very hot” days in a year will decrease from 600 to 200 million, while the hot days exceeding two months, which is an extreme event that has rarely occurred in contemporary times, will affect 2.3 million people.

3.5 Exposure and Vulnerability The impacts of extreme and non-extreme events and the likelihood of disasters depend not only on the events themselves but also on exposure and vulnerability to a large extent. Exposure and vulnerability are key determinants of disaster risks and their impacts (IPCC 2012). Exposure refers to the presence of people, livelihoods, environmental services and resources, infrastructure; or economic, social or cultural assets in places that could be adversely affected by extreme events. One of the major causes of the increase in economic losses from disasters is the higher-level exposure of human beings and economic assets. Vulnerability refers to the propensity or predisposition to be adversely affected. In case of identical levels of exposure, the severity and

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types of adverse impacts depend on vulnerability (IPCC 2012). In developed countries, extreme events cause predominantly economic losses; whereas in developing countries, they result in huge economic losses plus severe casualties. Between 1970 and 2008, more than 95% of extreme event-related deaths occurred in developing countries. This difference results mainly from different levels of vulnerability and exposure (Zheng 2012).

3.5.1 Observed Exposure and Vulnerability Changes With the economic and population growth and the increase in extreme rainstorm events, population and GDP exposures to rainstorms and flood disasters tend to be on the rise in China as a whole, both peaking in 2010 before fluctuating and decreasing (high confidence). In terms of the affected population, there was a multi-year average of 83.08 million plus a yearly increase of 1.4958 million people exposed to rainstorms and flood disasters over the period of 1984–2019, and the peak values of population exposure for all regions appeared in 2010–2015, of which North China and Northeast China reached the maximum of population exposure to rainstorms and floods from 2000 to 2015, and then showed a decreasing trend. In light of GDP affected, there was a multi-year average of CNY 604.8 billion plus a yearly increase of CNY 29.979 billion over 1984–2019, and all regions reached the max values of GDP exposure to rainstorms and flood disasters during 2010–2015. Among them, Southwest China had the highest GDP exposure to rainstorms and flood disasters in 2005–2015 and then showed a downward trend. From 1984 to 2019, the average population and total economic output affected by rainstorms and floods in East China were the largest, reaching 19.69 million and 160.4 billion CNY respectively (Fig. 3.11, Wang et al. 2014). With socio-economic development, better infrastructure, enhanced disaster prevention and mitigation efforts, population vulnerability to rainstorms and flood disasters has been declining. But the economic vulnerability is still in a wavelike trend in China (medium confidence). Over 1984–2019 the population vulnerability to rainstorms and floods (the ratio of the disaster-affected people to the total population is the index of population vulnerability) was 4.49%, showing a decreasing trend generally (− 0.18%/year), of which the most vulnerable region in population was Southwest China (10.09%). From 1984 to 2019, China’s economic vulnerability to rainstorms and floods was 0.30%, without marked changes, of which central China was the region with the highest vulnerability in economy to rainstorms and flood disasters (0.57%) (Fig. 3.12, Wang et al. 2014).

Fig. 3.11 Changes in population and GDP exposure to rainstorms and flood disasters in China from 1984 to 2019

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Fig. 3.12 Changes in population and economic vulnerability to rainstorm floods in China from 1984 to 2019

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3.5.2 Possible Changes in Socio-economic Exposure and Vulnerability to Rainstorms and Flood Disasters With the global warming of 1.5–4.0 °C, there will be possible increases of 42%– 100% in flood-affected areas, 14–46 times in economic exposure and 4–17 times in direct economic losses (medium confidence). The severity of the rainstorms and flood disasters was represented by changes in the return periods of the 30-year, 50year and 100-year events from 1981 to 2010. Return periods of the 100-year floods could decrease by 29%, 32%, 41%, 50%, 58% and 58% at the warming levels of 1.5 °C, 2.0 °C, 2.5 °C, 3.0 °C, 3.5 °C and 4.0 °C (Fig. 3.13a–f). The 100-year floods would become 50–100-year events at the warming levels of 1.5 °C and 2.0 °C, and 20–50-year events at the warming levels of 2.5 °C, 3.0 °C, 3.5 °C and 4.0 °C (Jiang et al. 2020a, b). Projections of flood-affected areas against different levels of global warming and analyses of the twenty-first century SSP GDP datasets indicate that the increase in economy and affected area under the intensifying global warming climate lead to the increased changes in total amount of GDP influenced by flood disasters significantly (Fig. 3.14). From 1981 to 2010, floods affected an area of around 1.2 million km2 and an annual GDP of USD 320 billion or 14% of the national total GDP. From the baseline period of 1995–2004 (warming of 0.7 °C above the pre-industrial level) to the global warming of 4.0 °C, it is projected that flood-affected area will increase at a rate of 200,000 km2 /0.5 °C (i.e., the flood-affected area will increase 200,000 km2 or so for every 0.5 °C rise in global mean temperature) and by 42% and 100% compared to the base period in the warming scenarios of 1.5 °C and 4.0 °C respectively. With the increase in the affected area (Fig. 3.14b) and total GDP of China (Fig. 3.14a), the total GDP exposured to floods will show a rise markedly. The growth rate of economic exposure is about USD 2.2 trillion/0.5 °C from the base period to the global warming of 4.0 °C, and is about 14 times and 46 times that of the base period, respectively, against the global warming of 1.5 °C and 4.0 °C (Fig. 3.14c). Based on the future changes of flood intensity, economic loss vulnerability curve and economic exposure, the losses of rainstorm and flood disasters in China will increase to be 4–17 times the 2006–2018 level in the warming scenarios of 1.5–4.0 °C (Fig. 3.15).

3.5.3 Possible Changes in Socio-economic Exposure and Vulnerability to Droughts With the global warming of 1.5 °C to 2.0 °C, direct economic losses from droughts in China might be 3–6 times those of the base period (1986–2005). The marked increase in future economic losses is caused mainly by the increase in severity and duration of drought and socio-economic aggregate within the areas exposed to droughts, as well as the increased vulnerability to drought (medium

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Fig. 3.13 Changes in the 100-year flood return period in warming scenarios of 1.5 °C, 2.0 °C, 2.5 °C, 3.0 °C, 3.5 °C and 4.0 °C

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Fig. 3.14 Changes in total GDP of China affected by rainstorm and floods (a), affected area (b), and economic exposure (c) over 1981–2010 and under the warming scenarios of 1.5 °C, 2.0 °C, 2.5 °C, 3.0 °C, 3.5 °C and 4.0 °C

confidence). Against the backdrop of global warming, China will probably face more severe drought events (referring in this book specifically to a combination of drought events caused by meteorological, agricultural, hydrological, and socio-economic factors). With global warming, drought intensity will increase from severe drought over the base period (1986–2005) to extreme drought at global warming levels of 1.5 °C and 2.0 °C (Fig. 3.16a). Annual mean drought area will increase from about 610,000 km2 over the base period to 710,000 km2 against the global warming of 1.5 °C and 880,000 km2 or so against the global warming of 2.0 °C (Fig. 3.16b)

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Fig. 3.15 Changes in flood-caused losses (historical record losses) in China from 1984 to 2018, and changes in such losses under global warming scenarios of 1.5 °C, 2.0 °C, 2.5 °C, 3.0 °C, 3.5 °C and 4.0 °C

while the frequency of drought events will show an declining trend (Fig. 3.16c) (Su et al. 2018). During 1984–2015, the annual direct economic loss from droughts exceeded CNY 44.4 billion in China, accounting for 20% of the total loss from meteorological disasters. Against the global warming of 1.5 °C, the drought-caused direct economic loss will be 3 times that of the current base line period (2006–2015) and will become even higher under the global warming of 2.0 °C, or 2 times the loss level of the 1.5 °C the warming (Fig. 3.17a). A significant increase in future economic loss will be caused not only by increased intensity and duration of drought events, but also by socio-economic growth and greater vulnerability in the drought-exposed areas. With the development of economy and society, the contribution of drought loss to the annual GDP of the same year will drop from 0.23% in the base period to 0.16% when the global temperature rises by 1.5 °C. However, with the temperature rising continuously, the trend of reduction in drought loss contribution to GDP will be reversed. When the global warming reaches 2.0 °C, the contribution of drought loss to GDP will probably return to the level of the base period (Fig. 3.17b). Therefore, if global warming is held within 1.5 °C, hundreds of billions of yuan (CNY) in economic losses can be saved.

3.5.4 Possible Changes in Population Health Exposure and Vulnerability to Heatwaves Under the global warming scenario of 1.5 °C and 2.0 °C, the death toll caused by high temperatures in Chinese cities will probably reach 80,000–140,000 with the improvement of adaptation capacity not taken into account, or the death toll will be 40,000 to 70,000 with the adaptation capacity considered. Global warming

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Fig. 3.16 The mean drought intensities (a), drought areas (b) and frequencies (c) in China during the base period (1986–2005) and under the global warming scenarios of 1.5 °C and 2.0 °C

Fig. 3.17 Direct economic loss from droughts (a) and its contribution to GDP (b) under the global warming scenario of 1.5 °C and 2.0 °C

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kept below 1.5 °C rather than 2.0 °C means tens of thousands fewer heatwaverelated deaths in Chinese cities (high confidence). The gender and age structure of the population in the 5 SSPs were simulated by 31 CMIP5 models, and the mortality risks from high temperatures in Chinese cities were evaluated from the perspectives of disaster factors, exposure and vulnerability using the internationally used distributed hysteresis nonlinear model. In addition, in the risk assessment, special consideration is given to the change of vulnerability resulting from the improved adaptability in the future (Wang et al. 2014). According to the mean outputs of the 31 CMIP5 models, heatwaves will occur in the cities at a rising frequency before 2050 in the RCP2.6 (representing the global warming of 1.5 °C) and the RCP4.5 (representing the global warming of 2.0 °C) scenarios. After 2050, the growth rate of heatwave weather frequency will approach 0 in the scenario of RCP 2.6 or slow down in the RCP4.5 scenario. In the global warming of 1.5 °C or 2.0 °C, the average annual number of heatwave days in 2060–2099 will increase probably by 32.6% and 45.8% compared to the high temperature days in 1986–2005 (Fig. 3.18). It can be inferred from the relationship between the mortality rate of different gender and age groups (working population age: 15–64 years old) and the mean temperature in major cities of China that the mortality rate will be relatively on the rise with the increase (high temperature) or decrease (low temperature) in temperature after the most suitable temperature range (Fig. 3.19). A combination of projections of heatwave events and population vulnerability indicates that heatwave-induced deaths among every million people in Chinese cities will probably reach 50–70 (60–80) with the global temperature rise of 1.5 °C (2.0 °C) when the improvement of adaptation capacity is considered, but the death toll could increase from 100–130 to 140–170 if the adaptation capacity improvement is not taken into account. When the global warming is 1.5 °C–2 °C (Fig. 3.20). As aging becomes all the more prominent in China, heatwave-induced deaths will become much more among the non-working population (age below 15 and above 64) than

Fig. 3.18 Frequency and intensity of high temperatures in large cities in China from 1960 to 2099. Curves and shadows denote the overall mean and range of GCM outputs. Values for 1961–2005 are reference values (black line and gray area); values for 2005–2099 are projections (blue lines represent the RCP2.6 scenario and red lines represent the RCP4.5 scenario of greenhouse gas emission) (Wang et al. 2019)

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Fig. 3.19 Relationship between relative mortality risk and changes in temperature in typical Chinese cities. a Male working-age population, b male non-working age population, c female working-age population, and d female non-working age population

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Fig. 3.19 (continued)

Fig. 3.20 Heatwave-related mortality rate for the period of 1986–2005, under the global warming scenario of 1.5 °C and 2.0 °C, and in the 5 SSPs (dots and lines represent multi-model ensemble mean and change range, respectively)

at present while the death toll among the working population can decrease slightly compared to the present level. Although heatwave-induced deaths are still higher among females than among males, as the gender ratio dwindles, heatwave-induced deaths will exhibit a narrowing gender difference (Fig. 3.21).

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Fig. 3.21 Comparison of heatwave-related mortality rates according to gender (a) and age (b) for the period of 1986–2005, under the global warming scenario of 1.5 °C and 2.0 °C and in the 5 SSPs (bars and straight lines represent multi-model ensemble mean and change range, respectively)

3.6 Future Climate Change Risks Climate-change risks “arise from the interaction of climate-related hazards (including hazardous events and trends) with vulnerability and exposure of human and natural systems” commonly known to include extreme climate and weather events, probability of future adverse climate events, possible losses from climate change, probability of possible loss, etc. with the characteristics of uncertainty, future events, damage and relativity. Sources of climate change risks are of two major types. The first type is about the average climate conditions (temperature, precipitation trends), belonging to gradually changing events. The adverse effects of the gradual events take a long time to emerge as a result of the slow progression of changes, so their potential tremendous impacts and long-term consequences could be severely underestimated. Most climate system risks fall under this category. Climate impacts accumulate and worsen over time and space, undergoing a transition from quantitative change to qualitative change and finally causing risks to burst out as disasters. The second type includes extreme weather and climate events (i.e. tropical cyclones, storm surge, extreme precipitation, river floods, heatwaves, cold waves, and droughts), and some of the extreme events are emergencies. In light of the event occurrence features, such type of risks are often caused by extreme weather and climate events, closely associated with the disaster-causing thresholds of the climate system. The disastercausing thresholds are correlated to the exposure and vulnerability of the climate system. Under the same weather and climate conditions, the higher the systematic exposure and vulnerability, the lower the disaster-causing thresholds, and the higher the possibility of disaster occurrence. “Risk-bearing objects” (RBOs) are socio-economic and resource environments that experience negative effects, including people, livelihoods, environmental services and resources, infrastructure, and economic, social or cultural assets, etc. Exposure and vulnerability are two attributes of RBOs. The former refers to the number of RBOs present in places or settings that can be adversely affected, while

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the latter refers to the propensity or tendency to be adversely affected, often characterized by sensitivity and susceptibility. Separate, climate change and extreme weather events do not necessarily lead to disaster, but must intersect with vulnerability and exposure before bringing risks possibly into being. The magnitude and development patterns of the RBOs determine not only exposure and vulnerability (abilities to tolerate extreme events) but also have direct effects on the magnitude and rate of anthropogenic climate change. The global climate system is very complex, and there are many factors contributing to climate change. Uncertainties still remain in the scientific understanding of climate change trends. In particular, no precise judgement can be formed as to climate change trends and their specific impacts and harm on different regions. Nevertheless, from the perspective of risk assessment, climate change is one kind of huge environmental risks for human beings.

3.6.1 Water Resources Global warming would likely increase the intensity of urban flooding and disaster risk; climate change would raise the risk of regional drought that would threaten crop production in the major food-producing areas (medium confidence). The national water resources vulnerability would increase in the future. Under the RCP2.6, RCP4.5 and RCP8.5 emission scenarios, the risk and vulnerability of China’s water resources system under the impact of future climate change will change significantly. By the 2030s, China’s overall vulnerability will increase, the areas of moderate and above vulnerability regions will expand drastically, and the area of extreme vulnerability will also further expand. Under RCP4.5, the comparison of the number and percentage of China’s water resource vulnerable provinces under the impact of current and future climate change (Figs. 3.22 and 3.23) shows that the number of provinces with different vulnerability levels varies greatly with the number of low vulnerability provinces dropping sharply, from 14 to 0 (41.0% down to 0.0%), the number of medium–low vulnerability provinces dropping, from 4 to 3 (12.0% down to 9.0%), but the number of medium vulnerability provinces increasing from 3 to 13 (9.0% up to 38.0%) and the number of extreme vulnerability provinces also rising from 3 to 6 (3.0% up to 18.0%). The numbers of provinces with no vulnerability, medium–high vulnerability and high vulnerability do not have any changes, but the geographical locations are seen to have changed with regional area expanded significantly. Compared with RCP4.5, the water resource vulnerability of the Inner Mongolia Autonomous Region under RCP2.6 is higher. Under RCP8.5, Shaanxi and Gansu provinces are not only still in the high vulnerability group, but also have slightly higher vulnerability indices than in the RCP4.5 scenario. In the future, extreme events such as intense precipitation and floods will probably increase in parts of China; floods and droughts will be on the rise, resulting in adverse effects on sustainable socio-economic development. Global

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Fig. 3.22 Comparison of the numbers of vulnerability provinces in terms of water resources in China in the 2030s under the influence of current and future climate changes (RCP4.5) in the 2030s

Fig. 3.23 Percentage of vulnerability provinces in terms of water resources in China in the 2030s under the influence of current and future climate changes (RCP4.5)

change will lead to increases in extreme hydrological events, floods and droughts in the arid regions of Northwest China. With global warming, glaciers in mountainous areas are retreating at an accelerating rate, the ice and snow water reserves are decreasing, and some rivers show the turning point of glacier melting. The change of glaciers has already had an important impact on the amount and distribution of water resources within a year. Extreme floods in Xinjiang show a trend of regional aggravation, particularly prominent in southern Xinjiang. Changes in extreme floods for major rivers in the Tianshan Mountains are closely related to regional warming and the increase of extreme precipitation events there. In the future, sea level will

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continue to rise, high water level will rise; and extreme events such as rainstorms and strong storm surges will occur more frequently with much stronger intensity. Due to downstream water jacking, the discharge capacity of the pipe network and pump stations will be weakened, the flood protection capacity of the original design standard will be significantly reduced, urban drainage will become more difficult, and the risk and severity of urban flooding in China will be on the rising side. Global climate model simulation outputs suggest that in the future the Qinghai-Tibet Plateau region will also experience greater warming range than the rest of China. Sustained summer warming will further melt glaciers in the water sources region. The occurrence frequency of glacier lake outburst, ice avalanches and snow-melt floods and other disasters is likely to increase further. Global climate change, coupled with the increase in water demand from socio-economic development and in heat wave days, droughts and water shortage will occur at higher frequencies, affecting a wider scope and more domains, and causing more severe damage in the future.

3.6.2 Agriculture Frequent occurrence of extreme climate events such as high temperature and droughts in the context of climate change adversely impact the yield and quality of wheat, corn and other food crops (high confidence). Global warming results in the intensification of high-temperature stress, raising the risk of reduction in wheat yields in the future. In the filling stage of wheat quality formation, hightemperature stress can generally increase the protein content of wheat grains, while at moderate high temperature, the dough strength is enhanced and the quality of wheat is improved. But when the temperature exceeds 30 °C, the formation of glutenin macromer (GMP) can be affected, resulting in weak dough strength and poor wheat quality. Droughts slow down the starch accumulation in wheat grain, lower amylose, amylopectin and total starch content of wheat grain, and reduce grain weight and wheat yield. Drought stress can also alter wheat endosperm starch components, grain size distribution, crystallinity and major gelatinization parameters, and further deteriorate wheat quality. The global warming of 1.5 °C and 2.0 °C can lead to the reduction in China’s corn yield by 0.1% and 2.6%. Even with the CO2 fertilization effect taken into account, the global warming of 2.0 °C can still reduce 1.7% of corn yields. Under the global temperature rise of 1.5 °C and 2 °C, the corn yield in Northeast and Northwest China growing areas tend to increase, but decreases in North China and Southeast China growing areas. High-temperature stress during florescence and grain filling stages can cause corn yields to drop, increasing crude protein, crude fat and lysine content but decreasing crude starch content in the corn grain. Drought during florescence may increase starch content and decrease protein content, starch granular size and the proportion of long chain in amylopectin, resulting in the deterioration of the corn grain quality. The spatial distribution of precipitation becomes the direct cause for the difference of loss extent in different regions. So, the rain-fed spring corn in

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the western oasis farming area is faced with high drought risks, requiring vigorous development of water-saving irrigation. The summer corn production area in North China has the most severe drought-induced yield loss and needs special care about climate-change-induced drought risks. Under RCP8.5, the loss of corn yields induced by climate change in North China, South China, Xinjiang, and part of Northeast China and Northwest China will exceed 10% by the end of the twenty-first century (2070– 2099) relevant to the base period (1981–2010) (medium confidence). Under RCP4.5, the potato yield on the Loess Plateau of China will exhibit a general decreasing trend in the future (2011–2060). Climate change and extreme events pose a considerable threat to such cash crops as cotton and oil crop. Extreme high and low temperatures both affect cotton yield and quality. Extreme high temperature can inhibit photosynthesis of the cotton leaves and reinforce respiration and transpiration of the cotton plants, causing cotton plant photosynthate deficiency, internal water imbalance, low pollen activity, increased sterile seed numbers, flower and boll shedding, boll weight loss, and eventually a drop in cotton yield and quality. Extreme low temperatures can affect the activities of antioxidase and the content of osmoregulation substance, lowering pollen activity, destroying leaf chlorophyll, and limiting photosynthesis. To what extent extreme low temperature affects cotton yield and quality is related to how low the temperature is and how long it lasts. Flood disasters cut down cotton yield mainly by lowering boll number and mid-summer boll number per plant. Without countermeasures taken, the temperature rise of 1.5 °C will cause a reduction of 20%–30% in soya bean yield in China and the 2.0 °C warming can bring 30%–50% loss in soya bean yield. With adaptation measures taken, a warming of 1.5 °C and 2 °C is expected to decrease soya bean yield by 0%–5%. By 2100, climate change will lead to a 7%–19% reduction in soya bean yield in China (Chen et al. 2016). Against the backdrop of future climate change, soya bean yields in the United States and Brazil, two major producing countries, will drop by 0%–50%. The trend of “contracting north and expanding south” in the world soya bean production will intensify further and the world soya bean trade flows will undergo significant changes. Future climate change will cut down the rapeseed yield in China by 18,300– 26,300 t, mainly in the coastal regions of South China, the Sichuan Basin and the lower reaches of the Yangtze River. Moreover, rapeseed yield volatility will also show a strengthening trend in the future. While temperature rise can boost crop seedling-stage metabolism and is good for rapeseed growth and safe overwintering, early summer high temperature is prone to the reduction of rapeseed yield and quality. Excessive temperature at the maturity stage of rapeseed can decrease seed oil content, while low amount of total sunshine hours, droughts and early-summer high temperature tend to cause a drop in rapeseed quality. Under the context of climate change, peanut growth period will be shortened in most parts of China, which can cause a reduction in unit yield and a large drop in total yield of peanuts after the mid-twentyfirst century. Rising temperature and decreasing precipitation can increase peanut pest and disease incidence.

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3.6.3 Cryosphere The positive (beneficial) effects of cryosphere changes on socio-economic system mainly comes from its huge service function provided for human society, while the negative (disastrous) impacts mainly comes from the adding risks to the socio-economic system. The positive and negative impacts of cryosphere changes are illustrated in Fig. 3.24. Climate change will lead to greater cryospheric instability and uncertainties, thus increasing the frequency and intensity of cryospheric disasters and exerting negative impacts on the socio-economic system to a larger extent. Analyses of the cryospheric impacts on and adaptation to the socio-economic system are intended to maximize cryospheric resources in serving the socio-economic system while minimizing cryospheric change-related risks faced by the socio-economic system. In the coming decades, the potential risks of glacial lake outburst will increase as the consequence of more glacial lakes formed by the Himalayas glacier retreat. It is projected that the change in average high-water level of coastline cities around the world, 136 of which are most severely affected, will exceed the sea level rise by about 10% in the future. Currently, over 300 million people live in low-elevation coastal areas, suffering from an annual loss of tens of billions of US dollars. Roughly estimated, about 1.3% of the world’s population are exposed to the ranges of once-ina-hundred-year floods. Sea level rise means significantly increased risks of potential damages. Without effective adaptation measures, the potential damages will reach 10% of the global GDP by the end of 2100.

Fig. 3.24 Positive and negative impacts of cryosphere

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3.6.4 Ecosystem Climate change can cause risks of ecosystem loss in China. The risks are mainly reflected in the reduction of net primary productivity (NPP), degradation of species and loss of biodiversity. In the scenarios of the near-term warming of 0.84 °C to the long-term warming of 2.74 °C, the risk area will increase from 1.326 million km2 or 13.8% of the national total area to 3.019 million km2 or 31.5% in the short run. In the near term, major risk areas are concentrated in the Qinghai-Tibet Plateau, Northwest China and Central China, while in the long term, the Qinghai-Tibet Plateau will face far larger risks than other parts of China. Therefore, under future climate change, the Qinghai-Tibet Plateau will probably become the area with the greatest loss of ecosystem diversity in China. The increasing frequency, scope and intensity of extreme events will pose serious threats to ecosystem services, environment and resource security. The increase of extreme drought events will do no good to the increase of ecosystem carbon sink. In the future, the cold-temperate and mid-temperate zones will witness a possible increase in fire frequency, scope and intensity. The Greater Khingan Mountains in China will face much larger risks of fire. The current carbon emission from forest fires ranges between 10.2 and 11.3 TgC/a in China. According to the current fire prevention capacity, emission intensity will be increased further in the future, which can be a great threat to the carbon sink function of the forest ecosystem. Global climate change and human activities are jointly aggravating the risks of regional desertification, soil erosion and rock desertification in China, severely threatening the ecosystem functions. Under RCP4.5, desertification in China’s arid zone will deteriorate in 2014–2099, while, in the RCP8.5 scenario, areas with worsened desertification will account for 74.51%. Simulations indicate that with a temperature rise of 4 °C, soil erosion in river basins is reduced by 2.3 × 104 t, while constant temperature and more river basin precipitation can lead to more soil erosion. For example, soil erosion increases by 17.73% when temperature rises by 3 °C with precipitation increasing by 15% in the case of the Dayang River Basin in Liaoning Province. In the Tanghe River Basin, soil erosion increases by 9.16% with temperature rise of 3 °C plus precipitation increase of 4%. Soil erosion in some regions will lead to rocky desertification because of bedrock exposure induced by surface soil loss. Changes in global precipitation patterns triggered by climate change will cause the salinity of regional soil bottom or groundwater to rise to the surface along with capillary water, which will cause soil salinization after water evaporation, particularly in arid and semi-arid areas in Northwest China. Extreme climate events will lead to ecological disasters and risks such as fires, insect pests and diseases. Regional warming and drying induced by climate change will also have an important impact on the incidence of fires, insect pests and diseases. In the RCP2.6, RCP4.5, RCP 6.0 and RCP8.5 scenarios, regions exposed to high and very high risks of forest fires will increase by 0.6%, 5.5%, 2.3% and 3.5% in China over 2021–2050, of which the increase scope in North China appears the most obvious. In different scenarios for longer periods, total occurrence density of

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forest fire (annual median 0.36/1000 km2 ) will increase by 30%–230% in Northeast China and northern China over 2081–2100. Global warming will enable insects (such as Dendrolimus tabulaeformis) to shift their distribution range further north. In different climate scenarios (RCP2.6, RCP4.5, RCP6.0 and RCP8.5), Loxostege sticticalis overwintering zone will expand and shift further north to varying degrees by the 2050s and 2070s compared to the present state. Under the background of future climate change, changes in biodiversity distribution will aggravate the risks of biodiversity loss and species extinction. In China, among the 91 kinds of amphibians, the highest number of species, whose distribution range will lose by 40%–60%, is 18–29; and reptilians have the largest number of species with less than 20% distribution range loss, or 58–77 of all 115 kinds of species, whilst 4–8 species lose over 60% of their distribution range. Moreover, analyses of over 134 amphibian species in China indicate that in the RCP2.6, RCP4.5, RCP6.0 and RCP8.5 scenarios, most amphibians will suffer a distribution range loss of 20%, over 90% of species will move north to find suitable habitats; over 95% of species will migrate to higher elevations, and over 75% of species will shift to the west of their current localities. Among the 114 species of birds, the birds with proportion of distribution range loss less than 40% are the most, being 44– 59 species, and those lose 60% of their distribution range are 1–6 species. By 2050, highly endangered animals will account for 5%–30% of the total. Of the 208 endemic and endangered species in China, 135 species will face a suitable distribution range loss of over 50%. In the CMIP5 scenario, giant panda will lose 52.9%–71.3% of their habitats, and in the RCP8.5 scenario, their suitable habitats and staple food bamboo climate suitable area will have a decrease of 25.7% by 2050 and 37.2% by 2070. Sichuan golden snub-nosed monkeys (Rhinopithecus) will experience a far greater suitable habitat loss, probably up to 51.22%. In the RCP2.6 and RCP8.5 scenarios, black muntjac (Muntiacus crinifrons) will respectively see suitable habitat loss of 11.9% and 36.9% and core area loss of 20.5% and 55.2% by 2050. It is projected that highly-endangered wild plants will take up 10%–20% of all plant species by 2050 to be assessed. The superposition and synergistic effects of future climate change and nonclimate factors will increase the vulnerability of typical marine ecosystem and reduce its self-adaptive capacity to environmental change (Table 3.2).

3.6.5 Human Habitat Future climate change will impact human habitat in terms of population health, living conditions, urban lifeline and ecological environment, etc. (Fig. 3.25). Climate change coupled with rapid urbanization leads to the urban “fiveisland-effect” (heat, rain, arid, wind and turbid islands). Urban agglomeration has changed the spatial pattern of surface thermal field in the city clusters. With time going, the intensification of urban heat island effect will continue in the coming decades. The combined impacts of climate change and urbanization will drive cities

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Table 3.2 Vulnerability and key risks of typical marine ecosystems in China Climate change factors

Anthropogenic activities

Vulnerability and key risks

Warming ocean and heatwave Ocean acidification Sea level rise Extreme precipitation, drought and cold wave Rising typhoon strength

Destructive fishing Overfishing Reclamation works Development and construction of coastal zones Input of terrestrial pollutants

High incidence of coral death from heat bleaching, decreasing coral diversity, community structure change, phase transition and degradation of the coral reef ecosystem, decreasing complexity of 3-D structures, decrease in coral reef calcification, slowing-down growth of reef Decreasing tropical mangrove biodiversity, changes in species composition, biodiversity increase of high-latitude mangroves, expansion and northward shift of mangrove distribution range with biological invasion and competition to be enhanced possibly, further leading to the change of mangrove ecological niche, considerable threats to nearshore mangroves as the result of sea level rise Tropical seagrass growth, to be affected by temperature rise, including phenological events such as flowering, seed diffusion and germination, as well as species abundance and distribution; sea level rise mainly affecting seagrass meadow habitat suitability and further causing possible damage and destruction to seagrass meadows Increasing and intensifying interference of extreme climate events like typhoons and precipitation on typical marine ecosystems Increased risks of regional species extinction, decline in fishery productivity, damage to marine tourism, as well as weakened function of wave prevention, shoreline protection and reef protection Anthropogenic activities coupled and synergized with climate change aggravating the vulnerability and risks of typical marine ecosystems

to face greater risks of extreme high temperature. The precipitation trend towards extreme events are likely to grow more prominent, with areas exposed to high rainstorm and flood risks all concentrating in central-east and coastal areas of China. Such a trend of changing towards extreme precipitation is growing more obviously in the cities. With the progress of urbanization, the faster the development rate of urbanization, the higher the probability of significant increase in extensive rainstorm-induced water-logging in urban regions.

Fig. 3.25 Impact of future climate change on human habitat

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Large cities and urban agglomerations in coastal areas tend to be highly vulnerable to the devastating impact of sea level rise due to their dense population and wealth. Three major city agglomerations in the eastern coastal areas (Beijing-Tianjin-Hebei, Yangtze River Delta and Pearl River Delta), are the most important strategic economic zones in China, accounting for only 5% of the national land area but 23% of the national population and 39% of China’s GDP. Coastal cities in these three regions are faced with growing threats of sea level rise-induced storm surge and seawater invasion. For example, flood control walls in the Bund of Shanghai are designed to guard against once-in-1000-year floods. If sea level rises by 20–50 cm, the standard of coastal dike for the Yangtze River Delta needs to be lowered from the once-in-100-year to once-in-50-year water levels. Due to the impact of such factors as sea level rise and ground subsidence, the actual design standard for flood control walls in the urban section of the Huangpu River have been reduced to once-in-200-year level. With intensity, frequency and duration increasing, extreme precipitation events will be more likely to occur. In the RCP8.5 scenario, mid-high latitude precipitation presents an increasing trend during the mid-twenty-first century. Under the global temperature rise of 1.5 °C and 2 °C, China will see more severe extreme precipitation events in the eastern and southwestern parts and the Qinghai-Tibet Plateau; the national mean intensity of severe precipitation events will increase by about 30% by the end of the twenty-first century; the current once-in-50-year precipitation events will probably become once-in-several-year events. For inland regions with remarkable heat island effect, a significant increase in hourly precipitation intensity has been identified in the city clusters. There are stronger signals of urbanization having a positive impact on the increase of precipitation in the three major city agglomerations of Beijing-Tianjin-Hebei, Yangtze River Delta and Pearl River Delta, and particularly, in the Guangdong-Hong Kong-Macao Greater Bay Area, urban agglomeration, which is located in the center of the extreme hourly precipitation intensity high-value zone in China. With the persistent heat island effect in the developing process of urbanization, it can be expected that the extreme trend of urban hourly precipitation will be further enhanced in the future. Changes in meteorological conditions are very likely to hinder the diffusion of air pollutants (high confidence). Take Beijing for instance. Days of clear sky without haze in winter were at a probability 50%, lower in the second half of the twentieth century than in the first half. Based on multi-model RCP8.5 scenario simulation analysis, the number of such days will decrease further to 60% in the future. The dynamic downscaling projections of typical months in the Beijing-Tianjin-Hebei agglomeration under the RCP8.5 scenario indicate that, generally, there will be a decline in wind speed, relative humidity and boundary layer height but a rising trend in temperature and annual average air pollutant (PM2.5 , SO2 and NOx ) concentrations, which pointes to a potential risk of deteriorated air quality in the Beijing-TianjinHebei region in the future. Projections of black carbon aerosol emissions in the policy-controlled emission scenario suggest that there will be a precipitation drop plus an autumn and winter temperature rise for the Beijing-Tianjin-Hebei agglomeration as against a slight summer drop and winter level-off in temperature for the

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Pearl River Delta. The warming and drying climate can restrict urbanization scale and population growth in areas with severe water shortage.

3.6.6 Human Health Global climate warming can lead to a rise in heatwave-related mortality risks. Under RCP8.5, temperature change-caused excess mortality is on a net increase for 23 countries around the globe, 1.50% for China (95% CI: −2.00%–5.40%). The Guangzhou case indicates that climate change will intensify the negative impacts of changing climate on people’s health in the future population growth and aging scenario. Taking appropriate measures can partially offset the increased years of heat-related life loss. In combination with demographic studies, it is found that heat wave-induced excess mortality in 2031–2080 can increase by 35% in relevant to the 1971–2020 level under the RCP8.5 emission scenario. Mortality risks of cardiocerebrovascular diseases and respiratory diseases will increase remarkably with time going in the 2020, 2050, and 2080 in Beijing, and the increase is far greater in the high emission scenarios than in the low emission scenarios. Climate change can cause wider spread and higher risks of vector-borne diseases. Global warming spreads most vector-borne diseases to higher-latitude and higher-elevation regions. For example, climate change can allow more areas favorable for the spreading and prevalence of Dengue fever. Dengue fever projection based on biologically-driven models indicates that in all RCP scenarios all risk areas in China extend remarkably north and the at-risk population increase significantly. Currently (1981–2010), 168 million people in 142 counties (districts) of China are at high risks of Dengue fever. In the RCP2.6 scenario, the high-risk areas of Dengue fever will cover 277 million people in 344 counties (districts) by 2050 and 233 million people in 277 counties (districts) by 2100. Under the RCP8.5 scenario, the high risk range of Dengue fever will expand further, with 490 million people in 456 counties (districts) by 2100 to be affected.

3.6.7 Major Projects Adverse impact of climate change on the operation of major water conservancy projects would bring significant disaster risks. Increase in extreme precipitation will contribute to more water into the Three Gorges Reservoir. When the water quantity into the reservoir exceeds the original design storage capacity and corresponding normal storage level, risks of reservoir operation will occur. Extreme weather and climate events in the Three Gorges Project and the neighboring areas will probably happen more frequently with higher intensities in the future, which will in cure excessive floods and put pressure on the flood control capacity of the Three Gorges Project. Moreover, the increase in extreme precipitation intensity and frequency can

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also lead to higher occurrence probability of sudden debris flow and landslide in the reservoir area, posing threats to reservoir management, dam safety and flood control. Under the two future climate change scenarios of RCP4.5 and RCP8.5, the occurrence chances of the same drought in flood season, non-flood season and the whole year in the water source area of the South-to-North Water Diversion Project and the water receiving area of Haihe River go up to different degrees compared with the present situation, especially the overlap probability of the same drought in flood season and the same severe drought in non-flood season rises more obviously. In the future, temperature and precipitation will be in an increasing trend in water source areas along the eastern and middle routes of the South-to-North Water Diversion Project, while runoffs in the upper reaches of Hanjiang River will show the tendency of decreasing first and then increasing compared with the baseline period. The growth in runoffs is exceeded by the increase in evaporation, making it not sufficient to offset the rise in water demand. Therefore, water shortage problem in North China can not be fundamentally resolved and water supply will remain a challenge in the future. Climate change poses prominent risks to safe operation of engineering projects within the permafrost region. Climate and engineering thermal disturbances have considerable impacts on the bridges and road-bridge transition sections of the Qinghai-Tibet Railway. Investigations to 164 bridges totaling 220 km in length indicate that 83% of the road-bridge transition sections have encountered noticeable settlement and deformation, amounting to 70 mm depth on average. At the same time, the settlement of bridge protection cone, surface cracking and bumps, and the freeze–thaw process difference in some localized Subgrades in writer give rise to the overflow of water on frozen layer at the foot of subgrade slope, resulting the problems like ice cones. The abnormal development of water in the frozen layer under some bridge pile foundations has caused serious frozen soil degradation of the surrounding permafrost and settlement of the pile foundations. Qinghai-Tibet AC-DC Power Grid Interconnection Project is one of the key projects under the aegis of China’s Western Development Strategy, consisting of three parts: the 750 kV Xining-Golmud power transmission and transformation project, the ± 400 kV Golmud-Lhasa DC power transmission and the 220 kV Central Tibet power grid project. In particular, the Golmud-Lhasa line has a total length of 1038 km, 550 km of which traverses permafrost regions and there are 1207 tower foundations in the permafrost area, accounting for 51% of the total foundations of the whole line. This high voltage direct current (HVDC) transmission line, the first of its kind built at an elevation of 4000–5000 m in the world, was put into operation upon being completed on December 9, 2011 and has played a strategic role in safeguarding and promoting sustainable socio-economic development in Tibet. The permafrost landscape traversed by the power transmission line is featured with poor thermal stability, strong hydrothermal activities, high proportions of thick underground ice layer and ice-rich frozen soil, and extreme sensitivity to environment changes. Permafrost engineering problems such as frost heave, thaw settlement and upward freezing pulling once posed serious threats to the design, construction and safe operation of the project, which would be further aggravated by the constant permafrost degradation caused by climate change.

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During the building process of the China-Russia Crude Oil Pipeline (CRCOP), vegetation eradication destroyed the surface energy balance, affected the permafrost thermal state, broke the hydraulic channel and caused ponding in the pipe trench, accelerating the degradation of the surrounding permafrost. Along the pipeline route, the climate has been getting warmer, which, coupled with intensifying human activities, has caused temperature rise in the permafrost and its continuous degradation. Accordingly, surface subsidence, water ponding and longitudinal crack development within the pipe trench area are likely to occur, and finally the water seepage in the trench can further accelerate the surrounding permafrost degradation. The pipeline is equivalent to an internal heat source that keeps heating the surrounding permafrost, forming a thawing circle that grows with the progression of operation time. Permafrost melting and consolidation settlement around the pipeline caused by climate warming and engineering heat disturbance will have brought potential threats to the safe and stable operation of the pipeline. Knowledge tips: tipping point, black-swan event, gray-rhino event, emerging risks In recent years, “tipping points”, “black-swan” events, “gray-rhino” events and “emerging risks” have gradually become household words in the climate and environmental change circle. These four concepts fall under the same category but carry different connotations, as illustrated below. Tipping points generally refer to an assumed critical threshold value of a system upon its transformation from one state to another completely new state. This transformation might be abrupt and/or irreversible. For the climate system, this term refers to an assumed critical threshold when global or regional climate changes abruptly from one stable state into another state under the impact of human activities (Kopp et al. 2016; IPCC 2019). The components of Earth system prone to the impact of tipping points are called tipping elements. Once the tipping elements break through the tipping points, they might trigger a series of abrupt changes and nonlinear responses or accelerate certain positive or negative feedback of the climate system, thus producing a global cascade effect and finally exerting significant impacts on human existence and civilization. Currently, nine elements have been recognized as being very close to the tipping points, namely, frequent droughts in the Amazon tropical rainforest, overall decline in Arctic sea ice extent, slowdown of the North Atlantic Thermohaline Circulation since 1950, occurrence of boreal forest fires and pests damage, massive mortality of coral reefs, accelerated melting of Greenland ice sheet, permafrost degradation, accelerated melting of ice sheet in the west Antarctic and Wilkes Basin in the east Antarctic (Steffen et al. 2018; Lenton et al. 2019). “Black swan” and “gray rhino” events: black swans were rarely seen and so this term has been used to describe the occurrence of events hard to predict (swans black in color are not rare now, but this connotation has already been well established). In this regard, “black-swan” events refer in general to

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events which are hard to predict, occur quite out of expectation, but produce considerable negative impacts. In addition to being unexpected and producing an extreme impact, a “black-swan” event has another important attribute, that is, in spite of its unexpectation, human nature drives people to concoct explanation for its occurrence in hindsight, making it to be considered explainable and predictable. For instance, the outbreak of COVID-19 at the end of 2019 was a typical “black-swan” event. “Black-swan” events in the climate system refer to the climate events of low likelihood and high impact (LLHI), such as the collapse of the Larsen A, B and C Ice Shelf in the west Antarctic in 1995, 2002 and 2017 respectively, resulting in continued ice mass loss in this region, with a total loss of 2720 billion ton of mass loss in the Antarctic ice sheet between 1992 and 2017, which is equivalent to raising seal level by 7.6 mm. The mass loss rate from the Antarctic Peninsula due to ice shelf collapses increased from 7 billion ton per year to 33 billion ton per year (The IMBIE Team 2018). Another example is the massive collapse of No. 53 glacier in Arucuo Lake in Ngari, Tibet on July 17, 2016, which dumped about 700,000 m3 of ice blocks to the lake bank killing 9 local herdsmen and burying nearly 100 livestock (Wu et al. 2019). “Gray-rhino” events and “black-swan” events are two somewhat opposite concepts. Gray rhinos are relatively docile but when they rush to come they run extremely fast and people cannot escape from it. For this attribute, this term is used to refer in general to the events that show early signs but are not given due attention and finally cause serious consequences. Therefore, “gray-rhino” event is defined as a potential risk with high probability and huge impact, which may occur after a series of warning signals and signs. At present, the long-term climate change characterized by warming is a gray-rhino event in that even though the real threats are not yet felt, persistent warming has led to increasing and intensifying extreme weather and climate events. The adverse impacts of these events on the natural and socio-economic systems are highly possible to occur, which will leave no chance for people to turn back. The warming climate, if not held in check, will very possibly become “gray rhino” risks that are serious threats to global sustainable development (Pan and Zhang 2018). Emerging risks refer to the probability of a new type of adverse impacts arising in a certain region as a result of climate change or natural and socio-economic changes; or risks resulting from indirect, transboundary or long-distance climate change and natural and socio-economic maladaptation measures. Emerging risks are characterized by newness, systemization and extremity. Newness means that there is no historical prevention experience for reference, and that no technological measures currently available are effective. It takes time to gradually recognize such risks and time to gradually improve the plans to prevent and defuse emerging risks. Systemization refers to the serious crisis in which various disaster factors interweave and superimpose on the social systems and produce a “domino” effect. The links between various

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systems and domains in the modern society are so close that once a local risk occurs, the entire society may be widely affected, involving a wide range of areas and a large number of people. The damage will spread to a even larger area quickly, and the diester loss will show a nonlinear amplified response. Global warming has been triggering a series of changes in the climate system or corresponding spheres, and some emerging risks have appeared, as exemplified by significantly higher probabilities of forest fire in high-latitude regions and heatwave over oceans. Before 2012, scientists had no idea of oceanic heatwave. Marine heatwave can lead to massive mortality of marine organisms, species changes and community reconstruction, and hence alter the structure and functions of the whole ecosystem. Besides, morine heatwave can also impact the products and services of the ecosystem. For example, fish-catching and biogeochemical processes, can bring serious socio-economic and political influences (Smale et al. 2019). Thomas et al. (2018) studied the global daily mean sea surface temperature data from 1982 to 2016 and 12 global Earth System models from 1861 to 2100 finding that global warming climate will result in more frequent, extensive, intense and enduring heatwaves over oceans. Cryosphere is the sphere most severely affected by global warming. As the world gets warmer and warmer, there is an abruptly rising probability for pathogenic microorganisms to be released from cryosphere, which is a severe challenge to the global ecosystem. However, this problem is yet to be further studied. In 2016 anthrax broke out in Siberia, killing more than 2000 reindeer and hospitalizing 96 people. Relevant studies have shown that it was anthrax spores infected by a thawed deer carcass due to the melting of permafrost that caused the outbreak. Besides, there are studies showing that a 30,000-year-old giant virus revived from the Siberian permafrost can still attack its target—single-cell ameoba. As global warming intensifies, cryosphere will speed up its release of unknown microorganisms, and send more viruses into lower-stream oceans and rivers along with polar and mountain glaciers’ meltwater. With such a huge number of virions spreading and surviving in the new ecosystem and a high probability of infecting other types of hosts, tremendous impacts will occur to the new host ecosystems (Chen et al. 2020a, b). Atlantic meridional overturning circulation (AMOC) has weakened by 15% since the 1950s (Caesar et al. 2018). Together with the rapid melting of the Greenland Ice Sheet, the further slowdown of AMOC will destabilize the West African monsoon, and cause drought events in Africa’s Sahel region. It will also possibly cause the Amazon River to become dry, destroy the East Asian monsoon and allow the heat in the Southern Ocean to accumulate, which can further accelerate the loss of Antarctic ice (Lenton et al. 2019). The rapidly melting Greenland Ice Sheet and the collapse of some Antarctic ice shelves will result in a sea level rise of 10 m on a century-tomillennium time scale (IPCC 2019). The disappearance of glaciers in the Himalayas will significantly change the runoff processes of the glacier-fed big rivers, threatening

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the existence, water security and food production of over a billion people in the lower stream (Immerzeel et al. 2010). Figure 3.26 shows some of the potential tipping points in the climate system and their cascade effects. It is worth noting that even if the global mean temperature rise is controlled within 1.5–2 °C above the pre-industrial level as is proposed in the Paris Convention, it is not possible to rule out the possibility of pushing the Earth System in the direction of irreversible “hothouse” Earth by such tipping points and cascade effects (Steffen et al. 2018). We have been possibly unable to determine whether the tipping points will be broken through by the climate system, but we can lower such risks by reducing emissions in the hope of slowing down its rate of impact (Lenton et al. 2019).

Fig. 3.26 Illustration of tipping points and their cascade effects on the climate system (Steffen et al. 2018; IPCC 2019)

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Chapter 4

Adaptation and Mitigation: Measures, Actions and Effects

Adaptation and mitigation are two main ways to address climate change. Adaptation is the process of adjustment to actual or expected climate change and its effects. In human systems, adaptation seeks to moderate harm or exploit beneficial opportunities; in natural systems, human interventions may speed up adjustment to the expected climate change and its effects. Mitigation involves human interventions to reduce emission sources or enhance the sinks of greenhouse gases. The objective of mitigation is to limit the global average temperature increase to a certain target above pre-industrial levels so as to reduce climate change risks and impacts. There are both synergies and trade-offs between adaptation and mitigation measures; adaptation and mitigation actions should be advanced within the framework of sustainable development. This chapter begins with an introduction to China’s climate change adaptation strategies, technology and measure options, and an evaluation of its adaptation actions and outcomes against the backdrop of global adaptation action. It then moves to China’s emission reduction policies, technology and measure options, and analyses its mitigation actions and outcomes against the backdrop of global mitigation action. Finally, it ends with an integrated assessment on China’s synergized adaptation and mitigation measures, actions and effects, with particular regard to agriculture and forestry carbon sinks as well as urban planning and governance. Evaluations and analyses in this chapter indicate that a “double stringent” adaptation and mitigation strategy needs to be adopted by China and the world. Enhancing mitigation actions targets the lower global temperature rise, while adaptation is to meet the higher warming scenarios. The two need to be put together in consideration, coordinated and balanced in practice, synchronized and given equal attention. Adaptation and mitigation actions taken separately by various departments should be put under synergistic management and optimization to create the best possible policy portfolios. In addition, it is worth noting that the comprehensive and profound socio-economic transformations required to meet the Paris goals may bring about new adaptation demands.

© Science Press 2023 D. Qin et al., The Change of Climate and Ecological Environment in China 2021: Synthesis Report, https://doi.org/10.1007/978-981-99-4487-3_4

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4.1 Climate Change Adaptation 4.1.1 Global Progress Climate change adaptation is an important means of global climate governance. Adaptation-related knowledge and governance systems were incorporated by Future Earth Strategic Research Agenda 2014 as a grand challenge to global sustainable development. Adaptation has been a key assessment object and major assessment target in the IPCC AR synthesis and special reports. In the contribution of IPCC Working Group II (WGII) to the IPCC AR5, over half of the main assessment conclusions are adaptation-related. In this regard, adaptation also makes the core evaluation point in China’s climate change and eco-environment series of scientific assessment reports. Adaptation research is still growing in width and depth. The research scope has expanded gradually from cost–benefit analyses, optimization and efficiency methods to multi-dimensional comprehensive assessments that integrate risk and uncertainty dimensions to the broader policy and ethics framework. Besides, many studies view adaptation in light of its coherence with risk and risk composition, breaking adaptation down to exposure reduction, vulnerability reduction and resilience building, and stressing the active, responsive and synergistic nature of dynamic adaptation. Another research hotspot is related to adaptive capacity and adaptation costs, analyzing adaptation from the perspective of object, subject, behaviour and outcome. And climate resilience building is revealed as both a key component of active adaptation and a necessary means to sustainable development. Adaptation has gradually become one of the core elements in the global response to climate change. The IPCC ARs, one upon another, served not only to highlight the importance of climate change adaptation but also to push forward global efforts to strengthen adaptation-related policies and actions. Alongside, the developed countries took the initiative to set forth independent climate change adaptation strategies, frameworks and actions. As early as in 2005, Finland was the first to release a national adaptation strategy, followed by France, Spain, the Netherlands, Australia, the UK, Germany, Denmark and the European Union (EU). In 2013 the United States announced the President’s Climate Action Plan to drive forward domestic adaptation and mitigation efforts. Most developing countries, tend to take adaptation merely as part of the national climate change response strategy due to limitations in their knowledge and capacity to adapt to climate change, but some developing countries also worked out separate adaptation policies one after another. With the establishment of the National Adaptation Programme of Action (NAPA) for the least developed countries (LDCs) at the 7th Conference of the Parties (COP7) (UNFCCC) in 2001 and the launch of the National Adaptation Plan (NAP) for all the developing and the least developed parties under the Cancun Adaptation Framework in 2010, countries like India, Vietnam, Bangladesh, and Nigeria began researches in preparation for building national adaptation strategies (Chao et al. 2014).

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International cooperative adaptation actions are in full span. Since the day the United Nations Framework Convention on Climate Change (UNFCCC) came into effect, international climate change adaptation strategies and policies have been through five stages of evolution, namely, the initial stage of slow development (1994–2001), the adaptation science and technological debate stage (2001–2007), the balanced adaptation and mitigation stage (2007–2010), the fortified adaptation action stage (2010–2015) and the all-rounded adaptation action stage (2015 to postParis era) (Chen 2020). Currently, international cooperation on adaptation to global climate change spans mainly across the agriculture, ecosystem, water resources, public utility, infrastructure and risk management fields and involves food security, climate resilience building, water resources management, public utility services, infrastructure and supply, natural disasters and poverty risks, emergency management and legislation (Jiang et al. 2021).

4.1.2 Adaptation Strategies Climate change adaptation refers to the adjustments in ecological, social or economic systems in response to climate change and its effects, involving changes in processes, practices, and structures so as to moderate or even offset potential damages and to benefit from opportunities associated with climate change. Climate change, extreme weather/climate events in particular, aggravates the resource and environment bottlenecks and poses severe threats to global food, water, ecological, energy security as well as personal and property safety. IPCC’s Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX) points out that irrational development processes will aggravate climate change and thus increase disaster risks and damage, while active mitigation and adaptation can reduce disaster risks and enhance social, economic and environmental sustainability. Adaptation strategies effective in controlling climate risks are those taking into full account vulnerability and exposure changes and their association with development goals and climate change. By reducing exposure and vulnerability, the resilience against the potential adverse impacts of various climate extremes can be enhanced and accordingly the losses and impacts. On people’s lives, property and health can be reduced. Climate security is an important component of the national security system and of the sustainable socio-economic development strategy. China attaches great importance to climate change adaptation issues and has taken active positive adaptation actions. This is a prerequisite for transition towards ecological civilization and beautiful China and an inevitable choice for participation in global governance. An integrated national top-down adaptation strategy is pivotal to China’s adaptation to climate change (high confidence). Adaptation to climate change is not only the intrinsic request for China to build of an ecological civilization and achieve sustainable development, but also an important component of climate and national security. China attaches great importance to climate change adaptation issues and has taken the initiative to align adaptation actions to national economic and

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social development plans, by formulating mid- and long-term adaptation plans for key sectors, near-term action and mid- and long-term plans, in a bid to consolidate the integrated adaptation strategy. The National Climate Change Adaptation Strategy, was released together with a series of major policy documents, laws and regulations on adaptation and has informed the adaptation policy formulation and implementation at the national level. The associated departments and local governments have tailored concrete adaptation policies, measures and actions according to their respective mandates and domain characteristics, incorporated adaptation needs into socio-economic and ecological development tasks, coordinated and strengthened adaptation efforts of the climate-sensitive and vulnerable sectors, zones and groups, and built constantly upon the adaptation mechanisms of “government stewardship, multi-stakeholder coordination, public participation and legislative backup”. China’s practice of sectoral and regional adaptation collaboration can effectively balance the holistic with the local, the far-future with near-future actions in general, thus providing favorable conditions for the multi-stakeholder mechanism to mature (high confidence). In sectors more easily prone to extreme weather/ climate events and disasters, i.e., water resources, permafrost, ecosystem, agriculture, tourism, transportation, energy and manufacturing, human habitat, population health and major engineering projects, adaptation requires systematic consideration of a multitude of sustainable development goals, covering disaster prevention and mitigation, energy efficiency and emission reduction, ecosystem protection, poverty alleviation and development. In the Belt and Road Initiative and other national initiatives of strategic importance, regional and sectoral collaborations are strengthened to see that key adaptation tasks are generated and implemented according to actual situations. Efforts are made to strictly observe the ecological red lines and always put preservation first so that integrated protection and rehabilitation of landscapes, forests, croplands, lakes, grasslands, sands and glaciers can be advanced in a well-coordinated and balanced manner. Pilot demonstrations of climate-resilient and sponge cities are strengthened, and experiences and best practices are summarized and replicated, so that collaborative adaptation to climate change can be enhanced. Government manages and guides via planning and policy coordination. An action mechanism has taken shape involving various departments in near- and far-future adaptation decision-making collaboration and all walks of life in participation, and the multi-stakeholder mechanism for climate change adaptation is maturing. In its climate change risk prevention actions, China seeks to enhance climate resilience via a sustainable way of development turning from emergency response to risk management by coupling the soft adaptation of management institutional innovation with the hard adaptation of infrastructure construction (medium confidence). A “resilience”-oriented adaptation strategy requires that the adaptation and mitigation decision-making should be better coordinated and that institutional set-up, decision-making coordination, legislative, financial and R&D backups should be put in place to push forward innovations in the risk governance mechanism. It also requires that the disaster control and emergency management mechanisms should be improved to strengthen weather and climate

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disaster monitoring, early warning and prediction. And it is essential that risk assessment and zoning should be conducted to provide for the transition from emergency response to risk management. Finally, infrastructure construction is to be intensified to better guard against weather and climate disaster hazards. Enhanced resilience not only stresses not on minimization or avoidance of potential extreme losses but further on enhancement of overall socio-economic adaptivity from the perspective of risk management so as to turn crises into opportunities and deliver sustainable development.

4.1.3 Adaptation Technologies and Measure Options Effective adaptation technologies and measures can reduce the adverse impacts and future risks of climate change (high confidence). Climate change casts longterm accumulated adverse impacts on agriculture, water resources, natural and ecological systems, bio-diversity, major engineering projects and infrastructure. It is, therefore, necessary to make scientific assessments of climate change impacts on various sectors and regions, so as to identify the positive and negative impacts and potential future risks from climate change for feeding the formulation of responsive adaptation technologies and measures. For its immense territory, China differs vastly from region to region in terms of natural conditions and socio-economic development levels. In this regard, adaptation measures developed for and implemented in different regions and sectors need to be tailored to local natural conditions and socio-economic development levels. Meanwhile, climate change impacts and risks vary according to the local natural conditions and socio-economic development levels rather than administrative divisions, so the development of adaptation technologies and measures should traverse sectors and regions to lower cost and strengthen collaboration in practice. Advanced adaptation technologies and measures are available in the international community for various business sectors in China to absorb and learn. The Global Commission on Adaptation (GCA) is committed to building an action platform for decision-makers, investors and research institutes to work together for solutions to political, financial and technological obstacles to current adaptation efforts. From the perspective of policy decision and action backups, GCA has identified a number of sector-specific adaptation technologies and measures, including crosssectoral and cross-domain cost–benefit adaptation technology analyses and adaptation effect assessments. In agriculture, it has developed physiological and genetic stress-resistance techniques for different crop varieties, designed and applied agrometeorological risk insurance mechanisms, and developed climate-smart agricultural production mode, and technology integration. In the field of water resources, it has developed risk-specific water distribution mechanisms and technologies, as well as pricing mechanisms and techniques for water-saving, carried out climate-adaptive watershed management, and established a water monitoring system based on satellite data coupled with hydrological information to monitor and assess water resources

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and water environment condition in real time. In the field of climate-resilient city construction, it has developed the technology for visualized simulation of climate change impacts on the cities based on the coupling of topographic, meteorological, climatic, satellite remote-sensing data, and developed nature-based solutions to urban climate change adaptation. In infrastructure, there are climate risk assessments on key infrastructure (energy, transportation, water supply, environment, etc.); technological standards and specifications for climate-resilient infrastructure; and systematic planning methods and procedures (Global Commission on Adaptation 2019). China has adopted step-by-step adaptation technologies, measures and actions responsive to different sectors and regions, which, based in general on the guiding principle of “moderating harm and exploiting beneficial opportunities”, and has paid off with fairly good results (high confidence). What adaptation technologies and measures to take is closely related to the objects, subjects, behaviors and effects of adaptation. The adaptation object refers to the change of climate state and its time and space scale, extreme events, etc., the adaptation subject refers to the natural ecosystem, human system and related support systems, the adaptation behavior refers to the response of seeking advantages and avoiding disadvantages, and the adaption effect includes the ecological, social and economic benefits or results of adaptation actions. Governments at all levels in China have incorporated adaptation tasks into the national economic and social development plans, had their respective adaptation plans drafted under the guidance of China National Plan for Coping with Climate Change and implemented on the basis of sector- and regionspecific environmental conditions and climate change impacts. However, compared with the mitigation technologies and measures, some adaptation actions are not so soundly supported by policy and legislative, financial, technological and capacitybuilding backups for full and smooth implementation due to the wide spectrum of regions and sectors involved. Besides, for the lack of multi-stakeholder participation, some adaptation technologies and measures failed to be adopted and play effective roles. It is essential that historically viable local knowledge be fully excavated to help fix the adaptation technologies and measure options and get them better geared to local circumstances in practice (Tables 4.1 and 4.2). For adaptation technologies and measures to be effective in mitigating climate change impacts and reducing future climate change risks, it is essential that they must be implemented. Although climate adaptation plans have been developed at the national level and down to various local levels spanning across such sectors and domains as economy, society, ecology and environment, the adaptation technologies and measures contained appear to be all-inclusive but tend to be too general to be sufficiently responsive, letting alone a lack of effect or outcome assessment for those already carried out or implemented. Therefore, it is necessary to conduct integrated analyses on the adaptation technologies and measures and to carry out close cooperation among regions and across domains to jointly advance the production and implementation of adaptation technologies and measures. It is necessary that governments at all levels, communities based in climate change impact zones, the general public and various stakeholders should join in with scientists, researchers and

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Table 4.1 Sector- and domain-specific adaptation technologies and measure options in China Sectors/domains Adaptation technologies and measure options Water resources

• • • •

Water-saving technologies Construction of water conservancy infrastructure Development and utilization of unconventional water resources Artificial precipitation enhancement

Agriculture

• • • •

Adjusting the crop planting structure Improving the layout of crop varieties Improving multiple cropping index (MCI) Popularizing stress-tolerant crop variety development techniques, healthy livestock and poultry production techniques and integrated pest control techniques

Cryosphere

• Whole-process disaster risk management and control measures • Enriching knowledge and skills of self-help and mutual rescue to improve local residents’ ability to avoid disasters, and carrying out refined monitoring of the permafrost

Terrestrial ecosystems

• • • •

Marine ecosystem

• Marine ecological restoration measures • Marine biodiversity and habitat conservation measures • Measures to control habitat destruction by human activities

Tourism

• • • •

Transportation

• Enhancing transport system security • Revising the technical standards for traffic engineering and operation related to climate change • Road safety publicity • Road meteorological disaster early warning measures

Energy

• • • •

Manufacturing

• Planning the construction of industrial parks scientifically • Strengthening extreme meteorological disaster monitoring and early warning • Adjusting manufacturing layout according to climate conditions • Adjusting industrial and product structures in response to changes in climate-related consumption demand

Population health

• • • •

Legislative and administrative control measures Spatial planning and isolation measures Ecological restoration measures Ecological engineering construction

Strengthening tourism resource conservation Developing climate-adaptive tourism products Strengthening tourism infrastructure construction Measures for disaster early warning and crisis management measures

Scientific dispatching measures of energy supply Improving disaster prevention standards for energy infrastructure Energy emergency responses to meteorological disasters Technology of energy efficient utilization

Integrated prevention techniques of urban compound disaster risk Strengthening target-oriented adaptation measures Comprehensively planning urban infrastructure construction Construction of climate-smart cities

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Table 4.2 Region-specific adaptation technologies and measure options in China Regions

Adaptation technologies and measure options

North east China

• Adaptation measures responsive to increase in thermal resources, aggravation of meteorological disasters, plant pest and disease damage, and black soil degradation in agriculture • Enhancing optimal allocation of water resources, watershed-scale extreme disaster forecast, early warning and emergency response capacity • Establishing long-term wetland ecosystem protection mechanism and enabling science and technology to play greater roles in permafrost wetland protection • Putting ice and snow resources under scientific planning, effective development and utilization

Beijing-Tianjin-Hebei (BTH) region

• Enhancing the pollution monitoring, and early warning and the pollutant source control to win the battle against air pollution • Implementing the water management strategy for the new era and the most stringent water conservation, and pushing for unified water management in the BTH region • Scientifically planning the urban lifeline systems and forging climate-smart cities • Ensuring smooth transformation to an ecological civilization by following a path of green development

Yangtze River Delta

• Protecting the estuary eco-environment and fortifying the estuary ecosystem stability • Conducting marine environment monitoring and marine disaster early warning and forecast, and developing integrated coastal zone management • Taking engineering and non-engineering measures to enhance flood disaster risk control capacity in the Yangtze River Delta

Middle and upper reaches of the Yangtze River

• Pushing eco-environment conservation and rehabilitation and promoting sustainable watershed riparian ecosystem management • Strengthening hydrological and biological links between water systems, implementing responsive lake ecology and biodiversity protection, and enhancing watershed management • Curbing river and reservoir water pollution and lowering reservoir eutrophication risks (continued)

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Table 4.2 (continued) Regions

Adaptation technologies and measure options

Guangdong-Hong Kong-Macao Greater Bay Area

• Conducting health risk assessment and health surveillance and early warning of people with high temperature disasters to prevent heat disaster risks • Improving urban atmospheric environment and holding epidemic risks under check • Integrating engineering and non-engineering adaptation countermeasures to create favorable conditions for enhanced regional flood risk prevention and overall adaptation capacity • Scientifically regulating and optimizing water resources allocation to safeguard water resources security in the Guangdong-Hong Kong-Macao Greater Bey Area

Both sides across Taiwan Strait

• Improving basic infrastructure for enhancing climate resilience • Building upon adaptation-related work systems and mechanisms to provide better institutional backup • Advancing the construction of sponge cities • Controlling unwarranted expansion of artificial coastlines and strengthening coastal adaptation

Arid Areas in Northwest China

• Strengthening ecological restoration and protecting mountain ecosystems • Setting the ecological protection red lines and protecting and restoring desert ecosystem • Optimizing the agricultural structure and developing high-efficiency oasis ecological agriculture model • Developing high water and fertilizer efficiency farming techniques for arid areas, making full use of the regional climate advantages and expanding the production of high-quality vernacular agricultural products

Loess Plateau

• Developing high-efficiency dry farming and raising the sustainability of agricultural development • Adopting sustainable management measures and promoting vegetation restoration • Integrating the vegetation and engineering measures to prevent soil erosion

Qinghai-Tibet Plateau

• Augmenting basic scientific research and enhancing the ability to monitor climate and eco-environment changes • Developing key technologies for ecological protection and construction and enhancing the integrated function of ecological shelterbelts • Adjusting the structure and development patterns of regional agriculture and animal husbandry according to climate conditions • Enhancing publicity and education on ecological and environmental protection and rehabilitation (continued)

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Table 4.2 (continued) Regions

Adaptation technologies and measure options

Yunnan-Guizhou Plateau

• Establishing disaster early warning systems and raising natural disaster prevention and control capacity of the Karst areas • Carrying out integrated rocky desertification control projects in Karst areas to reduce soil erosion • Protecting bio-diversity and guarding against biological invasion in a scientific manner • Planning and building cross-border ecological protection network to ensure ecological security

decision-makers in designing the adaptation programs and testing the effectiveness of the technologies and measures in practice. It is also necessary that the regionand sector-specific adaptation technologies and measures be well interconnected, and quantitative analyses be made as to the feasibility and economic viability, on the basis of which further cost–benefit analyses are to be made to assess the climate adaptation effects and to facilitate the demonstration and extension of the adaptation technologies and measures.

4.1.4 China’s Adaptation to Climate Change: Actions and Effects 1. Adaptation actions China is one of the countries most severely affected by climate change. China attaches great importance to the climate change issue and regards it as a key national socioeconomic development strategy to respond actively to climate change. With the development and implementation of relevant plans and institutions, a fully-fledged adaptation policy and law system has been put in place. The Chinese government started to establish relevant institutions to tackle climate change in 1990; enacted China’s Agenda twenty-first century in 1994 as the first official confirmation of the importance of climate change adaptation; set up the National Climate Change Response Coordination Group in 1998, the National Expert Committee on Climate Change in 2006, and the National Leading Group on Climate Change in 2007. Since 2008, a white paper entitled Responding to Climate Change: China’s Policies and Actions has been released every year. It was clearly stated in the 2010 Twelfth Five-Year Plan for National Economic and Social Development of the People’s Republic of China that climate change factors should be taken into full account in planning and actualizing productivity distribution, infrastructure and key construction projects to raise climate resilience in key sectors such as agriculture, forestry, water resources and in coastal and ecologically fragile regions. With the promulgation of the China’s National Programme to Address Climate Change

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in 2010, China became the first developing country to set forth and implement a national climate change programme. In 2012, China set up the National Center for Climate Change Strategy and International Cooperation (NCSC) to conduct researches on policies, regulations and plans to deal with climate change. China released the National Strategy for Climate Change Adaptation in 2013, and developed and implemented the National Plan on Climate Change (2014–2020) in 2014. The Thirteenth Five-Year Plan for National Economic and Social Development of the People’s Republic of China (2016–2020) approved in 2016, requires that climate change factors be fully considered in socio-economic activities related to urban and rural planning, infrastructure construction and productivity distribution, the relevant technical specification and standards be developed or adjusted in due course of time, and the climate change adaptation plans be implemented. It also requires that the systematic observation of and scientific research on climate change be strengthened, and prediction and early warning systems be improved, so as to enhance resilience against extreme weather and climate events. Currently, China is drafting the National Strategy for Climate Change Adaptation 2035. Meanwhile, China has also made improvements to laws and regulations, having promulgated and implemented the following laws and regulations successively: the Emergency Response Law of the People’s Republic of China (PRC) (enacted in 2007), the Environmental Protection Law of PRC (revised in 2014), the Meteorology Law of PRC (revised in 2016), the Land Administration Low of PRC (revised in 2020), and the Regulation on the Defense against Meteorological Disasters (in 2017). All measures for implementation laid down by various localities also include the content of adaptation to climate change (Fig. 4.1). In light of scientific assessments on climate and eco-environment evolution, there have been the Assessment on the Environmental Evolution in Western China published in 2002, the assessment report of Climate and Environment Changes in China in 2005, the assessment report of Climate and Environmental Change in China: 2012, and the assessment report of Climate and Environmental Change in China: 2021. These assessment reports together have formed a unique Chinese characteristic in that they are comprehensive and systematic assessments made in reference to the IPCC assessment reports on China’s socio-economically-related changes in climate and eco-environment data viewed throughout from a perspective of the climate system. They present an objective full picture of China’s latest developments in the field of climate and eco-environment evolution. Besides, they play a significant role in feeding national decision-making and medium- and long-term planning, and advancing climate science and professional talent cultivation. China has initially established a funding mechanism for climate change adaptation. This mechanism sees to it that adaptation is financed predominantly by government fiscal fund, backed up by commercial funds and market inputs, and complemented by international bilateral or multilateral adaptation funds and interested corporate or individual fund inputs. In 2010 the Ministry of Finance and six others jointly enacted the China’s Measures for the Administration of Clean Development Mechanism Funds, which clearly stipulates that such funds should be used for enterprises’ activites related to climate change such as adaptation and mitigation

4 Adaptation and Mitigation: Measures, Actions and Effects

Fig. 4.1 China’s action roadmap on climate change

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activities. The central and local governments’ huge investment in water conservancy, sponge city construction, major ecological and agricultural infrastructure projects as well as eco-compensation and disaster relief on fallow land and cultivated land restored to forest and grassland have actually contained the factors to adapt to climate change and contributed to the formation of a fund-raising mechanism featuring government leadership, sectoral collaboration and civil society participation. China has vigorously implemented key action projects to adapt to climate change. First, ecological civilization construction. Since the 1990s, the 18th CPC National Congress in particular, China has taken a series of ecological protection actions and put forward a number of countermeasures for adapting ecological protection to climate change. Green development makes one of the five new development concepts defined at the Fifth Plenary Session of the 18th CPC National Congress. One after another, different localities across the country set up the forest resource management and protection system and policies of eco-compensation for the protection of natural forests, ecological public-welfare forests, and grasslands, and profusely increased investment in forest-steppe vegetation protection to raise public awareness and interest. With the promulgation of the Opinions of the General Office of the State Council on Improving the Compensation Mechanism of Ecological Protection, a market-based multi-stakeholder eco-compensation mechanism has gradually come into being. And the successive promulgation of National Main Functional Area Planning Zones, National Ecological Functional Area Planning, Outline of National Key Ecological Function Protection Area Planning and Outline of the National Plan for the Protection of Ecologically Fragile Areas made it a strategic component of ecological civilization construction to strengthen protection and management of national key ecological function zones. The Decision of the Central Committee of the Communist Party of China on Some Major Issues Concerning Comprehensively Deepening Reform adopted at the Third Plenary Session of the 18th CPC Central Committee in 2013 covered in a separate chapter the demarcation of ecological conservation red lines and the establishment of the land and space development and protection system. Released in 2017 were Several Opinions on Delineating and Strictly Protecting the Ecological Conservation Redlines and Plan for Reform of the eco-environment Damage Compensation System. In recent years, China has been vigorously pushing forward a number of ecological projects, including the Three-North Shelter Forest Programme, Project of Returning Farmland to Forest and Grasses, Beijing-Tianjin Sandstorm Source Control Programme and other major forestry ecological construction projects. Also an ecological protection and restoration campaign has been lunched covering mountains, rivers, forests, farmland, lakes, and grasslands, which can help advance integrated rehabilitation of key areas such as the Three-RiversSource Area in Qinghai, rocky desertification Karst areas, Beijing-Tianjin sandstorm source areas and Qilian Mountains and drive a new round of conversion of cropland into forestland and grassland and key forest shelterbelt construction projects. Second, water conservancy construction action. A large number of controlled water conservancy projects have been completed and put into operation, including the Yangtze River Three Gorges, Yellow River Xiaolangdi, Huaihe River Linhuaigang, Nenjiang

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River Nierji and Guangxi Baise engineering projects, which has resulted in significantly enhanced major river regulation capacity. China has initiated the water allocation work for 59 inter-provincial rivers, including the Taihu Lake Basin, trunk streams of Songhuajiang and Liaohe rivers, Xin’anjiang River and Wujiang River, for the purpose of regulating basin-wide water allocation for living, production and ecological needs. Many water storage, diversion and drawing projects have been constructed, particularly the South-to-North Water Diversion Project designed to form a nationwide water network transferring water from the Yangtze River, Yellow River, Huaihe and Haihe Rivers (“four horizontal” west-to-east rivers) via three diversion routes (“three vertical” south-to-north routes) to balance water resource distribution across the mainland of China, which has greatly enhanced China’s water resource control capacity as well as the drought and flood disaster prevention and control capacity. Efforts have been made to build sponge cities in active response to the increasing extreme precipitation events and the flood control capacity has been improved. In fact, China has been trying to build a water-efficient society for lower water consumption and higher water efficiency so as to effectively curb climate change impacts on water resources. 2. Effects and Problems The above actions have advanced China’s adaptation to climate change, producing ever-increasingly prominent effects and stronger capacities. Governments’ adaptation awareness has been getting stronger (high confidence). With the promulgation and implementation of relevant laws and regulations, the advent of pilot climate-resilient cities, and the increase in media reports and coverage, governments have developed stronger awareness of climate change adaptation. In light of infrastructure, they now adjust and revise technical standards for infrastructure design, construction, operation and scheduling, maintenance and repair according to changes in climate conditions based on scientific assessments on adaptation cost and environmental benefits for the updates. They now incorporate climate change impact and risk assessment as an important component of applications submitted for project approval and access management. They also put in place disaster monitoring, early-warning and emergency response mechanisms to safeguard the smooth operation of key infrastructure projects. Drought and flood disaster prevention and climate change risk coping capacities are being enhanced (high confidence). Drafting of the national and provincial drought resilience plans has been accomplished, which helped bring into being a drought prevention and disaster reduction system suited to socio-economic level and enhance the overall drought resilience and integrated management. The National Mountain Torrent Disaster Prevention and Control Plan has been completed. In key mountain torrent disaster areas, the disaster prevention and reduction system has been built mainly on the basis of non-engineering measures such as monitoring, communication, forecasting and early warning, etc., combined with engineering measures, whereas in other areas the disaster prevention and reduction system has been put in place initially based primarily on non-engineering measures to minimize casualties and property losses. Mountain torrent prevention and control projects have been

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implemented in batches nationwide, mainly covering disaster survey and assessment, non-engineering measure construction and flood control engineering measures for key mountain torrent ditches (mountain streams). Over 2013–2016, a mountain torrent disaster survey and assessment program was carried out at the national level to offer data support to early warning, forecasting and engineering measures for major target counties in China. Up to now, China has established over 2000 mountain torrent disaster monitoring and early warning platforms, sufficient to form a monitoring and early warning network suited to China’s national situations and a hazard mitigation system based on residents’ monitoring and prevention efforts. The goal of “timely early warning, rapid response, fast evacuation and effective risk avoidance” has been virtually met, with the disaster prevention and mitigation effects being seen. The number of annual average mountain torrent-related deaths has dropped by over 60% compared with pre-project figures. Integrated management of major rivers, soil and water conservation in mountainous areas, water source protection, rainwater collection and water saving, farmland capital construction, urban underlying surface reconstruction and green space construction projects have enhanced urban and rural coping capacity against drought and flood disasters as well as water shortage. R&D breakthroughs on key adaptation technologies have effectively backed up the implementation of the Qinghai-Tibet Railway, West-to-East Gas Transmission, South-toNorth Water Diversion and some other major engineering projects, greatly improving the capacities of western ecologically fragile areas, northern arid zones and eastern energy-hungry areas in coping with climate change risks. The “3S” technologybased monitoring and early warning of extreme weather/and climate events and climate-related disasters have been effectively improved, The meteorological, disastrous and agricultural information assistant team and reporting system have been built, resulting in higher overall coping capacity against extreme meteorological disasters. The flood control and drought relief accountability system has been set up at various local levels with the local chief executive responsibility system at the core. Flood regulation and prevention plans as well as emergency water dispatching plans have been upgraded, and the national drought situation monitoring system has been built, which greatly improved the drought and flood disaster coping capacity. Analysis and application of the three-dimensional satellite and radar monitoring products have enabled continually-refined environmental and meteorological forecasts. The South-to-North Water Diversion project has achieved marked effects. By the end of 2018 the eastern route had successively accomplished water transfer targets for 5 consecutive years; the middle route had set an uninterrupted safe water supply record of over 1480 days; and the eastern and middle routes had transferred more than 22 billion m3 of water, marking a significantly higher water supply guarantee rate for over 40 large and medium-sized cities including Beijing, Tianjin and Shijiazhuang, and directly benefiting over 100 million people. Moreover, among the 172 major water conservancy projects of water saving and water supply 133 have been commenced, and 23 have been basically finished and begun to yield benefits. Rural water projects, intended to consolidate and improve rural drinking water safety, have benefited over 78 million people and lifted the rural tap water penetration rate to 81%.

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Ecological conservation and restoration are generating remarkable effects (high confidence). Since the establishment of the first natural reserve in 1956, China has built 463 national-level natural reserves and 2750 local reserves of various types at different levels up to now, totaling 1,471,700 km2 in area. Vigorous efforts have been made to prevent and control ecological degradation. According to the results of the first-time national water conservancy survey, and the soil and water conservation survey China had a total soil erosion area of 294,900 km2 . Results of the fifth National Land Desertification and Sandification monitoring showed that desertification and sandification areas had amounted to 2,611,600 and 1,721,200 km2 respectively by 2014. Forest area accounted for merely 8.6% of China’s total land area in 1949, and this figure had risen to about 20% according to the 7th forest resource inventory. A research paper published by NASA in February 2019 pointed out “the world is literally a greener place than it was twenty years ago”, “the global green area has increased by 5%”, and “China and India are leading the increase in greening on land”. The first ecological water replenishment has been completed in the middle route of the South-to-North Water Diversion Project. In September 2018, the Ministry of Water Resources of P. R. China and Hebei provincial government jointly launched pilot projects of groundwater recharge for the treatment of over-exploited rivers and lakes in North China, replenishing groundwater at key sections of the Hutuo, Fuyang and Nanjuma rivers with water drawn from the middle route of the South-to-North Water Diversion Project. By now 500 million m3 of water has been injected to revive the three rivers with a total water surface area of 40 km2 . By June 3, 2020, safe water transfer of the middle route of the water diversion project had lasted for 2000 days, with 30 billion m3 of water transported northward, benefiting over 60 million people. In particular, the water supply reliability index for downtown Beijing has been raised from 1 to 1.2, and the yearly rise of shallow groundwater level in Hebei Province has lifted from 0.48 m before the treatment to 0.74 m. However, China’s adaptation to climate change is mainly manifested in the policy, system and key actions while its implementation in practical work is still very limited. A rather high proportion of adaptation actions are not consciously initiated and planned from the perspective of climate change adaptation. In this regard, there is still a long way to go. The adaptation backup system is yet to be improved. Adaptation legislation requires further replenishment as climate change factors were not taken into full consideration in various plans formulated. The emergency management system needs to be strengthened with regard to the large gap between the disaster monitoring system in place and the adaptation needs as well as the lack of sufficient disaster monitoring, forecast and early warning capacities in some localities. The adaptation funding mechanism is not sound yet and the government fiscal inputs are not sufficient. Scientific and technological support is not strong enough; inventories of viable adaptation technologies are lacking at the national, departmental, sectoral and regional levels; available technologies are not targeted to climate change factors. Adaptation capacity needs to be further enhanced. Climate change impacts have not been fully addressed in the preparation and revision of technical standards for infrastructure construction, operation, dispatch, maintenance and repair. Urban

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lifeline systems, i.e., power supply, heating, water supply, drainage, gas and communications, are not resilient enough against extreme weather/climate events. Agricultural and forestry infrastructure are backward; some farmland irrigation systems are aging and in disrepair; climate change factors are not fully taken into account in the construction, operation and management of water conservancy facilities; and fishing ports are obviously too old to serve as havens. Agriculture lags behind in terms of planting system, variety layout, condition monitoring and diagnosis. The existing technical equipment is not in a good position to cope with the rising complexity and expansion of agricultural disasters. In some localities, not strategic arrangement has been made yet as to water resource reallocation; urban and rural water supply is not sufficiently guaranteed; an integrated flood control and disaster relief system is not in place for the treatment of major rivers; and drainage capacity is insufficient for major waterlogging-prone areas. Forest fire and forest pest monitoring and early warning systems, forest fire barrier systems and emergency response systems are yet to be improved. Wetland and desert ecosystems want better adaptation to climate change and stronger resilience against disasters. The mining, construction, transportation and tourism sectors are short of the ability to guard against extreme weather and climate events. Climate The impact of climate change on population health is not monitored, assessed or warned of soundly. The existing epidemic prevention and control systems are not sufficient to effectively curb vector-borne diseases. While China has been constantly strengthening its ecological construction, the measures taken addressed the adaptation to climate change positively in the past but failed to fully consider the future impact of climate change. It is full of uncertainties whether such measures can guarantee ecosystem adaptability under the 1.5–2 °C or higher global warming scenarios. Measures are still lacking to effectively cope with either the inundation risks of coastal low-lying areas and islands or the shoreline erosion risks. Ecological crises such as coastal wetland declines, mangrove drowning and coral reef bleaching are yet to be effectively curbed. Compared with such traditional sectors as agriculture, forestry, water resources, oceans, ecosystems and population health, the economic and social sectors lag behind remarkably in adaptation to climate change, and the adaptation work has not even started in some industries and domains, thus much remains to be done to raise the socio-economic resilience. Public adaptation awareness needs to be enhanced. It is essential to give full play to the leading role of the government, to engage diverse mass media and modern IT technology in climate change adaptation education and outreach, to incorporate the adaptation knowledge into school education, to organize sector- and domain-specific adaptation skill training, to encourage and advocate sustainable adaptive lifestyles, to raise awareness of public participation in community adaptation, and to bring out changing consumption patterns. It is necessary to improve climate change information release systems and to increase the transparency of decision-making associated with climate change so that climate change governance will be made more scientific and democratic. The civil society organizations and non-governmental organizations should play a bigger part, and promote the general public in all walks of life to get involved in adaptation and mitigation actions against global climate change.

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4.2 Climate Change Mitigation 4.2.1 Global Progress 1. IPCC Assessments The IPCC Working Group III contribution to the IPCC’s Fifth Assessment Report (WG III AR5) published in 2014 called for the global greenhouse gas (GHG) emissions to be limited to 30–50 Gt CO2 eq (or 60–100% of the 2010 level) by 2030 in cost-effective scenarios that are about as likely as to limit warming to less than 2 °C. By the middle of the twenty-first century, global GHGs emission needs to be reduced to 40–70% of the 2010 level, and nearly zoro by the second half or the end of the twenty-first century. It is pointed out in the report that the global longterm goal of limiting climate warming to 2 °C can only be achieved by massively reforming the energy system, paying attention to land use and making carbon dioxide removal (CDR) a key technical means. It is essential that the energy supply sector be reformed substantially to ensure that CO2 emission from this sector declines constantly to reach 90% below the 2010 level between 2040 and 2070, and in many scenarios even declines to below zero thereafter. Deep decarbonization of electricity generation is a robust feature of the 2 °C warming level and requires 80% reduction in CO2 emission by 2050. Contribution of renewable energy, nuclear energy, fossil fuel-based carbon capture and storage (CCS), carbon–neutral or low-carbon fuel using bio-energy with carbon capture and storage (BECCS) to primary energy supply is 3–4 times the 2010 level (around 17%). Most emission reduction pathways to meet the 2 °C of global warming require CDR technologies such as BECCS, afforestation, and direct air carbon capture (DACC) technology after 2050. To meet the 2 °C warming level, it is essential that the investment portfolio be altered: annual inputs on fossil fuel mining and electricity generation are to drop by 20% (or USD 30 billion), while annual inputs on low-carbon fuel (renewable and nuclear energy) will increase by 100% (USD 147 billion) from 2010 to 2029. The 1.5 °C warming requires net zero emissions of GHGs to be realized by 2050 (high confidence). In October 2018, IPCC published the Special Report on Global Warming of 1.5 °C, which made a comprehensive assessment of global climate change in the context of the global warming of 1.5 °C, impacts, adaptation, mitigation and their interaction with sustainable development, deepening the understanding of the global warming of 1.5 °C. Major mitigation-related conclusions in the IPCC’s Special Report on Global Warming of 1.5 °C include: in order to achieve the global warming of 1.5 °C in relative to the pre-industrial level, CO2 emissions need to be reduced by about 45% by 2030 from the 2010 level and reach carbon neutral by 2050. Around USD 900 billion worth of investment will be needed annually during the period of 2015–2050 to limit global warming below 1.5 °C, which is 12% higher than in the 2 °C warming scenario. There are multiple synergies and trade-offs between the 1.5 °C pathways and mitigation options and the sustainable development goals.

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In August 2019, IPCC published a special report of climate change and land (SRCCL), which pointed out that keeping global warming to well below 2 °C can be achieved only by reducing greenhouse gas emissions from all activities including land and food. Mitigation-related conclusions in the special report are: sustainable land management, such as sustainable forest management, can prevent and reduce land degradation, maintain land productivity, and sometimes reverse the adverse impacts of climate change on land degradation. All the assessed modeled pathways that limit warming to 1.5 °C or well below 2 °C require land-based mitigation and land-use change, with most including different combinations of reforestation, afforestation, reduced deforestation and bioenergy. It was pointed out by Working Group I report of IPCC AR6 that over the period of 1850–2019, a total of 2390 ± 240 Gt CO2 (Gigaton carbon dioxide) of anthropogenic CO2 was emitted. Limiting human-induced global warming to a specific level requires limiting the cumulative CO2 emissions, reaching at least net zero CO2 emissions, along with strong reductions in other greenhouse gas emissions. The report believed that global surface temperature would continue to increase until at least the mid-century under all emissions scenarios considered. Strong, rapid and sustained reductions in greenhouse gas emissions would limit climate change. The global warming of 1.5 °C or even 2 °C will be exceeded during the twenty-first century unless drastic reductions in CO2 and other greenhouse gas emissions occur in the coming decades. If global warming is expected to be limited to 1.5 °C in the twenty-first century, the remaining carbon budget will be 400 Gt CO2 in reference to the 2019 cumulative emissions; even if warming is limited to 2 °C, the remaining carbon budget will be a mere 1150 Gt CO2 (likely 67%). 2. Net-zero Emissions Strategies of Major Countries and Regions in the World by 2050 The EU proposed to achieve net-zero greenhouse gas emissions by 2050, aiming to drag the world along onto the 1.5 °C pathway. In December 2019, the European Commission published the European Green Deal, seeking to make Europe the world’s first “climate-neutral” continent by 2050. In March 2020, the EU submitted to the UNFCCC its long-term strategy for achieving climate neutrality by 2050, and released the Eurpean Climate Law. Germany, France, UK, Italy and Sweden pledged to deliver this goal by 2050 while Finland and Austria proposed in official documents to reach climate neutrality in 2035 and 2040 respectively, leaving space for the relatively less developed countries of the EU. After the outbreak of the COVID-19 pandemic, the EU approved a e1.82 trillion seven-year green recovery funding package, most of which will be spent on green development and greenhouse gas emission reduction activities in the hope of revamping the economy. A sweeping package of policy proposals unveiled following the announcement of its target signal means that the EU 2050 climate-neutrality is in actual operation and in progress. The EU’s action has a tremendous impact on international response to climate change, fundamentally changing global pathways for addressing climate change. Following China’s announcement of its goal of achieving carbon neutrality before 2060, the EU unveiled new 2030 emissions reduction targets. On October

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6 2020, the EU declared to raise its emission reduction target for 2030 from 40% under the Paris Agreement to at least 55%, which the target proposed in the European Green Deal in December 2019 was 55%. The EU process has clearly demonstrated the EU’s determination to take the lead in economic transformation and technological innovation. Future emissions reduction is more of economic and technological rivalry. Developed countries including the United States, Japan and Korea have set their respective 2050 carbon neutral goals and noticeably raised their 2030 emission reduction targets. On June 30 2020, the United States House Select Committee on the Climate Crisis released an action plan, which is utilized as the roadmap to move the United States toward net-zero greenhouse gases emission by 2050. This report entitled Solving the Climate Crisis: The Congressional Action Plan for a Clean Energy Economy and a Healthy, Resilient, and Just America is full of many detailed and actionable climate solutions. This report considered that the Congress should enact solutions to benefit American families in communities across the nation. It calls on the Congress to boost American economy to grow and put Americans back to work in clean energy jobs; to protect the health of all families; to make sure that the American communities and farmers can withstand the impacts of climate change; and to protect America’s land and waters for the next generation. This new action plan report set out a number of goals, including reducing 45% of greenhouse gases emissions by 2030. It also requires all new vehicles to achieve zero greenhouse gas emissions by 2035 and new medium-duty and heavy-duty vehicles to eliminate greenhouse emissions by 2040. The report, also requires to eliminate overall emissions from the power sector by 2040 and from all economic sectors by 2050 to make the United States carbon–neutral. It highlights the United States’ global leadership in zero-emission technologies and strong manufacturing. President Biden proposed carbon neutrality in the United States by 2050 upon assuming the presidency in January 2021. On April 22nd 2021, the United States announced that it would cut emissions 50% below the 2005 levels by 2030. After China announced efforts to reach carbon neutrality commitment before 2060, Japan declared in October 2020 that it would aim to achieve carbon neutrality in 2050 and then in April 2021 that it set the 2030 emissions reduction target to 47% below the 2013 level. Korea pledged in October 2020 to achieve carbon neutrality by 2050. In addition, in October 2021 Australia announced its zero-emission target by 2050. Major economies having made carbon neutrality commitments will lead the globe onto carbon–neutral pathways (high confidence). Major G20 member countries that have declared their carbon neutrality targets now account for about 70% of the global CO2 emissions. These countries are major technology exporters and leaders in the global climate change cooperation, so their commitments to carbon neutrality will basically determine the globe pathway to carbon neutrality. 3. Progress in Building Zero-carbon Cities Cities are at the center of global low-carbon development. More and more cities are developing with stronger willingness to pursue low-carbon development.

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They have proposed to reach zero greenhouse emissions by 2050 or by an even earlier date. According to the UN statistics, up to the United Nations Climate Action Summit in September 2019, 102 cities around the globe had made commitments to net-zero CO2 emissions by 2050.1 According to incomplete statistics, a dozen cities including Melbourne, Copenhagen and Stockholm have pledged to achieve net-zero emissions in the time earlier than 2050. These pioneer low-carbon cities have developed plans and detailed programs to push forward low-carbon transformation in the economy, society, energy and technology sectors in action. An increasing number of cities have declared their zero-emission targets, taking the lead in the global urban emission reduction action. Cities having made zero-emission commitments are those with leading positions in the global socioeconomic development. They are ahead of others in terms of economic development and upon reaching higher economic levels, they pay more and more attention to the environment. The socio-economically advanced cities, such as Paris, London, New York, Tokyo, Sydney, Melbourne, Vienna and Vancouver, all have proposed to achieve net zero emissions, and some of them would achieve net zero carbon emission as early as by 2030. 4. Zero-carbon Energy Development The global price of renewable energy has dropped below that of fossil fuel (high confidence). By 2020 a number of projects around the globe have generated feed-in tariffs of 1.35 US cents/(kW·h) or 0.1 CNY/(kW·h), far lower than those for fossil fuel. Over the past decade, the price of solar photovoltaic (PV) modules has dropped by 92%. By 2019, even in China where coal-fired power price is low, there had been a new 20 GW PV power plant generating lower feed-in tariffs than existing coal-fired power plants. By July 2020, the non-subsidized PV projects approved by the National Energy Administration, P. R. China have amounted to 34 GW. The rapid drop in renewable energy price has changed the energy development layout. Since 2021, almost all large-scale photovoltaic and wind power plants have been subsidy-free. New nuclear power has lower feed-in tariffs than fossil fuel-fired power (high confidence). Meanwhile, the global first 6 third-generation nuclear power plants which were put into operation in China between 2018 and 2019 generated electricity at a feed-in tariff of 0.42 CNY/(kW·h), which is the same as or lower than the feed-in tariffs of local coal-fired power plants. Being the earliest installed and put into operation, the third-generation nuclear power units had a much higher investment than expected; however, the actual feed-in tariffs can already compete with those of coalfired power units. Under the pressure of atmospheric haze control, many provinces are very active in developing nuclear power. At the same time, with the development 1

Blazhevska, Vesna. 2019. In the Face of Worsening Climate Crisis, UN Summit Delivers New Pathways and Practical Actions to Shift Global Response into Higher Gear-United Nations Sustainable Development. https://www.un.org/sustainabledevelopment/blog/2019/09/in-the-faceof-worsening-climate-crisis-un-summit-delivers-new-pathways-and-practical-actions-to-shift-glo bal-response-into-higher-gear/.

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of small-scale nuclear power plants, nuclear heating and nuclear hydrogen producing technology, the utilization of nuclear energy has a very broad space for development in the future.

4.2.2 Mitigation Technology and Measure Option 1. Key Emissions Reduction Sectors to Reach Climate Targets According to the domestic and international studies on climate change mitigation, the energy and economic sectors need remarkable transformation to achieve the 2 °C and 1.5 °C temperature rise globally. If global warming is to be kept below 2 °C and 1.5 °C, a significant and rapid reform needs to be conducted on energy supply (high confidence). The global total emission was about 52 Gt CO2 eq. in 2019 and is estimated to reach 52 to 58 Gt CO2 eq. by 2030. If global warming is to be kept below 1.5 °C (not above or not much above 1.5 °C), it is essential that the annual global total emission should be reduced by half before 2030 (25 to 30 Gt CO2 eq.). Although it is still technologically feasible to avoid going above 1.5 °C of warming, the realization of the above emissions reduction target does require comprehensive transformation of behavior patterns and technological means. For example, it is estimated that by 2050 the contribution of renewable energy to power supply would reach 70% and 85% in the 1.5 °C pathway. Energy efficiency and fuel conversion measures are of critical importance in the transportation fields. Lower energy demands, higher food production efficiency, changing dietary choices, and less food loss and waste will also have tremendous impacts on emission reduction. Innovative policies are required to keep temperature rises below 2 °C and 1.5 °C. Although rapid transformation occurred in certain technologies or sectors in history, transformation required to keep global warming below 2 °C and 1.5 °C is unprecedented in terms of scale and extent. Such an extensive and rapid transformation has never been experienced. It involves energy, land, industry, cities and other systems and also cuts across technological domains and geographical regions. The ambitious transformation above mentioned needs huge investments in lowcarbon technologies and energy efficiency fields. And to keep warming below 1.5 °C requires 5 times more fiscal inputs into the low-carbon technologies and energy efficiency fields by 2050 compared with the 2015 investment. Major strategies towards delivering the 1.5 °C warming level include: (1) complete low-carbon transformation of the electrical power system to achieve zero or negative emissions in the current power sector by 2050; (2) vigorous advancement of electrification in all sectors on the basis of the transformation of the electric power sector; (3) comprehensive energy-saving action to make up for the high cost of power sector transformation in the process of deep emission reduction and save the expenditure of the terminal sectors; (4) BECCS-based emission reduction option for the power sector to achieve deep emission reduction up to negative emissions; (5) industrial sectors

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with emission reduction difficulties resorting to innovations in production processes and techniques, e.g. using hydrogen as technological material or raw material. 2. Emission Reduction Technologies for Major Sectors For China, the emission reduction strategy it adopts is consistent with the global strategy in general. The current energy consumption situation in China determines that greater efforts are required in emission reduction countermeasures to meet the target of the Paris Agreement. Researches on China’s emission reduction scenarios and pathways indicate that deep emission reduction needs to be achieved mainly in such sectors as energy, industry, construction, transportation and land use. The energy industry is the most important sector for emission reduction. This sector needs achieving deep transformation. In order to reach the emission reduction pathway for keeping global warming below 1.5 °C, China’s energy system needs to achieve zero or negative emissions by 2050, and the proportion of renewable energy such as hydropower, wind power and solar energy will be significantly increased. By 2050 non-fossil energy is to account for over 50% of primary energy (in the 2 °C pathway) and over 75% (in the 1.5 °C pathway). Fossil fuel combustion needs to adopt the CCS technology. Key technologies include the low-cost solar PV power generation technology, photothermal power generation technology, inland wind power, offshore wind power, hydro power (including large- and small-size hydropower plants), bioenergy utilization technology, nuclear power and particularly the advanced nuclear power technology, other nuclear power technology, CCS technology for fossil fuel BECCS, stable power supply technology of power grids, power storage technology (including pumped, battery and hydrogen energy storage), etc. In the industrial-sector deep emission reduction pathways, the first and foremost is to push forward high-level electrification. The industries with emission reduction difficulties such as iron and steel, cement, chemical industry and petrochemical industry, need innovating processes and technologies. Hydrogen can be used instead of coke as a reducing agent for metal smelting, and so can be used as raw material in producing petrochemical and chemical industrial products. The transportation industry is also driven towards comprehensive electrification: transition to electric vehicles and hydrogen fuel cell-powered heavy-duty vehicles for land transportation, and to fuel cell or biofuel (aviation) for large-scale water transportation, aviation and other sectors having difficulty in being electrified by 2050. Key technologies in the construction sector include ultra-low-energy buildings (ULEB), synchronized with comprehensive electrification, power plant and industrial waste heat for heating and cooling, electric heating, and low-temperature heating technology. The technical measures of emission reduction applicable to land use include farmland water and fertilizer optimization management, livestock and poultry feeding promotion technology, livestock and poultry manure treatment and resource utilization, afforestation and forest products management, wetland regetation restoration

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and reconstruction, etc. the screening of there measures focuses on the core issues of stimulating potential land service functions and ensuring food security. 3. Major Emission Reduction Policies Low-carbon development policy instruments include the following four types: (1), the command control type, which is mainly manifested as specific emission targets with rather strong administrative binding power; (2), the market mechanism type, which achieves the emission control targets via market forces; (3), the fiscal-taxiation regulating type, which realizes carbon emission control through fiscal or financial policies promulgated by the government; (4), the public participation type, which promotes low-carbon production and consumption behavior of the whole people by implementing some incentives. Virtually every country uses all such policy instruments basically, but in different portfolios. Developed countries and China adopt comprehensive policies that are strongly alike. Nearly all of them have had planned targets, energy-saving standards, emission standards and access standards as well as subsidization, taxation and investment policies. However, they may differ in policy intensity. The EU relies more on carbon trading policies while China and US on standards and subsidization policies. Policies required for China to meet the carbon neutrality goal mainly include definite long-term and five-year planning objectives, subsidization or pricing policies on zero-carbon technologies (particularly regarding CCS technology), carbon tax or carbon trading, carbon emission standards for products and services (including carbon labeling), industry emission reduction plans, technology with drawal policy for high-emission industries, zero-carbon financial policy, ultra-low energy consumption building standards, electric vehicle incentive policy, zero-emission incentive policy for aviation, carbon pioneer cities and enterprise incentive policy, transformation support policy for negatively affected industries, and innovation R&D support policy, etc.

4.2.3 China’s Emission Reduction Policies and Effects 1. Progress in CO2 Emission Control China’s total carbon emissions took on a somewhat periodical growth. It had steady growth of CO2 emission at an annual rate of 3.3% on average from 1990 to 2000, and rapid growth at an annual rate of 8.6% on average from 2000 to 2013. However, after 2013, the growth rate of carbon emission in China slowed down obviously, and the total carbon emissions even declined in 2015. Although CO2 emissions showed an increasing trend from 2016 to 2018, the annual average growth rate remained at about 2%. It is obvious that China’s CO2 emission has been experiencing a fluctuating plateau since 2013. On the one hand, China’s restructuring and technological advancement in energy sectors has effectively curbed the rise in total carbon emission. It is worth specially noting that the control of the national coal consumption

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has effectively held back the tendency of carbon emission growth. On the other hand, higher contribution of the third industry to GDP has also facilitated the relative drop in China’s carbon emission intensity. Amidst the COVID-19 pandemic, China’s economy grew by 2.1%; energy consumption by 2.2% and CO2 emissions by 0.2 Gt in 2020. As a result of energy transformation and economic restructuring, China might reach the peak of CO2 emission by 2030. China has pinned down its carbon neutrality target and pathways. At the 2015 UN Climate Conference in Paris, President Xi announced China’s intended nationally-determined contributions, the most important of which was striving to peak CO2 emissions by 2030. China’s CO2 emission per unit of GDP dropped by 48.1% in 2019 compared to that in 2005, achieving ahead of schedule its commitment of a 40% to 45% reduction in CO2 emission per unit of GDP in 2020 with respect to the 2005 level, which was made at the Copenhagen Climate Change Conference. On September 22nd 2020, President Xi added further at the 75th Session of the United Nations General Assembly that China would adopt more vigorous policies and measures to strive to peak CO2 emissions by 2030 and achieve carbon neutrality by 2060. Thus making greater efforts and contributions towards meeting the objectives of the Paris Agreement. These proposals suggest that China has taken a key step in pushing for the realization of the 1.5 °C goal within this century. In July 2021, China’s special envoy for climate change Xie Zhenhua said that China’s carbon neutrality target refers to the neutrality of the emission of greenhouse gases in all economic sectors, not just CO2 . To meet the 2060 carbon neutrality goal, it is necessary to profoundly transform the socio-economic, energy and technological systems. First, we must hold fast to the new development concept, carrying out industrial restructuring, transformation and upgrading to put in place a green, low-carbon and circular industrial mix giving priority to developing digital and high-tech industries, and transforming the iron and steel, cement, chemical and petrochemical sectors where emission reduction is difficult for cleaner production by innovating production processes and technologies, such as replacing coke with hydrogen as a reducing agent in metal smelting. Second, a sustainable energy system should be built on the basis of new energy and renewable energy, developing and making full use of the wind, solar, hydro and nuclear powers, encouraging the development of energy internet, smart grid and distributed generation, making rational use of the BECCS and Integrated Gasification Combined Cycle (IGCC) technologies, allowing for natural phase-out of coal-fired power plants upon the termination of life cycle as well as orderly and harmonious transformation of the coal industry. Third, coal should be replaced with electricity for end consumption in the industry, transportation and construction sectors with intensified efforts of electrification. As the use of fossil fuels and carbon emissions are reduced, the carbon absorption sink of forests should be increased to offset a small proportion of

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emissions for carbon neutrality. At the same time, efforts should be made to facilitate the amelioration of environmental quality in the hope of actualizing high-quality economic development and the new development concept. 2. Major Policy Measures China’s intended nationally-determined contributions submitted to the UN pledged to reduce carbon intensity by 40–45% by 2020, 60–65% by 2030, reach the peak of carbon emission by 2030 and make best efforts to peak early.2 Based on this commitment, China has promulgated a number of policies targeting specifically at the energy, construction and transportation sectors and adopted relevant emissions reduction measures. Meanwhile, the Chinese government has incorporated climate action targets into the five-year plans FYP for economic and social development of P. R. China, and enacted relevant laws and regulations to intensify efforts to address climate change and control greenhouse gas emissions. For instance, over the 10th FYP period, China prioritized the development of gas-for-oil, coal gasification, coal-to-liquids (CTL), and clean coal technologies; the 11th FYP proposed to enhance renewable energy development; over the 12th FYP period, several specialized renewable energy development plans and Strategic Action Plan for Energy Development (2014–2020) were launched; in 2016 the State Council issued the 13th FYP for Controlling Greenhouse Gas Emissions. In the 13th FYP, for Renewable Energy Development released by the National Development and Reform Commission (NDRC), China laid down the strategic goal of the increasing the share of non-fossil energy in total primary energy consumption to 15% by 2020 to speed up the replacement of fossil fuels. Changes in the energy structure will affect greenhouse gas emissions to a large extent. Development and utilization of renewable energy (such as biomass, hydro, geothermal, solar, wind and ocean energies) in place of traditional fossil fuel combustion is key to reshaping future global energy production, consumption and emissions. Developing renewable energy can significantly reduce carbon emissions and bring about the synergistic reduction of air pollutant emissions. Renewable energy power generation has been growing in terms of scale and consumption in recent years, having important effects on carbon and pollutant emission reduction. By 2019 China’s renewable energy had an installed power generation capacity of 794 GW, up 9% year-on-year, including hydro, 356 GW; wind, 210 GW; PV, 204 GW and biomass, 22.54 GW, which increase by 1.1%, 14.0%, 17.3% and 26.6% respectively. In 2019, renewable energy generation reached 2.04 trillion kW·h of electricity, marking a year-on-year increase of 176.1 million kW·h; renewable energy contributed to 27.9% of the total power generation, up 1.2 percentage points year-on-year, contributed by hydro, 1.3 trillion kW·h, up 5.7%; wind, 405.7 million kW·h, up10.9%; PV, 224.3 million kW·h, up 26.3%; and biomass, 111.1 million kW·h, up 20.4%. Since 2016 China has become the world’s first renewable energy consumer, and every year China contributes to nearly half of the world’s 2

UNFCCC. INDCs as communicated by Parties-China Submission. https://www4.unfccc.int/sites/ submissions/indc/Submission%20Pages/submissions.aspx

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newly installed renewable energy power generation capacity. In 2018 the increase in China’s renewable energy power generation accounted for 45% of the global growth, exceeding the sum total of all the members of the Organization for Economic cooperation and Development (OECD). China also takes a leading position in global nuclear power development. In 2019 China’s installed nuclear power generation capacity was 48.74 GW, up 143% from the 2014 level of 20.08 GW, and had 47 nuclear power generation units in operation, taking the third place in the world, after the United States and France. The total installed capacity of nuclear power accounted for 2.42% of China’s total installed power capacity. Total electricity generated increased from 133.2 billion kW·h in 2014 to 348.7 billion kW·h in 2019, accounting for 4.88% of the national total. There were 13 nuclear power generation units under construction in 2019, having a total installed capacity of 13.87 GW and remaining the first in the world on end. In 2013 China’s State Council released the Action Plan for Air Pollution Prevention and Control (“Ten Articles of Atmosphere”), making it clear that the overall air quality in China would be improved, heavily polluted days would be dramatically reduced and regional air quality would be significantly should be enhanced in the Beijing-Tianjin-Hebei, Yangtze River Delta and Pearl River Delta with five years’ hard efforts. Among the policy measures proposed, the development of clean energy, control of coal consumption and phase-out of outdated fuel-powered vehicles are the most important components. The action plan Ten Articles of Atmosphere strongly pushed forward energy restructuring in China and contributed significantly to the control of CO2 emissions. In 2018, the State Council issued the Three-Year Action Plan to Fight Air Pollution, proposing to drastically reduce greenhouse gas and major air pollutant emissions in three years by taking measures such as adjusting and optimizing the industrial structure and promoting green development of industries; speeding up adjustment of energy structure to build a clean, low-carbon and efficient energy system; actively adjusting transportation structure to develop a green transportation system; optimizing land use structure and pushing forward non-point source pollution control; implementing special initiatives to substantially reduce pollutant emissions; and intensifying region-wide collaborative prevention and control to effectively address heavily polluted weather.

4.2.4 Emission Reduction and Effects in China Low-carbon cities have played an important role in the progression of carbon emission control. On July 19 2010, the NDRC issued the Notice on the Pilot Work of Low-Carbon Provinces and Low-carbon Cities, designating the five provinces of Guangdong, Liaoning, Hubei, Shanxi and Yunnan, and the eight cities of Tianjin, Chongqing, Shenzhen, Xiamen, Hangzhou, Nanchang, Guiyang and Baoding as the first batch of low-carbon pilots. So far, three batches of pilot provinces and cities have been designated, covering 6 provinces and 81 cities in total.

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It was stated in the Joint Announcement on Climate Change made by China and the United States Heads of State in 2014 that China intended to achieve the peak of CO2 emissions by 2030 and to make its best efforts to peak earlier. This commitment was reiterated in China’s intended nationally-determined contributions submitted to the UN in 2015. Since then, some cities in China have been setting timelines for carbon emission peak. When selecting candidates for the third batch of pilot lowcarbon cities at the end of 2016, China required all applicant cities to incorporate the carbon emission peak target in their pilot implementation schemes. And the notice of the third batch of pilots released the ratified peaking timeline targets of the 45 pilot cities. After that, the first and second batches of low-carbon pilot cities also set their timelines for carbon emission peak. The low-carbon pilots selected are highly extensive in geographical scope and representative in city types. Based on integrated assessments of the low-carbon development status and policy innovations of the pilots, this piloting initiative has achieved positive results. In general, the pilot cities have performed well in terms of low-carbon development, having higher rates of reduction in CO2 emissions per unit of GDP than non-pilot cities and remarkably higher rates of reduction in carbon intensity than the national average. Meanwhile, low-carbon development knowledge and capacity have been enhanced largely in many localities; with the piloting initiative, the scientific understanding of the low-carbon development concept has been improved. Local governments have paid more attention to the coordinated promotion of green and low-carbon development with socio-economic development, which has played an important role in changing the traditional concept of crude development. A number of best practices and experiences have surged up in the piloting process, covering industrial transformation, energy transformation, technological progress, promotion of low-carbon lifestyle, and institutional system innovations driving green, low-carbon development and ecological civilization construction. Activities, such as pilot experience sharing, promotions and outreaches, have facilitated mutual learning related to the extension of low-carbon policy innovations, and effectively pushed forward the bottom-up implementation of the low-carbon development policies.

4.3 Synergized Effects of Adaptation and Mitigation 4.3.1 Adaptation, Mitigation and Their Interactions As two major approaches for addressing global climate change that differ in traits, adaptation and mitigation need to be treated equally (high confidence). Adaptation and mitigation are both for reducing the adverse impacts of climate change and promoting sustainable human development, but they differ in that mitigation is to change the climate system by reducing greenhouse gas emissions or increasing carbon sink, while adaptation is to alter natural or human systems to address actual or expected climate change and its impacts so as to cut down loss.

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Mitigation actions are implemented locally but their impacts can be global and longlasting. Adaptation actions are also taken locally and can have effects in a short term, but their benefits are mostly local or regional. It is of crucial importance to raise the resilience of the human and natural systems against expected future climate risks (Table 4.3). Even if emissions are reduced drastically around the globe, climate change has occurred and will continue to occur. Equal emphasis should be laid on adaptation and mitigation in responding to climate change; neither should be overemphasized to neglect the other. There are synergies and trade-offs between adaptation and mitigation (high confidence). Adaptation and mitigation interact within and between regions; they have crossing points in the water, energy, land use, and biodiversity sectors in particular. Some actions with both adaptation and mitigation features can work with synergistic effects. For example, building eco-industrial parks can raise urban resilience while remarkably saving energy and reducing emissions by such means as clean production, energy auditing, international certification of life cycle analysis, ecoindustrial symbiosis, urban symbiosis, etc. Other examples include forest land and wetland protection and ecosystem restoration, which can enhance the ecosystems while increasing carbon sinks. Photovoltaic sand control can stabilize sand while using renewable energy for power generation. On the contrary, deforestation and ecological destruction can increase carbon emissions while causing soil erosion, having adverse impacts on both adaptation and mitigation. Under many circumstances, adaptation and mitigation are hard to balance, and difficult trade-offs are required. For instance, engineering adaptation measures are often based on energy consumption and carbon emission; carbon neutrality, for requiring massive biomass utilization and carbon storage technology, may lead to land use, water resources and eco-environment hazard while delivering emission reduction targets (Fig. 4.2). Climate change responses are closely related to socio-economic policies; adaptation and mitigation actions should be advanced within the framework of sustainable development (high confidence). There are often no clear demarcation lines between climate and non-climate policies; synergies and trade-offs exist at the same time between the two. For instance, the process of mining, transporting and utilizing coal not only send off CO2 and pollutants but also adversely affect water resources, land use and eco-environment. Replacement of fossil fuels with renewable energy can reduce CO2 emissions while doing good to population health, ecoenvironment and energy security, thus having synergistic effects. However, extensive and quick “coal phase-out” will have an adverse impact on some industries and vulnerable groups. “Just transition” is also an issue worth special care. Incorporating adaptation and mitigation policy measures into current sectoral development plans and decision-making processes is conducive to ensuring long-term investment, more effectively using the financial and human resources, and facilitating fundamental transformation towards sustainable development, thus reducing the impact of development activities on the climate system from sources. In recent years, solar radiation management (SRM) and CDR have aroused great concern and controversy in the international community (high confidence). Among the two, SRM does not directly reduce CO2 concentration in the atmosphere

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Table 4.3 Differences between adaptation and mitigation Mitigation

Adaptation

Long-term goals

Reducing the adverse impacts of climate change and promoting sustainable human development

Major actions

To reduce greenhouse gas emissions; To increase carbon sinks

To reduce vulnerability; To raise resilience; To tap potential development opportunities

Action traits

Planned and proactive prevention

Planned and proactive prevention, and also passive response

Time scale

Effective in a long term

Take effects in a short term, some measures having long-term effects

Spatial scale

Act locally, benefit globally

Act locally; Local or regional benefits

Cost–benefit assessment

Uniform unit of measurement for emission reduction; Determination of emission reduction cost

Economic benefits easy to measure; ecological and social benefits hard to measure in monetary terms

Priority areas

Energy, industry, agriculture, forestry, transportation, construction, urban planning and design etc.

Agriculture, tourism, healthcare, water resource management, coastal zone, urban infrastructure planning, eco-environment protection, etc.; limate-sensitive secondary and tertiary industries (high-exposure sectors such as transportation, construction, mining, etc.; Industries affected indirectly like commerce, trade, finance, insurance and catering, etc.

Stake-holders

International organizations, central and local government decision-makers, NGOs, enterprises, everyone involved in generating a carbon footprint

Organizations and individuals affected by climate disasters, potentially vulnerable groups, central and local government decision-makers, NGOs, etc.

Climate equity

“Hitchhiking” in emission Regions or people most vulnerable to reduction; climate change are often not big carbon emitters Developed countries obliged to offer developing countries financial and technical help

but alleviates global warming by reducing solar radiation reaching to the ground, via stratospheric aerosol injection (SAI), higher cloud albedo over the ocean, higher land or ocean surface albedo (C2G2 2019). CDR is the biological, physical or chemical ways of carbon removal or transformation used to lower greenhouse gas concentration in the atmosphere, such as afforestation and forest ecosystem restoration, BECCS, direct air capture with carbon storage (DACCS), soil amendment with biochars,

Fig. 4.2 Illustration of the relationship between adaptation and mitigation

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enhanced weathering, marine alkalization, marine fertilization, etc. Besides, scientists have made assumptions like “targeted geoengineering” to preserve continental ice sheets (Moore, 2020). These technologies and measures are of adaptation or mitigation effects in theory but vary significantly in traits and maturity. Their massive application might bring about high uncertainties and new risks, and trigger justice, ethics and international governance problems, arousing great concern and controversy in the international community. For instance, stratospheric aerosol injection, once started, needs to be continued for a long time. While reducing global average temperature, it will alter global temperature and precipitation distribution, weaken vegetation carbon sink, aggravate marine acidification, and impact bio-diversity. Once it stops, temperature will rebound rapidly. Another example is that BECCS technology needs to rely on a large amount of biomass energy utilization to realize negative emissions, occupying a large amount of land and water sources, which may threaten food security (Chen and Xin 2017; Chen and Shen 2020). Knowledge Tips: Just Transition Meeting the carbon neutrality target implies profound transition of the socioeconomic and energy systems. The concept of just transition raised internationally advocates the adoption of responsive policy measures to facilitate the realization of the decent jobs for all, social integration and poverty eradication targets in the process towards meeting the target. Justice is one of the fundamental ethical values and principles of the society that stresses on righteousness of this value orientation. Fairness, however, is distinctly “instrumental” and highlights measurement by the same scale to evade double or multiple standards for social treatment. So, it can be said that justice is the conceptual and idealized fairness, while fairness is a realistic and concrete justice.

4.3.2 China’s Synergized Adaptation and Mitigation Measures, Actions and Effects Balancing adaptation and mitigation is one of the fundamental principles of China’s climate change response strategy. A careful review of China’s actions in pursuing low-carbon development and adapting to climate change revealed that there are synergies between adaptation and mitigation in the fields of agriculture and forestry carbon sinks as well as urban planning and rehabilitation. 1. Agriculture and Forestry Carbon Sinks China’s implementation of the forestry and ecological restoration project has resulted in a continued increase in its forest coverage, achieving carbon

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sink increase and adaptation targets at the same time (high confidence). China had a total forest area of 220 million hm2 and a forest coverage of 23.0% in 2019. Since the mid-1970s, China has been vigorously pushing forward the forestry and ecological restoration projects, typical of which are the Three-North Shelter Forest System Programme, Project of Returning Farmland to Forests and Grasses, and Beijing-Tianjin Sandstorm Source Control Programme. These projects have resulted in a substantial increase in vegetation coverage of the project areas and profound changes in China’s forest distribution. Take the Project of Returning Farmland to Forests and Grasses, as an example. With its implementation, the vegetation coverage of the Loess Plateau increased from 31.6% in 1999 to 59.6% in 2013. Carbon sink increase in the ecosystem of the Loess Plateau is attributed mainly to the cropland conversion project. The Loess Plateau ecosystem carbon sequestration increased by 96.1 million tons over 2000–2008, equivalent to 6.4% of the national total carbon emissions in 2006. In multiple future climate change scenarios, the distribution area of the evergreen broad-leaved tree species and deciduous broad-leaved tree species in typical subtropical forest areas in southern China will increase distinctly and cover the formerly coniferous forest-dominated areas. At the same time, the above-ground annual primary productivity of biomass will also rise dramatically, being conducive to both mitigation and adaptation. Many agriculture-related climate change response technologies and measures are good not only for increasing yield and economic returns but also for serving adaptation and mitigation purposes (high confidence). For instance, the water-saving irrigation technology cuts down energy consumption during the surface and underground pumping, water transportation and irrigation facility construction processes, and reduces greenhouse gas emissions. At the same time, improving water use efficiency can save agricultural water use by 12.97% and increase production by 30.15 million tons, thus achieving an economic benefit of CNY 1783.68/ hm2 . Conservation tillage measures can improve soil water utilization, reduce soil erosion, improve or maintain soil fertility, increase grain yield by 1.723 million t, and realize economic income of CNY 2192.53/hm2 . Besides, straw incorporation is another effective practice to increase carbon sinks and reduce emissions. It is worth promoting in that it serves adaptation via retaining fertilization and soil moisture while increasing organic matter in soil and stabilizing crop yields. There might be trade-offs between adaptation and mitigation actions in the agriculture and forestry sectors. For instance, planting trees in some parts of the Loess Plateau not suitable for afforestation or planting highly water-consuming tree species or at an unduly high density might lead to the phenomenon of “dry soil layer”. Blind expansion of afforestation are as might lead to community decline and ecosystem degradation. Therefore, ecological restoration needs to be comprehensively evaluated according to local conditions. 2. Urban Planning and Governance China is in the process of rapid urbanization, and synergized adaptation and mitigation are required for cities to address climate change (high confidence). Cities are the result of high-level density of population and economic activities.

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By the end of 2019, China had an urban resident population of 850 million and an urbanization rate of 60.6%. China is in the process of rapid urbanization, so cities are not only severely affected by climate change but also are an unneglectable source of increased carbon emission. Urbanization, city size, economic development, industrial structure, technological progress, level of opening-up, land use and spatial structure are major drivers of urban carbon emission. Formulating urban climate change response strategies, needs to address adaptation and mitigation as well as urban development targets comprehensively, which depends on government support, sectoral coordination and public participation. Fortifying urban planning and urban form management are pivotal to creating synergies between urban adaptation and mitigation capacities (high confidence). The urban form needs to be managed through urban planning from the perspectives of population density, land use and vegetation, architectural features, spatial organization structure, land use diversity, solar energy application, residential space distribution and infrastructure, etc. so as to enhance the urban resilience against climate change. Cities need to guard against low-density sprawl development; promote mixed and diversified land use; enhance the residence, job, and commercial service proximity and accessibility to reduce travel demands; and advocate travel on public transport and low-carbon mode of travel. These measures can enhance the adaptation and mitigation capacities of the cities at the same time. Concrete measures include: (1) strengthening protection and restoration of biological communities, reducing deforestation, and promoting reforestation and forest management to give full play to natural carbon sinks; (2) planning and developing green wedges between urban and suburban areas by leveraging on rivers, lakes, ecological wetlands, forest land, croplands and other natural ecological resources within the ecological protection boundaries delineated to raise urban ventilation and heat dissipation capacity so as to alleviate urban heat island effects; (3) intensifying public utilities and transportation infrastructure building, and steering relevant balance between group residence, employment and public facilities allocation to reduce urban traffic congestion, greenhouse gas and pollutant emissions from motor vehicles on road; (4) low-carbon industrial distribution to reduces energy consumption of pollution control and transportation via spatial agglomeration and industrial association. The pilot demonstrations of low-carbon, climate-resilient and sponge city have been conducted, and substantial progress has been made as to how cities address climate change. Since 2010 China has launched three pilot projects for low-carbon cities, with 81 pilot low-carbon cities from 6 pilot low-carbon provinces designated. In early 2017 a pilot project of 28 climate-resilient cities was launched, supporting the pilot cities to take the lead in rooting the urban resilience concept, undertake major adaptation actions, improve monitoring and early warning capacities, build up policy experiment bases and forge international cooperation platforms so that their climate change adaptation capacity may be comprehensively upgraded to allow for the national extension of their best practices by 2022. Over half of the cities are at the same time national-level pilot low-carbon, sponge, ecological garden and smart cities, which is good for pushing forward synergized adaptation and mitigation actions. The pilot projects made it possible for these cities to undertake loads

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of adaptation and mitigation initiatives in key fields such as urban planning, infrastructure, architecture and ecological green space systems. So far, lots of evaluations and summary analyses have been made on the outcomes of the low-carbon city pilots, but assessments of synergies between adaptation and mitigation are yet to be made.

4.3.3 Adaptation and Mitigation Strategies Under the Goals of the Paris Agreement In order to meet the Paris Agreement targets, global adaptation and mitigation requires a “double-stringent” strategy (high confidence). At the global level, mitigation is currently the best long-term adaptation strategy. Research on different emission scenarios to meet the Paris Agreement targets indicates that there will be marked temperature rise before 2050, differing not much from that of pathways for higher warming targets. Against the warming target of 1.5 °C, there will be a temperature rise of 1.6 °C and above by 2050, followed by a return to 1.5 °C by 2100 and rapid warming in the next decades in most scenarios. Under the warming target of 2 °C, adaptation requirements will be more stringent. That is to say, under the Paris Agreement targets, the “double stringent” adaptation and mitigation strategy is a must. Mitigation is to be geared to lower warming targets and adaptation, while adaptation should aim at the high temperature rise scenarios. The two need to be put together in consideration, coordinated and balanced in practice, synchronized and given equal attention. Adaptation and mitigation actions taken separately by various departments should be put under synergistic management and optimization (high confidence). The effectiveness of synergistic management depends on many factors such as knowledge, institution, technologies, governance capacity, etc. Best synergistic points are difficult to achieve, but it is viable to find the second best policy portfolios or those with the highest level of satisfaction based on certain decision-making principles. The IPCC reports recommend the multi-objective assessment techniques, participatory planning and decision-making approaches to develop adaptation planning and enhance synergistic management capacity. To meet the Paris Agreement targets, China has proposed to peak carbon emission before 2030 and reach carbon neutrality before 2060, indicating that socio-economic development is to undergo comprehensive and profound transformation. Rapid transformation in the energy sector is of particular significance and can bring about new adaptation demands (high confidence). Researches on carbon neutrality-related scenarios have suggested that by 2050 the zero-carbon energies such as renewable and nuclear energy should account for over 70% of the primary energy demand. Considering the impacts of climate change on energy, transportation and other infrastructures, China urgently needs to strengthen the corresponding adaptation measures. For instance, need to be taken full consideration for the layout of wind farms and PV power generation stations. The impacts of

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climate change on wind and light resource distribution; for hydropower dam construction, it is necessary to minimize its impact on eco-environment and upgrade its capacity of coping with flood disasters incurred by extreme precipitation. Following the sweeping electrification of the construction, transportation and other end users, the traditional and less-smart power grids will face greater power supply vulnerability and more pressing climate change adaptation risks.

References C2G2 (2019) Geoengineering: the need for governance. Carnegie Climate Geoengineering Governance Initiative, New York Chao Q, Liu C, Yuan J (2014) The evolvement of impact and adaptation on climate change and their implications on climate policies. Clim Change Res 10(3):167–174 (in Chinese) Chen M (2020) Progress and outlook of adaptation negotiation under the united nations framework convention on climate change. Clim Change Res 16(1):105–116 (in Chinese) Chen Y, Shen W (2020) Global governance of geoengineering: theory, framework and China’s strategies. China Popul Resour Environ 30(8):1–12 Chen Y, Xin Y (2017) Implications of geoengineering under 1.5 °C target: Analysis and policy recommendations. Clim Change Res 13(4):337–345 (in Chinese) Editing Commission of the Third National Report on Climate Change of China (2015) The third national report on climate change. Science Press, Beijing (in Chinese) IPCC (2018) Global warming of 1.5 °C. An IPCC special report on the impacts of global warming of 1.5 °C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty. Intergovernmental Panel on Climate Change, Geneva IPCC (2021) Summary for policymakers. Masson-Delmotte V, Zhai P, Pirani A, et al. Climate Change 2021: the physical science basis. In: Contribution of working group I to the sixth assessment report of the intergovernmental panel on climate change. Cambridge University Press, Cambridge Jiang X, Zhou Z, Lin Z et al (2021) International cooperation on adaption in post-Paris times: thoughts and prospect. Clim Change Res 17(4):484–495 Moore JC, Mettiäinen I, Wolovick M et al (2020) Targeted geoengineering: local interventions with global implications. Global Pol 12(S1):108–118 Wu S, Luo Y, Wang H et al (2016) Climate change impacts and adaption in China: current situation and future prospect. Chin Sci Bull 61:1042–1054 (in Chinese)

Chapter 5

The Development Pathways with Climate Resilience

To meet the temperature rising target of the Paris Agreement, the deep reduction in CO2 emission has to be carried out in China and the corresponding transformation of energy and socio-economic development pathway is required in the future. The development pathway with climate resilience emphasizes the paralleling abilities to address the impact of climate change and to coordinate with other social development targets during the process of implementing the emission reduction pathway. This chapter analyzes the emission reduction pathway for meeting the temperature rise goal of the Paris Agreement at first, and then integrates the related factors under the framework of climate resilience into the development pathway analysis. Since the framework covers many factors, this chapter mainly involves the following factors including the linkage with sustainable development goals, risk management in climate change, eliminating poverty, food security, water safety, nature-based solutions, fairness and ethics, etc. And then advice and suggestions for participating in international climate cooperation are brought forward to facilitate global climate governance and to help build a community with shared future for mankind. Finally, the development pathway for achieving climate resilience is proposed.

5.1 Global and China’s Carbon Emission Budgets and Implementation Pathway Under the Warming Targets of the Paris Agreement 5.1.1 Global and China’s Carbon Emission Budgets According to the report of IPCCAR5 WGIII, under the warming scenario of 2 °C, the global cumulative CO2 emission budget from 2011 to 2050 is 530– 1300 Gt CO2 , and the global cumulative CO2 emission budget from 2011 to 2100 is 630–1180 Gt CO2 . This emission budget is far less than the cumulative © Science Press 2023 D. Qin et al., The Change of Climate and Ecological Environment in China 2021: Synthesis Report, https://doi.org/10.1007/978-981-99-4487-3_5

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CO2 emission of 1890 Gt (1630–2125 Gt) CO2 from 1870 to 2011. This conclusion basically complies with the conclusion of IPCC Working GroupI (WGI). In the report of WGI, based on the simulation of the CMIP5 Earth system model, under the RCP2.6 scenario, the cumulative CO2 emission budget from 2012 to 2100 is 990 Gt (510– 1505 Gt)CO2 . The differences between the results of WGIII and WGI came from the different models (the IAM and the ESM), different beginning years and ending years for warming calculation (1861–1880 and 1850–1900), scenario quantities (the scenarios gathered by WGIII are more comprehensive) and greenhouse gas emission ranges (whether including CO2 related forest and land use) they adopted. The IPCC Special Report on Global Warming of 1.5 °C(IPCC SR 1.5), which was published in 2018, differs greatly from IPCC AR5 in terms of methodology, definition for temperature rise, non-CO2 emission contribution, and the remaining emission budget, etc. IPCC SR 1.5 points out that in order to meet the warming target of 2 °C, the global emission in 2030 has to be 20% lower than that in 2010 and near-zero emission has to be realized around the year 2075. In this sense, the emission reduction efforts have to be strengthened significantly under the warming target of 1.5 °C, including non-CO2 emission. The global emission in 2030 has to be 45% lower than that in 2010, with net zero emissions to be achieved around the year 2050. Meanwhile, the emission of methane and black carbon in 2050 has to be 35% lower than that in 2010. In the WGI report of IPCC AR 6 issued in 2021, under the warming target of 1.5 °C, the remaining carbon budget is 500 Gt CO2 after 2020 (50% likely) and 400 Gt CO2 (67% likely). While under the warming target of 2 °C, the remaining budget is 1350 Gt and 1150 Gt CO2 , respectively. This conclusion is not different much from the IPCC SR 1.5. The strict carbon budget constraints under the warming targets of 2 and 1.5 °C mean that the global remaining carbon emission budget will be exhausted soon. According to the latest global CO2 emission data, CO2 emission from energy combustion and industrial processes was 37.0 Gt CO2. in 2016. Hence, if the global emission remains at the level in 2016, the global remaining carbon budget will only support the emission for around 30 years under the warming target of 2 °C. If the warming target is 1.5 °C, the remaining time for the emission budget will be less than 15 years. What needs to be emphasized is that although an approximate linear relationship exists between warming and cumulative emission, there is large uncertainty in its proportion parameters, for the gap between its top and bottom limits may reach more than two times. Considering multiple emission allocation criteria, under the global 1000 Gt CO2 emission budget scenario, China’s cumulative carbon emission budget in 2010–2050 is 170–423 Gt CO2 to meet the global warming target of 2 °C. Many studies take 290–320 Gt CO2 as the emission budget range. If the target is 1.5 °C, China’s carbon emission budget is 190–230 Gt for 2010–2050.

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5.1.2 Global Emission Reduction Pathways Since 2012, the progress of research on the global emission scenario has been reflected in the representative emission pathways aiming at the warming targets of 2 °C and 1.5 °C. IPCC AR5, published in 2014, assessed multiple emission scenarios under the warming target of 2 °C (IPCC 2014). Its assessment result provided supports for the determination of the warming target in the Paris Agreement in 2015. IPCC AR6 WGI report exhibits the emission pathway, as shown in Fig. 5.1. What is shown in Fig. 5.1 is the global emission scenario targeting different radiative forcing levels under the framework of a large number of SSP scenarios. These emission scenarios mainly come from the global scenarios generated by a dozen global IAMs (IPCC AR6 WGI). If the warming target is 2 °C from the perspective of the global scenario, the main features are as follows. Many kinds of emission reduction pathways can be adopted to control global warming below 2 °C relative to the pre-industrial levels. These pathways require to have deep emission cuts over the coming decades. In addition, the emissions of CO2 and other long-life GHGs have to approach net zero by the end of this century. The implementation of these measures will bring huge challenges to technology, economy, society and systems. If the emission reduction efforts cannot be strengthened as soon as possible, and the available key technologies cannot be adopted, these challenges will be even harsher. Limiting warming to lower or higher temperature levels will pose similar challenges, with the only difference lying in the time scales. If GHG concentration reaches approximately 450 ppm CO2 equivalent or even lower by 2100, it is very likely(more than 66%) that the global warming in the twenty-first century can be controlled below 2 °C relative to the preindustrial levels. The characteristics of these scenarios are: the global anthropogenic Fig. 5.1 Global emission scenario

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GHG emission in 2050 will be 40–70% lower than that in 2010, and the emission will be near zero or even lower by 2100. If GHG concentration reaches about 500 ppm CO2 equivalent by 2100, it is most likely (more than 50%) that the warming will be controlled below 2 °C. If the concentration temporarily exceeds 530 ppm CO2 equivalent before 2100, it is somewhat likely (about 50%) that the warming will be controlled below 2 °C. Under these scenarios with 500 ppm CO2 equivalent, the global emission in 2050 will be 25–50% lower than that in 2010. The scenario with the emission to increase in 2050 will result in more dependence on the CDR technology.

5.1.3 China’s Emission Reduction Pathways 1. Emission Scenarios Significant progress has been made in the study of China’s emission scenarios since 2012. China is included in the global emission scenarios, so there are quite a few scenarios about China in the global scenario database. Both domestic and international research institutes have studied China’s energy and emission scenarios. The recent research progress has been in the emission reduction pathways for limiting warming to 2 and 1.5 °C. Emissions related to the technological process and land use are also included in some scenarios. Studies specially tailored for non-CO2 GHG have been increasing. Figure 5.2 shows the modeled energy demand scenarios in China and Fig. 5.3 is about the CO2 emission scenarios.

Fig. 5.2 Demand of primary energy in China

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169

Fig. 5.3 China’s CO2 emission scenarios

Currently, few domestic scenario studies can match with the carbon emission budget in China under the warming target of 2 °C, and scenario studies that are very likely (more than 66%) to achieve the warming target of 2 °C are quite limited. Some studies are capable of doing it, but the possibility is only 50% or more. These scenarios share some similarities: the proportion of renewable energy in primary energy has increased significantly. By 2050, this proportion will be 43–81%of primary energy. Nuclear power increases in all the scenarios, but the extent of the increase differs greatly. The nuclear power installed capacity is 140–510 GW in 2050, In some of these scenarios that limit warming to 1.5 °C, the nuclear power installed capacity can reach 510 GW in 2050, accounting for 42% of the total power generation. Under the scenario of high proportion renewable energy, which was developed by the Energy Research Institute, National Development and Reform Commission, renewable energy accounts for more than 70% of the overall primary energy demand, in 2050 while the nuclear power is only 150 GW. For the scenario of warming to 2 °C, CO2 emission by 2050 will be 65–70% lower than its peak value; as for the scenario of 1.5 °C, CO2 net zero emission needs to be realized in 2050 or soon after that (Fig. 5.3). Lots of studies on the future emission scenarios have demonstrated that, in order to meet the warming target of the Paris Agreement, deep emission cuts have to be implemented before 2050. and to reach CO2 emission peak as soon as possible. Scenario research results indicate that China needs to achieve the emission peak around 2025 so as to meet the warming target. 2. Energy Transition Pathways Chieving carbon neutrality and emission peak requires a significant transformation of energy system. The realization of net zero emissions from the energy systems by around 2050 will be a great support for reaching carbon neutrality by 2060. Main

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approaches for energy transition in China are to improve energy efficiency, to reduce the needs for energy services by energy transition and sustainable consumption, and to raise the electrification rate in end-use sectors and decarbonization of the power system, and the details include. From 2020 to 2030, China will develop low-carbon energy and begin to change the pattern dominated by fossil energy, promote a low-carbon mode of traditional energy and the industrialization of low-carbon energy. These efforts aim to make the fossil energy consumption reach its peak in 2030 or even earlier. The first is to control the total carbon emission. China is accelerating low-carbon transformation of energy system and industrial structure with the goal of carbon emission peak and non-fossil energy, and making the business model of large-scale promotion of non-fossil energy more and more mature. The second is to further reduce the cost of non-fossil energy through marketization, build a power grid system suitable for large-scale renewable energy access and promote the consumption and supply of green electricity. The third is to promote energy conservation in an allround way. So that the energy conservation of different sectors can reach the world’s leading level, and promote the popularization of advanced energy-saving technologies, for example, promoting ultra-low energy consumption buildings and implementing energy consumption standards for buildings. The fourth is to strengthen the international energy cooperation so as to lay the foundation for the transformation of energy import and export modes. From 2030 to 2050, China plans to accelerate energy technology innovation, industrial innovation and business model innovation, and increase the proportion of non-fossil energy significantly. Low-carbon energy will dominate energy consumption. All these efforts aim to lay the foundation for building climatefriendly energy system. The first is to decouple economic development from fossil energy consumption. New energy consumption needs will be basically met by nonfossil energy. The second is to build infrastructure networks for large-scale non-fossil energy development. The electricity from fossil energy will be substituted on an enormous scale, and the energy’s low-carbon level will be improved significantly. The share of non-fossil energy will in installed power generation and electricity generation account for more than 60% and more than 80% of respectively, making the carbon emission factor per unit of power generation drop greatly. The third is to build an advanced energy interconnection system. China will promote the construction of infrastructure such as smart grid, smart gas network, smart heat network, smart transportation and smart buildings, strengthen the integration and interaction of multi-networks, and, based on information technology, smart grid technology and energy storage technology, build a new type of cross-region power system that is featured with flexibility, interaction, self-healing and compatibility. The fourth point is about the full electrification in end-use sectors and the popularization of energy-saving technology.

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2. Assessment of Policy Pathways Studies on emission scenarios and transition pathways show that the implementation of these emission and transition pathways is closely linked with policies. Policies in scenario analysis generally vary as the model methods vary. Models for economy analysis, such as the CGE model, are mainly involved with economic and financial policies, like carbon tax and fiscal expenditure, etc. The policies linked with technical analysis models are more comprehensive, including economic and tax policies as well as industry policies, such as carbon tax, subsidies, energy conservation standards, emission standards, planning objectives, technology and industry access. There are other studies and assessments, considering the commitments in climate change negotiations to be one of the policies. Recent studies have put more attentions to the updated targets for Intended Nationally Dertermined Contributions (INDCs) and low emission strategies by 2050. These are what UNFCCC requires all the countries to submit. However, emission reduction targets normally come from the results of the scenario analysis, especially the emission reduction targets under the warming targets of the Paris Agreement. Among the emission reduction pathways for meeting the targets of the Paris Agreement, carbon pricing, especially carbon taxation, has been the policies analyzed by many researchers. In the CGE model, carbon tax is the main factor that facilitates the transition of economic development mode, which then contributes to emission reduction. Hence the carbon tax is more the report of the CGE model. On the contrary, the functions of the carbon tax and subsidies are similar in technical assessment models, and both of them exert impacts on the running cost of technology and allow for the increase in the cost of fossil fuel or the electricity generated by fossil fuel. In technical assessment models, the factors that influence the technical choices also include subsidies, standards, admittance and planning, etc. In this sense, the role of the carbon tax is relatively small. So the carbon tax in the reports of technical assessment models is much lower, sometimes even not required. Another key factor is that technical assessment models consider more about the decline in the cost of low carbon or even zero carbon technologies in the future so the role of carbon pricing may weaken accordingly. According to recent studies, in order to limit warming to 2 °C, the carbon tax will be 50–300 CNY/t CO2 in 2030 and 50–2300 CNY/t CO2 in 2050. However, some studies argue that because the costs low carbon and zero carbon technologies, have become much lower than that of fossil fuel technology the demand for carbon pricing is not so great. Technical assessment models offer a wider range of policies. The emission reduction scenarios and transition pathways of several technical assessment model groups have been analyzed, and their main policies and measures are shown in Table 5.1.

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Table 5.1 Summary of policies and measures Fields

Policies and measures

Energy

Control the growth of energy consumption, set total targets, and strengthen the development of clean energy Strengthen energy conservation, promote energy-saving standards, low-energy and low-carbon consumption, and develop energy-saving technologies on the basis of the existing achievements in vigorously promoting energy conservation No new coal-fired power plant to be built, except the IGCC power plant. Let coal-fired power plants be eliminated naturally and realize the transformation of the coal industry in an orderly manner Adopt economic, fiscal and tax policies, such as carbon pricing policy, as soon as possible after 2020 to promote the development of energy conservation and clean energy. The effect of China’s long-term adoption of administrative decrees and measures has been weakened, so it is necessary to turn to the policy system focusing on finance and taxation to promote energy transformation Promote the development of renewable energy vigorously and provide various policy supports, including subsidies and quota systems, so that renewable energy can achieve the goal of higher installed capacity in the next few years Promote the development of nuclear power vigorously, with the newly installed capacity to reach 15 million KW per year and the annual installed capacity of 400–450 million kW or more in 2050 Under the slow growth of energy consumption and vigorous development of clean energy in the future, the arrangement of energy base needs to be reconsidered, especially for some energy-dependent regions, such as Xinjiang. It is necessary to reconsider their economic development patterns, so as to avoid the possible regional problems caused by excessive dependence on fossil energies and major changes in the future Pay attention to the control of investment in fossil energy. Under the situation that the world has moved towards low-carbon energy, coal and oil will be reduced before 2050 greatly, which will result in long-term low prices. At present, the investment risk of coal and oil is great, such as investment in the coal chemical industry and foreign oil fields. The state needs to make clear policies to control it Formulate a roadmap for China’s energy development, promote the gradual implementation of energy transformation, design a smooth transformation plan, avoid the negative impact of energy transformation on economy and employment, and achieve the transformation under the conditions acceptable to the state and institutional arrangements

Transportation

According to the size of different cities, develop rail traffice and public transport vigorously, and build a slow green transportation system. Promote the development of electric vehicles and build infrastructure suitable for the development of electric vehicles. By 2030, all cities will own low-carbon transportation systems with no fuel vehicles to be sold. Develop hydrogen fuel cell-based ship, truck and aircraft technology. The transportation system will achieve near-zero CO2 emissions by 2050 (continued)

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Table 5.1 (continued) Fields

Policies and measures

Construction

Comprehensively develop low energy consumption and low emission construction. Adopt the most advanced international building standards, to make the buildings with low energy consumption and low CO2 emission occupy the main part of new buildings in the near future. By 2020, all new buildings will meet the requirements of low energy consumption and low carbon buildings, promote low energy consumption and ultra-low energy consumption of new buildings in rural areas, and with near-zero emission building technology promote the zero-carbonization level of rural buildings

Industry

Strengthen industrial energy conservation, vigorously promote electrification and renewable energy utilization, develop hydrogen-based energy, use CCS technology in steel, cement and other industries, and promote carbon pioneer enterprises with zero carbon targets

Consumption

Promote low-carbon life and consumption, encourage the public to take low-carbon travel, adopt carbon signs, and promote low-carbon consumption. Promote consumption- side incentives for low-carbon and zero-carbon products and services, such as linking government procurement to companies’ carbon neutrality commitments, regional product access systems, etc.

More vigorous policies and measures have to be taken to meat the warming target of 1.5 °C. Carbon net zero emissions will have to be achieved in energy activities in China by around 2050. Net zero emissions will probably better promote economic development. Main pathways for China to strive to achieve carbon neutrality by 2060 are as follows. (1) Electric power system will achieve zero emissions or even negative emissions of CO2 by 2050. Since the 14th five-year plan (FYP) of China, the development of renewable energy has been increased. More than 70 million kW of photovoltaic, 30 million kw of wind power and 10 million kW of hydropower will be added every year. From the 15th FYP, 100 million kW of photovoltaic and 50 million kW of wind power will be added every year. During the 14th FYP, 10 nuclear power generating units are added every year, with the newly installed capacity of 12 million kW. The number of newly added nuclear generating units will be increased to 13 every year after 2030, with additional 15 million kW of installed capacity. The coal-fired power units will stop generating electricity or be converted in to stand by power plants when reaching their life span (30 years), At the same time the coal-fired power units will begin to be transformed into peak-regulating units, and enter the stage of large-scale peak-regulating after 2025. Setting a corresponding price mechanism for coal power peak regulation can ensure the profit of coal power plants. The on-grid price of photovoltaic and other renewable energy can be reduced to less than 0.3 CNY/kW h, and the on-grid price of nuclear power can be cut to less than 0.35 CNY/kW h. Considering the system cost such as power grid, the average level of electricity price on the consumer side decreases on the whole. So, the power system can carry out deep emission reduction without increasing the electrovalence. After 2030, the BECCS technology is to be developed to realize, the goal of installed

174

(2)

(3)

(4)

(5)

5 The Development Pathways with Climate Resilience

capacity to be more than 200 million kW by 2050, and more than 800 million tonnes of CO2 will be captured every year. In this way, net zero emissions or even negative emissions will be realized in the power system by or before 2050. The power grid needs to be strengthened to build a power supply system suitable for near zero emissions. Under the scenario of near zero emissions in 2050, the electricity demand increases significantly. Intermittent power sources such as photovoltaic and wind power account for more than 50% of the power generation. Hydropower and biomass power account for more than 15%, nuclear power accounts for more than 30%, and the proportion of other fossil-energy power is around 7%. Such a power structure needs the support of a highly enhanced power grid. The base load power supply, peak load power supply and energy storage power supply all need to be matched with the power grid. Meanwhile, as the end-use sectors are fully or highly electrified, the load curve on the demand side will change greatly, which will increase the peak-valley difference, which also needs the support of the power grid. During the 14th FYP, it is necessary to begin to build the power grid system suitable for carbon neutrality according to the long-term development goals of the power grid. Clean energy needs to be utilized completely in transportation sector. Cars and buses become only battery-powered electric vehicles basically. Small-and medium-duty vehicles become mainly battery-powered electric vehicles. Some heavy-duty vehicles will use hydrogen-powered fuel cells. Small ships use batteries, while large ships use hydrogen fuel cells or biofuels. Hydrogen fuel cell technology is adopted in railways that are difficult to electrify. Small regional aircrafts are powered by batteries, and large aircrafts by hydrogen. Considering the R&D and commercial cycle of hydrogen-powered aircraft, it is also necessary to replace aviation kerosene with biofuel for existing fuel aircraft by 2050. During the 14th FYP period, the development of electric vehicles needs to be promoted continuously. After 2025, the price of electric vehicles is expected to be lower than gasoline or diesel vehicles, so there will be no more subsidies. During the 14th FYP period, some carbon pioneer cities are encouraged to take measures to promote the use of electric vehicles. For example, some areas only open to public transport and electric vehicles, and gas stations are to be moved gradually out of the city center. Meanwhile, the R&D of new technologies, such as fuel-cell driving technology, and the R&D of hydrogen-fueled aircraft. The construction sector needs to be fully electrified basically. During the 14th FYP period, the usage of electric cooking in office buildings, hotels and catering industries is clearly encouraged. The indoor pollution and residential pollution caused by indoor use of natural gas needs to be widely publisized and residents are encouraged to use electric cooking. In addition, the development of ultra-low energy consumption buildings is greatly promoted. In the future, electric heating, industrial waste heat heating, nuclear power plant heating, low-temperature nuclear heating and renewable energy heating will be the main heating sources. The level of electrification needs to be greatly improved in industries. With updated production process, electric power will be used for heating industrial kilns and boilers. Setting up central heating in industrial parks and CCS will be installed for large-scale thermal facilities using natural gas and coal for heating.

5.2 Addressing Climate Change and the Sustainable Development

(6)

(7)

(8)

(9)

175

For industries that are difficult to reduce CO2 emissions, such as iron and steel, cement, petrochemical, chemical industry and nonferrous metals, the process innovation has to be promoted. For example, hydrogen can be used as a reducing agent and raw material for production. Hydrogen comes from renewable energy and green hydrogen production from nuclear power electrolytic water, or from other hydrogen production by zero-carbon process. Innovative technology is needed for net zero emissions, such as hydrogenbased industry, hydrogen-powered aircraft, the technology of producing green hydrogen from electrolytic water with high efficiency and low cost, and new materials. The R&D investment is also needed immediately to ensure that China is at the front end of the new technology competition. Net zero emissions will bring significant social and economic impacts, so strategic preparation will be necessary. In the future, the industrial layout will be significantly affected by low-cost renewable energy and nuclear power, thus the relay out of China’s industry would occur in the future. The energy and economic transitions need to be fail transition or harmonious transition. Some industries are affected negatively in the transition, and there are still nearly 15 million employees being affected. This will impact the livelihood of nearly 40 million people. The EU plans to invest 3 trillion Euros in fair transformation so as to make sure that “no one is left behind”. Similar arrangements are needed in China. China’s cumulative GDP will reach about CNY 6000 trillion by 2050, and about CNY 10 trillion can be used as the funds for ensuring fair transformation. Biomass-based CCS technology (BECCS) in the carbon neutrality pathway will perform important functions after 2040. The application prospect of the direct air capture technology will also become broader, which requires technical preparation at an early stage.

5.2 Addressing Climate Change and the Sustainable Development 5.2.1 The Linkage Between Addressing Climate Change and Sustainable Development Goals Sustainable development is an important choice for human development. Sustainable development emphasizes the coordination of economic, social and environmental aspects, covering a wide range of areas. In 2015, the United Nations Summit on Sustainable Development adopted the 2030 Agenda, which means that global sustainable development has entered a new institutional framework. The 2030 Agenda aims to enhance the sustainability of all developed and developing countries. It claims to be human-centered and strives to promote global environmental security, sustained economic prosperity, fair and harmonious society and enhance the partnership of related countries. This is the roadmap for achieving global sustainable development

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by 2030. The 2030 agenda includes a political declaration, 17 goals and 169 concrete targets for achieving sustainable development (SDGs), as well as the implementing measures and follow-up actions. It advocates nationally determined contribution and provides universal objectives for countries to formulate sustainable development strategies. Goals and targets are important contents in the agenda, which involve a wide range of topics, including poverty reduction, hunger eradication, health and well-being, high quality education, gender equality, clean water and sanitary fixture, clean and affordable energy, decent work and economic growth, industry, innovation and infrastructure, inequality reduction, sustainable cities and communities, responsible consumption and production, climate action, marine and terrestrial creatures, peace and justice, strong institutions, partnerships that promote the achievement of goals, etc. In essence, it defines the global development vision by 2030. SDGs address the fundamental causes of poverty and are committed to meeting the general needs for development. It is assured that everybody has a share in the progress, so the involved factors cover much wider ranges, with more long-term goals. The 2030 Agenda covers three dimensions of sustainable development: economic growth, social inclusion and environmental protection. Climate change is part of the great challenges sustainable development faces. Sustainable development is closely related to climate change. Under the framework of sustainable development, addressing climate change does not merely mean the traditional notion of emission reduction and adaptation. It expands to society, economy, ecology and the Earth system. The recent studies have focused on the above aspects, including the quantitative impacts of mitigation on sustainable development goals, the linkage with environmental goals, poverty eradication, food security, water safety, nature-based solutions and fairness and ethics, etc. The assessment conclusion of the special report on global warming of 1.5 °C issued by IPCC (IPCC SR1.5)states that the mitigation choices for implementing pathways of limiting warming to 1.5 °C share several synergies and balances with SDGs, and that the number of synergies is higher than that of balances. The final effects of these synergies and balances depend on the direction and extent of the impacts, as well as on the content of mitigation measures and the transition management. Mitigation is directly linked with SDG 7 (affordable clean energy), SDG 8 (decent work and sustainable economic growth), SDG 9 (industry, innovation and infrastructure) and SDG 12 (responsible consumption and production). Meanwhile, the definition of climate resilience is connected to all SDGs. In China, the study on the linkage between emission reduction scenarios and SDG is also underway. Among the SDGs whose correlations have already been identified, the quantitative analyses of 10 directly correlated indicators have already been done, as shown in Table 5.2.

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Table 5.2 Quantitative results of part of the SDGs indicators under the pathway for limiting warming to 2 °C in China Associated SDG indicators

Units

2010

2015

2030

7.1.1 Proportion of population using electricity

%

–

100

100

7.1.2 Proportion of population using clean energy and technology

%

46.1

52.7

65.9

7.2.1 Proportion of renewable energy in primary energy

%

10.5

15.7

27.0

7.3.1 Energy intensity per unit GDP

t oe/million USD (price in 2005)

501

387

185

8.1.1 Annual average growth rate of real per capita GDP

%

17.7

11.1

6.2

8.4.2 Domestic material consumption, per capita domestic material consumption, material consumption per unit GDP

t oe/million USD dollar (price in 2005)

638

523

135

t

2.08

2.65

1.74

1 billion passenger-km

3980

5339.5

10,634

Railway passenger transport

752

912

1385

Air passenger transport

360.4

606.8

1841.9

Waterway passenger transport

7

7

7

3565

5209

10,713

Railway freight

2692

3347.5

5576

Air freight

12

20.5

70

Waterway freight

7949

10,122.5

18,136

Pipeline freight

209

430

1540

9.1.2 Different types of transport volume: Passenger transport and freight transport

Road passenger transport

Road freight

1 billion ton-km

9.4.1 CO2 emission per unit added value

kg CO2/ million USD (price in 2005)

1.92

1.23

0.44

12.2.2 Domestic material consumption, per capita domestic material consumption, material consumption per unit GDP

t oe/ million USD 457 (price in 2005)

335

135

Average t oe

1.69

1.49

1.74 (continued)

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Table 5.2 (continued) Associated SDG indicators

Units

2010

2015

2030

12.5.1 National recovery rate and recovery amount

Million t

–

1142.9

1314.4

5.2.2 Climate Resilience and Risk Management As human beings deepen their understanding of global climate change and its impact, climate resilience has gradually become an important concept and framework for climate change risk management. Climate resilience requires the following abilities for the social-ecological system: (1) absorb the external press brought by climate change and ensure the normal operation of the system; (2) adapt, reorganize and develop a more ideal system configuration, improve the sustainability of the system and promote better development; (3) make full preparations to deal with the impacts of climate change in the future. The climate resilience framework can not only deepen our understanding of environmental processes, but also provide a platform of cooperation and exchange for researchers, engineers, governments and policy makers to put forward sustainable countermeasures to deal with the impacts of climate change. Due to the influencing factors and the key characteristics of climate resilience, the whole implementation process of the resilience action framework should be a nonlinear “closed loop” (Fig. 5.4). The implementation of climate resilience actions at all levels and scales should include the following functions: (1) understand problems and set goals; (2) identify options and associated consequences; (3) propose solutions; (4) monitor progress and adjust plans as necessary (Chen et al. 2019).

Fig. 5.4 A general framework for implementing climate resilience actions (Chen et al. 2019)

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China is one of the countries most seriously affected by climate change (especially extreme weather and climate disasters, cryosphere disasters, sealevel rise, etc.). Since entering the new century, the Chinese government has attached much greater importance to capacity-building for disaster reduction and emergency response related to climate change. From the aspects of system construction, operation mode and experience summary, a framework for disaster reduction and emergency capacity-building with Chinese characteristics has been established. The framework comprehensively considers the strategic positioning, work deployment, institutional mechanisms, working means and resource utilization of disaster risk management from an international perspective, which is conducive to effectively improving the national and local disaster reduction and emergency management capacity and minimizing disaster losses. However, the impacts of recent climate disasters in China are still very huge. In 2021, the flood in Henan province deprived 309 people of their lives. The occurrence frequency of the extreme weather is increasing and the affected range is expanding. Hence, China has to put the response and adaptation to climate change in a more important and urgent position and incorporate it into its policies (Chen et al. 2019). Mitigation, adaptation and transformation should be combined together in China’s future climate resilience capacity building, and it is necessary to establish a comprehensive monitoring, evaluation, early warning and decisionmaking system to control the evolution of the regional social ecosystem. The detailed solutions and processes are as follows: (1) strengthening the positioning observation, remote sensing monitoring, model simulation, socio-economic statistics, field investigation and participatory interviews as well as the analysis and application of Earth big data; conducting regular and in-depth monitoring and assessment of climate change and its impacts, including current status and expected future changes; through in-depth evaluation of the system operation status, identifying the problems existing in the system and on this basis making good early warning; (2)carrying out multidisciplinary dialogues among different stakeholders to find out potential solutions to strengthen resilience building for specific issues; (3) comprehensively evaluating the costs, benefits and risks of the implementation of different schemes, and making the most reasonable decision and planning; (4) continuously monitoring and evaluating system dynamics, including the implementation of solutions, and adjusting the initial plan when there is a better solution (Fig. 5.5) (Su and Xiao 2020). In general, relevant departments in China need to greatly enhance their awareness of the impacts of climate change in the future disaster management program construction and practice. They have to continue exploring the concept of climate resilience comprehensively and deeply, from pre-disaster monitoring, assessment and prediction, early warning and prevention to post-disaster coordination and flexible response, so as to establish a more holistic, refined and participatory disaster risk management framework (Chen et al. 2019).

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Fig. 5.5 Schematic diagram of climate resilience building frameword (Su and Xiao 2020)

5.2.3 Addressing Climate Change and Air Pollution Control Coping with climate change and atmospheric pollution control are the focuses of China’s current policies in the field of environment. Since China announced its climate change action plan in 2007, climate change has become the main component of China’s policy. The Atmospheric Pollution Prevention and Control Action Plan announced by the State Council of the People’s Republic of China in 2013 pushed China’s long-term action to control air pollution to a new stage. By 2020, China’s air quality had been improved significantly, exceeding the planned target. Meanwhile, since 2013, China’s CO2 emissions have also changed the upward trend in the previous ten years and entered a slow-changing platform period. Many atmospheric pollution control policies, such as policies to control the use of coal and other fossil fuels, are highly consistent with the policies to control CO2 emissions. The major and internal causes of the long-term change in atmospheric aerosol pollution in China are the changes in pollutant emission intensity. Inter-decadal warming has been impacting the long-term change trend of atmospheric aerosol pollution in the key regions and localized areas of China, but is not the dominating force. Scientific observations show that the winter peak concentrations of main chemical components in near-surface aerosols in the Beijing-Tianjin-Hebei region decreased as a whole from 2006 to 2010 but continuously increased from

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2013 to 2017. From 2013 to 2017, with the implementation of the “Ten Articles of Atmosphere”, the mass concentration of PM2.5 decreased significantly. The change in aerosol concentration in the Yangtze River Delta and the Pearl River Delta from 2013 to 2017 was basically in line with that in the Beijing-Tianjin-Hebei region. During a period of time when pollution emissions change little (e.g., winter of a year), adverse meteorological condition is the necessary external condition for persistent aerosol heavy pollution in key areas of China. After the accumulation of pollutants, the meteorological condition of the boundary layer tends to significantly “deteriorate”, forming a distinct two-way feedback between adverse meteorological conditions and pollution. The interaction between climate change and air pollution threatens human health. Climate change increases the frequency and intensity of heatwaves, and the interaction between high temperature and particulate pollution can cause a series of cardiopulmonary health problems, which are mainly manifested in the impacts on non-accidental death, cardiovascular disease death, respiratory disease death and pulmonary function. In addition to high temperature, low temperature also shows a synergistic effect with particulate matter, increasing the risk of death from cardiovascular and respiratory diseases. Moreover, climate change may accelerate the generation of ozone by increasing the concentration of the main precursors of ozone, threatening people’s health. Coping with climate change and air pollution control have obvious synergistic effects, and there are also some trade-offs. Air pollutants and greenhouse gases are of the same origins. In most cases, fossil fuel combustion is the main cause for air pollution and also is the source of greenhouse gas emissions. To meet the warming targets of the Paris Agreement through the technology, policies and measures of deep emission reduction and to reduce the emission of GHG and air pollutants concurrently will bring significant synergy benefits to climate, environment and health. More and more studies believe that the benefits of global and long-term response to climate change should be mapped to more local, regional and short-term air quality improvement, which will help to improve the public’s intentions better to tackle climate change. According to the Assessment Report on Coordinated Management of Urban Carbon Dioxide and Air Pollution in China (2020) issued by the Environmental Planning Institute of the Ministry of Ecology and Environment, from 2015 to 2019, about one-third of the 335 prefecture-level administrative units and municipalities directly under the central government achieved the coordinated emission reduction of CO2 and major air pollutants. However, in practice, there are often problems of “low-carbon but not environmental protection” or “environmental protection but not low-carbon”. For example, some energy-saving technologies in the cement industry tend to increase dust and NOx emissions. As the end treatment technology of CO2 , CCS can reduce the energy efficiency of thermal power plants and consume additional fossil energy, thus reducing carbon emission but increasing air pollution. Coal power plants, steel mills and other industrial processes are equipped with desulfurization and denitration devices to control end pollutants, which reduces air pollution emissions but increases carbon emissions.

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The main ways to achieve synergistic benefits of climate response and air pollution control are to strive to reduce the use of fossil energy from the beginning, improve energy efficiency and optimize energy structure. This includes slowing down the growth of coal demand, improving the centralized utilization of coal, reducing and improving the utilization form of bulk coal, increasing the energy conversion efficiency of the coal-power life cycle (such as adjusting thermal power structure, increasing the proportion of high-flux and high-efficiency coal-fired power units, and eliminating outdated units with small capacity) and developing renewable energy such as hydropower, wind power, solar energy and biomass energy to replace fossil energy and to meet the new power demand, etc. With the application of lowcarbon and zero-carbon power, the promotion of electric vehicles by the transportation department can also contribute to the synergistic benefits of carbon emission reduction and air pollution control. In addition to local emissions, the emission transfer of greenhouse gases and pollutants caused by international trade have different impacts on the economy and health of different countries. With the rapid development of economic globalization, trade links between different countries are becoming closer and more frequent. International trade separates production and consumption, leading to the transfer of CO2 and pollutant emissions. Researches show that more than 20% of global CO2 emissions are related to international trade. China and other emerging markets have higher production-side emissions than consumption-side emissions, so they are net exporters of transferred emissions. On the contrary, most developed countries have higher consumption-side emissions than production-side emissions, and are net importers of transferred emissions. In addition, the coordinated treatment of climate change and air pollution reduces the concentration of man-made aerosol in the atmosphere generating additional warming effects. In order to achieve the warming tarsets of the Paris Agreement and air pollution control, it is imperative to step up efforts to reduce CO2 emission and control air pollution. The emission reduction measures focusing on the adjustment of energy structure and industrial structure can reduce the concentrations of other types of aerosols in the atmosphere that have cooling effects on the climate system while reducing black carbon aerosols, thus reducing the cooling effect of aerosols. However, as the retention time of aerosols in the atmosphere is relatively short, the impact is often regional. At present, the understanding of the aerosol impacts on climate remains highly uncertain.

5.2.4 The Linkage Between Addressing Climate Change and Other Systems Climate change is closely linked to other ecosystems, such as water-energy-food, land use, forests, oceans and biodiversity. To achieve the goal of carbon neutrality, China needs to pay attention to the relationship between the complex ecosystems.

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As the stress of climate change intensifies, the relationship between climate change and water-energy-food becomes crucial (Romero-Lankao et al. 2017; Kanakoudis and Tsitsifli 2019). Water, energy and food are critical factors associated with human survival, and conductivity and expandability exist among the three elements. Any kind of security problems from them may constitute national, regional and even global security problems through related transmission mechanisms (Hoff 2011). The water-energy-food Nexus (WEF-Nexus) system is vulnerable to climate factors. Climate change may affect the efficiency of energy and food production, resulting in the decline of available freshwater resources (Fig. 5.6). China is in the accelerating stage of new industrialization and urbanization, and there is a great demand for water, energy and food. China’s water consumption, energy consumption and food consumption all rank first in the world. Most of China’s water resources are concentrated in the south, while agricultural production and energy reserves are concentrated in the north. For the WEF-Nexus system, the spatial distribution of collaborative security is generally characterized as high in the south, low in the north, superior in the east and inferior in the west. The spatial and temporal distribution of water resources, energy and food is unbalanced and mismatched, which greatly affects resource flow and transformation efficiency (Zhi et al. 2020; Li and Zhang 2020). WEF-Nexus also involves land use, forests, oceans and biodiversity (FAO and UNEP, 2020). With the impacts of climate change on vegetation distribution and socio-economic development, land use pattern has changed. Under the influence of climate change and human activities in the past, the composition of part of the forest, grassland and meadow, desert and wetland ecosystems in China has changed. The future climate change will continue to exert its influence on these ecosystems. In the past, climate change has changed the growth and reproduction of some plants, Fig. 5.6 Connection diagram of water-energy-food

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and these effects will continue in the future. In particular, extreme events have a great adverse impact on the structure and function of the ecosystem. There is a risk of continued loss of germplasm resources such as breeding animals and cultivated plants. Meanwhile, the distribution area of many species may expand. Climate change has also led to significant changes in the marine system, such as the increase of harmful algal bloom, change of dominant species, northward movement of warm water species of marine organisms, coral bleaching in low-latitude tropical waters, increased risk of mangrove and sea grass death and survival of benthos under threat. “Nature-based solution” (NBS) is an effective way for dealing with climate change and coordinating multidimensional relationships including food, water, energy, land, ocean and biodiversiting. NBS is also an important solution to achieve carbon neutrality. The concept of NBS was first proposed by the World Bank in 2008. In 2016, the International Union for the Conservation of Nature (IUCN) defined NBS as through protection, the sustainable management and restoration of nature or improvement of ecosystem, effective actions tailored to local conditions can be taken to meet social challenges improve human well-being and bring biodiversity benefits. According to the relevant studies, NBS has planned to make a 37% contribution to the 2 °C warming target under the Paris Agreement from 2016 to 2030. In 2020, the contribution of NBS to the targets of the Paris Agreement was affirmed in the “Zero Draft of the Post-2020 global biodiversity framework” proposed by UN Convention on Biological Diversity (CBD). NBS offers many pathways for mitigating climate change, including afforestation, sustainable forest management (planted and natural forests), avoiding deforestation and forest degradation, forest fire management, mixed agriculture (animal husbandry) and forest system, farmland management (conservation tillage, paddy water management, farmland nutrient management), straw biochar utilization, sustainable grazing, grassland protection and restoration, peatland protection and restoration, as well as coastal wetland protection and restoration (Griscom et al. 2017; Shukla et al. 2019; Zhang 2020). The NBS pathways with the greatest mitigation potential in China include farmland nutrient management, afforestation, avoiding deforestation, peatland protection, biochar, paddy water management, etc. (TNC 2020). These NBS climate mitigation pathways also have great synergies in addressing challenges such as food and water security, human health, disasters, and loss of biodiversity. Meanwhile, NBS pathways are able to enhance the climate resilience of ecosystems and also conducive to improving the ability to adapt to climate change in socio-economic fields such as agriculture, forestry, animal husbandry, fishery, water resources, cities, health and coastal zones. China’s NBS have played an active role in addressing climate change. These measures mainly include ecosystem protection and restoration, sustainable utilization of resources, wildlife protection, pest defense, delimitation of ecological protection red line, determination of ecological functional area and establishment of natural reserve system, etc. In Saihanba Forest Farm in Hebei Province vegetation restoration has been realized through afforestation. The Ant Forest, which is an online public welfare activity, advocates green and low-carbon behavior through users’ participation in raising virtual trees. The Kubuqi global Desert “ecological economy

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demonstration area” in Inner Mongolia has realized the transformation from “sand advancing and people retreating” to “green advancing and sand retreating”. Zhejiang Province’s “Thousand Villages Demonstration and Ten Thousand Villages Renovation Project” has rectified polluting enterprises in Zhejiang Province, making green mountains and green waters reappear. The governance of the middle reaches of the Yangtze River has been carried out in Hubei and Jiangxi Provinces for the sake of freshwater management and adaptation to climate change. The mangrove wetland restoration action in shenzhen Bay Coastal Area has changed the trend of ecological function degradation of the mangrove welland system, through mangrove wetland protection, sustainable management and replanting of mangroves. China needs to strengthen the role of NBS when tackling climate change in the future. The NBS should be integrated into national governance, climate action and climate policy tools. The governance and financing of NBS at home and abroad need to be promoted and the nature should be endowed with higher values. The international and regional cooperation about NBS needs to be strengthened focusing on the Belt and Road Initiative green development of international alliance, actively promoting the NBS action initiative for “delineating the ecological protection red line”, taking NBS as a collaborative solution to climate change and biodiversity loss, and providing Chinese wisdom and solutions for the world environmental governance and sustainable development. In addition, the NBS needs to be integrated into the overall planning, system design, organization and implementation, performance evaluation and supervision of energy, grain, mountain, water, forest, field, lake and grass. The balance between terrestrial ecosystem and marine ecosystem need to be considered comprehensively and the relationships among energy, water and food should be coordinated. China needs to set appropriate green development guiding objectives according to different environmental capacities and resource carrying capacities, and carry out regional coordination from the aspects of resource category, development intensity and utilization efficiency. The development of water-energy-food in function areas needs to be under differentiated control, the long-term observation and systematic research on offshore ecosystems need to be strengthened, including China’s marine work in addressing climate change. The multi-level policies for biodiversity conservation must be improved and new conservation technology for species diversity needs to be developed. The building of the biodiversity protection network needs to be enhanced, including protecting restoring species habitats and biodiversity through sustainable management and actions to restore nature or improve ecosystems. In a word, China needs to enhance the security of the water-energy-food system and the ability of ecosystems to cope with climate change.

5.2.5 Tackling Climate Change and Eradicating Poverty Poverty eradication is the primary goal of global sustainable development. Climate change may exacerbate the problem of poverty, and China has made important contributions to the achievement of the global poverty reduction

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goal. Climate change will aggravate the risk of extensive, serious and irreversible impacts on human and social ecosystems, especially in developing countries, leading to the emergence of new poor people in low-income, middle-income and even highincome groups. Since the implementation of the 2030 Agenda, positive progress has been made in terms of global poverty reduction. However, COVID-19 began to spread globally, bringing a great impact on the global economy, thus causing tens of millions of people to fall into extreme poverty, especially in the least developed countries (WHO 2020). China has made tremendous efforts to reduce poverty. Since the Communist Party of China (CPC) Central Committee of China put forward the concept of targeted poverty alleviation in 2013, China has innovated the poverty alleviation working mechanism, and shifted the poverty alleviation policy from offering assistance to boosting development. Strengthening ecological construction is a significant step for poverty alleviation in the response to the adverse effects of climate change. By the end of 2020, under the current standards, 98.99 million rural residents had been lifted out of poverty. China has become the first developing country in the world to achieve the UN’s poverty reduction goal, contributing more than 70% to global poverty reduction. Climate change policies and actions may affect the income and livelihood of some populations, but they also provide new opportunities for rural areas to get rid of poverty and become better off. Climate change measures, especially carbon peak and carbon neutral targets, have a far-reaching impact on coal and other high energy consumption and high pollution industries, resulting in unemployment or the decline in employee income. If measures to promote reemployment and social security are not in place, new poor people may appear. However, promoting fair transformation and developing green and low-carbon industries also bring new opportunities for rural areas to get rid of poverty and become better off. For instance, since the 18th National Congress of the Commauist Party of China, poverty reduction through clean energy has served as an important poverty alleviation policy in China. From 2014 to 2019, there were 26.36 million kW photovoltaic poverty alleviation power plants built totally nationwide, benefiting nearly 60,000 poor villages and 4.15 million poor households. About CNY 18 billion revenues can be obtained from these power plants every year, and accordingly 1.25 million public welfare posts have been placed. From 2017 to 2019, China allocated a total of CNY 1.3 billion from the central government budget to build rural hydropower plants for poverty alleviation with an installed capacity of 324,000 kW, and more than 30,000 registered impoverished households have benefited from the hydropower development. Since 2012, 31 large hydropower plants with 64.78 GW installed capacity have been built in poor areas, generating a large number of local employment opportunities. In addition, emission reduction policies such as carbon sink trading provide new ideas and methods for targeted poverty alleviation. For example, China Certified Emission Reduction (CCER) certification of agriculture and forestry was carried out in poor areas in Hubei Province, and a targeted poverty alleviation pilot of carbon sequestration per plant was underway in severely impoverished villages of Guizhou Province. Such measures have not only increased farmers’ income, but also enhanced their awareness of coping with climate change through training. Poverty alleviation is only the first

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step. The goal of carbon peaking and carbon neutrality will cause profound social and economic transformation, scientific and technological progress, as well as policy guidance, which can create more and more new development opportunities for green development into invaluable assets.

5.2.6 Addressing Climate Change and Fairn Ethics The issue of climate is indeed a natural science issue, but its nature involves complex problems such as economy, politics, law, ethics and so on. Fairness has always been the core issue and basic principle of addressing climate change. It involves intergenerational equity and intragenerational equity and is the key factor to achieving global sustainable development. Evaluating climate policy should be based on sustainable development and equity because equity is an important cornerstone of international climate cooperation. All parties in global climate governance recognize the importance of fairness and equality; however, there are often great differences on what fairness is and how to reflect fairness in the construction and development of the international system. The option of discount rate in the comprehensive evaluation model implies different understandings of the connotation of fairness and priority. Some people set a higher discount rate, pay more attention to the survival and development of modern people, and tend to believe that future generations are more affluent and can bear more costs for adapting to future climate change. Others choose a lower discount rate and take the intergenerational equity into account. They tend to believe that modern people should reduce emissions as soon as possible to avoid greater losses in the future as the result of climate change. The bottom-up emission reduction mode of the Paris Agreement cannot avoid the debate on fairness. The assessment results of different international institutions on the emission reduction gap and national NDC efforts reflect different equity concepts. Some people believe that the marginal cost of emission reduction varies greatly among different countries, and China’s emission reduction target still has a big room for improvement. Different from this, some studies believe that China has a made a large contribution to global emission reduction (Jiang et al. 2019; Teng 2019). In the post-Paris process, fairness remains the focus of the game among major countries, aiming to the issues such as global inventory, enhancing actions, and strengthening mechanisms and measures to provide supports to developing countries. China has a vast territory and there exist big regional differences in the impacts from climate change. The regional differences have to be considered in the policy-making process for tackling climate change. Climate change has different impacts on different regions, and there are also temporal and spatial differences in terms of resources, economic development level, industrial layout, carbon emission intensity, emission reduction targets and transfer of emissions among different provinces. Hence, when formulating climate change policies, differentiated policies have to be proposed according to local conditions, so as to optimize the

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allocation of resources and better mobilize the enthusiasm of all localities to deal with climate change. Under the targets of the Paris Agreement, achieving carbon neutrality means profound social and economic transformation, so the issue of fair transformation has attracted great attention. Achieving carbon neutralization not only needs the transition of the energy system to realize zero or even negative emissions, but also needs all sectors and industries to realize carbon peaking as soon as possible and implement deep reduction as much as possible. During there processes, the impacts on coal and its relevant industries bear the brunt, which the livelihoods of the affected vulnerable groups. Thus, promoting fair transition has become an important part of strategies in different countries when dealing with climate change (Zhang 2020).

5.3 Global Climate Governance to Help Build a Community with a Shared Future for Mankind The core of global climate governance is to curb climate change in a more fair and effective way, to turn the challenges and pressure of coping with climate change risks into opportunities and driving forces for global green and low-carbon development, and to achieve a win–win situation between climate protection and human economic and social development. This process itself is an exploration and practice of building a community with shared future for mankind, and it is an important component of global governance. The Paris Agreement in 2015 marked a new historical stage of global cooperation in addressing climate change. In September 2020, China put forward the long-term goal of achieving carbon neutrality by 2060, which means that China will move towards the path of green, low-carbon, circular sustainable development while ensuring sustainable economic and social development. Guided by the concept of building a community with a shared future for mankind, China will play a more active role in the global climate governance by means of multi-party cooperation, inclusiveness, mutual learning and win–win cooperation.

5.3.1 Global Climate Governance System and Its Challenges 1. Global Climate Governance System and China’s Contribution Global climate governance refers to the collection of policies and actions to address climate change from global to regional, national and local levels as wells individuals. Tacking climate change requires global joint efforts to achieve fruitful results. The current global climate governance system is a compound mechanism with international climate change law as the core. This compound mechanism mainly includes the international law system composed of the UNFCCC, the Kyoto Protocol, the Paris Agreement and the decisions made in the conferences of the

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parties; the control mechanisms for greenhouse gas emissions and climate change adaptation actions taken by the Montreal Protocol and other climate change-related treaties, and international organizations such as the International Civil Aviation Organization and the International Maritime Organization; multilateral mechanisms such as G20 and the Major Economies Forum on Energy and Climate; political guidance and action from intergovernmental cooperation platforms or initiatives for global response to climate change; the promotion of tackling climate change as well as green and low carbon development supported by the Belt and Road Initiative and other government and non-governmental transnational cooperation mechanisms; and international cooperative actions on climate change initiated by non-state actors. It also includes the judgment of the academic community as a whole on climate change and its response and impact on international and national decision-making. The international climate change law system has established the basic principles of global cooperation in dealing with climate change, but it also faces new challenges. The international climate change law system is legally binding on sovereign states as Parties. Therefore, it is at the core of global climate governance. However, in recent years, various non-state actors have actively participated in global climate governance. Their participants, fields and forms are diversified, and their actions are not bound by international law. While actively promoting countries to fulfill their international treaty obligations, the non-state actors also bring challenges to the international law system. The international climate change law system itself has also changed during the developing processes in recent 30 years. The associated parties have differences in understanding the “principle of fairness, common but differentiated responsibilities and respective capabilities” established by the UNFCCC. However, the guiding ideology advocated by this important principle, still applies to the guiding principle of common but differentiated obligations of countries according to their historical responsibilities and respective capabilities for global climate change, Meanwhile, under the international climate change law system, the performance rules of the parties have also changed significantly, which are mainly reflected in the way of undertaking emission reduction obligations, the main body of providing financial support, the procedural rules of performance, etc. China has always been an important participant in the construction of the global climate governance system and will play a more active role in the future. On December 21st, 1990, the 45th session of the United Nations General Assembly adopted the Resolution 45/212, which decided to establish the Intergovernmental Negotiating Committee for a Framework Convention on Climate Change Later, the United Nations Framework Convention on Climate Change (UNFCCC) was adopted on May 9th, 1992 and entered into force on March 21st, 1994; the Kyoto Protocol was adopted on December 11th, 1997 and entered into force on February 16th, 2005; adminnd the Paris Agreement was adopted on December 13th, 2015. International negotiations on climate change have gone through a long and tortuous process, and China has always been an active participant in the establishment of an international system to deal with climate change. At the UN Climate Change Conference, Paris 2015 Chinese President Xi proposed to jointly create a future global governance mode of doing everything according to one’s ability, win–win cooperation, upholding the

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rule of law, fairness and justice, inclusiveness, mutual learning and common development. China is the largest developing country and the second largest economy, and these ideas will not only be the basic guidelines for China to promote the implementation of the Paris Agreement and the follow-up system construction, but also the direction for China to further participate in the global system construction actively and constructively with a responsible attitude. 2. Global Climate Governance Pattern After the Paris Agreement The Paris Agreement is a landmark document in the process of international climate governance, marking a new stage in the global response to climate change. The Paris Agreement entered into force on November 4th, 2016. It reaffirms the “principle of equity”, “principle of common but differentiated responsibilities” and “principle of respective capabilities” as defined in the UNFCCC. It claims clearly to hold the increase in the global average temperature to well below 2 °C above pre-industrial levels and pursue efforts to limit the warming to 1.5 °C. It also establishes the action mechanism with “national determined contribution” as the core concept. It is the first climate agreement that covers all countries and has been unanimously agreed. And it is the first time that developed and developing countries have promised to undertake their respective obligations and contributions in a differentiated manner within a unified institutional framework. Unlike the Kyoto Protocol, the Paris Agreement defines a “bottom-up” action mechanism with NDC as the core concept. In order to make up for the insufficiency of global action strength that may result from this mechanism, the Paris Agreement also establishes a global review mechanism with a five-year cycle, which aims to promote countries to raise emission reduction gradually in the future in the way of only increasing but not decreasing. The Paris Agreement can promote the process of the global response to climate change and facilitate the low-carbon transformation of the global economy with urgent global long-term emission reduction targets. From the perspective of mechanism, the entry into force of the Paris Agreement can have a far-reaching impact on economic development, energy consumption, environmental governance, financial mechanism, and technological innovation. It has greatly boosted the confidence of industry and commerce in green and low-carbon transformation, significantly increasing green investment, supply and employment, and sending a positive signal that the world will achieve green, low-carbon, climate adaptive and sustainable development. The Paris Agreement establishes the goal of “achieving balanced carbon neutrality between anthropogenic greenhouse gas emissions and sinks by the end half of the twenty-first century”. Compared with before, it emphasizes the urgency of low-carbon and even non-carbon energy more explicitly. Since CO2 emissions from energy consumption account for about two-thirds of all greenhouse gas emissions, net zero emissions in the second half of the twenty-first century mean the need to end the era of fossil energy and establish a low-carbon or even zero carbon energy system dominated by new and renewable energy. This will accelerate the revolutionary change of the energy system around the world.

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In the post-Paris Agreement global governance, the core issues will be how to build mutual trust through setting up the principle of transparency, exerting constraints on the Parties’ performance and encouraging actions to deal with climate change. The Paris Agreement adopts the mode of nationally determined contribution in which the efforts are determined by countries themselves. As for the degree of the effort made by each country for the mitigation, adaptation and support, or whether these objectives are realized or not, neither of them was the obligation of the Parties under the Paris Agreement. Political accountability for the progress of the Parties in fulfilling their substantive obligations can only be based on transparency and procedural obligations. Therefore, strengthening transparency has become the basis and key to ensuring the effectiveness of the Paris Agreement system. The “bottom-up” commitment mode of the Paris Agreement cannot decompose and implement the global quantitative goals to all countries, which brings uncertainty to the realization of the global goals. In order to achieve the global warming target of 2 °C, developing countries need an additional USD 300 billion to USD 1 trillion in financial support every year. In the construction of the future global climate governance system, both governments and academia need to pay more attention to the differences in technology application costs caused by resources, industrialization and urbanization stages, infrastructure and human resources and put forward more practical and fairer action measures accordingly. Global climate governance faces challenges and variables, but it has not changed the overall trend of global cooperation in dealing with climate change. In 2017, the Trump administration of the United States announced its withdrawal from the Paris Agreement. As the world’s largest economy and major emitter, the withdrawal triggered a further deficit in the already insufficient collective emission reduction and financial support in the world. According to the Nationally Determined Contribution of the United States, if there were no emission reduction at all, the global emission reduction gap would increase by 10%. And in recent years, the funds provided by the United States to developing countries to deal with climate change account for 12% of the total financial support form developed countries. The United States decided not to fulfill its obligation any more to provide financial support to developing countries, which will impose difficulties on the performance of developing countries and the global response to climate change. Facing the leadership gap in the global climate governance system after the United States’ withdrawal, the international community hopes that all major participants will shoulder greater responsibilities and play more active roles. In January 2021, the new President Biden of the United States signed an executive order on the day he took office, announcing that the United States will return to the Paris Agreement, and then the United States formally rejoined it in February 2021. In summary, global cooperation in dealing with climate change is the general trend. China has made it clear that the Paris Agreement is in line with the global development trend and cannot be lightly abandoned, and has proposed to adhere to the principles of fairness, common but differentiated responsibilities and respective

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capabilities. Meanwhile, China has constructively participated in and led international cooperation in addressing climate change in a bid to promote the implementation of the UNFCCC and the Paris Agreement. In September 2020, China announced that it would strive to achieve carbon neutrality by 2060. The EU issued the Green New Deal at the end of 2019, promising to achieve climate neutrality by 2050, and formulated the road map of policies and measures in seven aspects including energy, industry, construction and transportation etc. Even during the period when the Trump administration of the Unite States announced its withdrawal from the Paris Agreement, the state-level actions in the United States to deal with climate change continued. So far, more than 100 countries and regions around the world are willing to become carbon neutral by 2050. These trends indicate that the development and competition in the field of low-carbon technology will be an important area of concern for all countries in the future. 3. Global Governance System Under the COVID-19 Pandemic The COVID-19 pandemic has brought about a profound and complex impact on the international community, but it has only temporarily reduced global greenhouse gas emissions. The COVID-19 pandemic, which began at the end of 2019, spread rapidly in the world and changed the global political and economic development prospects, leading to a short recession in the global economy and aggravating the tendency of anti-globalization. The global polarization between the rich and the poor has become even more serious under the pandemic. Traditional multilateral cooperation mechanisms cannot effectively cope with many global problems, including infectious diseases, which has brought a complex and far-reaching impact on the international community (Zhang 2020). The economic stagnation caused by the pandemic has led to a temporary reduction in global greenhouse gas emissions. The short-term emission reduction is mainly concentrated in the road transportation, power and industrial sectors, of which the aviation industry has the largest emission reduction, but has a small contribution to the overall emission reduction. In early April 2020, the daily CO2 emissions of global fossil fuels decreased by 17%, and from January to April 2020, the daily CO2 emissions of global fossil fuels decreased by 7.8–8.6% compared with those in the same period in 2019. The follow-up conditions will depend on the duration of the pandemic and the control measures (Le Quéré et al. 2020). The study of post-pandemic emission scenarios shows that if countries can focus their post-pandemic economic stimulus plans on low-carbon areas, it will help to achieve the objectives of the Paris Agreement (Forster et al. 2020). Thus, all countries have the opportunity to strive for green, circular and low-carbon development and create win–win situations for pandemic control, economic development and low-carbon construction (Yu 2020).

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Addressing climate change remains a long-term and deep-seated challenge for human society. The outbreak of COVID-19 is a sudden and urgent crisis impacting human health and life, while climate change is a deep challenge that threatens human survival and development on a much longer-time scale. While the COVID-19 pandemic has destroyed the stability of the international community and become an uncertain factor that hinders global economic development, it has also provided historic opportunities for solidarity and cooperation among all countries. All of the countries need to reach the consensus that economic recovery can be realized by means of green and low-carbon development. Facing major crises such as the COVID-19 pandemic and climate change, human beings need to rethink the relationship between mankind and nature, respect nature, conform to nature and protect nature. Meanwhile, human beings need to pay more attention to the harmonious coexistence between man and nature, make overall plans for the current and long-term development, and take precautions to meet global challenges.

5.3.2 Sustainable Management Concept of Earth System and Scientific Assessment Support 1. The Concept of Sustainable Management of Future Earth System The scientific community has put forward new ideas to reduce the irreversible deterioration of climate and ecological environment caused by excessive interference of human activities. With the rapid growth of the world economy and population, human society is facing severe challenges brought about by the changes in global environment. In order to provide the necessary theories, research means and methods for global sustainable development, the Future Earth (FE) research programme was set up in June 2012, aiming to facilitate the close combination of natural science and social science, popularize knowledge to society and provide evidence for decision makers. With all these efforts, global sustainable development will be promoted. In January 2019, the Future Earth announced the establishment of the Earth Commission jointly with the International Union for Conservation of Nature. The Earth Commission brought together the world’s top scientists to carry out the assessment of the Earth system, and to set scientific goals for the Earth’s life support system (such as water resources, land, ocean, biodiversity, etc.) similar to the “global warming of no more than 2 °C above the pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5 °C” as stipulated in the Paris Agreement in a bid to support measures for the safety status of the Earth system with stability and resilience. The Earth Committee proposed the concept of a “Safe and Just Corridor” for the development of the Anthropocene, a pathway through which the Earth system can continue to support the prosperity and development of all life, including human beings. This concept aims to guide cities, enterprises and other actors to set goals and carry out the sustainable management of the Earth system on a

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global scale. The Earth Committee has been also aware that the populations that have the lowest resilience and adaptability and contribute the least to emissions are often affected most by the changes in environment. Things like biodiversity may never return to their Holocene state. In addition to the fairness of human beings, themselves, it is necessary to take into account the basic fairness of other creatures on the Earth, promote the harmonious coexistence and coordinated development between man and nature, realize the sustainable development transformation of human society, and protect the green planet. 2. Support and Guidance of Scientific Assessment of Climate Change The previous assessment reports of IPCC have continuously strengthened the authenticity, severity and urgency of global warming and become the most important scientific basis for global climate governance. In order to explore the causes and impacts of global climate change, the World Meteorological Organization (WMO) and the UN Environment Programme jointly initiated the establishment of IPCC in 1988. Scientists recommended by governments of different countries conduct systematic assessments of climate change based on the research results published all over the world. These reports have gathered the latest scientific research results of climate change in the world and gone through strict expert and government review processes, having been considered as authoritative and mainstream consensus documents on scientific understanding of climate change. The conclusions of these reports on the authenticity, severity and urgency of global warming have a profound impact on the trend of climate change response mechanism. They have not only promoted the formulation of the UNFCCC, the Kyoto Protocol and the Paris Agreement, but also become the major scientific basis for the governments of various countries to formulate their own policies and measures to address climate change. The focus of IPCC assessment has shifted from the scientific facts of climate change to the response mechanism and effectiveness. IPCC assessment has been closely connected with the SDGs, and will continue to have a profound impact on the trend of global climate governance. Based on the previous four assessment reports, IPCC AR5 quantitatively assesses the cumulative emission budget under the 2 °C warming target for the first time. It is considered that the global average surface warming at the end of the twenty-first century and beyond mainly depends on the cumulative emission of CO2 , In the future, compared with the warming of 1 °C or 2 °C above pre-industrial levels, the global risk will be at a medium to high-risk level. The scenario that is most likely to control the global warming within 2 °C above pre-industrial levels in 2100 is to control the greenhouse gas concentration at 450 ppm CO2 equivalent. The special report on the global warming of 1.5 °C released by IPCC in 2018 pointed out that achieving the warming target of 2 °C requires reducing CO2 emissions by 20% from 2010 to 2030, reaching net zero emissions around 2075. By the end of 2017, since industrialization, human beings had emitted 2200 billion tonnes of CO2 . At present, the CO2 emitted by human activities is 42 billion tonnes per year. Under the probability levels of 50% and 66%, limiting warming to 1.5 °C requires the cumulative emission of no more than 580 billion tonnes and 420 billion tonnes respectively, which means that even if the current

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emission rate remains the same, the total emission budget under the 66% probability level will be exhausted within 10 years. IPCC AR6 WGI report was released in August 2021. It recognizes that there is a quasi-linear relationship between global warming and cumulative anthropogenic CO2 emissions. The cumulative CO2 emission per 1 trillion tonnes will increase the global surface temperature by 0.27–0.63 °C, with the best estimate of 0.45 °C. Under the probability of 50%, limiting warming to 1.5 °C means 500 billion tonnes of CO2 emission budget, but if the warming target is 2 °C, the emission budget is 1350 billion tonnes, slightly higher than 1120 billion tonnes in AR5. Such series of assessments covering the scientific facts, emission budget, pathways and technology options of climate change have closely, connected science to policy closely, strengthening the scientific basis of global actions to deal with climate change, and affecting the formulation of national strategies and policies in this domain in all countries. In particular, IPCC AR6 is closely related to the 2 °C warmiy target of the Paris Agreement and its “pursuing efforts to limit the temperature increase to 1.5 °C”. It highlights the guiding role of providing solutions to the practical problems faced by global sustainable development and will promote the realization of global emission reduction targets under the new climate governance pattern.

5.3.3 Coordinate International and Domestic Efforts to Actively Tackle Climate Change 1. Addressing Climate Change and Building an Ecological Civilization Actively coping with climate change is in line with the thought of ecological civilization. Adhering to green, circular and low-carbon development is an important measure to promote high-quality sustainable development. In April 2015, China issued the Opinions on Accelerating the Construction of Ecological Civilization, pointing out that we should accelerate the construction of ecological civilization from a global perspective and promote global ecological security. The concept of ecological civilization proposed by China is not only the inheritance of sustainable development, but also the extension and expansion of the theory of sustainable development. On the one hand, the theory of ecological civilization is highly consistent with the concept of sustainable development. The two notions are highly unified in terms of development venation and implementation approaches. Both emphasize man and man that green economy is the inevitable choice to achieve sustainable development, and sustainable development can be achieved through green, low-carbon and inclusive economic growth. On the other hand, ecological civilization emphasizes the harmonies between man and man, and also between, man and nature. It views the relationship between man and ecology from the perspective of the rise and fall of civilization, and more highlights the shaping and transition of the view of values. Through the transformation of ideological concept and ethical values, ecological civilization guides the transformation of development concepts and behavior, and then

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promotes a series of changes in industrial structure, growth pattern and consumption pattern. Therefore, it is not only the transformation of development pathways, but also the transformation of development thinking. Fundamentally, addressing climate change lies in changing the patterns of economic growth and social consumption, adjusting the industrial structure, promoting technological innovation, improving energy efficiency and emission reduction, and optimizing the energy structure. This is consistent with the goal and policy of promoting the construction of ecological civilization, and the two interlinked notions will be important measures to promote China’s high-quality sustainable development. Striving to achieve carbon neutrality by 2060 means that efforts need to be made to support the sustainable development of economy and society with more efficient and minimum resource and energy consumption. The determination to realize carbon neutrality by 2060 is actually to strive to implement the long-term deep decarbonization transformation pathway guided by the 1.5 °C goal. Take the energy system as an example. It will be necessary to build a “net zero emission” energy system with new and renewable energy as the main part by 2050, in which non-fossil energy will account for more than 70% to 80% of the whole energy system.1 It is necessary to develop circular economy, digital economy and hightech industries, promote low-carbon by digitization, control the development of high energy consuming and heavy chemical industries, adjust the product and industrial structure, and reduce greenhouse gas emissions during the process of maintaining sustained economic development. Meanwhile, implementing NBS in agriculture, forestry, land use, grassland and wetland, strengthening the protection, governance and restoration of the ecological environment, and improving the service function of the ecosystem as well as increasing carbon sinks will be important measures for China’s future development transformation. China has only 30 years of transition period from carbon peaking to carbon neutrality, which means that China needs to carry out much larger-scale energy consumption and economic transformation and support sustainable economic and social development with the least resources and energy consumptions. Taking this as guidance, China needs to coordinate the two overall situations of domestic sustainable development and global response to climate change, follow the concept of green, circular and low-carbon development, identify the of low-carbon economic development path that is compatible with the global climate change and emission reduction targets and promote the energy revolution and the transformation of economic development mode so as to create a win– win situation in economy, people’s livelihood, resources, environment and climate change mitigation. The 14th FYP for China’s National Economic and Social Development and the Outline of Long-term Goals for 2035 clearly put forward the needs to actively respond to climate change, implement the nationally determined contribution goal of China to climate change in 2030, and formulate an action plan for peaking carbon emissions 1

Summary of the Comprehensive report on “China’s Long-Term Low-Carbon Development Strategies and Pathways”, Institute of Climate Change and Sustainable Development, Tsinghua University, July, 2020.

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by 2030. It is imperative to pursue efforts to achieve carbon neutrality by 2060 and adopt more powerful policies and measures. 2. Addressing Climate Change and Building a Community of Shared Future for Mankind Global climate governance is a global issue that best reflects the common destiny of mankind in today’s world. Actively participating in the construction of the global climate governance system is an important practice for China to promote the construction of a community with a shared future for mankind. China actively advocates the concept of building a community with a shared future for mankind and, with the strong responsibility of a responsible power, promotes the development of the global governance system in a fairer and more reasonable direction. “Promoting the construction of a new type of international relations and a community with a shared future for mankind” has become the general goal of great power diplomacy with Chinese characteristics and has been included in the basic strategy for the development of socialism with Chinese characteristics in the new era. In its longterm practice of participating in global climate governance, China has formed a systematic view on the subject. With win–win cooperation, fairness and rationality as the core notions, it includes the thought of social justice in Chinese traditional culture, Chinese international relations theory, new international relations and the concept of a community with a shared future for mankind (Bo 2019). Building a community with a shared future for mankind provides a higher-level conceptual basis for China to promote global climate governance, and also offers China’s concept, discourse, pathway and vision for global climate governance (Li 2018). China has actively and constructively participated in global governance and multilateral processes, and made positive contributions to the adoption of the Paris Agreement. This is also a concrete embodiment of building international relations with mutual respect, fairness and justice, and win–win cooperation, and building a community with a shared future for mankind. China advocates the new concept of global climate governance featuring win– win cooperation, fairness, justice and common development, and regards the cooperative response to climate change as an opportunity to promote the sustainable development of all countries. Addressing climate change is the common interest of all mankind. All countries have strong willingness to cooperate, extensive cooperation space and converging interests, but there are also complex contradictions and games among countries and national interest groups. It is the most challenging international issue with intergenerational externality that human society has to face. Speaking at the general debate of the 75th session of the United Nations General Assembly, Chinese President Xi pointed out that mankind needs a self-revolution to accelerate the formation of green development and lifestyle, and build ecological civilization and beautiful Earth. The Paris Agreement on climate change represents the general direction of the global green and low-carbon transformation and is the minimum action to be taken to protect the Earth. All countries must take decisive steps to establish a new development concept of innovation, coordination, green, openness and sharing. They need to seize the historic opportunity of a new round

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of scientific and technological revolution and industrial reform, promote the “green recovery” of the world economy after the pandemic, and bring together a strong synergy for sustainable development. China has promoted the construction of the Green Silk Road by strengthening exchanges and cooperation in addressing climate change, marine cooperation, wildlife protection and desertification control. The Belt and Road Initiative was launched by China’s national leader, covering a wide range of fields including policy coordination, unimpeded trade, financial integration, facilities connectivity, and people-to-people bond. The Belt and Road Initiative adheres to the principles of extensive consultation, joint contribution and shared benefits, and upholds the concepts of openness, integrity and environmental friendliness. It is an important platform to promote the construction of a community with a shared future for mankind. Countries along the Belt and Road Initiative have huge populations, relatively high carbon energy endowments, and fragile ecological environments. They face challenges in various aspects such as economic development, energy structure and environmental protection. Overall, in these countries, economic growth has not been decoupled from resource consumption and pollutant emission, and they are in the key period of green and low-carbon transformation. The dilemma between economic development and fragile ecological environment is the challenge for the countries and regions along the Belt and Road Initiative. According to the statistics of Hopkins University, from 2000 to 2015, most of China’s investment in Africa was in renewable energy industry, among which USD 10 billion was invested in hydropower, and about USD 1.5 billion was invested in solar, wind and geothermal power generation; only USD 2.2 billion was invested in coal-fired power and USD 1.9 billion in gas-fired power generation. This means that China’s investment in non-fossil energy projects was far more than that in fossil energy projects in the power industry of African countries (Brautigam 2018). To build a Green Silk Road, China and countries along the route must estimate the pressure on the ecological environment caused by crossborder economic cooperation from the perspective of top-level design. It is necessary to prepare countermeasures in advance to mitigate the possible negative impacts on the ecological environment. Ultimately, the Belt and Road Initiative serves for the construction of a community with common prosperity, sustainable development and a shared destiny. China has put forward the long-term goal of striving to achieve carbon peaking by 2030 and carbon neutrality by 2060, which is a concrete action of China’s adherence to the concept of ecological priority, and green, circular and low-carbon development. China will move towards the path of green, circular and low-carbon development while ensuring sustained economic and social development. And China will provide its own experiences for the transformation of global low-carbon development. Guided by the concept of building a community with a shared future for mankind and by the principles of multi-party cooperation, inclusiveness, mutual learning and win– win cooperation, China will promote the cooperation among countries in addressing climate change. It is the inevitable path for constructing an international peaceful and stable order which is essential to the realization of the Chinese Dream. And it is also

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the strategic choice to safeguard national interests as well as the common interests of the world.

5.4 Addressing Climate Change: Our Shared Future According to the report of IPCC AR6 WGI, in the next two or three decades, the global warming is likely to reach and even exceed 1.5 °C. The probability of concurrent extreme events in many regions of the world will increase. Heatwaves tend to be accompanied by drought. Extreme sea level events, characterized by storm surges, ocean surges and tidal flooding will be superposed by the composite flood events caused by severe precipitation. This kind of extreme events will intensify in the future. By 2100, on the premise of effective measures, more than half of the coastal areas will encounter once-in-a-century extreme sea level events every year. Superposed by extreme precipitation, the extreme sea level events will result in more frequent occurrences of floods. In particular, the outburst of critical elements of climate change, such as the collapse of the Antarctic ice sheet and the sudden change of ocean circulation cannot be ruled out. Once it happens, it will bring very serious damages to the Earth’s living environment. The eport of IPCC AR6 WGI clearly states that the warming is triggered by greenhouse gas emissions caused by human activities. In order to avoid severe effects, human society must take measures to control the rise of temperature. For China, it is likely that the warming will exceed the global average, and the negative impacts will be more serious. Recent climate disasters have been a very clear signal. The impacts of climate change do not result in immediate and drastic change, but these impacts have already been observed and felt. Such changes makes our life impossible to go back to the past, and this change will become more and more obvious in the future. The goal of warming set by the Paris Agreement is a goal that needs the efforts of the whole human society. It is our shared future. For the warming target of the Paris Agreement, the global CO2 emission needs to be reduced by more than 50% by 2050 (2 °C warming target), and the net zero emissions of CO2 to be realized around 2050 (1.5 °C warming target). The objectives of the Paris Agreement can be achieved with joint efforts, but such efforts require great input and have to be carried out immediately. With technological advances, the costs of photovoltaic and wind power have drastically declined, and, moveover, the nuclear power technology has been more and more mature, so the cost is also going down gradually. As the economy aggregate keeps increasing, we are confident that we are capable of coping with climate change. By November 2021, 136 countries and regions in the world have formally committed to realizing carbon neutrality target by 2050, covering nearly 88% of global emissions. In December 2019, the EU announced that it would achieve greenhouse gas neutrality by 2050. In September 2020, China announced striving to

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achieve carbon neutrality by 2060. The EU, the United States, Japan and other countries and regions have increased their emission reduction targets by 2030 significantly. China has also increased the 2030 target originally promised in the Paris Agreement, and set targets for the emission reduction of non-CO2 greenhouse gases. After assessing China’s scenario studies, this book believes that China is likely to achieve deep CO2 emission reduction or net zero emissions by 2050. so as to support the goals of the Paris Agreement. Implementing such emission reduction pathways, needs to increase investment in zero-carbon power, including renewable energy (such as photovoltaic, wind power and hydropower), nuclear power and power grid construction. In this way, the power system will meet the net zero emission target by 2050. The rapid decline in the cost of photovoltaic and wind power, as well as the maturity and cost reduction of advanced nuclear power technology, enables the power system to achieve net zero emissions at a relatively low cost. New power negative emission technologies, such as biomass power generation, adopt CCS technology, with which the negative emission of the power sector can be realized. On the premise of achieving net zero emissions or even negative emissions in the power sector, the basic strategy for other sectors is to promote electrification. The level of electrification in the industrial, construction and transportation departments has to be enhanced significantly. A high proportion of end-use electrification will be achieved in these sectors. Some industries that are difficult to be electrified, such as aviation, shipping, steelmaking, petrochemical and metal smelting, have to adopt innovative technologies, such as hydrogen-based technology, to achieve near-zero emission. Through using low-cost renewable energy and nuclear power to generate green hydrogen, the power system can achieve zero carbon emission in the whole life cycle. With the above measures, China’s energy activities may achieve net zero emissions by around 2050, supporting the goal of carbon neutrality by 2060. According to the research and assessment, the total investment required to achieve net zero emissions of energy-related activities around 2050 is about CNY 120–150 trillion from now to 2050. Over the same period, China’s total GDP will be more than CNY 4000 trillion. In terms of total GDP, the economic transformation of energyrelated activities can be supported. On the basis of energy system emission reduction, nature based solutions are also an important way to achieve carbon neutrality. These measures include afforestation, desert control, ecosystem protection and restoration, sustainable utilization of resources, wildlife protection, pest defense, delimitation of ecological protection red line, determination of ecological functional areas, and the establishment of the natural reserve system, and so on. Achieving the warming targets of the Paris Agreement can better support the realization of SDGs. Energy and economic transformation, which is targeted for carbon neutrality, can also boost employment, increase the total economy and enhance income growth. Meanwhile, energy and economic transformation can better reduce the emission of gases related to atmospheric haze and significantly improve the air quality. And such a transformation can help reduce water demand. Global cooperation in dealing with climate change is an important embodiment of achieving global social goals. The United Nations has set the realization of the Paris Agreement goals

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as an important task. China’s carbon neutrality strategy can better promote international cooperation, strengthen the multi-cooperation mechanism based on the UN, and promote the construction of a community with a shared future for mankind. As stated in the IPCC assessment reports and the assessment conclusions of this book, climate change will have significant impacts on the world and China. Decisionmaking needs to be based more on the disasters with small probability but potentially catastrophic effects, and adaptation strategies should be raised to a very important level. On the basis of these assessment reports, it is imperative to formulate preventive measures for disasters with small probability of occurrence but huge impact so as to avoid negative social consequences. According to the IPCC AR6 WGI report, even if strong efforts are taken to achieve the warming target of 1.5 °C, the warming would be still likely to exceed 1.5 °C in the next 20 years. Therefore the effects of warming will become obvious and rapid, and the adaptation strategies will become extremely important. It is necessary to establish a strong system of adaptation measures in the near future to prevent the occurrence of more frequent extreme events and the occurrence of unprecedented extreme events. To avoid the extreme events like the floods that killed hundreds of people in 2021, the construction of a holistic adaptation system is needed. The construction of the multi-level, cross-system and all-region adaptation system has to be carried out under a higher level of understanding of the impacts of climate change.

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