A push to promote wood as a source of renewable, low-carbon energy has set off a debate among scientists about the implications for the climate and forest ecosystems. Much of the discussion has revolved around forests in the southeastern United States, where a wood pellet industry is booming as the region supplies wood for European power plants, where the fuel has been deemed “carbon neutral.” Other parts of the world are also starting to tap into wood for electricity. Some scientists say that sustainable logging for energy recycles carbon as new forests grow back. But others caution this process could take decades, whereas carbon emissions from burning the wood are happening now.