The Amazon rainforest was broadly a net carbon sink across the basin.

For decades, the Amazon was described as one of Earth’s great carbon sinks. Its forests take up carbon dioxide and store carbon in wood, roots and soils, helping to slow the rise of CO₂ in the atmosphere.

By the mid-2010s, researchers already knew that this sink was weakening. A 2015 study of hundreds of forest plots still found that Amazon forests were taking up more carbon than they released, but the rate of uptake had fallen as tree mortality increased.

A clearer regional picture emerged in 2021. Researchers analyzed 590 aircraft profiles collected over four parts of Amazonia between 2010 and 2018. The southeast stood out: it was a net carbon source, and the broader eastern Amazon emitted more carbon than the west. The southeast had also experienced especially high levels of deforestation, warming and dry-season stress.

That does not mean the entire Amazon has definitively become a carbon source. A 2024 synthesis found that estimates for the whole basin still differ, with some methods producing a small net sink and others a small net source. But the southeastern result was much more consistent across methods.

The older shorthand treated the Amazon too uniformly. Large areas of intact forest still store and absorb enormous amounts of carbon, but the basin now contains regions whose carbon balance has shifted in the opposite direction.