Trees growing in the Amazon floodplains emit more than 20 million tons of methane (CH4) per year, as much as is produced by all the world’s oceans combined (Nature, December 4). The findings were produced by a group of researchers from the Open University in the UK, in collaboration with Brazilians from various institutions, including biologist Luana Basso, from the Nuclear and Energy Research Institute (IPEN), and chemist Luciana Vanni Gatti, from the Greenhouse Gases Laboratory at the Brazilian National Institute for Space Research (INPE). The group analyzed the methane emissions of 2,300 trees in regions adjacent to the Negro, Solimões, Amazon, and Tapajós rivers between 2013 and 2014. To do so, they installed small chambers on the trunks to collect air. When analyzing CH4 concentration levels, they found that the trees emitted 21.2 million tons of CH4 per year. The authors explain that the trees act as chimneys, funneling the methane produced in the soil through their trunks and releasing it into the atmosphere. “This makes floodplain trees one of the primary sources of methane emissions in the Amazon,” explains Luana. Methane is one of the three major greenhouse gases. “Although this is how forests naturally function, it is important to understand the production dynamics of this and other gases so that we can predict how the forest will behave under various possible climate change scenarios,” says Luciana.