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. 5 graphs that show how the record-breaking El Niño will affect the world 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.
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.
Scientists call for ‘emergency’ measures to save sea life from El Niño 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. 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.
Extract — continue reading at the source.
