The current El Niño is already the strongest on record and is forecast to get even stronger, peaking around November or December. Though it should be over by June next year, the effects of this monster event will continue to be felt long after that. This would release huge quantities of carbon dioxide and also make the whole region permanently drier, because much of the rainfall in rainforests comes from the water evaporating from trees.
The most ambitious ideas to save the world from El Niño El Niños occur when warm water that has built up in the western Pacific spills east across the equator, making the surface of the eastern Pacific warmer than usual. An El Niño is said to be happening when the sea-surface temperature in one region along the equator is 0.5°C above average; at the time of writing, it is 3.4°C and climbing. One reason why El Niños end is that the warm water that spreads across the Pacific slowly disperses.
Some of it flows away from the equator and the water also cools as it transfers vast amounts of heat to the atmosphere, which leads to a sudden jump in global surface temperatures. This year’s average temperature is on track to tie with 2024’s at around 1.6°C above the pre-industrial level, and 2027 is expected to reach 1.7°C or more. The next year could be a bit cooler if a La Niña makes the Pacific soak up more heat than usual, but we are on the brink of permanently crossing the 1.5°C threshold we were meant to avoid.
What happens below the surface of the Pacific also plays a key role in bringing about the end of El Niños. For instance, the arrival of warm water in the eastern Pacific triggers gigantic underwater waves known as Rossby waves that travel westwards. When these hit the continental shelf in the western Pacific months later, they bounce back eastwards in the form of cold, faster-moving Kelvin waves.
These thin the layer of warm water in the eastern Pacific when they arrive several weeks later, helping deeper, colder water reach the surface and bring the El Niño to an end. The combined forecasts of computer models suggest that this El Niño will be over by June next year, but individual models vary. Some suggest it could persist well into the northern hemisphere’s summer.
We can’t predict with any certainty how this event will end, says McPhaden. The 1997 El Niño ended with a bang, with sea-surface temperatures in the eastern equatorial Pacific plummeting by 8°C in a month, followed by a strong, long-lasting La Niña. But the next strong El Niño in 2015 faded gradually and was followed by a weak, short La Niña.
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