About half of carbon dioxide emissions are absorbed by trees and other plants. This carbon dioxide uptake is threatened by droughts, which are increasing in frequency. For the first time, scientists synthesized all known drought manipulation studies to determine how drought kills trees. They found that hydraulic failure is a universal component of tree death. Hydraulic failure is when a tree’s water-transporting tissue is disrupted by embolisms. Carbon starvation also occurs, but it is not universal.