Influence of human and natural forcing on European seasonal temperatures

It is the regional and seasonal expression of climate change that determines the effect of greenhouse warming on ecosystemsand society1. Whereas anthropogenic influences on European temperatures have been detected over the twentieth century2, 3, it has been suggested that the impact of external influences on European temperatures before 1900 is negligible4. Here we use reconstructions of seasonal European land temperature5, 6and simulations with three global climate models7, 8, 9 to show that external influences on climate—such as the concentrations of stratospheric volcanic aerosols or greenhouse gases, other anthropogenic effects and possibly changes in total solar irradiance—have had a discernible influence on European temperatures throughout the past five centuries. In particular, we find that external forcing contributes significantly (p<5%) to the reconstructed long-term variability of winter and spring temperatures and that it is responsible for a best guess of 75% of the observed winter warming since the late seventeenth century. This warming is largely attributable to greenhouse-gas forcing. Summer temperatures show detectable (p<5%) interdecadal variations in response to external forcing before 1900 only. Finally, throughout the record we detect highly significant summer cooling and significant winter warming following volcanic eruptions.