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