An Amazon collapse could 'come sooner than we thought'
Up to half of the Amazon rainforest could turn into grasslands or weakened ecosystems in the coming decades, a new study shows, as climate change, deforestation and severe droughts like the ones the region is currently experiencing damage vast areas beyond recovery .
Those stresses in the most vulnerable parts of the rainforest could ultimately push the entire forest ecosystem, where a tenth of the planet's land species live, into acute water stress and beyond a tipping point that would cause a forest-wide collapse, researchers said.
Although previous studies have assessed the individual impacts of climate change and deforestation on the rainforest, this peer-reviewed research shows that published Wednesday in the journal Natureis the first major study to focus on the cumulative effects of a range of threats.
“This study puts it all together and shows how this tipping point is closer than other studies estimate,” said Carlos Nobre, an author of the study. Dr. Nobre is a Brazilian earth system scientist who studies how deforestation and climate change can permanently alter the forest.
The study overlayed data on forest cover, temperature and rainfall patterns, and then took into account other variables that could make different parts of the forest more or less vulnerable, such as the presence of roads or legal protections, to map where the rainforest is located. most located. will probably transform.
The regional profiles that emerged showed that a tenth of the Amazon region was highly vulnerable to transformation into grasslands or degraded ecosystems with fewer trees. Another 47 percent of forests have moderate potential to transform, including largely pristine areas that are more vulnerable to extreme droughts like the current one.
These changes could push the forest to a tipping point that would lead to the collapse of the entire forest ecosystem.
“We don't really know when we are going to achieve this,” said Bernardo Flores, a postdoctoral researcher at the Federal University of Santa Catarina and lead author of the study. But, he added, as evidenced by last year's drought, “we've gotten there faster than we thought.”
Lincoln Muniz Alves, a climatologist at the National Institute for Space Research in Brazil who was not involved in the study, said the research contributed to a growing body of knowledge about the forest's resilience to the variety of challenges it faces. confronted. “The study makes progress in understanding the tipping point,” he said. “In general, previous scientific papers have mainly examined the impact of deforestation.”
Recent research has shown that parts of the southeastern Amazon forest that have suffered large-scale deforestation and fires have already started emitting more carbon dioxide than they absorb, because the rainforest there has already been damaged beyond the point of recovery.
The collapse of part or all of the Amazon rainforest would release the equivalent of several years' worth of global emissions, possibly as long as 20 years, into the atmosphere as the trees, which store vast amounts of carbon, are replaced by degraded ecosystems. And because those same trees pump enormous amounts of water into the atmosphere, their loss could also disrupt global rainfall patterns and temperatures in ways that are not yet well understood.
The researchers also estimated the limits of what the forest can withstand in terms of various threats. Global warming must not exceed 1.5 degrees Celsius, deforestation must be kept below 10 percent of the original tree cover and the annual dry season must not last longer than five months for the forest to remain intact, it shows the study.
To do this, governments must not only halt carbon emissions and deforestation, but also restore at least 5 percent of the rainforest, the study said.
“If you exceed these thresholds, the forest can basically collapse or merge into other ecosystems,” said Dr. Flores. “There is probably one tipping point in the system that is formed by the interaction of these different stressors.”
However, there are still unknowns. Researchers don't fully understand why some trees die after a drought while others don't; different biodiversity profiles in different regions make general conclusions difficult; and crucially, scientists still do not fully understand the complex interactions between factors such as drought, deforestation and other threats.
Still, says Marina Hirota, a professor at the Federal University of Santa Catarina and another author of the paper, governments should not wait until there is more clarity before taking action. “Sometimes it takes a little longer for science to really figure out what we need,” said Dr. Hirota. “Are we going to wait and blame uncertainty for our inaction?”
Raymond Zhong reporting contributed.