Decreasing aerosols increase the European summer diurnal temperature range.

The diurnal temperature range (DTR), the difference between daily maximum and minimum temperature, is important for the impact of extreme temperatures, but despite physical links to aerosol forcing previous studies have struggled to attribute observed DTR changes to aerosols. Using causal inference, we can clearly identify aerosols as a driver of European DTR change since 1940. Following a decrease from the 1940s, since the 1980s the European DTR has increased by about 0.5K due to a reduction in European aerosol emissions leading to cooler nights relative to days. Agreement between causal effects estimated from observations with those estimated for two CMIP6 models evaluates the models' microphysical and radiative parameterizations. From causal effects, we also derive effective radiative forcing estimates of aerosols on surface shortwave during European summer, which amount to [-1.7; -1.5] Wm in observations and one model, while it is less negative in the other model ([-0.9; -0.8] Wm).