Over the last several years researchers have said that the Amazon is on the verge of transforming from a crucial storehouse for heat-trapping gasses to a source of them, a dangerous shift that could destabilize the atmosphere of the planet.

Now, after years of painstaking and inventive research, they have definitively measured that shift. 

In a study published Wednesday in Nature, a team of researchers led by scientists from the Brazilian National Institute for Space Research, reported results from measuring carbon concentrations in columns of air above the Amazon. They found that the massive continental-size swath of tropical forest is releasing more carbon dioxide than it accumulates or stores, thanks to deforestation and fires.  

“There is no doubt that the Amazon is a source,” said Luciana Gatti, the lead author of the study. 

Researchers had based their previous estimates on models that relied on imprecise measurements, so Gatti—who wanted to test her own recent findings that showed the Amazon becoming a carbon source—set out to actually measure whether carbon dioxide in the air above the forest was changing.

With the help of a government grant, Gatti and her colleagues built a sprawling state-of-the-art lab north of Sao Paulo and from there, sent specially designed suitcases filled with glass measurement flasks to four remote locations, in distinct regions, deep in the Amazon. Local pilots then flew with these flask-filled suitcases above the forest, where they took measurements starting at 4,420 meters (about 14,5000 feet) in a descending column, down to about 300 meters (just under 1,000 feet). 

“They’re like little Pepsi bottles made of glass. Stacks of them in the suitcase, and the suitcases have plumbing in them, and they get strapped into the seat by the pilot,” explained Scott Denning, a climate scientist at Colorado State University, who wrote a companion piece in Nature about the Gatti-led research, but was not an author. “When they get to a certain altitude, they suck in air samples, and then when the pilot lands, they send the suitcase back to the lab and then they analyze the air. And they do it again, every two weeks. For nine years.”

“It’s an amazing and heroic effort,” Denning added.

Denning explained that researchers have relied mostly on remote sensing via satellite and hands-on measuring of tree size across 300 small plots in the Amazon. But the Amazon is usually covered by clouds, making satellites an imperfect tool, while hands-on measuring is time consuming and inadequate given the vastness of the area.

“There’s been a slew of papers that have said that the Amazon sink is going away or has gone away, but there’s always concern that the data are not representative,” Denning said, referring to the forest’s ability to store carbon. “So, it’s nice to have someone finding that same thing in the air that the measuring tapes are finding on the ground and the paint-by-numbers remote sensing is finding through the clouds. Three methods are coming to the same conclusion.”

Over the course of the study, from 2010 to 2018, Gatti and her colleagues analyzed 600 of the “atmospheric carbon vertical profiles.” They found that carbon emissions in the eastern Amazon, where deforestation rates are higher, are greater than those in the western part of the Amazon.  The southeastern part of the Amazon, closer to population centers and under more pressure from logging and cattle ranching, became a net carbon emitter over the time period they studied. The authors link these net carbon emissions to deforestation and fires, particularly in the dry months of August, September and October. 

“All of these things are converging:  There’s warming, there’s deforestation and there’s fire—all happening in the eastern Amazon,” Denning said. “Because of that the forest is no longer taking up CO2.”

‘Is This a Rainforest?’

Trade winds blow hot tropical air over the Amazon from the Atlantic, from east to west, essentially hitting a wall in the Andes, where water gets released from the atmosphere and forms the massive Amazonian river system that stretches across an area almost as large as the United States.

When Gatti analyzed the air samples, she found that as it passed above the eastern Amazon the air was being enriched by carbon dioxide. But the air reaching the western Amazon was being depleted of carbon dioxide.

“The western part of the Amazon is wet beyond your sodden imagination,” Denning said. “And that part of the forest is taking up carbon, on net. The eastern Amazon is more vulnerable to heat and drought. The western Amazon doesn’t burn.”

Generally, temperatures across the tropics have remained relatively stable, but in the southeastern Amazon they’ve risen dramatically, especially in the dry season.

“The southeast is 28 percent deforested and has 24 percent precipitation loss, and the temperatures in August and September have changed 3.1 degrees,” Gatti explained. “This is unbelievable in a tropical latitude to have this kind of change in temperature. Is this a rainforest?”

Her worry now is that the western Amazon will soon look like the eastern part, as pressure from logging, agriculture and mining begin to mount deeper into the forest.

“We’re scared that what’s happening in this region will be the future of the other regions,” she said.