Tropical forests stop absorbing carbon during El Niño, study warns 2026 could be worst year yet

Tropical forests in South America may fail to act as a carbon sink during El Niño events, according to research published in 2023 by more than 100 scientists led by Amy Bennett of the University of Leeds. The study measured over half a million trees across six South American countries over more than 30 years, finding that during the 2015-2016 El Niño, when land temperatures were at least 1°C above average, some forests effectively stopped absorbing carbon. The U.S. National Oceanic and Atmospheric Administration has confirmed an El Niño is currently underway. There have been twice as many "very strong" El Niño events in the past 60 years as in the 60 years prior. Scientists warn 2026 may be the warmest year on record, and the current El Niño began with oceans already unusually warm. The Amazon rainforest stores approximately 123 billion tonnes of carbon. The study found drier forests at the Amazon's edge were especially vulnerable: a 0.5°C temperature increase caused these forests to lose 0.5% of their aboveground carbon. Tree mortality doubled for medium and large trees during El Niño, with larger, less-dense-wood trees dying at higher rates, pointing to hydraulic failure rather than slow carbon starvation. The research, republished from The Conversation under a Creative Commons license, suggests adaptation to seasonal drought may not protect forests from extreme events. Climate extremes may already be pushing Amazon-edge forests beyond their capacity to adapt, risking catastrophic carbon losses.