Climate Change 2001:
Working Group I: The Scientific Basis
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Executive Summary

This chapter evaluates the suitability of models (in particular coupled atmosphere-ocean general circulation models) for use in climate change projection and in detection and attribution studies. We concentrate on the variables and time-scales that are important for this task. Models are evaluated against observations and differences between models are explored using information from a number of systematic model intercomparisons. Even if a model is assessed as performing credibly when simulating the present climate, this does not necessarily guarantee that the response to a perturbation remains credible. Therefore, we also assess the performance of the models in simulating the climate over the 20th century and for selected palaeoclimates. Incremental improvements in the performance of coupled models have occurred since the IPCC WGI Second Assessment Report (IPCC, 1996) (hereafter SAR) resulting from advances in the modelling of the atmosphere, ocean, sea ice and land surface as well as improvements in the coupling of these components.

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Final Assessment

Coupled models have evolved and improved significantly since the SAR. In general, they provide credible simulations of climate, at least down to sub-continental scales and over temporal scales from seasonal to decadal. The varying sets of strengths and weaknesses that models display lead us to conclude that no single model can be considered "best" and it is important to utilise results from a range of coupled models. We consider coupled models, as a class, to be suitable tools to provide useful projections of future climates.

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