The role of forests in climate regulation is still greatly underestimated

If the need to speed up efforts to combat deforestation still has to be persuaded, a report published Monday, October 24 by the World Resources Institute (WRI), a US think tank specializing in environmental issues, provides additional arguments. This study, titled Not Just Carbon, emphasizes that forests are more important than decision-makers usually think in terms of climate regulation: beyond the carbon cycle, they have effects on temperature and precipitation, which affect the local, regional and global levels almost never taken into account. .

Today, forests are primarily a source of carbon dioxide emissions₂ They release carbon when they are destroyed, decomposed or burned and – and as a carbon sink – trees sequester it as they grow. Better protecting it could thus contribute to about a third of the mitigation efforts needed by 2030 to limit global warming to 1.5°C. But forest ecosystems have many other effects on the functioning of the climate system as a whole. “It also has biophysical effects by playing a role in the transfer of heat and moisture between the Earth’s surface and the atmosphere.”Frances Seymour, a forestry specialist at the Water Resources Institute, explains.

The four main influences of forests on climate, other than those related to carbon, have been clearly demonstrated by science. Albedo is the reflective force of the surface: Photovoltaic surfaces reflect a lot of solar energy back into space and can have a cooling effect. Conversely, the boreal forest canopy, for example, is much darker than the snow below, absorbing this energy and contributing to global warming. The trees then release moisture into the air and act as a kind of natural air conditioning, a phenomenon called “transpiration evapotranspiration.” The “rough” or uneven character of the canopy also affects wind speed and turbulence, helping to carry heat and moisture away from the surface of the earth. Finally, trees release small particles, aerosols, which interact with the atmosphere.

Transport of moisture across continents

Taken together, all of these effects have an effect on the production of clouds that contribute to the cooling of the planet. “After the major storms that destroyed part of the forests in the lands in 1999, we can observe a decrease in clouds in the area”, confirms Dennis Lusto, director of research at the National Research Institute for Agriculture, Food and the Environment (Inrae) who specializes in the interactions between forests and climate. According to recent scientific work, when these non-carbon dynamics are taken into account, the impact of tropical forest destruction on global warming increases by 50%. “Therefore, tropical forests are much more important for climate regulation than previously thought, which means that a larger share of funding for combating deforestation must be allocated to them.”Frances Seymour insists.

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