The IPCC AR6 Working Group I gives new understandings of the predictability, irreversibility and deep uncertainty of various elements of the climate system. This paper summarizes the above three aspects of cryospheric changes in global and regional scales. In general, on the hemispheric and global scales, regardless of the emission scenario, all cryospheric elements could have certain predictability in the 21st century, i.e., they all change in the direction of melting or degradation, mostly irreversible. However, on the regional scale, short time scales and long-term commitment, different cryospheric elements may exhibit large internal variability, poor predictability and even deep uncertainty.
In the IPCC Sixth Assessment Report, the latest monitoring and simulation results indicate that the current rate of sea level rise is accelerating (3.7 mm/a) and will continue to rise in the future, showing an irreversible trend. Under low emission scenarios (SSP1-1.9) and high emission scenarios (SSP5-8.5), global mean sea level (GMSL) is projected to rise by 0.15-0.23 m and 0.20-0.30 m by 2050, respectively. By 2100, GMSL is projected to rise 0.28-0.55 m and 0.63-1.02 m, respectively. Antarctica ice sheet instabilities are significant sources of uncertainty affecting future sea level rise projections. Regional relative sea level rise is an important driving factor affecting extreme still water levels.
Marine Ice Sheet Instability (MISI) and Marine Ice Cliff Instability (MICI) and the acceleration of ice streams will increase the estimated GMSL in the future. After 2100, with the continuous heat uptake of deep ocean and the continuous loss of ice sheet mass, sea level rise will last for thousands of years (high reliability).
A major deficiency of present-day sea-level studies is the prediction of high sea-level scenarios at the end of the 21st century. Under the impacts of climate warming and polar amplification effect, the collapse of Antarctic ice shelf may accelerate. The intensification of hydrofracturing process and ocean stratification can increase the melting on and beneath the ice shelf, respectively. However, these physical processes have not been well implemented in the models.
By the end of the 21st century, the tidal amplitude in most coastal regions of the world will change significantly. Human factors such as land reclamation and different land management policies in coastal areas will affect the impact of global sea level rise on tidal amplitude. Therefore, the impact of ice sheets on global and regional sea level changes has important practical and long-term significance for China’s future coastal infrastructure and ecological environment protection.
IPCC AR6 was formally approved at the 14th joint session of Working Group I of the IPCC and accepted by the 54st session of the IPCC on August 2021. Assessment content related to the ocean circulation of chapter 9 “Ocean, cryosphere and sea level change” is synthesized in this paper. Compared to the former IPCC reports, AR6 further confirmed the influence of human activities on ocean circulation, and provided the projected results based on the newest numerical simulations. AR6 pointed out that, surface salinity contrasts are increasing (virtually certain), and fresh ocean regions will continue to get fresher and salty ocean regions will continue to get saltier in the 21st century (medium confidence). The upper ocean has stably stratified since at least 1970 over the vast majority of the globe (virtually certain), and the upper ocean stratification is projected to increase (virtually certain) while the mixed layer depth is projected to mostly shoal under high emissions scenarios (low confidence). The frequency of marine heatwaves has doubled since the 1980s (high confidence) and the duration has become longer (medium confidence), furthermore the projection shows such trend will continue. Of the four eastern boundary upwelling systems (EBUS), only the California current system has experienced upwelling-favorable wind intensification since the 1980s (medium confidence), and the EBUS will change with a dipole spatial pattern of reduction at low latitude and enhancement at high latitude (high confidence). Under all SSP scenarios, the Atlantic Meridional Overturning Circulation (AMOC) will decline over the 21st century (very likely). The decline will not involve an abrupt collapse before 2100 (medium confidence). AR6 has added the high resolution numerical simulation experiments which could resolve mesoscale eddy, such experiments could effectively improve the simulation of Sea Surface Temperature (SST), air-sea flux and dynamic sea-level change.
Taking the grid daily precipitation data (CN05.1) observed by China surface meteorological stations from 1986 to 2005 as the observation data, the performance of 21 global climate models were evaluated based on the high-resolution downscaling daily dataset NASA Earth Exchange/Global Daily Downscaled Projections (NEX-GDDP) with the resolution of 0.25° (~25 km×25 km). Six intensity indices, annual maximum daily precipitation (RX1D), the largest consecutive precipitation for five days (RX5D), total wet-day precipitation (PRCPTOT), simple daily precipitation intensity (SDII), cumulative precipitation in the 95 and 99 quantiles (R95p, R99p), and five frequency indices, heavy rain days (R50), cumulative precipitation days in the 95 and 99 quantiles (R95T, R99T), consecutive wet days (CWD), consecutive dry days (CDD), were selected for evaluation. The results show that: (1) It is difficult for models to capture the linear variation of extreme precipitation indices. Even for the best performance model, GFDL-ESM2G, only 45% of the simulated indices present the positive correlation with the observation. (2) The performance of models on the climatological means is better. CSIRO-MK3-6-0, NorESM1-M and MRI-CGCM3 have better performance on the intensity indices. The inmcm4, IPSL-CM5A-MR and MIROC5 have better performance on the frequency indices. The three best synthetical performance models are CSIRO-MK3-6-0, inmcm4 and MRI-CGCM3. (3) Considering the performance of 11 extreme precipitation indices in the climatological means and trend, GFDL-ESM2G, CSIRO-MK3-6-0 and ACCESS1-0 have relatively higher performance.
Based on the station observation data from 1980 to 2016, the CWRF model’s ability to simulate area rainfall and extreme precipitation events in the Yangtze River basin was evaluated. The results showed that the CWRF model well reproduced the spatial distribution of precipitation in the Yangtze River basin and the monthly/seasonal variation characteristics of area rainfall in different regions from 1980 to 2016, and the CWRF model performance was better in winter and spring than in summer and autumn. CWRF model had a systematic overestimation on area rainfall in the Yangtze River basin, and the simulation capability for area rainfall in the middle and lower reaches of the Yangtze River was higher than that in the upper reaches and the Jinsha River. This may be due to the inadequate representation of observation area rainfall caused by the complex topography and the scarcity of stations in the upper reaches of the Yangtze River basin and the Jinsha River area, as well as the lack in simulation capabilities of the CWRF model. CWRF model also presented certain capabilities to simulate extreme precipitation events, which could well reflect the wetting trend of the middle and lower reaches of the Yangtze River. Additionally, the weakening trend of extreme precipitation in the upper reaches of the Yangtze River and the increasing trend in the middle and lower reaches of the Yangtze River could be reflected. However, the numerical simulation capability for extreme daily precipitation and precipitation in complex terrain were insufficient.
Based on the Universal Thermal Climate Index (UTCI) from the ERA5-HEAT reanalysis data, China was divided into eight regions by using the rotating empirical orthogonal function method (REOF), namely the Yangtze River Valley (YR), the South China (SC), the North China (NC), the Northwest China (NW), the Northeast China (NE), the Northern of Xinjiang (NJ), the Southern of Xinjiang (SJ), and the Western of China (WC). The variation characteristics of human thermal comfort of the eight regions in China in summer during 1980-2019 were analyzed and the variation reason of UTCI was also explained preliminarily. The results are as follows. In summer, UTCI has been increasing in each region of China, with the largest increase rate in NW where the average UTCI increase rate is 0.053℃/a, and in nighttime, the increase of the minimum UTCI is particularly significant in WC, NW, and SJ, respectively augmented by 112%, 34% and 33%, compared with the increase rate of their maximum UTCI. With the increase of UTCI, the days of strong heat stress and the frequency of the events of strong heat stress for lasting in most areas, have been rising in summer, except for WC. The area with the largest increase rate is NC, with the increase rate of 1.7 days per decade and 2.4 times per decade, respectively. From the analysis of influencing factors, it is found that the rise of UTCI in summer of China is caused by the increase of air temperature, dew point temperature and radiation temperature and the decrease of wind speed. Among the four climatic factors, air temperature is the main climatic factor for the rise of UTCI in China, which the average contribution rate is 49%, and except for SC and WC, radiation is the second largest factor in most areas, while the contribution of other climate factors mainly depended on the variable trend of each region in China.
Belt and Road (B&R) countries have been suffering from various climate risks for a long time, including water related problems, such as water shortage and flood hazard. By evaluation of water-related adaptation measures proposed in the Nationally Determined Contributions (NDCs) submitted by B&R countries, it’s found that the risks related to climate change and water resources have been widely concerned, and most countries have put forward targeted adaptation measures more or less such as optimizing water resources management, improving water resources utilization efficiency, improving risk early warning capabilities and infrastructure construction. However, there are still a few problems including that the lack of adaptation related content in the NDCs of some B&R countries, which are mainly composed of Central and Eastern Europe (CEE) countries; The scope of risk concerns in West Asia/the Middle East and Central Asia is not comprehensive enough to assess and plan for future potential flood risks; In Central Asia, South Asia and the Middle East, where water disputes are prominent, there is a lack of appropriate international cooperation mechanisms. There is a lack of attention to the water environment in most countries. In order to improve the adaptation capacity of B&R countries, and build a sound climate adaptation system, it is necessary to improve NDC report, establish an international cooperation mechanism, and increase the attention and investment in climate change research, ensuring the green and sustainable development of the Belt and Road Initiative.
In order to discuss the supply security of the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) in the process of carbon neutrality and low-carbon power transition, a dynamic CGE model was built for the GBA. Fifty-one scenarios were designed to simulate the annual variation range of each type of power generation, and the maximization of social welfare was taken as the evaluation index. The optimal time node and development speed of coal power decommissioning to minimum guaranteed capacity and complete decommissioning, as well as gas power capacity to peak were studied. The results show that the coal power generation capacity will be decommissioned by 6.6 billion kW∙h per year from 2020 to the minimum guaranteed capacity in 2032, and then it will be completely decommissioned by 4.0 billion kW∙h per year in 2045. The gas-power generation capacity will increase by 6.1 billion kW∙h per year from 2020 to reach the peak in 2038, and then retire at the rate of 5.1 billion kW∙h per year to maintain a minimum guaranteed capacity of 132.3 billion kW∙h in 2050. Further, according to the constant growth rate of local total electricity generation from 2020 to 2050, the growth rate of non-fossil power can be obtained, and the combination of the development rate of coal power, gas power and non-fossil power is the most economical. Compared with the baseline scenario, the optimized power transition combination scenario can reduce the fossil energy consumption by 110 million tce, reduce carbon emissions by 280 million t CO2, increase the added value of the power sector by CNY 23.8 billion, and increase the added value of other sectors by CNY 17.2 billion. The optimal power generation speed regulation strategy proposed in this study is conducive to supporting the economic, effective, safe, reliable, coordinated and orderly transition of the power system in the GBA and the formulation of low-carbon policies.
The research attempts to provide a comprehensive and systematic analysis of recent progress in the field of climate communication, with the purpose of explaining why the public lacks trust in climate science. The research first presents a picture of recent work on public climate perceptions and the social, political, and economic factors behind. It then analyzes the work on media coverage of climate change and related media effects in various countries. Furthermore, the research puts emphasis on analyzing social and psychological factors that affect public climate perceptions and attitudes. On the basis of the literature analysis, this study points out that the global climate communication research has important implications for the development of Chinese climate communication research, and China’s specific national conditions will provide a wealth of opportunities for theoretical development and practical application of Chinese climate communication. Chinese climate communication scholars should pay special attention to the multi-dimensional factors of Chinese public climate attitudes, so as to adopt diversified communication strategies to encourage the public to consciously participate in climate-friendly practices.
