• Posted August 24, 2025

Where Would Planting Trees Help Most With Global Warming?

It’s a simple and common prescription for global warming and fire suppression: Plant more trees.

But where they’re planted makes a real difference, new research shows.

"Our study found more cooling from planting in warm, wet regions, where trees grow year-round," study first author James Gomez, a graduate student at UC Riverside, said in a news release. "Tropical trees not only pull carbon dioxide from the air, they also cool while releasing water vapor."

His team recently reported its findings in the journal npj Climate and Atmospheric Science. 

They found that trees planted at higher latitudes, like the U.S., could actually have a slight heating effect. 

"It’s not that planting [there] doesn’t help — it does," Gomez said. "But the tropics offer the strongest returns per tree."

The new research echoes an earlier UC Riverside study. It found that planting trees could cool Earth’s surface more than once anticipated. That research weighed the chemical effects of trees interacting with the atmosphere, while the new study focused more on the physical effects of tree planting.

Those effects include evapotranspiration — or in simple terms, "tree sweating." 

Roots of trees suck water from the soil. It travels up through the trunk and into leaves, where some evaporates into the air. This cools the tree and the air, as well.

"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."

Researchers noted that the resulting humidity can mean more clouds, and the water vapor itself helps reduce the amount of sun that hits the ground. 

The upshot: A modest cooling effect. 

Worldwide, it translates to an average 0.01 degree Fahrenheit.

In the tropics, though, it’s more significant — as much as 0.8 degrees F in some places, researchers said. 

Add to that the process of capturing and storing carbon dioxide from the air, and the worldwide effect of adding trees grows to about 0.15 degrees F, the study found.

"Though the non-CO2 effects are small, it is good news that they are not warming, which prior studies have indicated is likely," Gomez said.

His team based its research on what it described as a "relatively realistic scenario," planting trees in areas where they had been removed and would not displace people or farmland. The analysis relied on data from 12 climate models.

It also looked at trees and fire suppression — a key issue in regions like Western states, where wildfires are a perennial threat.

In some cases, the study found, trees can help prevent fires. That includes tropical savannahs, because trees are more fire-resistant than grasses. 

But in the northeastern U.S. and parts of Canada, trees would probably cause more fires and absorb too much sun, reducing cooling, the study found.

"What we need is a Goldilocks zone of trees in each region," Gomez said. "Just the right amount to have the strongest and most positive climate effects."

More information

The International Tree Foundation has more about planting trees to ease global warming. 

SOURCE: University of California-Riverside, news release, Aug. 18, 2025