New research shows that the reforestation climate-cooling effect depends more on where trees are planted than on how many are planted.
Planting trees has become one of the world’s most popular climate solutions. Governments, companies, and nonprofits have pledged to plant billions, or even trillions, of trees in an effort to absorb carbon dioxide and slow global warming.
But according to new research, simply planting more trees may not be enough. Scientists say the reforestation climate-cooling effect depends heavily on where it occurs, sometimes even more than on the number of trees planted.
The study, led by researchers at the University of California, Riverside, used advanced climate modeling to examine how forests influence temperature in different parts of the world. The findings suggest that location plays a surprisingly important role in determining whether new forests cool or warm the climate overall.
At first glance, this may seem counterintuitive. Trees absorb carbon dioxide through photosynthesis, storing carbon in trunks, roots, and soil. Because carbon dioxide is a major greenhouse gas, removing it from the atmosphere generally helps reduce warming.
However, forests also influence the climate in other ways beyond carbon storage. One of the most important factors is albedo, which refers to how much sunlight a surface reflects back into space. Snow, deserts, and grasslands tend to reflect more sunlight, while forests absorb more heat because their darker surfaces trap solar energy.
In colder or snow-covered regions, planting dense forests can sometimes reduce reflectivity enough to offset some of the climate benefits from carbon absorption. By contrast, tropical forests often produce a much stronger reforestation climate-cooling effect because they absorb carbon efficiently and help cool the atmosphere through evapotranspiration.
Evapotranspiration occurs when trees release water vapor through their leaves, which cools the surrounding air and influences cloud formation and rainfall patterns. This means forests affect climate not only chemically, through carbon storage, but also physically, through the energy and water cycles.
The reforestation climate-cooling effect is often strongest in tropical regions, where forests absorb carbon and cool the atmosphere through evapotranspiration. Photo by Mojahid Mottakin on Unsplash.
The UC Riverside study found that tropical and temperate regions generally produce stronger cooling benefits than some northern boreal regions. In many cases, where trees are planted matters more than planting as many trees as possible. That insight could reshape how reforestation projects are planned globally.
Over the past decade, large-scale tree-planting campaigns have become central to many climate pledges. Yet scientists increasingly caution that not all reforestation projects provide equal environmental benefits.
Planting monoculture forests, introducing trees into natural grasslands, or restoring forests in unsuitable climates can sometimes harm biodiversity or create weaker climate outcomes. The new research suggests climate strategies should focus not just on tree quantity, but on ecosystem suitability and regional climate impacts.
This does not mean tree planting is ineffective. Forest restoration remains one of the most important nature-based climate solutions available.
Global forests currently absorb billions of tonnes of carbon dioxide each year while also supporting biodiversity, protecting soil, regulating water cycles, and reducing erosion. However, the findings reinforce the idea that reforestation is scientifically complex.
The reforestation climate-cooling effect varies with latitude, rainfall, cloud cover, surface reflectivity, and interactions between forests and atmospheric systems. Researchers say this complexity highlights the importance of using climate models and ecological data when designing restoration programs.
The study also emphasizes that restoring existing degraded forests may often be more beneficial than creating entirely new forests in unsuitable locations. Protecting mature forests is especially critical because older ecosystems store enormous amounts of carbon and support highly developed ecological networks. In some cases, preserving existing forests may provide greater climate benefits than planting new trees elsewhere.
The findings arrive during a period of growing interest in nature-based climate solutions. Around the world, governments and businesses are investing heavily in reforestation and carbon offset programs.
Yet critics have warned that some tree-planting campaigns oversimplify climate science by focusing primarily on headline numbers such as “millions of trees planted.” The UC Riverside research suggests a more strategic approach is needed.
Rather than maximizing tree counts alone, future projects may need to prioritize restoring forests in locations where climate cooling, biodiversity, and ecosystem resilience align most effectively.
Importantly, forests also provide benefits beyond climate mitigation. They support wildlife habitat, improve air quality, reduce flood risks, and sustain local livelihoods. That means even forests with smaller direct cooling effects may still hold major ecological and social value.
Still, a more accurate understanding of the reforestation climate-cooling effect could help policymakers design projects that deliver stronger long-term outcomes.
Climate change is already altering ecosystems worldwide, making restoration decisions increasingly important. As temperatures rise and landscapes shift, choosing the right places for reforestation may become just as important as planting trees themselves.
The study ultimately challenges a simple narrative: more trees do not automatically equal more climate cooling. Instead, forests function as part of a highly interconnected Earth system in which geography, climate, and ecology all matter. For future reforestation efforts, success may depend not only on how many trees are planted, but on planting the right trees in the right places.
