Can Reforestation Really Cool the Planet and Where Should Trees Be Planted?

Planting trees on a large scale is often presented as a major solution to combat global warming. However, its actual impact on temperatures remains poorly understood and heavily depends on the locations chosen. A recent analysis reveals that reforestation can indeed cool the Earth, but with highly variable results depending on the regions and strategies adopted.

Forests affect the climate in two ways. On one hand, they capture carbon dioxide, reducing its accumulation in the atmosphere and cooling the planet. On the other hand, they alter the local environment by changing the reflection of sunlight, water evaporation, and surface roughness. In tropical areas, trees promote evaporation and create clouds that reflect sunlight, thereby lowering temperatures. Conversely, in cold regions such as Siberia or Canada, dark forests absorb more heat than snowy surfaces or grasslands, which can locally warm the atmosphere.

Three reforestation scenarios were compared using advanced climate models. The first envisions massive reforestation across nearly 900 million hectares, primarily in temperate and boreal zones. The second focuses on tropical regions, while the third, more modest scenario, covers about 440 million hectares. The results show that all these scenarios lead to global cooling, but with marked differences. The tropical scenario, although less extensive, provides cooling nearly as effective as the most ambitious one, as it avoids the warming effects observed at high latitudes.

Locally, reforestation clearly cools the tropics by increasing humidity and cloud cover. In the Amazon, Central Africa, and Southeast Asia, temperatures drop due to increased shade and evapotranspiration. In contrast, in boreal zones, replacing snow and grasslands with forests darkens the soil and traps more heat, offsetting some of the benefits related to carbon capture.

Another important phenomenon is the distant influence of forests. For example, reforestation in Europe or North America can alter atmospheric and oceanic currents, affecting temperatures in distant regions. Thus, poorly located projects could even worsen warming elsewhere, particularly by amplifying heatwaves or disrupting rainfall patterns.

The study emphasizes that the location of new forests is as crucial as their size. Targeted reforestation in tropical and subtropical zones maximizes climate benefits, while planting trees in polar or temperate regions can sometimes have the opposite effect. Climate policies must therefore consider these complex dynamics to optimize the impact of reforestation projects.

Finally, even in the best-case scenario, reforestation can only reduce global temperatures by a few tenths of a degree by 2100. This remains insufficient to meet the Paris Agreement goals without a drastic reduction in greenhouse gas emissions. Forests play an essential role, but they cannot replace an ambitious energy transition.

Credits and Attributions

Primary Source

DOI: https://doi.org/10.1038/s43247-026-03331-3

Title: Reforestation scenarios shape global and regional temperature outcomes

Journal: Communications Earth & Environment

Publisher: Springer Science and Business Media LLC

Authors: Nora L. S. Fahrenbach; Steven J. De Hertog; Felix Jäger; Peter J. Lawrence; Robert C. Jnglin Wills