A landmark long term study published by an international coalition of climate scientists reveals that South American tropical forests effectively stop absorbing carbon dioxide CO2 from the atmosphere during severe El Niño cycles. The findings present a grim warning for global climate models, as the Amazon rainforest the planet’s largest terrestrial carbon reservoir holding roughly 123 billion tonnes of carbon faces an unprecedented compound crisis driven by intensifying global heatwaves and compounding multi year droughts.
To map these shifts researchers spent over three decades tracking the growth and survival rates of more than 500,000 individual trees across 4,000 distinct species spanning six South American countries. While mature, healthy rainforests typically serve as reliable carbon sinks by locking atmospheric gases into new plant biomass, the study proved that extreme El Niño phases completely disrupt this equilibrium. During the severe 2015–2016 El Niño, when regional land temperatures hovered at least 1.0°C above baseline averages, the extreme heat caused parts of the Amazon basin to completely lose their carbon sink capacity.
Surprisingly, the study revealed that the drier, seasonal forests sitting at the outer margins of the Amazon were the most acutely vulnerable to these climate shocks. Evolutionary adaptations to regular seasonal dry spells proved entirely insufficient against extreme El Niño anomalies a mere 0.5°C localized temperature spike triggered a corresponding 0.5% collapse in total aboveground carbon storage within these peripheral zones.
Rather than succumbing to gradual carbon starvation via closed leaf pores, the forest’s largest canopy trees died off at double their typical rates. The selective mortality of large, low-density wood species points directly to catastrophic hydraulic failure a lethal phenomenon where intense atmospheric moisture demands snap the internal water columns within a tree’s vascular network.
The immediate ecological danger is magnified by current climate indicators. With global temperatures threatening to shatter historical records, the latest El Niño has taken hold over oceans and atmospheres that are already significantly warmer than any previously recorded baseline. Because the margins of the Amazon have experienced rapid, sustained warming over the past thirty years, these ecosystems are being hit by a major climate anomaly before recovering from prior multi-year stress. This compounding pressure threatens to trigger tree mortality and sudden carbon feedback loops on a scale never before witnessed in modern climate history.