Human-induced changes in extreme cold surges across the Northern Hemisphere.

Extreme cold surges, very large temperature drops over a short period of time, have serious impacts on human health, energy supply and ecosystems. While changes in temperature variability and cold extremes in a warming climate are well understood, changes in extreme cold surges and their driving mechanisms are not. Here we show that extreme cold surges have robustly weakened in middle-to-high latitude continents during autumn and winter but have remained almost unchanged in lower latitudes. By diagnosing near-surface thermodynamic budget, we find that this change is mainly induced by anthropogenic forcing. Greenhouse gas forcing decreases the meridional temperature gradient and associated variability in middle-to-high latitudes but has minimal impact in lower latitudes. This leads to similar spatial pattern of changes in nonlinear horizontal temperature advection that dominantly drives the extreme cold surges. Influenced by the same mechanism, extreme cold surges during winter across middle-to-high latitudes will continue to weaken in the future, with an 8%-13% reduction in their strength by the end of the century under the SSP 3-7.0 scenario.