Hummer Greener Than Prius?
Very interesting post...got me thinking.
My ClimatePrediction.net client is currently chewing away on a pair of scenarios which, the app tells me, have approximately 3000 hours (wall-clock) to complete. By your figures, I'm adding roughly a ton of CO2 to the atmosphere for every four iterations I process (assuming I only leave the computer on to run CPDN, which is questionable).
If this is correct, it would perhaps be well for the Boinc people to call this out on their FAQ...