Planting trees is widely recognized as an effective strategy against global warming, thanks to their ability to absorb CO2. However, a recent study published in Nature Communications highlights a paradoxically negative effect in some cases. The transformation of light soils, which reflect solar energy, into dark forests absorbs more heat, calling into question the universal effectiveness of reforestation.
The albedo question
The study points to the importance of albedo, the ability of surfaces to reflect sunlight, in assessing the climatic impact of reforestation. Terrain such as snow-covered ground, with its high albedo, becomes less reflective once wooded, increasing heat absorption. The results indicate that the climatic benefits of planted trees are overestimated by 20 to 80% if the effect of albedo is not taken into account.
Identification of suitable areas
Study co-author Susan Cook-Patton stresses the importance of choosing reforestation sites wisely. The study provides maps to guide decision-makers towards regions where reforestation would have the most positive climatic impact. Wetlands and tropical areas, such as the Amazon and the Congo Basin, are identified as ideal for their potential to store carbon with minimal impact on albedo.
Limitations of universal reforestation
Reforesting temperate grasslands and savannahs, where clear soil plays a crucial role in solar reflection, could be counterproductive. This cautionary note is intended to qualify the overall enthusiasm for reforestation, without consideration for local specificities. Cook-Patton highlights the need to target reforestation efforts to maximize climate yield per hectare, in the face of limited resources.
The study does not question the value of reforestation per se, but calls for a more strategic approach. By concentrating tree-planting efforts in areas where they are most beneficial to the climate, it is possible to maximize environmental benefits while avoiding undesirable effects. Cook-Patton underlines the importance of this research for targeted and effective climate action.
