As trees grow, they absorb ever greater amounts of CO2 from the atmosphere. Consequently, the health of trees both determines climate and is determined by it. During heat waves and droughts, trees stop growing and almost entirely stop absorbing carbon. And because carbon is responsible for the increase in extreme weather events, the result is a vicious circle. Certain tree species, however, are largely able to compensate this effect: milder springs promote earlier "leafing out," which lengthens the period of growth during which trees metabolize CO2.
