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Despite humans' insistence on leveling forests, trees still cover almost one-third of the earth. That's fortunate, because they reduce the amount of carbon dioxide in the atmosphere by converting CO2 into biomass (such as leaves and branches). However, trees covering 30 million acres are cut down each year -- to harvest wood and to clear land for agriculture -- a process that destroys biomass and so releases CO2 back into the atmosphere. Deforestation in the world's tropical regions alone emits more carbon dioxide than cars, trucks, and airplanes combined.

To help stop tropical deforestation, NRDC has joined forces with Call for Leadership, a U.S.-based group whose members include Kenyan Nobel Peace Prize laureate Wangari Maathai, U.S. senators John Kerry and Richard Lugar, and the chairmen of such corporations as Marriott International and Dow Chemical. Call for Leadership members are working to build consensus around anti-deforestation policies that could be included in proposed U.S. climate legislation as well as in the international climate agreement that will be negotiated in Copenhagen this December. One approach under consideration: creating economic incentives to conserve forests.