The Amazon rainforest, long called the « lungs of our planet » for its role in absorbing and storing carbon dioxide, now often releases more carbon than it takes in, according to a new study. Years of deforestation, drought and fires have weakened the forest's ability to soak up CO2, and the researchers found it is only in the wettest years that the rainforest comes close to carbon neutrality.
The study, published in the journal Nature, was led by Brazil's National Institute for Space Research and included an international team of researchers. They analyzed 15 years of atmospheric carbon measurements collected by research planes. The years were grouped by two main factors: the level of human activity, including deforestation, logging and the use of fire to clear land, and the amount of climate stress, such as drought or heat waves.
The results showed a clear pattern. In wet years with low human activity, the Amazon was nearly carbon neutral. It remained a slight source of carbon, but the researchers wrote that it « did not significantly contribute to the global carbon balance » in those years. When drought or heat was mild but deforestation and wildfires increased, net carbon emissions from the Amazon jumped dramatically. The worst years combined intense climate stress, including events such as El Niño, with heavy damaging human activity. Those years were still close in emissions to the second group, which led the researchers to conclude that most of the carbon the Amazon emits comes from human activities, predominantly land-use change.
Jen Johnson, an assistant professor of ecology and evolutionary biology at the University of Kansas and a coauthor of the study, said global climate factors matter, but « people's choices about how to use and live on the land surface in this region are key to understanding the movement of carbon between the land and the atmosphere. »
The findings build on earlier warnings. A 2021 study found that as large areas of the forest were cut down or burned, its capacity to capture carbon was shrinking. In 2023, a year of extreme drought and high temperatures, researchers showed the Amazon became a net source of carbon emissions, releasing between 10 and 170 million tons of carbon instead of absorbing it. In 2019, more than 74,000 fires were burning in Brazil, mostly in the Amazon, about 80% more than the year before. Although often described as wildfires, many are set by ranchers clearing land for cattle to meet demand for beef.
Deforestation also makes the region drier, which makes it harder for the remaining forest to recover. Johnson warned of a possible tipping point, where gradual drying and forest loss reinforce each other and shift the ecosystem toward drier forests or other types that store far less carbon. « The more carbon from the Amazon that moves into the atmosphere and stays there, the more trouble our climate system is in, » she said.
The researchers argue the trend can still be reversed through policy. « Measures to bring deforestation down to zero are required to manage net carbon emissions from the Amazon, » Johnson said. « It's not something that's out of our control because it's being driven by global climatic factors. It's something very much under the control of governments and individuals. »