What is El Niño?

Centuries ago, Peruvian fishermen noticed that every few years, the Pacific Ocean became unusually warm around Christmas time, and fish disappeared. Because of the timing, they called it El Niño – Spanish for “the boy”, referring to baby Jesus.

Usually, the eastern Pacific stays cool thanks to trade winds – permanent easterly winds blowing near the equator. Cold water flows northward along South America's coast through the Humboldt Current. At the same time, the trade winds push warm surface water towards Southeast Asia, allowing cold water to rise from the depths to replace it.

During El Niño, these winds weaken, so the warm surface water stops moving westward and drifts back east. The cold deep water near South America struggles to the surface, warming the upper layers of the ocean. Plankton dies, fish migrate, and severe consequences are felt far beyond the Pacific.

Why does it matter?

The ocean surface in the western Pacific is normally warmer than in the east, so the air above it rises, drawing in surface air from the Americas and creating easterly winds across the Pacific.

During El Niño, that temperature contrast flips. The eastern Pacific warms unusually, air rises there instead, and the winds reverse direction, blowing toward the Americas.

Enter the jet stream: it’s a fast-flowing current of air high up in the atmosphere, like a river, typically at the altitude of commercial planes. It carries weather systems like storms, rain, and cold snaps around the planet.

When El Niño warms the tropical Pacific more than usual, it shifts the jet stream southward along with the storms it carries. That leads to unexpected drought in some regions and heavy rainfall in others, resulting in crop failures and rising food prices worldwide.

Climate change amplifies El Niño’s effects: a warmer ocean and atmosphere means more energy available for heatwaves and extreme rainfall.

What does it mean for Europe?

The effects for Europe aren’t straightforward. As one of the less affected continents, El Niño reaches Europe through a chain of knock-on effects rather than directly.

The warm Pacific pumps heat into the upper atmosphere, generating large wave patterns that ripple thousands of kilometres toward Europe. By the time they arrive, they shift the pressure balance over the North Atlantic, and that balance is what really determines European weather.

That brings us to NAO, the North Atlantic Oscillation: the pressure difference between Iceland and the Azores, which dominates European weather far more than El Niño does. El Niño can nudge the NAO in a particular direction, but it doesn’t control it. Forecasters treat it as one input among several, not a reliable predictor on its own.

When El Niño shifts the jet stream southwards, the UK and northern Europe generally experience drier and warmer summers. Southern Europe then often sees a wetter summer. The 2023-24 El Niño – one of the five strongest on record – helped push 2024 to the hottest year ever. By summer, the El Niño had passed, but the heat hadn't: that year, heatwaves killed over 62,700 Europeans.

El Niño winters in Europe are also slightly warmer than average. Partly because the rising global temperatures have already raised the baseline, and partly because El Niño’s knock-on effects thousands of kilometres away tend to push mild Atlantic air over the continent rather than cold air from the east. Scandinavia and countries like Germany and England therefore tend to be warmer and wetter during El Niño.

A Godzilla El Niño won’t cause this – climate change does – but it will add to it and make it harder for Europe to ignore.