Faster than expected drying in Western Europe: mechanisms, attribution and implications

For at least three generations of models, global climate projections indicate that anthropogenic emissions of greenhouse gases emissions are likely to induce an important drying during spring and summer over most of Europe, whose rate and amplitude however strongly vary across models within each phase of the Coupled Model Intercomparison Project (CMIP). In order to reduce this intermodel spread, various analyses have been conducted to identify key drivers and have reported both radiative (i.e., anthropogenic aerosols) and dynamical (i.e., large-scale atmospheric circulation) mechanisms, as well as possible land surface feedbacks. The present study aims at better understanding these processes, first in a single atmospheric model, then in two subsets of coupled ocean-atmosphere models. The results are qualitatively consistent with previous studies, but point to a mismatch between models and observations over recent decades (1979-2022). This mismatch is unlikely to be due to dynamical causes, but points to systematic errors in the simulated radiative forcing by sulfate aerosols. Moreover, a Bayesian statistical method is used to constrain the CMIP6 projections and highlights a faster than expected drying in Western Europe. The study also has implications for the tuning of the aerosol radiative forcing and the interpretation of former attempts to constrain climate change based on the instrumental temperature record.