South American tropical forests risk turning from carbon sinks to carbon sources during extreme climate events like El Niño. Teo Tarras / Shutterstock Tropical forests draw down and store large quantities of CO₂ from the atmosphere. The Amazon rainforest in South America, for example, stores approximately 123 billion tonnes of carbon – more than is stored in any other terrestrial ecosystem in the world. But these forests are facing a critical challenge. Research from 2023, which was carried out