This paper interprets the main conclusions of the Working Group II report of the IPCC Sixth Assessment Report on observed and projected impacts and risks of climate change. The report shows that climate change is already causing widespread adverse effects on natural and human systems, with compounding risks and extreme events increasing in intensity and frequency under climate change. At present, there are more than 127 kinds of key risks in different regions and sectors, which will have more widespread and irreversible impacts on people and ecosystems as climate warming and ecological social fragility intensify. Compared with the Fifth Assessment Report, the Sixth Report further expands the framework of risks, summarizes 8 representative key risks, and evaluates the risk level of 5 “reasons for concern” in a more comprehensive way. The assessment results are conducive to deepening the understanding of the impact of climate change and formulating timely action countermeasures.
Chapter 2 of Working Group II's IPCC Sixth Assessment Report suggests that prior reports underestimated impacts of climate change on terrestrial and freshwater ecosystems due to complex biological responses to climate system. Anthropogenic climate change has led to deterioration of ecosystem structure, function and resilience, biome shifts and structural changes within ecosystem, increased wildlife diseases, increased area burned by wildfire, localized species extinctions and more extreme events. Under the scenario of temperature rise of 2-4℃ in the future, the percentage of species at high risk of extinction will be 10% to 13%, the wildfire burned area will increase by 35% to 40%, risks of tree mortality will exceed 50% in forest area, biome shifts on 15% to 35% and carbon loss continues to increase. The continuous increase of global temperature will aggravate the severe and irreversible impacts of these risks. The resilience of biodiversity and ecosystem services to climate change can be increased by human adaptation actions and mitigation measures including ecosystem protection and restoration. Aggravated climate change hinders the development and implementation of ecosystem-based adaptation. The long-term impacts of climate change need to be considered and the deployment of adaptation should be accelerated to ensure their effectiveness.
Water security is the centrality in adapting and mitigating climate change. It is also critical in meeting the Sustainable Development Goals (SDGs). In the IPCC Sixth Assessment Report (AR6), Working Group II established Chapter 4 of “Water”. This Chapter assesses observed and projected climate-induced changes in the water cycle, their current impacts and future risks on human and natural systems. This chapter also assesses the current and future water scarcity risks, the benefits and effectiveness of water-related adaptations. The assessment results show that human-induced climate change has led to an accelerated global hydrological cycle, thereby affecting water security and exacerbating water-related vulnerabilities. Water-related risks are projected to increase with every degree of global warming, especially in more vulnerable and exposed regions. Limiting global warming to 1.5℃ would effectively reduce future water-related risks, and contribute to meet the triple goals of water security, sustainable and climate-resilient development. China is experiencing high water security risks, and has a grand societal demand on scientific and technological advancements in water security. In future, water security research needs to emphasize the ecological and hydrological effects of gray and green infrastructure, three-dimensional water scarcity assessment, water-food-energy nexus, and the development and application of Earth System Simulators.
Groundwater is increasingly important for agricultural and domestic purposes. It is a key resource for achieving the United Nations’ Sustainable Development Goals. The quantity and quality of groundwater can be directly or indirectly affected by climate change. The IPCC Sixth Assessment Report (AR6) provides a new understanding of trends in groundwater on a global and regional scale in the past and for the future. The results show that: (1) Groundwater storage has declined in many parts of the world, most notably since the beginning of the 21st century, due to the intensification of groundwater-fed irrigation; (2) Groundwater abstraction is projected to further increase in the future with climate change, including the withdrawals from non-renewable groundwater in major aquifers worldwide; (3) Across the tropics and semi-arid regions, intensification of precipitation is projected to increase due to climate change, and this may increase episodic recharge of groundwater; while in higher altitudes, warmer climates may have led to reduced spring-time recharge due to reduced duration and snowmelt discharges. Stepwise ecological restoration in degraded groundwater areas is an important measure to combat climate change and ensure water security.
Compared with the IPCC Fifth Assessment Report (AR5), the assessment object of the Sixth Assessment Report (AR6) on agriculture extends from the crop production system to the food supply chain system, and the evidence of the adverse effects of climate change on crop production is strengthening. Climate change has changed the suitable planting areas of crops, making the planting boundaries of crops in the middle and high latitudes and temperate regions move to high latitudes and high altitudes. Anthropogenic warming has slowed crop yield growth, increased surface ozone concentrations have reduced crop yields, and methane emissions have exacerbated this adverse effect. Climate change aggravates crop diseases, pests and weeds, and the high incidence of extreme weather events exacerbates food insecurity and pushes up international food prices. Adaptation measures can help mitigate the adverse effects of climate change, and nature-based adaptation options have high potential for enhancing the climate resilience of crop production systems and ensuring food security. Starting from ensuring national food security and major strategic needs, the enlightenment of IPCC AR6 report on China’s agricultural response to climate change is as follows. Firstly, under the background of climate change, the transformation of crop planting suitable areas and the northward movement of planting belt have important strategic value, which need to be paid great attention to and reasonably plan the layout of agricultural production. Secondly, to strengthen the system and capacity-building of agro meteorological disasters and pest control to ensure the stability of grain production. Thirdly, to pay attention to the impact of climate change on international crop production and grain trade, coordinate food resources in domestic and international markets, and ensure food security; Finally, to promote efficient coordination between agricultural greenhouse gas emission reduction and crop production, and contribute to the realization of national emission reduction targets.
The content of Chapter 6 from the Sixth Assessment Report (AR6) contributed by the IPCC Working Group II assessed the impacts and adaptations of climate change on cities, settlements and key infrastructure. The impact of climate change on cities has gradually increased in depth and scope. The dynamic interaction of urban systems with climate change has intensified the risks of cities and settlements. Adaptations through social infrastructure, Nature-based Solutions and grey/physical infrastructure all contribute to urban Climate Resilient Development. Meanwhile, the urban adaptation gap is found to be widespread all over the world. Climate Resilient Development requires collaborations among multiple actors, bridging policy action gaps and enabling conditions for adaptation action in cities, settlements and infrastructure. The experiences of AR6 show that cities in China should adopt climate resilient development paths to improve the adaptation and mitigation of climate change risks.
IPCC Working Group II has recently released the Sixth Assessment Report (AR6) of “Climate Change 2022: Impacts, Adaptation and Vulnerability”, in which Chapter 7 “Health, wellbeing and the changing structure of communities” assessed the current impacts, and projected future risks of climate change for health and wellbeing, taking into consideration determinants of vulnerability and the dynamic structure of human populations and communities. Particular attention is given to potential adaptation challenges and actions, as well as the potential of co-benefits for health associated with mitigation actions. The report clearly shows that climate-related illnesses, premature deaths, malnutrition in all its forms, and threats to mental health and wellbeing, are increasing. Cascading and compounding risks affecting health due to extreme weather events have been observed in all inhabited regions, and risks are expected to increase with further warming. Sustainable and climate-resilient development that increases timely and effective adaptation and mitigation more broadly, has the potential to reduce but not necessarily eliminate climate change impacts on health and wellbeing. The AR6 report highlights the severity of health effects of climate crisis and the urgent need to increase scientific and technological innovation, planning, action and funding support in the field of climate change adaptation.
Adaptation initiatives have positive impacts on reducing climate change risks to people and ecosystems. The Working Group II (WGII) contribution to the Sixth Assessment Report (AR6) of the Intergovernmental Panel on Climate Change (IPCC) provides a comprehensive assessment of the feasibility and effectiveness of adaptation, and an in-depth assessment of adaptation limits and maladaptation. Adaptation actions are increasing at the individual, local, regional, and national levels, but the risks of maladaptation should be considered when making decisions. Six feasibility dimensions (economic, technological, institutional, social, environmental, and geophysical) are used to evaluate the potential feasibility of 23 adaptation options, which are distributed in land & ocean and ecosystems, urban & rural and infrastructure systems, energy systems, and cross-sectoral. Among those adaptation options, the forest-based adaptation, the resilient power systems, and the energy reliability have high confidence and high feasibility. The feasibility and effectiveness of adaptation options will decrease with climate warming, and multiple options are needed to reduce climate change risks in the future.
This work is an interpretation of Climate Resilient Development (CRD) in the Sixth Assessment Report (AR6) Working Group II (WGII) of IPCC. The definition of CRD was introduced in the Fifth Assessment Report (AR5) of IPCC, the definition was updated in AR6 that CRD was defined as a process of implementing greenhouse gas mitigation and adaptation options to support sustainable development for all. The new definition reinforces the principle of fairness, and makes a detailed description of different social choices in the evaluation content, which enhances the operability of CRD, and emphasizes its urgency and irreversibility. The report expounds how to promote the realization of CRD in human and natural systems consider of adaptation. The urbanization trend brings opportunities and challenges to CRD at the same time. While urbanization intensifies the risk of climate change, it will also promote the CRD by driving the adaptation action of surrounding rural areas. Protecting ecosystem diversity helps to protect the ecosystem and improve its own resilience, but some adaptation actions will not be implemented at higher temperature rise level. The AR6 WGII assessment shows that, the current global CRD action is more urgent compared with the AR5 (2014), and we need to implement effective and equitable measures to deal with climate change.
Based on Clouds and the Earth’s Radiant Energy System (CERES) Energy Balanced and Filled (EBAF) Dataset Edition 4.1, historical spatiotemporal variations in radiation budgets at the top of atmosphere (TOA) and the Earth surface were compared between Coupled Model Intercomparison Project phase 5 (CMIP5) and phase 6 (CMIP6). Regions with high inter-model variability were identified in two CMIPs. The results show that ensemble means of radiation components, except surface upward longwave radiation in CMIP6 are in better agreement with CERES EBAF 4.1. Except downward longwave radiation at the surface, lower inter-model spread for other radiation components are found in CMIP6. Overestimation in global mean surface downward shortwave is reduced by 1.9 W/m2, and underestimation in global mean downward longwave radiation is reduced by 3.3 W/m2, in CMIP6. Spatially, larger deviations are found in TOA reflected shortwave and outgoing longwave radiation, as well as surface downward shortwave radiation around the North Pole in CMIP6 compared to CMIP5. Worse simulation is also found in CMIP6 for surface downward longwave radiation around 60° latitudes. In other regions, CMIP6 radiation components agree better with CERES EBAF 4.1 than CMIP5. Regions with relative large inter-model variability for surface downward shortwave and downward longwave radiation shrink from CMIP5 to CMIP6. However, regions with extreme large inter-model variability still keep almost the same for the two components in two CMIPs. Two CMIPs are similar in spatial distribution with large inter-model variability for surface net radiation. Tibet Plateau, equatorial Pacific, tropical rainforest, Arabian Peninsula and Antarctic coasts are important regions with extreme large inter-model variability for simulating radiation budgets at the TOA and the surface by Earth System Models.
The dry/wet climate change in early summer has an important impact on the industrial and ecological environment in Yunnan province. In this article, the evolution characteristics of aridity index (AI) were analyzed from 1961 to 2020 using observation data, and the probable trend in 2021-2080 was projected by using 20 CMIP6 models under SSP1-2.6, SSP2-4.5 and SSP5-8.5. The AI in early summer of Yunnan province showed a decreasing trend from 1961 to 2020, and it had obvious inter-decadal change characteristics, the climate of 1960s, 1970s and 2000s was humid, and the rest period was dry, 2000s (2010s) was the wettest (driest) decade since 1961. Under three SSPs from 2021 to 2080, the climate in early summer of Yunnan will be drier than the average of 1995-2014. The regional average AI over Yunnan would decrease by 13.9%, 17.9%, and 24.9% under SSP1-2.6, SSP2-4.5, and SSP5-8.5, respectively. Southwestern Yunnan will be the center of the largest decrease for wetness. The main influencing factor of climate drying is precipitation in 1961-2020, but it will be potential evapotranspiration in 2021-2080, which would increase gradually with time and the increase of emission scenario.
A mathematical model was constructed to analyze the economy of vessels’ shore power usage. In this model, a number of factors relevant to government policy, vessel operation, and port operation were considered. Additionally, both equivalent annual cost analysis and scenario analysis were employed. Based on this model, a case study was finished by taking a typical container vessel operated between Europe ports and Shanghai Port (particularly Yangshan phase III terminal). The results show that if all else under the reference scenario is held constant and no subsidy is provided, the cost of using shore power by vessels would definitely be higher than that of using auxiliary power, regardless of whether environmental protection tax (EPT) is levied. Then shipping companies would face uneconomical situation when they use shore power in this case. To make the use of shore power is economical, the vessel’s residual life should not be shorter than five years, or the subsidy standard should be higher than or equal to CNY 0.55 per kW∙h. To meet same requirement, the increase of EPT rate should not be lower than 458% of the assumed rate if only EPT is levied without subsidy, or the utilization rate of shore power should be bigger than or equal to 39%, or the supply time of shore power should be longer than or equal to 11.8 hours. However, it is almost impossible for shipping companies to use shore power if the charging standard of shore power is greater than or equal to CNY 1.73 per kW∙h, or the fuel consumption intensity is below 158.70 g/(kW∙h), or the price of compliant fuel oil is lower than CNY 2841 per t.
Based on panel data of 268 prefecture-level cities in China from 2009 to 2017, this study regarded the policy of the next-generation internet demonstration city as a quasi-natural experiment, and empirically tested the impact of the policy of the next-generation internet demonstration city on urban carbon emissions by using the Difference in Difference model (DID). The results show that the policy of the next-generation internet demonstration city can alleviate the carbon emissions of the city, and the carbon emissions of the city can be alleviated by 1.41%. This conclusion still holds after the robustness test. In the mechanism analysis, the policy of the next-generation internet demonstration city mainly alleviates urban carbon emissions through industrial structure optimization and green technology innovation. Further heterogeneity test shows that the construction of the next-generation internet demonstration city has a more significant emission reductions effect on large cities and high carbon emissions, while it aggravates carbon emissions in small and medium-sized cities.