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Global forests amid the strongest episode of El Niño on record
10/11/2026
Nezha Acil, Research Associate in the National Centre for Earth Observation, writes:
What is El Niño and how does it form?
The El Niño Southern Oscillation (ENSO) is a periodic warming of ocean surface temperatures over central and eastern Equatorial Pacific. It is part of a natural cycle that occurs every 2 to 7 years and lasts 9 to 12 months. It is the opposite of La Niña, which is the cooling phase of the cycle, generally of lower amplitude. Under neutral conditions, the air currents that blow across the Pacific Equator, called trade winds, transport warm surface water from Equatorial America to South-East Asia. When these winds weaken or reverse, oceanic heat accumulates over central Pacific and may move back toward South and Central America, preventing the upwelling of cold, nutrient-rich deep waters, affecting ocean circulation and displacing atmospheric convection eastward. These changes reshuffle weather patterns in different parts of the world through large-scale teleconnection.
What is exceptional about El Niño 2026?
The ENSO anomaly has usually been of 1 or 2 degrees Celsius above historical average, but current observations show an increase of more than 3 degrees Celsius (Niño3.4 ONI), which is unprecedented in meteorological records. The anomaly is expected to further increase, with a peak of up to 4 degrees Celsius in the coming weeks (November-December, lasting possibly until February). Strong ENSO episodes are called ‘super El Niño’.
Why does it matter?
ENSO alters the atmospheric circulation, causing shifts in the distribution of heat and rainfall across the world. The intensity of these changes varies considerably, but some patterns remain consistent. These typically include warmer and drier conditions in South-East Asia, drier conditions over northern Amazonia and wetter conditions in the Southern parts of South America and the Horn of Africa. ENSO may also suppress hurricane activity in the Atlantic, while increasing typhoon intensity and duration in the Pacific.
An unusually strong ENSO is expected to increase the likelihood of extreme heatwaves, drought or rainfall events. Increasingly severe or frequent extreme events, such as megafires and torrential floods, may have cascading consequences on both ecosystems and human populations. In many tropical regions, persistently warmer marine temperatures trigger extensive coral bleaching, which may lead to reef degradation, food web disruption and ultimately ecosystem collapse. Beyond their ecological significance, such changes have wide repercussions on the livelihoods of vulnerable communities, particularly those relying on traditional fisheries and coastal tourism. ENSO also poses serious risks to human health and socio-economy, including crop destruction compromising food security, smokes from wildfires worsening air pollution, fires and floods forcing populations to leave their homes, infrastructure damage from tropical cyclones, among other hazards.
Since early September, higher fire activities have already been detected in peatlands in Indonesia and Manaus forests in the Amazon, which could be the firsts signs of an exceptionally severe wildfire season. Concomitantly, heavy rainfall and river surges are being reported in South US and Argentina, consistently with ENSO projections.
What will be the impacts on forest ecosystems?
Forests are key ecosystems, regulating climate and water cycles, supporting biodiversity and sustaining human livelihoods. ENSO effects on forests are not direct and may take several months to become observable. Physical damage from strong winds, flooding and wildfire are the most immediate impacts. Disturbances affecting extended areas cause massive carbon releases to the atmosphere, adding to anthropogenic greenhouse gas emissions. This also means extensive habitat loss, threatening species survival and ecosystem integrity. Over longer periods of time, more latent effects may appear, such as hydraulic failure from prolonged drought and repeated intense heatwaves, leading ultimately to widespread tree mortality, which is already happening in the Amazon. Such large-scale perturbations may compromise forest integrity and ability to recover and face another ENSO episode.
How will both El Niño and climate change affect global forests?
Under global warming, ENSO is expected to accentuate environmental stress and exacerbate climate impacts. Forests, which play a fundamental role in carbon sequestration and climate regulation, are among the most threatened ecosystems. Their resilience across the world is already weakened by rising temperatures, pervasive human activities, such as illegal logging, and increasingly frequent and severe natural disturbances, including wildfires and insect outbreaks. The current exceptional ENSO is likely to amplify water deficits to uncharted conditions, putting drought-sensitive species at risk of massive mortality and this in different parts of the world. The 2023-2024 ENSO was not as strong as in 2015-2016, yet its effects were more detrimental across pantropical regions, notably in the Amazon, where forests were still weakened by the previous ENSO episode. Boreal forests, particularly the permafrost beneath them, are also at risk. The exceptionally severe 2023 drought and wildfires in Canada were also partly connected to ENSO. The ability of future forests to cope under such extreme and intensified disturbance regimes remains uncertain.
What could be done at COP31?
Every year, the world leaders gather at the UN Climate Summit to assess progress on climate action and negotiate commitments to reduce carbon emissions, mitigate climate impacts and protect ecosystems. This year’s Conference of the Parties (COP31) should treat the current Super El Niño as a global emergency. ENSO is expected to accelerate the harmful impacts of climate change, increasing the risk of ecosystem collapse and potentially jeopardising the lives of millions of people. With forest resilience already eroded by warming temperatures and growing anthropogenic pressures, it is crucial to act now more than ever. Governments should commit to more tangible actions to tackle climate change and strengthen resilience to extreme weather events. Reducing anthropogenic carbon emissions should be a priority, as it is the most effective way to slow down global warming and lessen the pressures on ecosystems. COP31 should move beyond policy pledges to more effective enforcement of forest protection, restoration and sustainable management. Also, more proactive strategies are needed to anticipate catastrophic impacts and act swiftly before they become increasingly difficult to manage or even irreversible. Governments should thus invest into deploying longer-term instruments to monitor Earth system more closely, combining both remote sensing and field observations, improving the accuracy of forecasting models and implementing more widely early-warning systems, such as near-real time fire and deforestation detection. As the current ENSO intensifies, COP31 is an opportunity to turn science-backed alerts and evidence into concrete actions, that effectively support ecosystem adaptation to increasingly extreme conditions. The actions taken now can contribute to shape how future forests will respond to climate change.