The Amazon is losing its ability to recover from disturbances such as droughts and land use changes, scientists reported on Monday, raising concerns that the rainforest is approaching a critical threshold beyond which it will end. replaced by grasslands, which would have huge consequences in terms of biodiversity and climate change.
The scientists said their research did not identify when that threshold, the tipping point, might be reached.
“But it’s worth bearing in mind that if we reach that tipping point, if the loss of the Amazon rainforest becomes irreversible, the effect on climate change will be significant,” said Tim Lenton, director of the Global Systems Institute, in University of Exeter, England.
Losing the rainforest could result in the release of up to 90 billion tons of heat-trapping carbon dioxide into the atmosphere, the equivalent of several years of global pollutant emissions. That would make it more difficult to limit global warming.
Among previous studies, there was a considerable degree of uncertainty as to when the threshold could be reached. But some research has concluded that deforestation, drought and other factors could lead to significant forest retraction (“dieback”) in the Amazon by the end of this century.
Carlos Nobre, a senior scientist at Inpa (Instituto Nacional de Pesquisas da Amazônia) in Brazil and one of the first to warn more than three decades ago about the potential loss of the Amazon, described the new study as “very convincing.”
“The study increased my anxiety,” said Nobre, who was not involved in the research.
Covering more than 5.1 million square kilometers, in Brazil and neighboring countries, the Amazon is the largest rainforest on the planet and serves a crucial purpose in mitigating climate change by absorbing more carbon dioxide from the atmosphere than it does. emits almost every year — in areas where the forest is already more degraded and destroyed, it already emits more carbon than it absorbs. In its diversity of plant and animal species, the Amazon is as rich as or richer than any other region on the planet. And it injects so much moisture into the atmosphere that it has the ability to affect the climate far beyond South America.
But climate change, combined with widespread deforestation and fires for agriculture and livestock, is harming the Amazon, making it hotter and drier every year. The region, one of the wettest on the planet, has experienced three droughts since 2000.
Most previous studies of the resilience of the Amazon have relied on models, or simulations, of how forest health might change over time. In the new research, the scientists used real observations: decades of remote sensing data from satellites that measure the volume of biomass in specific areas, data that offers a correlation to the health of the forest. Looking only at pristine parts of the rainforest, the researchers found that, since 2000, these areas have lost resilience. For example, forested areas are taking longer and longer to regain health after experiencing droughts.
“This lack of resilience demonstrates that, in fact, the forest has the ability to withstand only a certain threshold of damage,” said Paulo Brando, a tropical ecologist at the University of California at Irvine who was not involved in the study. “Recovery capacity is decreasing.”
But Brando said this was not necessarily a sign that reaching the tipping point was inevitable, and he pointed to the need to end deforestation and forest degradation in the region. “These systems are highly resilient, and the fact that we’ve reduced resilience doesn’t mean it’s been lost entirely,” he said. “If left untouched for some time, they come back very strong.”
The researchers found that more than three-quarters of the pristine rainforest lost resilience in the study period, and that the loss was greater in areas that are drier or closer to human activity, such as logging. The study was published by the scientific journal Nature Climate Change.
Chris Boulton, a researcher at the University of Exeter and lead author of the study, said the Amazon was like a giant water recycling network, with evaporation and transpiration from trees carried by the wind. As a result, the loss of part of the forest, and part of its moisture, leads to droughts elsewhere.
“You can imagine that as the Amazon starts to dry out, we’re going to see a more and more rapid loss of resilience,” Boulton said. Forests can then decline and die relatively quickly, and will become more like savannahs, overgrown with grass and with far fewer trees.
The loss of forest trees would not only return carbon trapped in their tissues to the atmosphere, savannas would absorb far less carbon than the large, broad-branched trees they would replace. A habitat like the savannah would also support a much smaller number of species.
Nobre said research shows that the Amazon “is on the precipice of this shift to a different ecosystem.” And if it did, he added, “this new ecosystem would be around for hundreds, maybe thousands of years.”
About 17% of the Amazon has been destroyed in the last 50 years and, although the pace of deforestation has slowed down for a few years in Brazil, it has recently resumed growth. The researchers said their work demonstrated that efforts to control deforestation would not only protect specific areas but would also have an effect on the resilience of the Amazon as a whole.
“They are absolutely correct,” Nobre said. “We have to reach zero deforestation, zero forest degradation”, adding that “we still have a chance to save the forest”.
Translation by Paulo Migliacci
