Circulation dampened heat extremes intensification over the Midwest USA and amplified over Western Europe
Jitendra Singh, Sebastian Sippel, Erich Fischer
Abstract
Abstract Globally heat extremes have intensified in recent decades. However, while Western Europe shows a remarkably strong intensification of heat extremes, the Midwest United States experienced only weak warming of warmest nighttime and even a weak decrease in the intensity of daytime heat extremes since 1979. Here, we show that for daytime heat extremes in the Midwest United States atmospheric circulation induced ~1 °C cooling since 1979, reversing the thermodynamic warming trend. The observed circulation-induced trend is outside the multi-model range and the overall trend at the very low end of it. In Western Europe circulation greatly amplified warming by ~1 °C, accounting to one third of observed trend. The observed circulation- and thermodynamic-induced trends, as well as the total observed trends are at the high end of the model range in Western Europe. Understanding whether the strong circulation-induced trends are externally forced or unforced internal variability remains key to constrain future trends in heat extremes.