Check out climateprediction.net

ClimatePrediction.Net gateway: But I thought the science was already settled?

The aim of climateprediction.net is to investigate the approximations that have to be made in state-of-the-art climate models (read more about this). By running the model thousands of times (a 'large ensemble') we hope to find out how the model responds to slight tweaks to these approximations - slight enough to not make the approximations any less realistic. This will allow us to improve our understanding of how sensitive our models are to small changes and also to things like changes in carbon dioxide and the sulphur cycle. This will allow us to explore how climate may change in the next century under a wide range of different scenarios. In the past estimates of climate change have had to be made using one or, at best, a very small ensemble (tens rather than thousands!) of model runs. By using your computers, we will be able to improve our understanding of, and confidence in, climate change predictions more than would ever be possible using the supercomputers currently available to scientists.