| The quality of global sea level pressure patterns has been assessed for
simulations by 23 coupled climate models. Most models showed high pattern
correlations. With respect to the explained spatial variance, many models
showed serious large-scale deficiencies, especially at mid-latitudes. Five
models performed well at all latitudes and for each month of the year. Three
models had a reasonable skill.
We selected the five models with the best pressure patterns for a more
detailed assessment of their simulations of the climate in Central Europe. We
analysed observations and simulations of monthly mean geostrophic flow
indices and of monthly mean temperature and precipitation. We used three
geostrophic flow indices: the west component and south component of the
geostrophic wind at the surface and the geostrophic vorticity. We found that
circulation biases were important, and affected precipitation in particular.
Apart from these circulation biases, the models showed other biases in
temperature and precipitation, which were for some models larger than the
circulation induced biases.
For the 21st century the five models simulated quite different changes in
circulation, precipitation and temperature. Precipitation changes appear to
be primarily caused by circulation changes. Since the models show widely
different circulation changes, especially in late summer, precipitation
changes vary widely between the models as well. Some models simulate severe
drying in late summer, while one model simulates significant precipitation
increases in late summer. With respect to the mean temperature the
circulation changes were important, but not dominant. However, changes in the
distribution of monthly mean temperatures, do show large indirect influences
of circulation changes. Especially in late summer, two models simulate very
strong warming of warm months, which can be attributed to severe summer
drying in the simulations by these models. The models differ also
significantly in the simulated warming of cold winter months. Finally, the
models simulate rather different changes in North Atlantic sea surface
temperature, which is likely to impact on changes in temperature and
precipitation. These results imply that several important aspects of climate
change in Central Europe are highly uncertain. Other aspects of the simulated
climate change appear to be more robust. All models simulate significant
warming all year round and an increase in precipitation in the winter
half-year. |