By 2050, up to 47 percent of the Amazon could hit critical ecological tipping points, researchers say, transitioning into savanna grasslands or other degraded ecosystems because of deforestation and human-driven global warming.
This could mean the large-scale collapse of a biome that has for 65 million years has served as the Earth’s carbon sink, absorbing billions of tons of carbon while largely weathering changes in climate.
A study published Wednesday in the journal Nature says that by 2050, 10 percent to 47 percent of the forest is expected to reach critical thresholds for warming temperatures, extreme droughts, deforestation and fires. The ensuing ecosystem transitions could expedite global warming by releasing stored carbon into the atmosphere, the researchers write.
“At the end of this process, our planet will reorganize itself, find a new equilibrium,” Bernardo M. Flores, the lead author of the study, said in an email. But “humans and other species will have to readapt to very unpleasant conditions,” such as “unbearable aridity” or higher temperatures, he added.
The peer-reviewed study is the first comprehensive look that combines several metrics to document the Amazon’s degradation.
The study’s authors list five critical thresholds, or tipping points, that shouldn’t be passed, including keeping global warming to under 2 degrees Celsius, or 3.6 degrees Fahrenheit, compared with preindustrial levels (one of the goals outlined in the 2015 Paris agreement), keeping annual rainfall in the Amazon above 1,000 millimeters and containing deforestation to 20 percent.
The study’s authors, though, recommended stricter thresholds that they refer to as “safe” boundaries: 1.5 degrees Celsius (2.7 degrees Fahrenheit), 1,800 millimeters of annual rainfall and deforestation levels of under 10 percent.
“When a forest reaches a tipping point, it becomes much more difficult, if not impossible, to control the variables that cause it to transition,” Flores said. The result is a degraded ecosystem with less resources for local populations, less rainfall and more greenhouse gas, he said. Humans must reduce global warming and end deforestation of the Amazon to prevent this, he said.
The Amazon rainforest has long had a net cooling effect on the planet, by a process scientists call evapotranspiration. Amazon water near the Atlantic coast evaporates into the air, floating inland before becoming rainfall. That same moisture evaporates again, and floats farther inland before repeating the process, spreading water deeper and deeper throughout the Amazon.
The Amazon contains up to 200 billion metric tons of carbon, the equivalent of 15 to 20 years of global emissions.
But the Amazon’s ability to function as a natural shield against global warming has been gradually diminishing because of repeated droughts and higher temperatures caused by human activities such as logging, cattle ranching and fires.
About 17 percent of what remains of the Amazon today “has been degraded by human disturbances,” the authors write. When including the impact of recent, repeated droughts, about 38 percent of the rainforest may have been degraded, they added.
The Amazon was struck by droughts in 2005, 2010, 2015, 2016, 2020 and last year, The Post reported. The pace of big droughts has accelerated from once every 20 years to two per decade.
Erica Fleishman, the director of the Oregon Climate Change Research Institute at Oregon State University and who was not involved in the study, said the recent paper “effectively highlights that the interaction of climate change and land use can have ecological effects” that are substantial and enduring, although not necessarily catastrophic or irreversible.
The Amazon’s destruction will likely hurt the forest’s ability “to sequester carbon and mitigate global climate change,” she said in an email.
To slow or reverse this trend, South American governments must reduce deforestation and promote restoration in degraded areas, especially in Brazil, the authors wrote. “Up to one-third of the total annual rainfall in Amazonian territories of Bolivia, Peru, Colombia and Ecuador depends on water originating from Brazil’s portion of the Amazon forest.”
Carlos Nobre, one of the study’s authors and an earth systems scientist at the University of São Paulo’s Institute of Advanced Studies in Brazil, was among the first academics in the early 1990s to suggest that the Amazon would reach a tipping point, and transform into a degraded ecosystem, resembling a vast pasture.
In an email, Nobre said that he is becoming increasingly confident that Brazil and its neighbors will eliminate deforestation by 2030, pointing to slowing deforestation last year documented by Brazil’s government and the Amazon Conservation Association, a D.C. advocacy group.
“We have to get to zero deforestation and degradation very soon, and it seems we are going in that direction,” he said.
But Nobre and Noah Diffenbaugh, a professor of earth system science at Stanford University who wasn’t involved in the study, expressed concern about humans successfully keeping temperatures under 1.5 degrees Celsius, referring to how 2023′s temperatures teetered near the threshold.
“Given that we have just had a single year at 1.5 degrees C[elsius] and annual emissions of greenhouse gases remain high, there is a real risk that long-term global warming exceeds that boundary,” Diffenbaugh said in an email.
From the Washington Post, by Andrew Jeong