final_program_abstracts[1]

11 IMSC Session Program
Influence of external forcing on European temperatures
Friday - Parallel Session 6
Gabriele Hegerl 1 , Juerg Luterbacher 2 , Fidel Gonzalez-Rouco 3 , Simon Tett 1 and
Elena Xoplaki 4
1 GeoSciences, University of Edinburgh, UK
2 University of Giessen, Giessen, Germany
3 Universidad Complutense Madrid, Spain
4 Cyprus Institute, EEWRC, Nicosia, Cyprus
We use results from a reconstruction of seasonal European temperature and several
climate model simulations of the last millennium to show that external forcing has
influenced European past seasonal temperature variations . We use fingerprints for
external forcing that are averaged from the simulations as well as fingerprints from
simple climate models to attribute reconstructed seasonal changes to forcing. Results
show that regional reconstructed winter and spring temperatures have significantly
responded to external forcing. Approximately 25% of the variance of decadal winter
and spring temperatures can be attributed to external forcing over the entire time
period. A best estimate of 88% of the winter warming since the early 19 th century is
attributable to greenhouse gas and aerosol forcing. The winter season also shows a
significant, but noisy, short term response to volcanic eruptions, with warming in
Northern Europe both in ensembles of GCM simulations and observations a bit long
sentence. In contrast, the contribution of forcing to decadal variability of summer and
fall temperatures is small, making the most recent rate of warming in summer highly
unusual. Highly significant short term summer cooling can be detected immediately
after individual volcanic eruptions, and there may be a detectable response to solar
forcing in decadal variations in summer. These differences between the seasons
suggest that sub-annual information is needed to reliably predict impacts.
Abstracts 351