The Brazilian Amazon rainforest, victim of Man, has rejected since 2010 more carbon than it has absorbed, a major and unprecedented shift for this crucial ecosystem in limiting global warming, according to a new study.
Without forests, one of the “lungs” of the planet which absorbs between 25% and 30% of the greenhouse gases emitted by humans, climate change would be much worse.
But for several years, scientists have been worried about the loss of steam in tropical forests and fear that they may less and less play their role as carbon sinks.
The concern comes in particular from the Amazon rainforest, which represents half of the tropical forests on the planet.
The study, published this Thursday in
Nature Climate Change
by an international team looks at the Brazilian Amazon, which represents 60% of this primary forest.
Biomass loss
Between 2010 and 2019, this forest lost its biomass: the Brazilian Amazon thus emitted about 18% more carbon than it absorbed, with 4.45 billion tons rejected, against 3.78 billion tons stored.
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", explains a researcher at the French Research Institute for Agriculture, Food and the Environment (Inrae).
“Until now, forests, especially tropical forests, have protected us by helping to curb global warming.
But our last bulwark, the Amazon, is in the process of tilting, ”warns the researcher.
And "we do not know when the changeover could be irreversible".
" Breaking point "
With the melting of the ice caps, the thawing of permafrost or the disappearance of coral reefs, the decline of the Amazon rainforest is one of the “breaking points” or “tipping points” identified by scientists as key elements whose modification substantial could lead the climate system to a dramatic and irremediable change.
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 however 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.
By using a vegetation index from microwave satellite observations, which make 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, however large-scale.
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