Accelerated European Summer Warming Driven by Atmospheric Circulation Changes in Response to Aerosol Forcing

Compared to observations, climate models underestimate the recent increase of European summer temperatures, due to an underestimation of Quasi‐stationary Rossby Wave (QSW) trends over Europe. This is partially due to unpredictable internal variability and partially due to an underestimation of the predictable signal in response to external forcings. The analysis of a large ensemble of historical simulations shows that forcing factors generate changes in QSW and European summer temperatures consistent with those from observations but with a lower magnitude, making most of the observed changes predictable by the models through a signal adjustment. The analysis of single forcing experiments shows a major contribution of aerosols starting from 1980, when the reduction of sulfate aerosol emissions over Europe is associated with a longitudinal temperature asymmetry, which alters the atmospheric circulation. These results further demonstrate the need to account for model errors to best estimate past and future changes in climate.