Delayed emissions cuts lock in extreme El Niño for centuries
A new study warns that extreme El Niño events will become dramatically more frequent for centuries after emissions stop, with the risk rising sharply the longer cuts are delayed, threatening Southeast Asia with prolonged fires, haze and economic losses.
Extreme El Niño events will become dramatically more frequent for centuries after global emissions cease, a new study finds. The risk grows larger the longer the transition to net zero is delayed, locking in severe climate impacts for Southeast Asia long after the energy transition is complete.
Led by scientists at the University of Melbourne and the ARC Centre of Excellence for Weather of the 21st Century, the research used a single Australian climate model to run 1,000-year projections. In that model, extreme events made up just 1.73 per cent of all El Niño events before industrialisation. When emissions stopped in 2030, that share rose to 16.4 per cent-nearly ten times the pre-industrial rate. If emissions continued until 2060, the share of extreme events reached 26.3 per cent, about fifteen times higher.
A wider group of models showed a similar trend, with the share of extreme events roughly doubling under warming and staying high after emissions ceased. The persistence is traced to the deep ocean and the Southern Ocean, which continue to warm for centuries after atmospheric temperatures stabilise. This retained heat weakens trade winds and keeps the eastern Pacific warm, preventing the recovery of the critical temperature gap between the western and eastern Pacific.
With the Pacific’s average state held closer to El Niño conditions, extreme events become easier to trigger. Lead researcher Aditya Sengupta explains the mechanism. “The atmosphere and the ocean surface can adjust relatively quickly, while the deep ocean absorbs and releases heat over hundreds or even thousands of years,” he said. “This gives the ocean a long memory of previous greenhouse-gas emissions.”
Ocean memory drives prolonged risk
The deep ocean and Southern Ocean retain heat for centuries, keeping the Pacific in an El Niño-like state even after net zero is reached. This prolonged ocean warming draws tropical rain belts closer to the equator. With the eastern Pacific warming faster than the western side, less of a push is needed for rainfall to shift east, making more El Niño events extreme.
Co-author Associate Professor Andrew King stressed the urgency of early action. Reaching net zero earlier limits the changes occurring within the ocean and reduces the risk of leaving future generations with a substantially altered tropical Pacific, he said. The study was published on 13 October in Communications Earth & Environment.
Economic and health impacts of extreme events
Increased extreme El Niño frequency will intensify Southeast Asian fires, haze and associated billions in damages to agriculture, tourism and health. The Meteorological Service Singapore states that El Niño brings warmer, drier weather to the region, raising the risk of transboundary haze as conditions become conducive to peatland and vegetation fires.
Indonesia’s two most recent very strong El Niño years, 1997 and 2015, were severe fire years. The fires during the 2015 event burned 2.6 million hectares and were estimated to have cost Indonesia at least US$16.1 billion. Haze from the 1997-1998 fires caused about US$4.5 billion in tourism and short-term health costs across the region.
Drought and heat in past El Niño years have led to declines in annual rice and corn production. In some years, palm oil output has fallen, and analysts note prices tend to rise as supply tightens. This is critical for global markets, as Indonesia and Malaysia together account for more than 80 per cent of global oil palm fruit production.
By 7 September this year, fires in Indonesia had already released 76 million tonnes of carbon, putting 2026 on the same trajectory as the devastating 2015 season. Forecasts indicate the coming El Niño could be among the strongest ever recorded, with effects lasting well into 2027. For Australia, this heightens the risk of a fierce bushfire season.
Past extreme events offer a grim preview. The 1998 El Niño brought months of severe drought in Indonesia, allowing devastating forest fires to burn for weeks. In 1982, a strong El Niño caused catastrophic flooding in Peru and drought in southeast Australia that culminated in the deadly Ash Wednesday fires. The 2016 event triggered mass coral bleaching on the Great Barrier Reef.
The current El Niño is already slowing shipping through the Panama Canal and forcing fish to migrate. Scientists suggest the tropical Pacific could remain in an El Niño-like state for centuries. Aditya Sengupta shows the necessary response. This means it is imperative that rapid emissions cuts and long-term climate adaptation planning go hand in hand even after we reach net zero.
