How Well Do Coupled Models Simulate Today's Climate?

oupled climate models are sophisticated tools designed to simulate the Earth climate system and the complex interactions between its components. Currently, more than a dozen centers around the world develop climate models to enhance our understanding of climate and climate change and to support the activities of the Intergovernmental Panel on Climate Change (IPCC). However, climate models are not perfect. Our theoretical understanding of climate is still incomplete, and certain simplifying assumptions are unavoidable when building these models. This introduces biases into their simulations, which sometimes are surprisingly difficult to correct. Model imperfections have attracted criticism, with some arguing that model-based projections of climate are too unreliable to serve as a basis for public policy. In particular, early attempts at coupled modeling in the 1980s resulted in relatively crude representations of climate. Since then, however, we have refined our theoretical understanding of climate, improved the physical basis for climate modeling, increased the number and quality of observations, and multiplied our computational capabilities. Against the background of these developments, one may ask how much climate models have improved and how much we can trust the latest coupled model generation.