IPCC AR6报告解读：未来的全球气候——基于情景的预估和近期信息

doi:10.12006/j.issn.1673-1719.2021.239

摘要/Abstract

摘要：

依据IPCC第六次评估报告（AR6）第一工作组报告第四章的内容,对未来全球气候的预估结果进行解读。报告对21世纪全球表面气温、降水、大尺度环流和变率模态、冰冻圈和海洋圈的可能变化进行了系统评估,并对2100年以后的气候变化做了合理估计。评估指出全球平均表面气温将在未来20年内达到或超过1.5℃,平均降水也将增加,但随季节和区域而异,同时变率将增大。大尺度环流和变率模态受内部变率影响较大。到21世纪末,北冰洋可能出现无冰期;全球海洋会继续酸化,平均海平面将持续上升,百年内上升幅度依赖不同排放情景,都在2100年后继续升高。在最新的评估中采用多种约束方法,减小了预估不确定性的范围。AR6对于低排放情景以及“小概率高增暖情节”的关注为应对气候变化提供了更多、更完整的信息。综合报告的评估结果指出,未来需要进一步减小区域,特别是季风区气候预估的不确定性,并从科学研究和模式发展两方面加强我国气候预估能力的建设。

关键词: IPCC AR6, 气候预估, SSP情景, 气温, 降水, 环流, 海冰, 海平面

Abstract:

Based on the content of Chapter 4 from the Sixth Assessment Report (AR6) contributed by the IPCC Working Group I, we interpret the future projections of global climate change. The AR6 systematically assessed possible changes of global surface air temperature, precipitation, large-scale circulation and modes of variability, and changes in ocean and cryosphere, and further reasonably estimated the climate change beyond 2100. The assessments show that global mean surface air temperature would reach 1.5℃ or even beyond it. Mean-state and variability of precipitation would increase as well, but varying with seasons and regions. Large-scale circulation and modes of variability are more affected by internal variability rather than external forcing. By the end of the 21st century, ice-free period would be seen in the Arctic. Ocean acidification and increase of global mean sea level (GMSL) would continue at the century time scale with uncertain magnitudes depending on emission scenarios. The projected GMSL would go higher beyond 2100 under all the scenarios. Multiple constraining methods are introduced in this latest assessment, reducing the uncertainty range of future projection. By paying an additional attention to the low emission scenarios and low-likelihood high-impact storylines, the AR6 provided richer and more comprehensive information for addressing climate change. Integrating the assessment conclusions, we suggest that future studies need to reduce the projected uncertainties in regional climate change, especially in the monsoon regions, and that capability construction of climate projection in China need to be strengthened in both scientific research and model development.

Key words: IPCC AR6, Climate projection, SSP scenarios, Surface air temperature, Precipitation, Circulation, Sea ice, Sea level

周天军, 陈梓明, 陈晓龙, 左萌, 江洁, 胡帅. IPCC AR6报告解读：未来的全球气候——基于情景的预估和近期信息[J]. 气候变化研究进展, 2021, 17(6): 652-663.

ZHOU Tian-Jun, CHEN Zi-Ming, CHEN Xiao-Long, ZUO Meng, JIANG Jie, HU Shuai. Interpreting IPCC AR6: future global climate based on projection under scenarios and on near-term information[J]. Climate Change Research, 2021, 17(6): 652-663.

图/表 6

图1 基于CMIP6的历史模拟和未来预估的试验所关注的全球气候变化的物理指标注：(a)图中的全球平均表面气温为相对于1995—2014年的变化,如果相对于1850—1900年,整体提高0.82℃。(a)、(b)、(c)图上的数字表示使用的模式个数。SSP1-2.6和SSP3-7.0情景周围的阴影表示5%~95%的范围。本图来源于IPCC AR6第四章的Fig. 4.2。

Fig. 1 Selected indicators of global climate change from CMIP6 historical and scenario simulations. (a) Global surface air temperature changes, (b) global land precipitation changes, (c) September Arctic sea-ice area, (d) global mean sea-level change (GMSL). (Source: IPCC AR6 Chapter 4 Fig. 4.2)

图2 中期和长期预估下年平均地表气温的变化注：图中全球平均地表气温的变化都是相对于1995—2014年的多模式集合平均的空间分布。右上角的数字表示采用的模式个数。可靠性和显著性的定义详见IPCC AR6中第四章的4.2.6。本图来源于IPCC AR6第四章的Fig. 4.19。

Fig. 2 Mid- and long-term change of annual mean surface temperature (Displayed are projected spatial patterns of multi-model mean change in annual mean near-surface air temperature in 2041-2060 and 2081-2100 relative to 1995-2014 for SSP1-2.6 and SSP3-7.0.The number of models used is indicated in the top right of the maps. No overlay indicates regions where the change is robust and significant. Hatching indicates regions with no change or no robust significant change. Cross-hatching indicates areas of conflicting signals where at least 66% of the models show change greater than the internal-variability threshold but fewer than 80% of all models agree on the sign of change. Source: IPCC AR6 Chapter 4 Fig. 4.19. For the definition of robustness and significant change, please see section 4.2.6 in the Chapter 4 of IPCC AR6)

图3 长期（2081—2100年）预估下季节平均降水的变化注：图中预估的2081—2100年变化是相对于1995—2014年,冬季为12月至次年2月平均,夏季为6—8月平均。可靠性和显著性的定义详见IPCC AR6中第四章的4.2.6。本图来源于IPCC AR6的第四章的Fig. 4.24。

Fig. 3 Long-term change of seasonal mean precipitation during 2081-2100 (Displayed are projected spatial patterns of multi-model mean change in winter and summer mean precipitation in 2081-2100 relative to 1995-2014, for SSP1-2.6 and SSP3-7.0. The number of models used is indicated in the top right of the maps. No map overlay indicates regions where the change is robust and significant. Hatching indicates regions with no change or no robust significant change. Cross-hatching indicates areas of conflicting signals where at least 66% of the models show change greater than the internal-variability threshold but fewer than 80% of all models agree on the sign of change. Source: IPCC AR6 Chapter 4 Fig. 4.24. For the definition of robustness and significant change, please see section 4.2.6 in the Chapter 4 of IPCC AR6)

图4 多种证据约束下5个排放情景预估2081—2100年全球地表平均气温（GSAT）的变化。(a)无约束下预估的结果和不确定性,(b)约束后的预估结果和不确定性,(c) 3种约束后的预估结果的平均和模拟器估算的最优范围,(d)对CMIP6约束后的预估结果与模拟器的最优估计结果进行平均后的GMST序列注：对2081—2100年的GSAT变化预估是相对于1995—2014年平均。(a)图中白色横线为无约束下预估的结果,柱状图为5%~95%的不确定性范围。(b)图不确定性比无约束的不确定性的范围小,3种约束方法的差异导致约束后的结果稍有差异。(c)图中灰色为3种约束后的预估结果的平均,绿色为模拟器估算的最优范围。(d)图中右侧的y轴比左侧的y轴整体提高0.85℃。本图来源于IPCC AR6的第四章的Fig. 4.11。

Fig. 4 Multiple lines of evidence for GSAT changes for the long-term period 2081-2100, for all five priority scenarios, relative to the average over 1995-2014. (a) Future GSAT warming and uncertainty in the unconstrained projection, (b) future GSAT warming and uncertainty in the constrained projection, (c) the average of three constrained projection (grey) and the range estimated from emulator (green), (d) the average GSAT series of the constrained CMIP6 ranges and the emulator ranges. (The y-axes on the right-hand side are shifted upward by 0.85°C, the central estimate of the observed warming for 1995-2014, relative to 1850-1900. Source:IPCC AR6 Chapter 4 Fig. 4.11)

表1 基于多种证据进行约束20年平均意义下的全球表面气温的预估结果

Table 1 Assessment results for 20-year averaged GSAT change, based on multiple lines of evidence

表2 CMIP6多模式平均下年平均地表气温的未来变化

Table 2 CMIP6 annual mean surface air temperature anomalies

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