Under the battering of global warming and deforestation, the Amazon is approaching a "tipping point" more quickly than expected, which could transform the largest tropical forest in the world into savannah, a carbon sink vital for the balance of planet.

To arrive at this alarming new finding, published Monday in the journal Nature Climate Change, researchers analyzed 25 years of satellite data to assess the resilience of the Amazon rainforest to traumas such as fires or droughts.

And, this key indicator of the overall health of the Amazonian ecosystem has dropped over more than 75% of its surface and up to 50% in resilience capacity in the most abused places, especially near human activities or affected. by droughts, explains to AFP Tim Lenton, of the British University of Exeter, co-author of the study.

According to models, global warming alone could push the Amazonian forest towards an irremediable transformation into savannah.

The latest report from the IPCC, the UN climate experts, published a week ago, again alerted to this possibility, which according to certain models could be triggered around 2050.

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"But obviously it's not just climate change, people are cutting or burning the forest, which is a second pressure point," Lenton continues.

"These two factors interact, so there are concerns that the transition will occur even earlier."

In addition to the Amazon, systems as important for planetary balance as the ice caps, "permafrost" (permanently frozen ground, particularly in Siberia) which contains enormous quantities of methane or CO2, coral reefs, South Asian monsoon regime or Atlantic ocean currents, are threatened by these "tipping points", which could radically alter the world in which we live.

In the Brazilian Amazon, deforestation has reached record levels since President Jair Bolsonaro came to power in 2019. According to a recent study, Brazil's Amazon rainforest, which accounts for 60% of the total, has already gone from "carbon sink » a net carbon source, releasing over the last decade 20% more of this powerful greenhouse gas than it has absorbed.

The recent IPCC report underlined the extent to which natural ecosystems were threatened even though their good health could contribute effectively to the fight against climate change.

Land and vegetation have thus absorbed a third of CO2 emissions year after year since 1960.

Vital evidence

The transformation into savannah of the Amazon basin would therefore have enormous consequences, both regionally and globally, warn the authors.

Some 90 billion tonnes of CO2 - twice the annual global emissions from all sources combined - could then be released into the atmosphere... further accentuating the warming.

At the regional level, it is not the forest alone that would suffer: "if you lose the role of the Amazon in the rain cycle, there could be consequences for central Brazil, the agricultural heart of the country", underlines Tim Lenton.

To assess the resilience of the forest, the researchers analyzed data measuring its biomass and the “greenness” of the canopy.

“Many researchers have theorized a tipping point (…) Our study provides vital empirical evidence that we are approaching this threshold”, analyzes Niklas Boers, professor at the Institute for Climate Impact Research in Potsdam (PIK) and co-author of the study.

“If we lose too much resilience, dieback could become inevitable.

But it will only be obvious once the event that will cause the system to tip over has passed,” warns the researcher.

For Tim Lenton there might then be a slim chance of restoring the situation.

“If we could lower the temperature again, even after the tipping point, we could perhaps turn things around”.

But it would be necessary to count on techniques of massive extraction of CO2 from the atmosphere, non-operational, “and which involve their own risks”.

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