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

The changing character of mid-latitude cold air outbreaks in a warming climate remains unclear, primarily due to uncertainty associated with changing 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 medium-to-high-emission scenario simulations. We thereby quantify the thermodynamic climate-change effects of pre-industrial, 2 °C and 4 °C warmer climates compared to present-day climate for three cold surges in East Asia during winter 2020/21. The strongest warming occurs over northeast Asia, reaching up to +12 °C in a + 4 °C warmer climate and caused by the advection of less cold air from winter ice-free regions in the Arctic, where surface air temperature increases by over +20 °C. In contrast, over southern China, a moderate cooling is found from pre-industrial to present-day climates, due to the observed increase in aerosol concentration, peaking by the mid-21^st century and altering radiative balances. This cooling effect is likely to persist well into a + 2 °C-warmer climate; however, it may become undetectable at the end of the 21^st century (+4 °C warming). Our findings underscore the important thermodynamic impact associated with Arctic amplification and cooling effect of aerosol-induced changes in the radiation budget under a high aerosol emission scenario on East Asian cold extremes.