A groundbreaking study from the University of California, Riverside reveals that the climatic benefits of tree planting are highly dependent on geographic location, with tropical regions standing out as the critical zones where forestation efforts yield the most substantial cooling effects. This pioneering research, published in the reputable journal npj Climate and Atmospheric Science, challenges traditional assumptions by suggesting that while tree planting is globally beneficial for carbon sequestration, its localized temperature impacts differ considerably based on where new trees are established.
The study carefully analyzes data from 12 advanced climate models to assess the physical and biophysical influences of afforestation, beyond merely considering carbon uptake. Researchers found that trees planted in warm, humid tropical environments contribute more significant cooling compared to those in higher latitudes. The tropical trees’ ability to transpire year-round – releasing water vapor through their leaves – induces notable evaporative cooling, which works alongside carbon dioxide absorption to reduce ambient temperatures more effectively.
Transpiration acts much like human perspiration: as water is pulled from the soil through roots and evaporates from stomata in leaves, it cools both the tree and surrounding atmosphere. This “tree sweating” mechanism is most potent where water supply is abundant, such as tropical rainforests, enabling trees to moderate local climates by lowering surface temperatures and increasing humidity. These findings emphasize the importance of hydrological context in determining a tree’s cooling potential.
Beyond transpiration, the study highlights how increased atmospheric humidity from forests can promote cloud formation. Clouds then reflect sunlight, strategically shading the ground below and further suppressing surface warming. Additionally, water vapor itself absorbs certain wavelengths of solar radiation, acting as a natural filter that helps maintain cooler temperatures at ground level. The researchers quantified these combined physical effects as generating a weak global mean cooling of approximately 0.01° Fahrenheit, but this figure surged to about 0.1° Fahrenheit within tropical regions.
One striking example is central Africa, where tree planting was estimated to induce cooling effects as high as 0.8° Fahrenheit locally. These areas benefit from the dual effects of continuous transpiration and cloud coverage, making them hotspots for maximizing natural climate regulation. Importantly, when carbon sequestration is factored in — representing trees’ ability to pull and store CO2 — cooling effects are expected to amplify substantially, by about 0.15° Fahrenheit globally. This synergy between the carbon cycle and physical climate processes points to the multifaceted role forests play in mitigating warming.
On the other hand, the study draws attention to the nuances of tree planting in temperate and high-latitude zones. In these areas, trees might actually have a slight heating effect due to their darker canopies absorbing more sunlight than the snow or grass that previously covered the land. For instance, in parts of Canada and the northeastern United States, increased solar absorption caused by forests can lead to warming, counteracting the cooling advantages of carbon storage. Furthermore, these regions sometimes experience more fires linked to dense tree cover, diminishing the net benefits of forestation for climate mitigation.
Nevertheless, the researchers caution against interpreting this finding as a call to reduce tree cover in these northern areas. Forests provide vital ecosystem services beyond temperature regulation, including biodiversity support, carbon storage, and air purification. Instead, the study advocates for a carefully calibrated regional approach: employing a “Goldilocks zone” framework where tree density is optimized for maximum climate and ecological benefits without unintended side effects.
An additional layer of complexity uncovered by the researchers lies in how trees influence fire regimes across different biomes. In tropical savannahs, for example, tree presence can suppress wildfires, since trees retain moisture better than grasses and reduce fuel for fires. This suppression effect collaborates with the cooling mechanisms to provide strong positive impacts on the regional climate. Conversely, in some temperate zones, increased tree cover may raise fire risks under specific conditions, highlighting the variability of forestation outcomes worldwide.
The robustness of these findings stems from the researchers’ choice of a realistic forestation scenario. Instead of planting trees indiscriminately, the study modeled tree growth only in locations where forests had historically been removed, avoided potential deforestation hotspots, and carefully excluded areas used extensively for agriculture or inhabited by people. This nuanced approach improves the credibility of the results, helping to inform pragmatic policy decisions about reforestation as a climate intervention.
By integrating physical climate modelling and an understanding of ecosystem water cycles, this research offers a more holistic view of how forests interact with Earth’s atmosphere. It provides evidence that, while carbon sequestration remains crucial, the biophysical effects of trees—transpiration cooling, albedo changes, and cloud formation—must also be accounted for in climate models to accurately represent their net climatic impact.
These insights have significant implications for global reforestation initiatives, especially as policymakers and environmental organizations seek evidence-based strategies to harness nature-based solutions for addressing climate change. Prioritizing tropical regions for tree planting, safeguarding existing forests, and balancing forest density in temperate zones could make forestation efforts more effective in attenuating global warming, reducing wildfire risks, and supporting ecological resilience.
In sum, this UC Riverside study enriches our understanding of forestation’s nuanced role in Earth’s climate system. It underscores that the right tree in the right place can make a measurable difference not just in carbon reduction, but through an intricate set of physical processes that cool and stabilize the climate. As the world pursues ambitious tree-planting campaigns, these findings highlight the importance of strategic planning informed by regional climate dynamics and forest ecology.
Subject of Research: Climate effects of forestation and regional variability in temperature impacts
Article Title: Climate effects of a future net forestation scenario in CMIP6 models
News Publication Date: 8-Aug-2025
Web References:
https://www.nature.com/articles/s41612-025-01127-4
References:
npj Climate and Atmospheric Science, DOI: 10.1038/s41612-025-01127-4
Image Credits: Stan Lim/UCR
Keywords
Climate change mitigation, Climate change adaptation, Anthropogenic climate change, Climate change, Climatology, Atmospheric science, Earth sciences, Atmospheric chemistry, Atmospheric physics, Climate systems, Climate zones, Earth climate, Trees, Plants
