器测时期全球增暖趋势及其不确定性估计——基于IPCC科学评估的回顾与展望

Global warming trends and their uncertainty estimation during the instrumental observation period:A review and outlook based on IPCC scientific assessments

《巴黎协定》提出的温控目标未来还有多少升温空间?这是各国政府、科学家和公众所共同关心的问题.要准确回答这一问题,需要更高质量的基准气候观测数据集作为变暖事实检测的核心基础.针对近年来全球表面温度(global surface temperature,GST)偏差引起的讨论,政府间气候变化委员会(Intergovernmental Panel on Climate Change,IPCC)第6次科学评估报告(AR6)在遴选用以评估工业化以来地球增暖幅度的器测时期全球基准温度数据集时,在数据集的时间覆盖范围和空间抽样方面采用了更为严格的标准.所收录的5个全球基准数据集中:HadCRUT5(英国气象局和东安吉利尔大学)、NOAAGlobalT-Interim(美国大气海洋局/国家环境信息中心)、BE(美国Berkeley Earth团队)被完全采纳;GISS(美国美国航天局/戈达德航天科学研究中心)只采纳了1880年以来的数据,最新发布的China-MST-Interim(中国中山大学)则只采纳了其全球陆地气温(global land surface air temperature,GLSAT)分量China-LSAT;此外,AR6还参考了几个基于新方法(统计插补、数据融合和人工智能)对HadCRUT4重建数据集的评估结果.基于上述数据集,AR6报告给出了迄今最优的工业化以来(用1850~1900年平均值表示)的增暖估计,即最近10年(2011~2020年)全球平均增暖了1.09℃(0.95~1.20℃).但毋庸置疑,要彻底厘清这个问题的确切答案,未来还有许多工作要做.

Accurately understanding the past is essential for better predicting the future.Since the 19th century,people have been studying the key scientific question,“How much has the Earth warmed since the pre-industrial era?”Although the land surface air temperature/surface temperature can be considered one of the most precise“key climate variables”,the longstanding insufficient sampling of observations and data accuracy issues have prevented a perfect answer to this question.However,to accurately address this issue,a higher-quality global temperature baseline observational dataset is needed as the core foundation for detecting the fact of warming.The Intergovernmental Panel on Climate Change(IPCC)has consistently used global surface temperature warming as the basis for its scientific assessment reports.Scientists from Western countries such as the UK and the USA have conducted pioneering or in-depth research in the development of global land surface temperature datasets,deepening our understanding of the above-mentioned issue.Since the beginning of this century,with the fermentation of the“climate gate”event and the widespread discussion of the“global warming hiatus”by scientists around the world,the discussion of biases in global land surface air temperature/global surface temperature has once again gained attention from all sectors of society.In response to these discussions,the IPCC’s Sixth Assessment Report(AR6)has adopted more stringent standards in the selection of global baseline surface temperature datasets for assessing the extent of global warming since the industrial era in terms of the dataset’s temporal coverage and spatial sampling.In the end,five of the currently active global baseline datasets have been included in the final report of AR6:HadCRUT5(UK Met Office and East Anglia University),NOAAGlobalT-Interim(US National Oceanic and Atmospheric Administration/National Center for Environmental Information),and BE(US Berkeley Earth team)were fully adopted.GISS(US National Aeronautics and Space Administration/Goddard Institute for Space Studies)only adopted data from 1880 onwards.The newly released China-MST-Interim(Sun Yat-sen University,China)only adopted its global land surface air temperature component,China-LSAT.In addition,AR6 also referenced the assessment results of several datasets based on new methods(statistical interpolation,data fusion,and artificial intelligence)for reconstructing HadCRUT4.Based on the above datasets,the AR6 report provides the most optimal estimate of warming since the industrial era(represented by the average value from 1850 to 1900),indicating that the global average temperature has increased by 1.09℃(0.95 to 1.20℃)over the past decade(2011−2020).However,we also need to recognize that there are still many areas for improvement in the current baseline dataset.Firstly,the number of observation stations in the 19th century was very limited,leading to significant differences in the global average temperature among the five datasets during this period.Secondly,despite the sea surface area covering 71% of the world,there are still noticeable differences between the two global sea surface temperature datasets from NOAA and the UK Met Office.Thirdly,observations in the Arctic,Antarctic,and high-altitude areas are still not comprehensive enough,resulting in high uncertainty in temperature changes in these regions.Finally,there are still deficiencies in data resources,data processing techniques,and the estimation framework for uncertainty among different datasets,resulting in a certain level of structural uncertainty that has not been fully evaluated.Therefore,there is still a lot of work to be done to satisfactorily address these issues.Additionally,strengthening constructive communication between the scientific community and the public is also an issue that we need to seriously consider at present.