Countries around the world are increasingly turning to tree-planting initiatives as a natural solution to climate change, but new research suggests that the effectiveness of these efforts depends less on the number of trees planted and more on where they are located. A recent study by ETH Zurich demonstrates that reforestation strategies can achieve similar global cooling outcomes using significantly less land if forests are planted in the most climatically advantageous regions.
Public enthusiasm for reforestation has grown through global campaigns such as the Trillion Tree initiative, which promote large-scale planting to absorb carbon dioxide. Estimates suggest that hundreds of millions of hectares of land could potentially be reforested, capturing vast amounts of CO₂. However, the new study challenges the assumption that simply maximizing tree coverage will deliver optimal climate benefits. Instead, it highlights the importance of strategic placement, showing that poorly located forests may offer limited or even counterproductive results.
To better understand these dynamics, researchers used advanced Earth system models to simulate three global reforestation scenarios. Unlike earlier studies, they incorporated both biochemical effects—such as carbon absorption through photosynthesis—and biophysical effects, including changes in surface reflectivity (albedo), evapotranspiration, and land surface properties. These combined factors determine how forests influence not just carbon storage, but also temperature, moisture, and atmospheric circulation patterns.
The findings reveal a striking insight: two scenarios with vastly different land requirements—differing by roughly 450 million hectares—produced nearly identical cooling effects. This demonstrates that strategic placement can dramatically improve efficiency. Tropical regions, particularly the Amazon basin, West Africa, and Southeast Asia, offer the greatest potential for climate cooling. In these areas, forests both store large amounts of carbon and enhance cooling through high rates of evapotranspiration, which releases moisture into the atmosphere and lowers local temperatures.
In contrast, large-scale reforestation in high northern latitudes such as Canada, Siberia, and Alaska can have unintended warming effects. Snow-covered landscapes naturally reflect sunlight, but dark tree canopies absorb more solar radiation, reducing reflectivity and increasing local temperatures. This albedo effect can offset or even outweigh the benefits of carbon sequestration, making such regions less suitable for climate-focused forest expansion.
The study also emphasizes that the impacts of reforestation extend far beyond local environments. New forests can alter atmospheric and oceanic circulation, influencing weather and climate patterns thousands of kilometers away. These complex, non-local effects mean that tree planting in one region can produce unexpected consequences elsewhere, reinforcing the need for coordinated global planning.
Despite its promise, the researchers caution that reforestation alone cannot solve climate change. Even under large-scale scenarios, the maximum projected reduction in global temperature is about 0.25°C by 2100. While meaningful, this contribution is small compared to the reductions needed to stabilize the climate. The study concludes that tree planting must be implemented in a “climate-smart” manner—targeting the most effective regions, avoiding monocultures, and integrating scientific insights—while remaining secondary to the urgent need for rapid reductions in fossil fuel emissions.
https://phys.org/news/2026-03-reforestation-greater-effect-climate-trees.html