Late 1980s abrupt cold season temperature change in Europe consistent with circulation variability and long-term warming

Abstract

Cold season temperatures in Europe have increased rapidly by about 1.2°C in the late 1980s, followed by relatively modest and regionally flat temperature trends thereafter. The abrupt change affected the entire European continent and coincided regionally with abrupt hydroclimatic changes such as a widespread reduction in snow days in Switzerland. However, the drivers and causes of the event are not well understood. Using a dynamical adjustment method based on statistical learning, we find that the continental-scale late 1980s abrupt winter warming and regional decreases in snow days can be attributed to cold conditions in the mid-1980s followed by a few exceptionally warm seasons. Both are caused by random atmospheric circulation variability superimposed upon a long-term and relatively homogenous warming trend, and do not require an external cause or change of the underlying dynamics of the system. This explanation is consistent with simulations from a 21-member regional climate model ensemble, in which four members display comparable abrupt temperature increases regionally driven by circulation and a long-term externally forced response. Overall, our analysis provides an observation-based interpretation of abrupt temperature change at the continental scale, associated hydroclimatic changes regionally, and its drivers. Furthermore, our method might contribute to improved mechanistic understanding of different observed climate phenomena in many regions of the world that experience high variability.