Forestry and science

What role do forests play in the current climate and their global warming fate? A difficult question, as tropical deforestation, linked to demographic expansion in these regions, does not appear to be slowing down. Already, blows from extreme weather events, reinforced by greenhouse gas emissions, are raising fears that the Amazon rainforest has reached a “tipping point.”

Vast areas will then turn into wooded savannahs, disrupting regional ecosystems, but also the distribution of rainfall on the South American continent, which explains a book where the “powers” ​​of forests do not contain anything magical but are revealed through a scientific approach. ¹.

Deforestation or reforestation can have alarming effects. Deforestation in the equatorial region will directly warm it through the disappearance of evaporation from the trees, while the local absorption of solar energy will nevertheless decrease through increased albedo. But deforestation in the northern region, such as the taiga in Canada or Siberia, will have the opposite effect. During winter, it will be colder, because the albedo of a snow-covered meadow is higher than that of a coniferous forest.

The astute reader will have already guessed that for temperate regions, both situations will arise depending on the characteristics of the place (snow or rain, availability or lack of water in the soil in summer, size of the forest, etc.). In China, the 1.7 million hectares planted over the past 20 years show a 1°C decrease in average annual temperature (more decrease during the day and less at night) compared to crop areas if we observe temperate zones.

It is the opposite at high latitudes. An additional complication: afforestation of a semi-arid tropical area could lead to its heating, because evaporation would be low, due to the lack of water, and would not compensate for the lower albedo and thus greater absorption of solar radiation. So you should think twice before deciding on such an action.

The matter is further complicated by the role of forests in distributing rainfall. It participates in the process of “recycling” the continents – the return of water to the atmosphere after evaporation and transpiration – and accounts for the majority of precipitation over vast areas: within China, the lands south of the Amazon, and the central and western Sahel region. Therefore, the water resources of large populations depend on forest policies implemented thousands of kilometers away.