avatarQuentin Septer

Summary

The Amazon Rainforest is facing critical threats from deforestation, climate change, drought, logging, wildfires, and the edge effect, pushing it towards a potential ecological collapse by 2050.

Abstract

The Amazon Rainforest, essential for global ecological balance, is under severe threat due to human activities and climate change. Deforestation has cleared vast swathes of the rainforest for agriculture and cattle pastures, with an estimated 17% lost since the 1970s and another 38% degraded. The "edge effect," where forest fragments are more vulnerable to environmental stressors, is exacerbating the situation, making the rainforest more flammable and less resilient to climate change. Scientific studies warn that if current trends continue, nearly half of the Amazon could reach a tipping point by mid-century, transitioning into a savanna or grassland, which would have devastating impacts on the global water cycle and climate regulation. The urgency to halt deforestation, reduce greenhouse gas emissions, and restore degraded areas is paramount to prevent the Amazon from reaching this critical threshold.

Opinions

  • Dolors Armenteras Pascual emphasizes the importance of recognizing the edge effect's significant impact on the Amazon's health, which has been historically underestimated.
  • Bernardo Flores highlights the illegality of most deforestation and road-building activities in the Amazon, which facilitate further degradation and wildfires.
  • Carlos Nobre stresses the necessity of achieving zero deforestation and degradation, and the restoration of degraded areas to avoid the Amazon's tipping point, while also expressing concern over the global failure to adequately address climate change.
  • Scientists, including those who contributed to the recent Nature paper, are increasingly alarmed by the proximity of the Amazon's tipping point and the potential for irreversible ecological damage.
  • The consensus among experts is that immediate and decisive action is required to save the Amazon Rainforest, with a particular focus on curbing global warming to 1.5 degrees Celsius above pre-industrial levels.

Life on the Edge (of the Amazon Rainforest)

The “edge effect” is the Amazon Rainforest’s silent killer.

An aerial image of cattle pastures and a soybean plantation in a deforested area of the Amazon Rainforest near Porto Velho, Brazil. Image credit: Bruno Kelly/Amazônia Real

You don’t need to look far to see evidence of the Amazon Rainforest’s destruction. Vast swathes of the rainforest have been clear cut and converted into cattle pastures and farms raising maize and cotton and soybeans, among other crops. Tens of thousands of square kilometers go up in flames across the Amazon Basin every year; some 10,000 wildfires have blazed through 11,000 square kilometers of the rainforest so far this year alone. Millions of miles of roads, most of which are illegal, cut through the rainforest like the boring holes of termites through the bark of a Brazil nut tree.

At least 17 percent — about 1.1 million square kilometers — of the Amazon Rainforest has been deforested by human beings since the 1970s, and most of this deforestation has occurred since the turn of the century. Another 2 million square kilometers of the rainforest, an area about the size of Mexico, has been degraded by climate change, drought, logging, and wildfire.

“These are the four main drivers of degradation in the Amazon,” Dolors Armenteras Pascual, an ecologist at the National University of Colombia who has studied Amazonian ecosystems for decades, told me via a Zoom chat. She counted them off on her fingers. “Climate change, drought, logging, and wildfire — they’re common all over the Amazon.”

“Degradation means that you still have standing forest,” Armenteras Pascual continues, “but you are losing some of the structure, some of the functioning. You might even look and think it’s really a beautiful forest, but it’s not so healthy.”

One way to think about the degradation of the Amazon Rainforest is in terms of “water stress.” Hot, dry air saps the Amazon’s soil of its moisture. Tree roots struggle to draw water from desiccated earth. Some trees die as a result. Others begin to decline in health, losing their ability to absorb and evapotranspire water and perpetuate the humidity that is characteristic of the Amazon Rainforest. A recent Nature study on the Amazon tipping point estimates that 17 percent of what remains of the Amazon Rainforest has been degraded by a combination of climate change, drought, deforestation, and wildfire.

“But there is another driver of degradation in the Amazon Rainforest,” Armenteras Pascual tells me. “It’s called the edge effect. The edge effect is very important. It was ignored for a long time, but it’s become a very important thing because once you start measuring it, you see that the impact is much bigger than we thought.”

When considering the edge effect, the Nature study mentioned above found that 38 percent of the Amazon Rainforest has been degraded, rendered more flammable and more vulnerable to climate change.

An aerial image of a forest edge near Flona do Jacundá in Rondônia, Brazil. Image credit: Bruno Kelly/Amazônia Real

“Imagine,” Armenteras Pascual implores me. “You have an intact forest, a big piece of intact forest, right?”

I nodded. “Mhm.”

At 6.7 million square kilometers in size — an area about twice the size of India — the Amazon Rainforest accounts for half of the remaining rainforest on Earth. It is the largest swathe of contiguous forest left on the planet, and its continuity is vital to its functioning.

“You have this humongous forest, and it’s a system,” Armenteras Pascual continues. “And it’s functioning very well. The trees are absorbing water and that water evaporates back into the atmosphere. We’re talking about humid forests, right? The humidity is part of the characteristic of the Amazon forest.”

Moisture from the Atlantic Ocean rolls inland off the coast of Brazil, much of which falls as rain over the Brazilian Amazon. The trees of the Amazon, some of which can grow more than 250 feet tall, absorb this rainfall through their roots and evapotranspire this water back into the atmosphere through the stomata on the surface of their leaves. A single mature tree in the Amazon Rainforest recycles 1,000 liters of water per day. “One thousand liters per tree per day,” Armenteras Pascual says. This water is cycled and recycled from tree to tree across the rainforest, which flows gradually westward in atmospheric currents that sweep across the Amazon Basin. A single water molecule can be recycled eight times — by eight different trees — before leaving the rainforest by way of the Amazon River, or rising to form clouds that drift across the South American continent and around the globe. In this manner of cycling and recycling water from tree to tree across the rainforest, the Amazon generates up to half of its own rainfall. “The Amazon forest itself,” the science journalist Daniel Grossman wrote in a feature story for Nature last year, “helps to create the conditions that nourish it.”

All this moisture creates the humid conditions in which the Amazon and its three million species have evolved, and on which these species have evolved a reliance. The species of the Amazon Rainforest — everything from a bullet ant to a kinkajou to a Harpy eagle to a Demerara Falls tree frog — depend on the moisture that is cycled and recycled by the Amazon’s 390 billion trees. So do the 40 million human beings who live in the Amazon Basin, including 2.2 million Indigenous peoples of more than 300 ethnicities.

“But when you build a road,” Armenteras Pascual says, “or you deforest, or you make a soy field or whatever, you create fragments of forest. So suddenly the forest is no longer continuous, and you have an edge. The forest stops here.”

Deforestation isn’t limited to a single, massive plot of the Amazon Rainforest. Deforestation frontiers, as they’re known, are scattered across the Amazon, even in “central and remote parts of the system,” the recent Nature paper states. The forest is cleared and converted into a cattle pasture here, a soybean farm there, a gold mine over there. You can see this for yourself. On Google Earth Engine, an extension of Google Earth, you can view satellite images of any place on our planet, and see first hand how that place has changed over the last forty years. Take a look at the Amazon Basin and play the timelapse, and you’ll see patches of the rainforest disappear year over year. You’ll see islands of forest gradually surrounded by pastures and cities and farmlands. You’ll see roads growing and extending deeper and deeper into the Amazon Rainforest like neurons sending axons and dendrites through brain tissue. Some 3.46 million kilometers of roads (the vast majority of which are illegal) carve their way through the Brazilian Amazon alone. Tied end to end in one long string, all these roads could wrap around our planet 85 times.

All these roads, mines, pastures, and farmlands carve the Amazon up into smaller and smaller fragments of forest. The forest has more edge as a result. More and more of the Amazon Rainforest exists on the edge of deforested land. At a glance, this forest on the edge looks healthy, “but it’s already been degraded,” Armenteras Pascual says. “It was something else before.”

In the absence of shade cast by the surrounding forest canopy, the trees on these edges of the Amazon Rainforest are more exposed to wind and sunlight and dry air. “The microclimate changes,” Armenteras Pascual says. “The forest dries out.” Some trees die from this lack of moisture and this abundance of wind and sunlight. Surviving trees are degraded. This is what is known to ecologists as “the edge effect.”

Dolors Armenteras Pascual calls this process an “ecological cascade.” Overtime, these edge effects penetrate deeper and deeper into the forest. As more trees die and struggle to draw and transpire water, larger tracts of forest — tracts further away from the forest’s edge — are killed and degraded.

A 2020 study published in Scientific Reports examined the extent of edge effects in the Brazilian Amazon. In the Brazilian Amazon, the study found, edge effects can spread more than half a kilometer into the rainforest. In some places, edge effects can penetrate more than a kilometer into the surrounding forest. On a landscape as massive as the Amazon Basin, that might not seem all that far; but when considering the 3.46 million kilometers of roads that have carved the Brazilian Amazon into fragments of its former self, only a small fraction of the rainforest exists far enough away from a road (or some other deforestation frontier) to be unaffected by the edge effect. More than 80 percent of the Brazilian Amazon has been degraded — and is continuing to be degraded — by edge effects. The story is the same across much else of the Amazon Rainforest (and, it should be said, much else of the planet’s remaining forests, beyond the Amazon Basin, as nearly 70 percent of the world’s remaining forests exist within 1 kilometer of a road).

“Would it be fair to say that the edge effect makes parts of the Amazon more vulnerable to climate change?” I asked Dolors Armenteras Pascual.

“Absolutely,” she said. “There’s science behind that as well.”

Another study, presented at the American Geophysical Union’s annual fall meeting in 2022, analyzed satellite imagery of the Amazon Basin from 1985 to 2020. The team, led by Ling Meng, an assistant professor of Earth and Environmental Sciences at Vanderbilt University, found that land surface temperatures in parts of the Amazon affected by the edge effect tend to be warmer than large, contiguous tracts of rainforest — those more distant from the forest’s edge. They also found that the parts of the Amazon impacted by edge effects tend to have fewer trees — less “aboveground biomass,” in the words of the study. And fewer trees, of course, store less carbon and filter less water, making these tracts of forest more exposed to blazing temperatures and dry air. Meng’s team also found, unsurprisingly, that most of the Amazon’s wildfires burn near a forest edge. About 82 percent of wildfires to burn in the Amazon Rainforest between 1985 and 2020 burned within a kilometer of the forest’s edge, the study states, “but this distance increased under recurring burns or a warmer dry season. These findings indicate forest degradation leads to higher vulnerability at forest edges under a warmer and drier climate in the Amazon.”

Nearly all of the deforestation, and all of the road building, in the Amazon Rainforest is illegal, Bernardo Flores, a researcher at Brazil’s Federal University of Santa Catarina who studies climate change in the Amazon Rainforest, told me. “Roads facilitate all kinds of illegal activities that lead to deforestation and forest degradation,” Flores says. A 2014 study published in Biological Conservation found that nearly 95 percent of deforestation in the Amazon takes place within five kilometers of a road or one kilometer of a navigable river.

And once a part of the Amazon is deforested, wildfire tends to follow.

Perhaps the term “wildfire” is misleading, as most of the fires that burn in the Amazon Basin are intentionally started by human beings. “In some of the places where deforestation is going on,” Armenteras Pascual tells me, “humans cut the forest just before the dry season so they can burn and clear the land when the dry season begins. That’s business-as-usual in the Amazon.” Farmers burn their pastures and farmlands during the dry season to renew their grass and provide their soil with nutrients. (Then the rain comes, providing their crops with ample water to grow.) These are called “deforestation fires,” and they are the most common cause of wildfire in the Amazon Basin. Of the 983 major wildfires to burn in the Brazilian Amazon in 2022, for example, about 700 blazed in regions that had been deforested within the previous three years.

What is often unintentional, yet all-too-common, is when these deforestation fires enter the standing forest — the forest on the “edge.” Simply put, the edge effect makes the rainforest more flammable, and more susceptible to the effects of climate change and drought. Forests on the edge are drier, more exposed to wind and sunlight, blazing temperatures and dry air. “If the forest is very dry,” Armenteras Pascual says, “it’s very likely that a pasture fire [or deforestation fire] will enter the standing forest. The more edge, the more likely it is that fire will enter the forest.”

The forest, already degraded by the edge effect, is further degraded by wildfire. Trees die, replaced by more fire-tolerant (and flammable) plant species, like ferns and palm trees and invasive grasses. “So there’s a feedback loop,” Armenteras Pascual continues. The edge effect degrades the forest in a way that predisposes it to wildfire, and wildfire further degrades the forest, making it more likely to burn again. It’s a vicious cycle.

“Fire is a contagious process,” Bernardo Flores told me. “When a forest burns, trees die, releasing organic matter above the soil and opening the canopy. Hence, more fuel is available and more sunlight and wind can desiccate this fuel, causing the ecosystem to become more flammable. The consequence is that burnt forests are much more likely to burn again than the unburnt forest.”

Deforestation in the state of Rondônia in western Brazil. Image credit: NASA’s Earth Observatory

Bernardo Flores, as I mentioned earlier, is a researcher at Brazil’s Federal University of Santa Catarina who studies climate change in the Amazon Rainforest. He’s also the lead author of a Nature paper that has made waves in the media and scientific community as of late. “I’m still processing the implications of the paper,” Flores told me a couple weeks back.

The paper, “Critical transitions in the Amazon forest system,” examined the trends contributing to the degradation of the Amazon Rainforest — climate change, drought, deforestation, wildfire, edge effects — and developed models projecting these trends into the future. The forecast is gloomy. By 2050, Flores and his team’s models show, temperatures over the Amazon Basin are expected to be 2 to 4 degrees Celsius warmer than they are today, depending on greenhouse gas emissions over the next two and a half decades. The Amazon’s dry season may grow a month longer than the dry seasons of today. Wildfires are expected to increase in frequency and severity.

As a result, Flores and his team estimate that nearly half the Amazon may reach a “tipping point” by 2050, at which point it will cease being a rainforest at all and collapse into an arid swathe of savanna and grassland.

The team also found that the rainforest is particularly vulnerable along its edges. Ten percent of the Amazon Rainforest has a “relatively high transition potential,” the study states. Ten percent of the rainforest, in other words, is facing a high risk of collapse. Portions of the rainforest bordering the savannas of Guyana, Venezuela, Colombia, and Peru are “bistable,” teetering on the edge of a collapse into a non-forest ecosystem. The same is true of more central portions of the rainforest, including those along Trans-Amazonian highways like Brazil’s Highway BR-319. “Smaller areas with high transition potential were found scattered within deforestation frontiers,” the study states, “where most forests have been carved by roads.”

Road networks give people access to tracts of rainforest that were once remote and essentially inaccessible. The only way to get there was by boat, aircraft, or on foot. But roads pave the way for loggers and farmers, along with the heavy machinery needed to transport the rainforest’s felled trees, some of which weigh several tons.

“Road networks facilitate illegal activities, promoting more deforestation, logging and fire spread throughout the core of the Amazon forest,” Flores and his colleagues write. These portions of the Amazon Rainforest — these forests on the edge — suffer a dual burden. Not only are they dried out and degraded by the edge effect, but that degradation renders them more assailable to deforestation, wildfire, and climate change.

In a sense, the future of the Amazon Rainforest can be seen along its edges. When a road is built, deforestation tends to follow. After deforestation comes wildfire, and after a tract of the Amazon burns, it’s more likely to burn again. The microclimate begins to change. The soil grows hot and dry, baked by sunlight and aerified by wind. The forest can only tolerate so much of this. If conditions persist, eventually, the rainforest can’t grow back.

Formerly pristine tracts of the Amazon Rainforest, degraded by the edge effect (along with climate change, drought, deforestation, and wildfire) begin to lose biodiversity. Fewer tree and other plant species are able to grow in these warmer, more arid conditions. Pristine forests become “degraded forests.” Degraded forests become “degraded open-canopy ecosystems,” in the words of Flores, “which are non-forest areas dominated by forest trees that tolerate fire and exotic invasive grasses that keep the ecosystem flammable.” Taken to its extreme, these degraded open-canopy ecosystems become white-sand savannas. These are “natural Amazonian ecosystems,” Flores says of white-sand savannas, “that have been expanding in floodplain areas after forest wildfires.”

In other words, this transition from pristine forest to arid savanna is already happening in pockets of the Amazon Rainforest hard-hit by climate change, drought, deforestation, wildfire, and edge effects. And the same ecological cascades that degrade portions of the Amazon near the forest’s edge are happening on a larger scale. If half of the Amazon collapses by the midpoint of this century, as Flores and his team’s models show may occur if global warming and rates of deforestation and degradation continue unabated, the “Amazon forest system” as a whole is on pace to collapse.

“It’s not like half of the Amazon will collapse and the other half will go on just fine,” Armenteras Pascual says. “The whole system might collapse — the whole system in terms of hydrology, which is probably the most important role of the Amazon globally, its role in cooling the climate…It’s a whole system. The moisture cycle is what collapses. That’s what we mean when we talk about the ‘tipping point’. Everything will collapse.”

“If nothing is done to prevent fire from penetrating remote areas of the Amazon,” Bernardo Flores told me, “the system may eventually collapse from megafires and become trapped in a persistently flammable open-vegetation state.”

An area of ​​felled and burned forest near the municipality of Apuí, Amazonas, Brazil. Image credit: Bruno Kelly/Amazônia Real

Bernardo Flores and his colleagues aren’t the first scientists to warn about the Amazon tipping point, and they certainly won’t be the last. Carlos Nobre, a climate scientist and senior researcher at the Institute for Advanced Studies at the University of Sao Paulo, Brazil, has been studying climate change in the Amazon for nearly four decades. Nobre was, in fact, among the first climate scientists studying climate change in the Amazon. In 1991, Nobre published a paper showing that, if deforestation in the Amazon and global climate change were to continue unabated, half of the Amazon would collapse into a degraded open-canopy ecosystem.

Nobre — along with Flores and nearly two dozen other researchers — also co-authored the recent Nature paper on the Amazon tipping point. The study, Nobre told me, “was really one more study showing that we are very close to the tipping point in the Amazon. If we continue deforestation, degradation, and global warming, the paper shows that by 2050 we may exceed the tipping point in the Amazon. This is much, much sooner than we previously believed possible, but that’s what this paper shows.”

“How close are we to the Amazon tipping point?” I asked Carlos Nobre.

“It depends,” he said. “If we get to zero deforestation and we reduce global warming, we may lose only 10 percent of the Amazon. If climate change and deforestation continue, we may lose up to half of the Amazon by 2050.”

“To avoid the tipping point,” Nobre continues, “we cannot exceed 1.5 degrees [Celsius] global warming. The way we are moving, we may reach 2.5 degrees global warming by 2050, and then we are going to reach the tipping point in the Amazon.”

As bleak as this might sound, Nobre still has hope for the future of the Amazon Rainforest. To save the Amazon, Nobre said: “We need to get to zero deforestation, zero degradation. We have almost two million square kilometers of forest degraded. So, let’s say that we stop deforestation and degradation, and then, between now and 2050, we restore one million square kilometers, 50 percent of this area. Then we might avoid the tipping point if global warming does not exceed 1.5 degrees.”

“These are big challenges,” Nobre says. “I’m not saying it’s going to be easy, but I’m optimistic that this is possible. I’m optimistic that we — the Amazonian countries — will do our part to end the destruction of the Amazon. What I’m not optimistic about is global warming.”

To limit global warming to 1.5 degrees, Nobre told me, would require a 50 percent reduction in global greenhouse gas emissions by 2030 and net zero emissions by 2050. In fact, in February of this year, scientists from the European Union’s Copernicus Climate Change Service announced that, from February 2023 to February 2024, global temperatures were on average 1.52 degrees Celsius warmer than pre-industrial temperatures. The 1.5 degree global warming threshold that Nobre and fellow climate scientists have for so long been warning us about has, for the first time in recorded history, already been surpassed.

In September 2022, a team of researchers headed by David Armstrong Mckay, a Research Impact Fellow at the University of Exeter & Global Systems Institute, published a paper in Science. The title of the paper, “Exceeding 1.5°C global warming could trigger multiple climate tipping points,” is telling. “Climate tipping points are conditions beyond which changes in a part of the climate system become self-perpetuating,” the study reads. “These changes may lead to abrupt, irreversible, and dangerous impacts with serious implications for humanity.”

Armstrong McKay and his colleagues “categorize the Amazon forest as a global core tipping element.” A collapse of the Amazon may emit as much as 120 billion tons of carbon dioxide into the atmosphere. Global temperatures may rise 0.3 degrees Celsius as a result. A collapse of the Amazon would mean a collapse of the Amazon’s water cycle as well, which would have widespread implications across the planet. Annual rainfall in the United State’s Pacific Northwest, for example, may decline 20 percent. Annual snowfall in California’s Sierra Nevada may decline 50 percent. “If we lose the forest,” Carlos Nobre told me, “we may have global impacts: in Asia, North America, and also in Antarctica.”

Armstrong McKay and his colleagues estimate that the Amazon may reach its tipping point, independent of deforestation, after the global climate has warmed somewhere between 2 and 6 degrees Celsius. The researchers also estimate that the Amazon may collapse after 20 to 25 percent of the rainforest has been deforested.

When considering the 1.52 degrees our planet has warmed since the dawn of the Industrial Age, and the 17 percent of the Amazon Rainforest that has been deforested (as well as the 38 percent of the forest that has been degraded) since the 1970s, it becomes apparent that the Amazon Rainforest is teetering on the edge of its tipping point, a fall from which would have serious implications for humanity and the planet at large. “We are very, very close to the tipping point in the Amazon,” Carlos Nobre told me.

Despite all of this, it’s not too late to save the rainforest, Nobre said. But we have to course correct, and fast.

“We are not moving in the right direction,” Nobre told me. “That’s my concern.”

Note: Portions of this story draw from a few pieces I’ve written recently, here on Medium and in other publications. If you’d like to read more of my reporting on the Amazon, check out this story in WIRED and this one in Live Science. For more information on the Amazon tipping point, check out this story in The Environment.

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