The one factor impacting efficacy of planting trees for the climate, according to a new study

“Our study found more cooling from planting in warm, wet regions, where trees grow year-round,” lead author James Gomez of University of California, Riverside (UCR) said. “It’s not that planting elsewhere doesn’t help — it does — but the tropics offer the strongest returns per tree.”

This is because in addition to capturing carbon, trees cool the planet in a number of other ways. One significant one, whose effects the study quantified, is evapotranspiration.

“It’s just like the way sweating cools your body,” Gomez said. “In the tropics, there is constantly water available for trees, and that increases transpiration.”

Water vapour from the trees can also reduce the amount of sunlight that reaches the planet’s surface by soaking up solar energy. And in some cases, trees can have a fire suppression effect. “In tropical savannahs… trees are much more fire resistant than grasses,” Gomez said.