Trees in the tropics cool Earth more than anywhere else

Planting more trees cools the planet and can help reduce fires, but the biggest climate returns per tree come from the tropics. That is the core message of new research, which shows that where we plant matters almost as much as how much we plant.

The study, led by the University of California, Riverside (UCR), found that forests help in two ways: they pull carbon dioxide from the air; and they change local physics at the surface and in the lower atmosphere.

Those physical effects are not uniform. In warm, wet regions they cool, while in some cooler, higher-latitude places they can nudge temperatures up.

Trees in the tropics work harder

“Our study found more cooling from planting in warm, wet regions, where trees grow year-round,” said study first author and UCR graduate student James Gomez. “Tropical trees not only pull carbon dioxide from the air, they also cool while releasing water vapor.”

“It’s not that planting elsewhere doesn’t help – it does – but the tropics offer the strongest returns per tree.”

Trees in the tropics can “sweat” day in and day out. Roots lift water, leaving open pores to take in CO2 for photosynthesis. Some of that water escapes as vapor, and the evaporation absorbs heat from the air and the leaves. The process is called evapotranspiration, and it represents nature’s air conditioning.

“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.”

The study also points to a second cooling pathway. As forests moisten the air, cloud cover can increase. Water vapor itself can soak up some incoming sunlight before it reaches the ground. Both effects dim the surface. Less sun at the surface means less heating.

Cooling depends on location

The team isolated these non-CO2 physical effects in climate models. Globally, the average cooling from the added trees was small, about 0.01°F. But the signal becomes meaningful in the tropics. There, the mean cooling reached about 0.1°F, with some hotspots – such as parts of central Africa – approaching 0.8°F.

When the researchers added in the expected carbon drawdown from new forests, the global cooling grew by roughly another 0.15°F.

The carbon part of the story is powerful, but the paper kept it “offline” as a first estimate. A follow-up study will simulate both the physical and carbon-cycle effects together, interactively, for tighter numbers.

“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.

Tree planting can backfire

Trees are darker than many open landscapes. In snowy or bright regions, more trees can absorb more sunlight. That can offset some of the cooling from evapotranspiration – especially where water limits tree “sweating” for part of the year.

In parts of Canada and the northeastern U.S., the models suggest new trees could slightly reduce net cooling and even raise local fire risk by drying fine fuels and trapping more heat at the surface.

“This is not an invitation to get rid of the trees growing there! They provide multiple benefits for ecosystems and diversity, reducing CO2 and cooling the surrounding areas,” Gomez said.

“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.”

Trees reduce fires in tropics

The analysis considered wildfires too. In many tropical savannas, adding trees can reduce burned area. That is because mature trees often resist fire better than grasses, and closed canopies can keep fuels cooler and wetter.

“In tropical savannas, and in other places around the world, trees are much more fire-resistant than grasses,” Gomez said.

In contrast, in some higher-latitude regions, the added absorption of sunlight and longer dry seasons can tilt conditions toward more frequent or more intense fires. The net effect depends on local fuel, moisture, and management.

A realistic planting map

The study did not take into consideration forests everywhere. It used a practical reforestation blueprint: plant where trees once grew, while avoiding displacing people and minimizing impacts on cropland. That approach keeps climate benefits aligned with social and food security realities.

To build confidence in the results, the team drew on 12 widely used climate models rather than relying on a single tool.

That ensemble approach smooths out quirks of any one model and better reflects the range of plausible outcomes considered in international policy analysis.

Smarter trees for a cooler planet

Trees are vital for meeting climate goals. But they are not a magic fix, and they are not all equal in their local effects. The best strategy should be targeted. Protect existing tropical forests first, then replant in tropical and warm, wet places where trees will thrive and “sweat” most.

Finally, restore in temperate regions with care, tuned to local albedo, water limits, and fire regimes. Everywhere, pair trees with deep emissions cuts.

The message is not to plant less outside the tropics. It is to plant smarter everywhere – and fastest where each tree does the most. In that spirit, the study offers both optimism and a map.

The planet can be cooled by growing forests, especially in the tropics. And with a “Goldilocks” mindset – neither too few nor too many trees for local conditions – we can stack climate wins with biodiversity and fire resilience, region by region.

The study is published in the journal npj Climate and Atmospheric Science.

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