The business world is gearing up to 'go green'. Although still being beaten into shape, California's September ruling to engage in a mandatory carbon cap, amongst other U.S. movements, is causing many businesses to rethink their environmental position and get ready to join the expected new carbon economy.

For now, trading in the United States is voluntary: 225 companies that have made promises to reduce greenhouse gases by 6 percent by 2010 are trading carbon credits on the Chicago Climate Exchange. Prices for the credits started around 90 cents per ton of carbon when the exchange was established in 2002; they now trade around $4.

Most experts said trading would pick up in California, which has passed greenhouse gas rules (they are being challenged in court), and in the Northeast, where a coalition of states are following California’s lead. But once national rules pass, as many experts predict, the market is expected to explode.

“This cottage industry has the potential to become one of the largest commodity markets in the world,” said Emma Stewart, director of research and development at Business for Social Responsibility, a nonprofit consulting and research organization.

For utilities and manufacturers, the ability to trade credits could take some of the sting out of regulation. “There is more certainty that we will be living in a carbon-constrained world through some sort of legislative activity, and that helps carbon take on a value,” said Sara S. Kendall, vice president for environment, health and safety for Weyerhaeuser, the forest products company.

That value, in turn, makes it easier to persuade shareholders and directors that it makes sense to invest in research on ways to cut emissions even beyond a mandatory level. - New York Times