Summary Points
- Tropical forests like the Amazon store over 123 billion tonnes of carbon but risk losing this capacity during climate extremes like El Niño, which disrupts their ability to act as carbon sinks.
- Increasing intensity and frequency of El Niño events, driven by warming oceans, threaten forest health, especially for trees at the forest edges that are already prone to drought.
- During severe El Niño episodes, large trees suffer higher mortality—mainly due to hydraulic failure—leading to significant and potentially irreversible carbon losses.
- Protecting tropical forests is critical for climate stability,without concerted efforts, their role in mitigating global warming could diminish as climate extremes become more intense.
How El Niño Affects Tropical Forests
Tropical forests, like the Amazon, are vital for absorbing carbon dioxide from the atmosphere. During normal years, trees take in CO₂ through photosynthesis, helping to fight climate change. However, during El Niño events, these forests struggle. Warmer temperatures and dry conditions cause trees to close their leaf pores, reducing their ability to absorb CO₂. Research shows that in years like 2015-2016, many forests in South America stopped acting as carbon sinks altogether. This is concerning because it means they release more carbon back into the air instead of soaking it up. With El Niño events becoming more frequent and intense, the risk of losing this natural climate buffer grows.
The Impact on Forest Health and Carbon Storage
A detailed study of over half a million trees in six countries revealed that drought-prone forests at the edge of the Amazon are especially vulnerable. When temperatures rise just half a degree Celsius, these forests can lose up to 0.5% of their stored carbon. Larger trees, which store the most carbon, suffered the highest mortality rates during El Niño, with some dying at twice the usual rate. The main cause appears to be hydraulic failure, where intense water demand breaks internal water columns in trees. As a result, many trees die faster, and the forest’s ability to store carbon diminishes. This damage could persist for decades, adding more greenhouse gases to the atmosphere and accelerating climate change.
What the Future Could Hold
Scientists warn that 2026 might be the warmest year on record, compounding the effects of current El Niño conditions. The oceans are already unusually warm, and air temperatures are high. The edges of the Amazon have experienced some of the fastest warming in the tropics over the past 30 years. When a major climate anomaly hits before forests recover, their structural stability weakens. If these trends continue, we could see unprecedented tree and carbon losses. Protecting these forests is crucial because they are our best natural defense against climate change. Strengthening efforts to maintain forest health and limit global warming offers hope for their future—and ours.
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