THE INTERPRETER

THE NEW YORK TIMES

August 6, 2021

Welcome to The Interpreter newsletter by Max Fisher, who with Amanda Taub writes a column by the same name.

On our minds: A phenomenon you will want to know about if you worry about the future of the planet: dieback. The Climate Change Time Bomb A billion-acre ecological time bomb may be about to go off — if it hasn’t already — converting much of the world’s oxygen into climate-heating carbon dioxide. The time bomb, manifest in the Amazon rainforest, is a phenomenon known as dieback.   But deforestation and climate change may soon lead to a permanent change in the region’s climate, scientists warn. The rainforest would be eroded past the point at which it can produce enough rainfall to sustain itself. More forest would die out, further reducing rainfall, in a self-reinforcing feedback loop of self-destruction that, once begun, might not be possible to stop. Before long, much of the world’s largest rainforest could disappear, receding into a vast savanna.   This would be a terrible loss in its own right, stripping the world of much of its biodiversity, and more broadly, a climate disaster without an equivalent in world history. The region would cease to absorb climate-warming carbon dioxide and, in the process, release up to six times the annual carbon output of every coal-burning plant on earth. I first wrote about dieback, as this phenomenon is known, in 2019. That year, Thomas Lovejoy, a prominent environmental scientist, told me the scenario was “close. It’s really close.”   He added, “And it can happen in a very short period of time.” Two years later, a series of alarming events and scientific findings suggest that the warnings may soon, or even now, becoming to pass. This rainforest, the size of a continent, is integral to not just the ecosystem of South America but also the stability of the global climate. Its plant life constantly absorbs huge amounts of carbon dioxide from the atmosphere and returns oxygen. “If you look at the current weather patterns,” Dr. Lovejoy told me this week, “it looks to me like the tipping point is here and now.” How does dieback happen?   Scientists began to document the process in the 2010s. In one experiment, researchers found that if they subjected a plot of rainforest to small fires over several years, and if rainfall also declined, then something snapped. The proportion of plant life that died after a single fire spiked from about 5 to 60 percent — ecological death.   The fires, it turned out, had burned out much of the dense forest floor, which normally acts as a brake on fire. Invasive grasses filled in, providing fuel for future fires. Fires also thinned the trees, allowing future fires to burn faster and hotter. But a drop in rainfall was the crucial ingredient. It slowed regrowth, keeping the plot sparse. And it dried out those invasive grasses, turning the forest floor into a layer of fast-burning kindling.   Years of development in the Amazon have effectively reproduced this experiment on an enormous scale. Fires, many set deliberately to convert rainforest into farmland, have thinned much of the rainforest, while also allowing invasive grasses to rush in. Roads and other construction have also bifurcated the rainforest, thinning it out and exposing forest edges that dry easily and make for especially potent fire spreaders.   If this happens in a large enough area, it can severely reduce rainfall — creating the conditions that led to sudden ecological death in the fire study. Normally, plant life absorbs rainwater and groundwater, then sweats it back out into the atmosphere as moisture, seeding more rain. Less forest means less rain. Possibly a lot less.   Climate change exacerbates every part of this cycle. It is shortening the rainy season and raising temperatures. Forests are drier and thinner. The tipping point, past which the rainforest can no longer produce enough rain to keep itself healthy is much easier to reach. This process can take on a momentum all its own. And it is thought to naturally spread. As one area experiences dieback, neighboring rainforest becomes more exposed while also seeing rainfall drop.   “The models and they’re pretty consistent,” Dr. Lovejoy said in 2019, “suggest that the combination of fire and climate change and deforestation will weaken the hydrological cycle of the Amazon to the point where you just get insufficient rainfall in the south and the east, and then part of the central Amazon, to actually support a rainforest.” Is dieback happening now?   In the last two years, Dr. Lovejoy said, signs of this process have accumulated. Rainfall is down, he said, and temperatures are rising. He cited a 20 percent drop in corn production as a particularly worrying indicator. Past research has identified corn as especially sensitive to environmental changes from deforestation and climate change.   Amazon deforestation has been accelerating, indicating that there may be more than fires at work. Last year, the rate of deforestation increased 12 percent from 2019, which was already a catastrophic year for the Amazon. And it may be increasing further. Brazilian government figures show record rates of month-by-month deforestation. Even more worrying, parts of the Amazon has already flipped from net absorbers of carbon dioxide to net emitters, according to research released last month. It is an indicator that the process may already be beginning.   What does it mean for the world? The potential loss of the Amazon rainforest would provide not one but two of the greatest accelerants to climate change since the industrial revolution.   First, it would significantly reduce the rate at which the earth naturally converts carbon dioxide back into oxygen. It would be as if the amount of carbon produced by factories and cars suddenly shot up worldwide, simply because there was less to counterbalance it. Second, the process of deforestation itself deposits shocking amounts of carbon.   The rainforest is estimated to store about 100 billion tons of carbon as plant matter. When that matter burns, the carbon gets released into the atmosphere. That’s nearly seven times the amount of carbon emitted by every coal plant worldwide in 2017. Replacing much of the Amazon rainforest with a hot, dry savanna would also devastate one of the world’s largest centers of unique plant and animal species as well as many Indigenous communities. The knock-on ecological effects are hard to anticipate, but nobody thinks they would be good — or limited to South America.   “It’s an emergency situation,” Adriane Esquivel Mueller, a University of Birmingham ecologist, told the scientific journal Nature last year. “We can fix this, but we need to act now.” Daniel Nepstad, an environmental scientist who studies the Amazon, told me this week, “I am worried by fatalistic responses to these new discoveries — the sense of resignation that there is nothing we can do to manage the forest dieback. There is actually a lot that we can do.”   He added: “Amazon forests are tenacious. Give them a chance — protect them from fire — and they come charging back.” To Dr. Lovejoy and others, the answer is difficult but obvious.   “Time to act,” he said, defining that action with one word: “Reforest.”