Planting trees fights warming, but insurers ponder risks; Carbon credits could be worth billions of dollars for nations that agree not to cut.

Paying landowners to let forests grow is promoted by the United Nations as a viable way to fight global warming, but experts first have to puzzle out how to insure trees against going up in smoke. Forest owners want full access to credits as fast as possible. But insurers suggest that half be retained in buffer funds in case forests vanish in a few decades. If a forest disappeared, the credits in the funds would go to them. "How much land managers will see of the price is what the excitement is about," said Frances Seymour, head of the Centre for International Forestry Research (CIFOR) in Indonesia.