Previous studies indicating the Amazon was becoming a source of CO2 were based on satellite data, which can be hampered by cloud cover, or ground measurements of trees, which can cover only a tiny part of the vast region. The research used small planes to measure CO2 levels up to 4,500m above the forest over the last decade, showing how the whole Amazon is changing. Losing the Amazon’s power to capture CO2 is a stark warning that slashing emissions from fossil fuels is more urgent than ever, scientists said. Growing trees and plants have taken up about a quarter of all fossil fuel emissions since 1960, with the Amazon playing a major role as the largest tropical forest. But even without fires, hotter temperatures and droughts mean the south-eastern Amazon has become a source of CO2, rather than a sink.

Most of the emissions are caused by fires, many deliberately set to clear land for beef and soy production. The giant forest had previously been a carbon sink, absorbing the emissions driving the climate crisis, but is now causing its acceleration, researchers said. The emissions amount to a billion tonnes of carbon dioxide a year, according to a study. The Amazon rainforest is now emitting more carbon dioxide than it is able to absorb, scientists have confirmed for the first time.