Just because you can't see it doesn't mean you can't sell it. In 2007, companies, nonprofits and countries traded more than 2.7 billion tons of CO2 - worth $59 billion - and many of the deals were struck at this powwow. As well as hustling for developing countries' carbon credits, this year's 2,600 attendees including execs from the likes of BP, Deutsche Bank and Toyota are expected to discuss the effects of the Bali climate agreement and new carbon-capture technology.