From the site’s FAQ:
Your computer downloads and unpacks the experiment itself. The experiment will be running within about five minutes of the download finishing.
Your computer will start calculating variables such as temperature, cloud cover and snow fall.
The experiment runs in two phases:
- Your individual climate model is checked by running it from 1920 to 2000. If your model is very inaccurate (for example, your whole world turns to ice), then your experiment will end. See the FAQs under Ending the experiment.
- If the climate that your computer works out for 2000 is reasonably like what exists today, phase two begins automatically. Your set of conditions will run forward to predict future climate for every month up to 2080. Once your experiment has made its prediction for 2080, the final results will be automatically sent back to Oxford University.
Check out the official site for more details.
You can also check out an interview with Professor Bob Spicer [Windows Media] from the Open University.