Mind-blowing. Unprecedented. Off the charts. Jaw-dropping. Godzilla-level. Superlatives have been flying about the current El Niño climate pattern, which is already the strongest on record months before it is expected to peak – and unusually, they are coming from scientists, rather than the media. So, what has made this such an exceptional event?
This will no doubt be the subject of many studies to come, but the broad picture is clear. Two main factors have driven the formation of this record-smashing El Niño, the first of which was set in motion long before it began.
To understand this El Niño, we have to understand La Niñas, the opposite phase of the climate pattern. During La Niñas, trade winds blow west across the equatorial Pacific, pushing surface waters warmed by the sun towards Australia and Indonesia. This piles up a layer of water known as the “warm pool”. And it really does pile up: sea level in the western Pacific rises as much as 20 centimetres.
The bigger the warm pool gets, the more unstable it becomes. If the trade winds holding it in place weaken or reverse direction, the warm water spills back across the Pacific, making surface waters along the equator abnormally warm – an El Niño event. So the extent to which an El Niño raises global temperatures and causes extreme weather depends on how big and hot the warm pool gets, and on how much of it moves east across the Pacific.
The warm pool gets hotter during La Niñas and colder during El Niños, but temperatures have been increasing over the past decades due to global warming, says Michael McPhaden at the US National Oceanic and Atmospheric Administration.
By late 2025, the heat content of the western Pacific was much higher than normal – although it wasn’t the highest on record. “Based on that alone, one might not have expected this event to become as strong as it has,” says McPhaden. “The highest heat content developed prior to the last El Niño in 2023 to 2024 due to the preceding ‘triple dip’, or three-year La Niña, associated with stronger-than-normal trade winds that piled up warm surface waters in the western Pacific for a prolonged period.” La Niñas typically last nine to 12 months.
The second key factor was a series of strong bursts of wind blowing east, pushing the extra-hot warm pool towards South America. This isn’t just a surface phenomenon, says McPhaden. Each wind burst creates a downward bulge in the layer of warm water, known as a Kelvin wave, which travels across the Pacific over the following six to eight weeks.
Every Kelvin wave increases the thickness of the warm layer in the eastern Pacific. Put another way, the bottom of the warm layer, or thermocline, becomes deeper. “The cumulative effect of successive westerly wind bursts and associated Kelvin wave responses led to an exceptional deepening of the thermocline in the eastern Pacific,” says McPhaden. “The thermocline is currently more than 80 metres deeper than normal in some areas.”
The deeper the thermocline, the harder it is for colder water to well up and reach the surface. So we now have a huge amount of extra warm water spreading across the surface of the Pacific and transferring stupendous quantities of heat to the atmosphere, with repercussions across the globe.
One strong wind burst in April was driven by three tropical cyclones forming in the western Pacific around the same time. Cyclones rotate anticlockwise north of the equator and clockwise south of it, so the winds closest to the equator always blow eastwards.
“The stronger the westerly wind nudge, the easier it is for El Niño to develop and strengthen,” says meteorologist and author Bob Henson, who pointed out at the time that these cyclones would boost the strength of the then-nascent El Niño.
In principle, it is possible that global warming played a role here, too, by increasing the odds of three cyclones forming around the same time, he says.
More widely, the question of whether global warming is making El Niños stronger is unresolved, says Michael Mann at the University of Pennsylvania. “It’s honestly an open question from my stance.”
The number of observed El Niño and La Niña events in modern times is too small to reveal any link. Some teams having been studying things like corals to try to extend the record back many centuries.
A recent study of corals in the Galapagos suggests there is a link, but Mann says there are crucial gaps in the coral record that mean no firm conclusion can be drawn. “We still do not have a reliable, continuous record of El Niño prior to the instrumental era,” he says.
Climate models are little help either, he says. “The models [are] nearly equally split as to whether the amplitude of El Niño events is likely to increase or decrease with anthropogenic warming.” What is clear is that warming amplifies the damage done by El Niños.
The current super El Niño will also lead to a big spike in global warming, says Mann. “It gives us a glimpse of what is coming down the pike if we continue to warm the planet with carbon pollution. Warmer oceans, more evaporation, bigger flooding events, hotter continents and worse droughts leading to more extensive and destructive wildfires.”