This pervasive vulnerability offers an early warning sign that the Amazon is approachingturning pointstudy authors say. Amid rising temperatures and other human pressures, an ecosystem could suffer sudden and irreparable death. More than half of the rainforest could be converted to savannah within decades – a transformation that would compromise biodiversity, alter regional weather patterns, and dramatically accelerate climate change.
Historically, the Amazon has been one of the most important “carbon sinks” on Earth, pulling billions of tons of carbon dioxide from the air and storing it in vegetation. Researchers fear that the sudden release of this carbon will make humanity’s most ambitious climate goal – limiting temperature rise to 1.5 degrees Celsius (2.7 degrees Fahrenheit) – out of reach.
“As a scientist, I am not supposed to be concerned. After reading this paper, I am very, very concerned,” said Carlos Nobre, a climate scientist at the Institute for Advanced Study at the University of São Paulo, who was not involved in the new research. Completely the wrong direction…If we cross the tipping point, that’s very bad news.”
Scientists say the Amazon is one of several “transformers” in the global climate. Rather than getting worse as the planet warms, these systems have the potential to suddenly switch from one phase to the next—perhaps with little warning.
Over the past 50 million years, the Amazon has been in the humid rainforest stage. The trees themselves ensured their continued existence: the evaporation of water from the leaves created an endless loop of rain, while a dense canopy prevented sunlight from drying out the soil. The forest’s features may have changed somewhat in response to ice ages, wildfires and rising seas, but it has always been able to return to its lush green state.
However, global warming and human-caused deforestation have hijacked this self-reinforcing system. Hotter conditions in the Atlantic Ocean prolonged the dry season in the Amazon by several weeks. By cutting roughly 17 percent of its treesPeople have undermined the water recycling mechanism in the forest. Trees stressed by drought are more susceptible to wildfire. The more trees die, the less rain falls, which in turn exacerbates tree death.
At a certain point, the ecosystem will lose more trees than it can recover in these hot, dry conditions. Dark, dense and humid tropical rainforests will give way to a more open savannah.
Mathematician Niklas Boerse, who contributed to the new paper, compared it to a person leaning on a chair. If they don’t lean too far, they can easily return to a four-legged position on the ground. But once they cross the tipping point, the entire system collapses. It is also much more difficult to get up again than it was to fall.
Scientists say satellite images analyzed by Bowers and his colleagues indicate that the Amazon is still teetering on the brink of an inversion. Looking at areas of forest with at least 80 percent of broadleaf tree cover — areas not severely affected by deforestation — the researchers found that the vast majority of forest patches recover more slowly after seasonal fluctuations than they did 20 years ago. The spaces in the driest southern reaches of the rainforest, as well as those closest to the roads, were the hardest hit.
“The loss of elasticity that we observed means that we are probably approaching that critical point,” said Boyers, who studies Earth system dynamics at the Technical University of Munich and the Potsdam Institute for Climate Impact Research. “But it also means we’re not past the tipping point, so there is hope.”
The Nature Climate Change paper does not specify when the Amazon may cross this dangerous threshold. Even after an ecosystem has been completely destabilized, it may persist until an external force – for example, a wildfire or severe drought – pushes it over the edge. Lead author Chris Bolton, a climate scientist at the University of Exeter, said the moment of no return may not be apparent until it is too late to do something.
“My friend uses Wile E.Coyote’s idea as he runs off a cliff,” Bolton said. “He looks fine, and suddenly he looks down and realizes he’s over the cliff.”
And that’s what makes this study – the first experimental assessment of instability across the entire rainforest – so valuable, he added. “If we show that one of these systems is heading toward a tipping point, that could make people wake up,” Bolton said.
For 10 percent of the known species living in the Amazon, the loss of the rainforest could signal the death knell. A catastrophic death would put the millions of people who depend on the ecosystem for food at risk; 70 percent of the rain that falls in northern Argentina, a breadbasket in South America, comes from the Amazon trees.
Bypassing the Amazon’s tipping point will also unleash several years of global greenhouse gas pollution into the atmosphere. Previously, Studies show Some regions of the Amazon emit about 300 million tons more carbon than they draw from the air – an amount roughly equal to the annual emissions from Japan.
Scientists have warned that the global warming consequences of suddenly losing half of the rainforest will be felt thousands of miles away and for centuries into the future. That could mean storm surges, exacerbation of wildfires, chronic food shortages and a one-foot rise in sea levels that inundate coastal communities. It could lead to other tipping points, such as the melting of the ice sheets or the disruption of South America monsoon.
However, unlike ice sheets and monsoon systems, which respond only to the amount of heat that humans trap in Earth’s atmosphere, the Amazon is pushed toward the tipping point by two forces: Elimination of Forests and climate change. This also gives the Boers hope, as it means that humanity has two strategies to protect the ecosystem.
“If we take one of those factors out of the equation, my hunch is that the system will be able to handle it,” he said. “That’s exactly what one has to say to the governments of Brazil, Colombia and Peru: Stop deforestation today.”
Terrence McCoy in Rio de Janeiro contributed to this report.
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