The Brazilian Amazon rainforest, victim of climate change and human activities, has rejected over the past ten years more carbon than it has absorbed, a major and unprecedented shift, according to a study published this week.
Without forests, one of the “lungs” of the planet which absorbs between 25 and 30% of greenhouse gases emitted by humans, climate change would be much worse.
But for several years, scientists have been worried about a loss of steam in tropical forests, and fear that they may less and less play their role as carbon sinks. And the concern comes in particular from the Amazon rainforest, which represents half of the tropical forests on the planet.
The study, published Thursday in Nature Climate Change by an international team, looks at the Brazilian Amazon, which represents 60% of this primary forest, and the findings are grim.
Between 2010 and 2019, this forest lost its biomass: the carbon losses of the Brazilian Amazon are about 18% greater than the gains, said in a statement the French Research Institute for Agriculture, Food and the environment (Inrae).
“This is the first time that we have figures which show that we have shifted and that the Brazilian Amazon is a net emitter of carbon, explains to AFP one of the authors, Jean-Pierre Wigneron, researcher. at INRAE.
For the moment, a priori, “the other countries are compensating for the losses of the Brazilian Amazon” and thus “the whole of the Amazon has not yet changed, but it could do so soon”, he continues.
“Until now, the forests, in particular the tropical forests, protected us by making it possible to slow down the warming, but our last bulwark, the Amazonia, is in the process of tilting”, warns the researcher.
The study also highlights the unrecognized but major responsibility for the “degradation” of the forest. Unlike deforestation which causes the wooded area to disappear, degradation includes everything that can damage it, without completely destroying it: weakened trees on the edge of deforested areas, selective cutting, small fires, tree mortality linked to drought. . Attacks less easily detectable than large areas razed to the ground.
Using a vegetation index from microwave satellite observations, making it possible to probe the entire vegetation layer and not just the top of the canopy, the study concludes that these forest degradations have contributed to 73% of carbon losses, against 27% for deforestation, which is however large.