The "cap and trade" scheme is to use market mechanisms to reduce emissions in the most efficient way possible, while also funneling money into new "clean" technologies. And carbon trading is big business. Last week in Cologne, Germany, the World Bank released its "State and Trends of the Carbon Market 2008", and the numbers are impressive: the global market for greenhouse gas emission offsets more than doubled in 2007, to 64 billion dollars – or 47 billion euros. But there are clouds on the carbon horizon.

Report: Steve Zwick