Amazon is Labyrinth of a thousand rivers. They are born at 21,000 feet by seasonal melting from Bolivia’s Sajama ice cap, and in the dark rocks of Peru’s Apacheta cliffs, where glacial leaching blows white through their pores. was born in They are born in the middle of the South American continent, in the Brazilian highlands, savannahs and sandstone ridges. Most are mere tributaries of tributaries and are the sources of much larger rivers (Caqueta, Madre de Dios, Iriri and Tapajos), all of which are already among the world’s largest rivers alone . Where these tributaries are empty and just south of the equator, they form the aorta of the Amazon Basin, over 10 miles wide at its widest point. From the Amazon’s most remote source to the mouth of the Atlantic Ocean, the water flows 4,000 miles, roughly the length of the Nile. Measured by the amount released into the ocean, it is equivalent to 12 dozen Mississippi rivers and one-fifth of all fresh water that reaches the world’s oceans. Amazon is the world’s largest river.
The consensus used to be that ecosystems were merely products of prevailing weather patterns. But in the 1970s, Brazilian researcher Eneas Salati proved that the Amazon, home to some 400 billion trees, creates its own climate. On an average day, from one large tree he releases over 100 gallons of water as steam. This is more than just lowering temperatures through evaporative cooling. As Salati discovered by tracking oxygen isotopes in rainwater samples, it also acts as a “flying river,” meaning that the forest’s own moisture, he said, cycles five to six times, ultimately increasing the amount of total rainfall. Spawns a rain cloud that produces 45%. By creating conditions for evergreen continental belts, this process is critical to the Amazon’s role as a global ‘sink’ for carbon.
But many scientists now fear that this virtuous cycle is breaking down. In just the last half-century, 17 percent of the Amazon—an area larger than Texas—has been converted to cropland or cattle pasture. Less forest means less rain is recycled, less steam cools the air, and less canopy blocks the sun. In drier, hotter conditions, even the thickest Amazonian trees shed their leaves and inhibit photosynthesis to conserve water. It’s a feedback loop only exacerbated by global warming. According to Brazilian earth system scientist Carlos Noblet, when deforestation reaches 20-25% of his original area, flowing rivers will weaken and the rainforest will not survive in much of the Amazon Basin. Instead, it will likely collapse into a shrub savannah in a few decades.
Much of the evidence for this theory, including Gatti’s air sample study, has come to light thanks to groundbreaking initiatives led by Noble himself. When Nobre began trying to predict the impacts of deforestation in his 1988, he had to do it at the University of Maryland because his home country lacked the computing power for serious climate modeling. did not. Brazil was so resource-poor that foreign researchers even dominated Amazonian fieldwork. But he spearheaded a program that, in the words of a Nature editorial, “revolutionized our understanding of the Amazon rainforest and its role in the Earth system.” Founded in 1999 and known as the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA), it unites disciplines that normally don’t collaborate, uniting chemists like Gatti with biologists and meteorologists. Funding came primarily from the United States and Europe, but Nobre argued that South Americans had taken the lead and produced a whole new generation of Brazilian climate scientists.
Until recently, Nobre worked under the assumption that the Amazon wouldn’t be a net carbon source for at least another few decades. But Gatti’s research isn’t the only indication that, as he told me on his Skype, “we are on the eve of this tipping point.” The rain machine is slowing down. Droughts used to occur once every few decades, and major droughts once every century or two. But since 1998 he has five, two of which are extreme. The impact is particularly severe in the eastern Amazon, which has already lost a staggering 30% of its forests. The dry season he was three months. Now four more in a row. In the driest month, precipitation fell by a third over the 40-year period, but average temperatures rose by 3.1 degrees Celsius. That’s three times his global annual increase in the fossil fuel age. In some areas the jungle is already overgrown.
Losing the Amazon, one of the most biodiverse ecosystems on earth, would be devastating for the tens of thousands of species that live there. Rising temperatures could also turn millions of people in the region into climate refugees. It also represents a more symbolic death, as “saving the rainforest” has long been an advocacy of sorts for all of modern environmentalism. But what worries scientists most is the potential for this regional ecological tipping point to have knock-on effects on the global climate. The Amazon’s flying rivers circulate over the continent, so impacts may already extend beyond the rainforest. In 2015, the populous southeast of Brazil experienced a historic water shortage. In 2021, a quasi-biblical sandstorm swept the region. The complete disappearance of flowing rivers could affect atmospheric circulation across South America, and affect weather as far away as the western United States.
