Amazon rainforest becoming a source of CO2, study finds

Much of the Amazon basin now emits instead of absorbing CO2, due to climate change and deforestation, according to a study released Wednesday.

A major transformation for this crucial ecosystem in limiting global warming.

Based on hundreds of air samples collected at various altitudes over the past decade, the study published in the journal

shows that in particular the southeastern part of the Amazon has grown from a well of carbon to a source of CO², the gas responsible for global warming.

+ 3 ° C compared to the pre-industrial era

In the last fifty years, plants and soils have absorbed more than a quarter of CO² emissions, even when these emissions have increased by 50%. 

So if the Amazon - which is home to half of the tropical forests that are particularly efficient at absorbing this carbon and which stores 450 billion tonnes of CO2 in its trees and soils - becomes a constant source of CO2, tackle the climate crisis would become even more difficult.

According to the study, several factors are responsible for this development.

“Deforestation and forest degradation reduce the Amazon's ability to act as a carbon sink,” the authors write.

Among the causes of this degradation, the forests burnt to make way for livestock and agriculture.

Climate change is also a key factor: temperatures during the dry season have gained almost 3 ° C compared to the pre-industrial era, almost three times the global average.

The combination of all these factors "calls into question the ability of tropical forests to sequester large volumes of CO² derived from fossil fuels in the future," notes Scott Denning of the University of Colorado in a commentary also published in Nature. .

This question has worried scientists for a long time, but satellite data has so far failed to provide a complete answer, especially due to clouds over the region.

"Tipping point"

To get around the problem, the team of Brazilian researchers collected 600 samples of CO² and carbon monoxide between 2010 and 2018 at altitudes of up to 4.5 km above the ground.

According to their findings, the northwestern part of the Amazon is at equilibrium, absorbing as much CO² as it emits into the atmosphere.

But the east, especially in the dry season, becomes a net source.

Another recent study, using another methodology, came to the conclusion that the Brazilian Amazon emitted between 2010 and 2019 almost 20% more CO² than it emitted.

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 "tipping points" identified by scientists as key elements whose substantial modification could lead to the climate system. towards a dramatic and irremediable change.