RIVERSIDE, Calif. — August 20, 2025 — Planting trees can help cool the climate and reduce wildfires, but the benefits are greatest in the tropics, according to a new study from the University of California, Riverside (UCR).

Published in npj Climate and Atmospheric Science, the study shows that while tree planting has a net positive effect on the climate worldwide, local temperature impacts vary by region. In higher latitudes, tree planting can sometimes produce a slight warming effect, whereas tropical trees provide the strongest cooling returns.

Why the Tropics Matter Most

“Our study found more cooling from planting in warm, wet regions, where trees grow year-round. Tropical trees not only pull carbon dioxide from the air, they also cool while releasing water vapor,” said study first author and UCR graduate student James Gomez. “It’s not that planting elsewhere doesn’t help – it does – but the tropics offer the strongest returns per tree.”

These findings build on earlier UCR research showing that tree planting may cool the planet more than previously expected. While prior work focused on the chemical effects of trees interacting with the atmosphere, this study emphasizes the physical processes at play.

How Trees Cool the Planet

One major mechanism is evapotranspiration, often called “tree sweating.” Tree roots draw water from the soil, which evaporates through pores in the leaves when they open to absorb carbon dioxide for photosynthesis.

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

Additional cooling effects include:

• Trees reducing sunlight that reaches the Earth’s surface.
• Water vapor increasing humidity, which can foster cloud formation.
• Water vapor itself absorbing some incoming sunlight.

Measured Cooling Effects

The physical effects of added trees yielded weak global cooling of about 0.01° F, but in the tropics this rose to 0.1° F, with some areas such as central Africa experiencing as much as 0.8° F of cooling.

When accounting for carbon sequestration, the cooling effect is expected to increase by another 0.15° F globally. Future research will refine these estimates by jointly simulating both the physical and carbon cycle effects of reforestation.

“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.

Fire Suppression Benefits

The study also revealed that trees can help suppress fires in certain regions. “In tropical savannahs, and in other places around the world, trees are much more fire resistant than grasses,” Gomez noted.

However, in some northern regions such as Canada and the northeastern U.S., tree planting may slightly increase fire risk and reduce cooling by absorbing excess sunlight.

“This is not an invitation to get rid of the trees growing there!” Gomez added. “They provide multiple benefits for ecosystems and diversity, reducing CO₂ and cooling the surrounding areas. What we need is a Goldilocks zone of trees in each region — just the right amount to have the strongest and most positive climate effects.”

Reliable and Realistic Results

The researchers used a realistic scenario, planting trees in areas where forests had been removed, avoiding deforestation, and limiting new plantings to areas that would not displace people or large amounts of farmland. To ensure robustness, they analyzed data from 12 climate models commonly used for international climate policy.

Summary

• Tree planting helps cool the planet and suppress fires, especially in the tropics.
• Evapotranspiration and reduced sunlight drive local cooling effects.
• Tropical regions can see up to 0.8° F of cooling, while global mean cooling is smaller.
• Carbon sequestration adds an estimated 0.15° F of global cooling.
• Trees reduce fire risk in tropical savannahs but may increase risk in some northern regions.
• Study used realistic planting scenarios and 12 climate models for reliability.

Original Publication
Authors: James L. Gomez, Robert J. Allen, Larry W. Horowitz, Steven T. Turnock, Rosie A. Fisher, Olivia E. Clifton, Bryan K. Mignone, Elena Shevliakova and Sergey Malyshev.
Journal: npj Climate and Atmospheric Science
DOI: 10.1038/s41612-025-01127-4
Article Title: Climate effects of a future net forestation scenario in CMIP6 models
Article Publication Date: 8-Aug-2025

Original Source: https://news.ucr.edu/articles/2025/08/18/trees-tropics-cool-more-burn-less

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