Fingerprint-based attribution and constrained projection of global risk of daily compound hot extremes

Our planet is experiencing more compound hot extremes (CHEs), i.e., hot days and nights occurring simultaneously. This increase in CHEs is harmful to natural and human systems. This study aims to determine the extent to which the increase in CHEs is directly caused by human activities and to assess the associated population exposure. Our findings show that human-made greenhouse gases (GHG) are the primary factor responsible for the rise in CHEs. GHG contributed to 121.2% of the increase in probability ratio during 1950–2014. GHG emissions not only increase the likelihood of CHEs but they also increase the proportion of CHEs with extreme hot days/nights, especially in mid and high-latitude regions. In the future, extreme heat is unlikely to occur only during the day or night, due to the growing risk of concurrent daytime and nighttime heat, if global GHG emissions are not limited. This rise of CHEs would cause serious impacts on human health, disproportionately affecting the most densely populated regions of the world.

地球正经历越来越多的复合高温极端事件（compound hot extremes, CHEs），即白天与夜间高温同时发生的现象。CHEs的增多对自然系统与人类系统均构成危害。本研究旨在明确CHEs增多在多大程度上由人类活动直接导致，并评估相关的人口暴露情况。研究结果表明，人为温室气体（greenhouse gases, GHG）是CHEs增多的主要原因。1950–2014年间，GHG对概率比增幅的贡献率达121.2%。GHG排放不仅提高了CHEs的发生概率，还增加了伴有极端白天/夜间高温的CHEs占比，尤其在中高纬度地区。若全球GHG排放未得到限制，未来极端高温将难以仅发生在白天或夜间——因为昼夜同时高温的风险正不断上升。CHEs的增多将对人类健康造成严重影响，且不成比例地影响世界上人口最稠密的地区。