The January 2021 Cold Air Outbreak over Eastern China: Is There a Human Fingerprint?

We analyzed the 3-day January 2021 cold event in China and its historical climate change background using a novel cold degree days metric in combination with a fingerprinting analysis technique designed specifically for extremes. Despite high impacts and the setting of a large number of cold temperature records, this was a relatively mild event regionally, with clear evidence that human influence on the climate has reduced the strength and probability of such events since 1961. Nevertheless, our inferences, which are made at the 5° × 5° scale using different model ensemble simulations, are relatively uncertain and should be used qualitatively. Studies have reported that the weakened winter Northern Hemisphere meridional temperature gradient (Ding et al. 2008) and Arctic sea ice loss (Mori et al. 2019) caused by anthropogenic warming may have induced more cold air outbreaks. Our results support the idea that anthropogenic warming has warmed cold outbreak events. Nevertheless, their impacts to, for example, people's perception of cold and heating energy demand, which are also affected by changes in exposure and vulnerability, may not have diminished accordingly.