Seminar

Abstract

The effect of greenhouse warming on ecosystems and society depends on the regional and seasonal details of future changes. Reconstructions of seasonal European temperature and three simulations over the past 5 centuries are used to investigate the influence of external forcing on seasonal temperature, and whether such forcing can be detected at the regional scale. It is shown that forcing has caused significant interdecadal temperature variations in winter and spring. External forcing, largely due to increases in greenhouse gas concentrations, is responsible for about 3/4 of the observed winter warming since the late 17th century. Average summer temperatures show a small, but significant response to external forcing prior to 1900, but no detectable influence over the entire reconstruction. In contrast, recent instrumentally recorded summer trends are highly unusual compared to past variability. Both summer and winter temperatures show significant short-term response to volcanic eruptions that are reasonably well simulated. However, the fingerprint of winter warming competes with strong dynamic winter variability, and is less robustly detectable than the summer response. Results also suggest a possible summer temperature response to solar forcing. This demonstrates, for the first time, that external forcing has a significant impact on European climate of the past few centuries, with strong seasonal differences which need to be considered when predicting impacts.