Parts of the Amazon rainforest emit more carbon dioxide than they absorb

2024-08-05 19:00:00

Due to deforestation, the southern Amazon rainforest now emits far more carbon dioxide (CO2) than it absorbs.

This is the result of an analysis of detailed aerial photos of the Brazilian states of Rondonia, Mato Grosso and Pará from 2016 to 2018. The causes of forest destruction are very different, where people often play a role.

Threatened “green lung”

South America’s Amazon rainforest is home to more than 10 percent of the world’s terrestrial species, according to a recent study published in the journal Nature. As this explains, the net cooling effect through water evaporation in the region helps stabilize Earth’s climate. In addition, rainforests store an amount of carbon equivalent to 15 to 20 years of global carbon dioxide emissions. But deforestation and other forest destruction threaten the Amazon rainforest’s role as the global climate’s “green lung.” Recent measures taken by Brazil’s current government have significantly reduced forest destruction.

“Although satellite methods provide greater coverage, their resolution is lower, making it difficult to quantify the extent and intensity of forest destruction,” write the authors of the current study, published in the journal Proceedings of the National Academy of Sciences. Reported in Proceedings of the Academy of Sciences (“PNAS”).

Treetop height determined by aircraft

Therefore, they used images of aircraft flying over the study area in 99 measurement zones at an altitude of 600 meters. So-called lidar technology is used: a radar-like method that is roughly equivalent to three-dimensional laser scanning. In this way, the team determined, among other things, the height of the tree canopy. The study area was flown twice, one to one and a half years apart.

The study area covers an area of ​​544,300 square kilometers, equivalent to 8.2% of the entire Amazon region (approximately 6,600,000 square kilometers). Csillik and his team found that 21.6% of the inspected area had forest damage. Among them, 0.7% comes from logging, 0.7% comes from farmland reclamation, and 2.8% comes from fires. Nearly all fires in the Amazon are started by humans, the team said. This resulted in 4.2% of the area being damaged by human activities.

Surprisingly, there was a lot of wind resistance

Csillik’s team attributed the damage to the remaining 14.7 percent of the damaged area to smaller natural and man-made disturbances that cannot be determined with a high degree of certainty. To the scientists’ surprise, wind protection (i.e. strong winds) caused a large proportion of the damage, as high as 2.7%. 62.1% of the area did not change between the two records. The researchers also found that 16.3% of the area had clearly visible forest growth.

However, this is not enough to offset carbon emissions in damaged areas, according to the study. During the study period, total carbon emissions were 134.6 million tons, of which 44.1 million tons were absorbed from the air through forest growth. This resulted in the region emitting 90.5 million tonnes of carbon per year between 2106 and 2018. However, the carbon balance of the soil was not considered. The authors conclude: “This study highlights the role of forest degradation in the carbon balance of this critical region of the Earth system.”

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