The El Niño Southern Oscillation system is a major driver of the Earth's climate variations, driven by fluctuations in the temperature in the surface waters of the Pacific Ocean. This has two phases, El Niño, in which surface temperatures are high, and La Niña, in which they are low (although the Pacific is not always in one of these phases, there are neutral periods when neither occurs). The impacts of these oscillations are complex, but overall, the El Niño phase is associated with warmer global temperatures, while the La Niña phase is associated with cooler global temperatures. The warmest year on record, 2024, was associated with an El Niño phase.
In March 2026, the European Centre for Medium-Range Weather Forecasts began issuing warnings that the Pacific Ocean might be going to enter an El Niño phase in 2026. This is in some ways surprising, the ocean was still in a La Niña phase in March, and predictions made this early in the year are not usually considered reliable. Furthermore, less than three years had passed since the most recent El Niño phase, which is in itself unusual.
However, the El Niño Southern Oscillation system does not operate in isolation. The temperatures in the Pacific surface waters during the 2015-2016 and 2024 El Niño events were significantly higher than the 1997-98 event, which was the warmest event of the 20th century. Furthermore, the La Niña phases bracketing these 21st century events were much less extreme than those around the 1997-98 event (that is the surface waters did not cool as much), so these events were much less extreme in the sense that they did not drift as far from the average sea surface temperatures over a longer period. In fact, the three most recent La Niña phases have been accompanied by Pacific Ocean temperatures warmer than during the 1997-98 El Niño event.
On 15 April 2026 the UK's Met Office issued a warning that there was likely to be a severe El Niño event in 2026-2027, and on 14 May, the Climate Prediction Service of the United States National Weather Service also issued a press release warning that their predictions gave an 82% chance of the Pacific entering an El Niño phase between May and July 2026, with a 96% chance that El Niño conditions would exist between December 2026 and February 2027.
The reason behind the earliness and severity of these warnings is based upon a change in how predictions are made. Previously, predictions have been made upon the temperature of the surface of the ocean, which has not allowed for very long predictions. However, recent research has shown that a much more accurate, and longer-term, prediction can be made if the temperature of the top 300 m is used.
In March 2026, the average temperature for the top 300 m of water in the central Pacific was already 1.0°C above baseline temperatures. This in itself is consistent with an El Niño, or even super El Niño event (an event, such as that in 1997-98, in which the surface waters of the Pacific are not just exceptionally warm, but at least 2.0°C warmer than the recent average sea temperatures). In the first week of April the temperature of these waters continued to rise sharply, reaching 1.6°C above baseline temperatures.
This has the potential to have a profound impact on the global average temperature. Predictions already suggested 2026 would be a hot year, with a 62% chance of being one of the four hottest years on record, and a 19% chance of being the hottest year (i.e. temperatures exceeding those of 2024). It has been suggested that there is a 30% chance of 2026 being the second year in which global average temperatures exceed 1.5°C above pre-industrial levels (defined as average temperatures between 1850 and 1900). The sharp increase in the temperature of the waters of the Pacific now makes these predictions look more-or-less inevitable.
An El Niño event has a number of profound affects upon the climate. South America tends to have much higher rainfall during El Niño events, while Indonesia, Australia, and Southeast Asia can suffer severe droughts. In India and Africa, rainfall patterns can be affected in less predictable ways, with some areas suffering high rainfall and flooding while others suffer severe droughts. Tropical storms become less common in the Atlantic, but more frequent in the Pacific.
This is likely to have implications for food production in many parts of the world, with a combination of droughts and floods triggered by an El Niño event coming at the same time as fertiliser shortages triggered by Iran having closed the Straits of Hormuz in response to the Israeli and US attack earlier this year, making famine events likely. At the same time, the agencies which might provide relief during such events are suffering from a much reduced ability to act following the withdrawal of funding by the US, UK, France, Germany, and Japan. This is situation is also likely to be impacted by predicted rises in fuel prices, also triggered by the war in the Gulf of Persia, further limiting international agencies ability to respond to any crisis.
A super El Niño event, starting from a base of record high sea temperatures, which now appears very likely, could have even more severe impacts. The super El Niño event of 1876 triggered a global famine which killed around 50 million people, about 3% of the world's population at that time. On this occasion the El Niño event caused the almost total collapse of the South Asian Monsoon, leading to the worst drought in 800 years, with concurrent droughts across Australia, Southeast Asia, Brazil, and North and Southern Africa (although it is also generally accepted that the high mortality rates in India were driven as much by the policies of the British colonial government as the drought itself).
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