Storylines reveal contrasting thermodynamic effects of climate change on 2020/21 East Asian cold extremes

The impact of climate change on the intensity of mid-latitude cold air outbreaks is a debated topic due to uncertainty associated with internal atmospheric dynamics. Here, we employ an event-based storyline approach in which the evolution of the large-scale atmospheric circulation is nudged to reanalysis data at different global warming levels based on historical and high-emission scenario simulations. We thereby quantify the thermodynamic climate-change effects of pre-industrial, 2ºC and 4ºC warmer climates compared to present-day climate for three cold surges in East Asia during the winter 2020/21. The strongest warming occurs over northeast Asia, reaching up to +12ºC in a +4ºC warmer climate and caused by the advection of less cold air from winter ice-free regions in the Arctic, where the change of surface air temperature exceeds +20ºC. In contrast, over southern China, a moderate cooling is present from pre-industrial to present-day climates, due to the observed and expected increase in aerosol concentration, which peaks by the mid-21st century and alters the radiative balances. This cooling effect is likely to persist well into a +2ºC-warmer climate; however, it may become undetectable at the end of the 21st century (+4ºC warming). In summary, our findings underscore the important thermodynamic impact associated with Arctic amplification and cooling effect of aerosol-induced changes in the radiation budget on East Asian cold extremes.