Climate Futures

I just read Ronald's Bailey's latest piece on climate change. Towards the end Bailey mentions that MIT prof "Richard Lindzen says he's willing to take bets that global average temperatures in 20 years will in fact be lower than they are now." This prompted me to ask the obvious question: why isn't there a Tradesports contract on this yet? The contracts would be around for a while, but Tradesports already has contracts on the 2008 Presidential elections, so it's not that much of a stretch.