Their product? Carbon offsets. One carbon offset, or credit, equals a ton of CO₂ removed from the air.

Hedge funds and investment banks are starting to trade offsets like stocks and bonds, betting they could soar in value if greenhouse gas caps are imposed. JPMorgan (JPM) expects to buy and sell hundreds of millions of offsets this year, up from tens of millions last year.

For several years, entrepreneurs have had modest success selling credits to corporations and consumers who want to be good citizens and offset the carbon that's produced when they drive cars or use electricity.

Many are deploying tried-and-true techniques such as burning the noxious emissions of landfills and cow manure and restoring forests. Others are testing grander but more controversial strategies, such as growing carbon-absorbing plankton in the South Pacific.

The voluntary market for U.S. offsets is still meager, though it more than doubled last year to $150 million to $200 million, says research firm Ecosystem Marketplace. In Europe, which has complied with mandatory carbon limits since 2005 under the Kyoto treaty, the offset market hit $10 billion last year. Sales in the USA, the world's biggest carbon emitter, could be as high as $175 billion by 2020 if a federal cap is approved, says research firm New Carbon Finance.