It’s no secret the Amazon is in trouble. The world’s largest tropical rainforest has weathered decades of deforestation due to logging and cattle ranching—and the situation grew particularly dire last year, when widespread fires scorched vast areas of the forest. Aside from their mind-boggling biodiversity, the Amazon and other rainforests across the globe have been a key buffer for climate change: Their trees and plant life soak up a significant percentage of human-generated carbon emissions. But a new study published in Nature shows that’s changing: Based on research in the Amazon and Africa, scientists have concluded that rainforests are absorbing significantly less carbon than they used to.
“Although intact tropical forests remain major stores of carbon and are key centres of biodiversity,” the authors write, “their ability to sequester additional carbon in trees is waning.”
That’s very bad news for us. According to the study, tropical forests across the globe act as “carbon sinks” and account for fully half of all the carbon stored in vegetation. If they lose their ability to store carbon, that will only accelerate the affects of climate change. As The Guardian points out, many plans for offsetting emissions involve preserving or regrowing tropical forests to do just that.
“Humans have been lucky so far, as tropical forests are mopping up lots of our pollution,” Simon Lewis, one of the authors of the study, told The Guardian, “but they can’t keep doing that indefinitely.”
To assess the relationship between tropical forests and atmospheric carbon dioxide, the researchers looked at the two largest expanses of rainforest on earth, in Africa and the Amazon. They measured tree growth over 30 years in 244 intact forests across 11 African countries and compared them with 321 plots scattered across the Amazon. Based on those measurements, they found that the Amazon’s ability to sequester carbon has been declining since the 1990s. Africa, meanwhile, stayed relatively steady until about 2010, when its forests also began to lose carbon to the atmosphere.
Using that data, the scientists developed a statistical model to predict how things would play out over the next few decades. Spoiler alert: It’s not looking good. The model “indicates a long-term future decline in the African sink, whereas the Amazonian sink continues to weaken rapidly.”
When averaged out globally, the scientists show that tropical forests reached peak carbon absorption in the 1990s—soaking up about 17 percent of human-generated CO2. By the 2010s, they estimate that rainforests were taking in just six percent, helped in part by widespread deforestation, droughts, and a massive uptick in carbon emissions. Based on that, the scientists conclude that tropical forest have already peaked as carbon sinks, and will be in “long-term decline” from here on out.
If the study did offer a shred of good news, it’s this: Forests and vegetation outside the tropics have begun to pick up some of the slack over the past two decades. The scientists found that carbon uptake across the Northern Hemisphere landmass increased in the 1990s and 2000s.
But most climate models—and most countries’ climate plans—rely on the power of the rainforest to soak up human-generated CO2. According to the data published here, the tropical carbon sink is on schedule to end “sooner than even the most pessimistic climate-driven vegetation models predict,” the authors write. With that in mind, Lewis had strong words for companies and governments that think purchasing emissions offsets or preserving tropical forests will be enough to stave off disaster.
“The use of forests as an offset is largely a marketing tool for companies to try to continue with business as usual,” he told The Guardian. “The reality is that every country and every sector needs to reach zero emissions.”
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