Comment on egusphere-2023-653

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> The internal variability of European summer temperatures has been linked to various mechanisms on seasonal to sub- and multi-decadal timescales. We find that sub-decadal time scales dominate summer temperature variability over large parts of the continent, and the mechanisms controlling such sub-decadal variations remain unexplored. Extremely warm summers occurring in sub-decadal periods when abnormally warm summer temperatures conglomerate are controlled by a strengthening of the subtropical gyre, an increase of heat transport, and an accumulation of heat content several years prior to an extremely warm European summer, thereby affecting ocean-atmosphere heat fluxes during extreme summers. This leads to a weakening and northward displacement of the jet stream and increased probability of atmospheric blocking over Scandinavia. Our findings link the occurrence of extremely warm European summers to the inertia of the North Atlantic, whose potential to improve the predictability of extremely warm summers several years ahead is of great societal interest, especially in a warming climate.