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.