Exacerbated summer European warming not captured by climate models neglecting long-term aerosol changes

Abstract In much of western-central Europe, summer temperatures have surged three times faster than the global mean warming since 1980, yet this is not captured by most climate model simulations. Here we disentangle this warming into thermodynamic and circulation-induced contributions, and show that the latter is the main reason why numerically simulated warming is weaker than observed. Crucially, regional climate models from the Coordinated Regional Downscaling Experiment with constant aerosol forcings systematically show the strongest discrepancies from observations: in these simulations, the regional brightening and associated thermodynamic warming due to aerosol reductions is not represented. We estimate an effect of ~0.5 °C over western-central Europe for our model ensemble, and the discrepancy to climate models with evolving aerosols increases in future projections. To better reap the benefits of regional high-resolution simulations, it is thus imperative to represent the relevant external forcings and associated responses across the entire climate model chain.