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The world’s greatest, richest rainforest could be heading for permanent collapse. With help from climate change and the chainsaw, the Amazon could begin a process of inexorable change towards semi-arid grassland or savannah.
If so—and the warning is inevitably provisional—this would amount to a climate catastrophe, and trigger other tipping points in the planetary climate system, with unpredictable consequences.
The latest finding, published in the journal Nature Climate Change, is based on statistical analysis of satellite records of the forest’s canopy, and it confirms that the ability of the forest to recover from droughts or fires has been weakening since the century began.
At 5.5 million square kilometres, the Amazon rainforest biome sprawls across the land surface of more than eight nations. It is home to one in 10 of the world’s known species of plant and animal, and more than 400 Indigenous peoples. And as researchers have repeatedly confirmed, it is a self-sustaining ecosystem: that is, it conserves and recycles its own rainfall, to keep itself moist and green. But it is vulnerable, and its apparent stability is being disturbed by human action.
The researchers found that although average rainfall in the region had not changed greatly in the last few decades, the dry seasons had become longer, and droughts more common and more severe. Overall, the forest’s biomass—the sheer bulk of root and branch, stem and foliage—had declined a little, but the loss of resilience, the capacity to bounce back, was more pronounced.
“The Amazon rainforest is a home to a unique host of biodiversity, strongly influences rainfall all over South America by way of its enormous evapotranspiration, and stores huge amounts of carbon that could be released as greenhouse gases in the case of even partial dieback, in turn contributing to further global warming. This is why the rainforest is of global relevance,” said Niklas Boers of the Potsdam Institute for Climate Impact Research in Germany, one of the authors of the report.
“Reduced resilience—the ability to recover from perturbations like droughts or fires—can mean an increased risk of dieback of the Amazon rainforest,” he added. “That we see such a resilience loss in observations is worrying.”
Boers and British colleagues began their work under an EU research program to study potential tipping points in the global climate system. In March 2020, researchers warned that both rainforests and coral reef systems could be stressed to the point of collapse. A few months later, a second study of the Amazon region found evidence of potential headlong forest loss.
And last year, a third team calculated that one or more such ecosystem collapses could trigger a whole cascade of global change, all of this because humans have kept on burning fossil fuels, changing the chemistry of the atmosphere, and devastating what had once been undisturbed wilderness.
The latest research looked at month-to-month changes in the Amazon in response to weather conditions and rates of regrowth after disturbances—fires, droughts, and forest clearance—to test the forest’s capacity to recover.
“Resilience dropped during the major droughts of 2005 and 2010, as part of an ongoing decline from the early 2000s to the most recent data in 2016,” said study lead Chris Boulton of the University of Exeter in the UK. “As a result, we would expect the forest to recover more slowly from a drought now than it would have 20 years ago.”
And, said Boers, deforestation and climate change are likely the main drivers of this decline.
“Resilience is being lost faster in parts of the rainforest that are closer to human activity, as well as those with less rainfall,” he explained. “Many researchers have theorized a tipping point could be reached, but our study provides vital empirical evidence that we are approaching that threshold.”
When such a collapse could become inevitable is not, and perhaps cannot, be known in advance. But climate models predict an overall drying of the Amazon region in response to ever-rising greenhouse gas emissions, and the consequent rises in average global temperatures.
“If too much resilience is lost, dieback may become inevitable,” said Boers. “But that won’t become obvious until the major event that tips the system over.”
Study co-author Tim Lenton, who directs the Global Systems Institute at the University of Exeter, said the study result “confirms that strongly limiting the logging, but also limiting greenhouse gas emissions, is necessary to safeguard the Amazon.”
