Climate Change Corp. has an interesting article about the Chicago Climate Exchange, which began in 2003 with just 13 companies and the City of Chicago as members, but has grown to more than 250 members today.

In 2006, CCX contracts covering 10 million (metric) tons of emissions were traded, up from just 1.5 million in 2005. And volumes continue to rise. In the first two months of 2007, more than five million metric tons were traded.

Many companies involved, like Green Mountain Energy, say they are seeking to gain experience in carbon trading markets in anticipation of mandatory caps, while prices are low and trades are less risky.

Some, like DuPont and IBM, are more concerned with documenting reductions they are making in hopes of getting credit for them when caps do become mandatory.

Others, including American Electric Power, also want to show their shareholders and consumers that they are being proactive on climate change..