Three years ago, a researcher collecting tree core samples in Connecticut was startled to see one of the trees begin to hiss and spit. Even more surprising, he found that the leaking gas could be set on fire. It’s been known since around the 1970’s that a relatively rare bacterial infection in trees responsible for the damaging rot known as wet wood can cause trees to emit methane, a greenhouse gas with 20 times the warming potential of carbon dioxide. Trees in wetland soils can also act as straws, sipping methane from soggy, oxygen-poor soil. Yale School of Forestry and...