final_program_abstracts[1]

11 IMSC Session Program
Enhanced evidence in climate models for changes in
extratropical atmospheric circulation
Wednesday - Poster Session 5
Felix Pollinger and Heiko Paeth
Institute of Geography, University of Wurzburg, Wurzburg, Germany
We investigate changes in extratropical atmospheric circulation during the winter
season as derived from the most recent multi-model ensemble of global climate
projections. This internationally coordinated systematic data base allows for an
accurate assessment of climate change signals against the background of model
uncertainty. A total of 133 individual climate change simulations from 24 different
climate models are used in this study.
The multi-model mean time series of the northern-hemisphere (NAM) and southernhemisphere
(SAM) annular modes and of the North Atlantic Oscillation (NAO) are in
line with the observed positive trends during the second half of the 20th century and
project a further strengthening until the end of the 21st century. For the North Pacific
index (NPI) the multi-model mean time series also indicate future strengthening but
with no correlation with the time series derived from the HadSLP2 data set.
To identify and quantify the impacts of prescribed radiative forcing against model
uncertainty we use a spectral approach based on a two-way analysis of variance.
For SAM and NAM the simulated changes are unambiguously related to
anthropogenic forcing and outperform the level of model uncertainty. This result
enhances the probability for severe regional impacts of climate change, in particular
over extratropical land masses. The climate change signals are noticeably weaker
under the B1 mitigation scenario than under the A2 business-as-usual scenario.
Furthermore we investigate the influence of two basic inhomogeneities of the AR4
multi-model ensemble relevant to atmospheric dynamics. The different treatment of
observed ozone depletion and assumed recovery has a significant impact on the
amplitude of future circulation changes on both hemispheres, whereas no systematic
effect is found with respect to the models’ top-of-atmosphere.
Abstracts 212