Climate scientists have been ringing the alarm for years about the increasing chance that the Amazon rainforest, now one of the largest carbon absorbers in the world, become a source of carbon within only 15 years. New research shows that this is already happening for some other types of tropical forests nearby.
This is largely due to deliberate forest burning. In South America, mining, ranching and soybeans often set trees on fire to make way for their activities, turning forests into open pastures.
That means that forests contain less leaves to suck greenhouse gases out of the atmosphere. To make matters worse, when a tree catches fire, it releases all the carbon it has stored during its lifetime, meaning the forests become a source of the planet’s emissions. And in the midst of the climate crisis, this problem is even more serious, as the forests under warmer and drier conditions do not produce enough humidity to extinguish the flames quickly, meaning more burns with less effort.
A new study, published in Science Advances on Friday, aims to see how the carbon uptake of South American forests has changed in recent years. To do this, the authors analyzed greenhouse gas monitoring data from 1987 to 2020 on 32 deciduous, semi-losing and evergreen forests – each of which has experienced deforestation – in the lush state of Minas Gerais in southeastern Brazil. In total, the area they surveyed covered approximately 81.5 acres (33 hectares).
By plugging this data into statistical models, the authors found that these forests now absorb an average of 2.6% less carbon per year than they did 33 years ago. At the same time, forest fires’ carbon emissions increased by 3.4% per year, meaning that they generally lose their ability to absorb the gas. These changes were enough to push forests over the edge from carbon sinks to carbon sources. The authors fear their findings could be extrapolated to tropical forests in the region as a whole.
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The data shows that the switch occurred in 2013. That year, the forests surveyed released an average of 0.14 US tons per 2.5 acres (0.13 tons of carbon per hectare), or the equivalent of driving 323 miles in a diesel car.
The authors’ findings are particularly troubling because separate examination recently discovered that the importance of carbon sequestration in tropical forests is almost as important as that of the Amazon rainforest.
The scientists note that not all is lost. We should take the pressure off these forests by curbing our greenhouse gas emissions and thus slowing the climate crisis. Brazil should also restore these forests’ ability to reduce carbon by protecting forests by halting deliberate combustion.
“The main way is conservation,” Vinícius Maia, a researcher at the Federal University of Lavras in Brazil, wrote in an email.
The authors say special efforts must be made to preserve deciduous forests, which are the driest and warmest species the researchers examined and saw an even sharper increase in carbon emissions. But really, this protection should extend to all of the foliage in the area.