The El Niño event that is developing over the Pacific Ocean is likely to be the strongest in living memory, the Met Office has warned.

The powerful natural climate phenomenon pushes up global temperatures and can increase the risks of extreme weather.

Added to the effects of human-induced climate change, the Met Office is warning that it is “very likely” to mean 2027 is the hottest year on record.

There is growing evidence that weather patterns around the world are already being affected, with below-average monsoon rains in India and suppressed hurricane activity in the Atlantic Ocean.

El Niño could put the UK at greater risk of a wet, stormy autumn.

“We should be clear that this is an unprecedented event”, said Prof Adam Scaife, head of long-range forecasting at the UK Met Office.

“I have never seen an El Niño signal this intense in our forecasts.”

El Niño is a naturally occurring weather pattern, which happens about every two to seven years, lasting for around a year.

Trade winds that typically blow from east to west across the Pacific Ocean can weaken or even reverse, allowing warm water to spread eastwards.

Heat is released from the ocean into the atmosphere, lifting global temperatures and shifting rainfall patterns.

Scientists declare an El Niño when sea surface temperatures in a key area of the Pacific are 0.5C or more above average.

Current measurements show that they are well over 2C above normal.

Latest forecasts from the Met Office suggest that these temperature anomalies could exceed 3C later this year as El Niño nears its peak.

This would be unprecedented in records going back to 1950, and probably the strongest event since the 19th century.

Very high temperatures in the deeper ocean – around 8C above normal at a depth of 100m (330ft) in some places – could help to supercharge this El Niño, essentially providing a reservoir of warm water fuel to reinforce the event.

“We have many months to go while this event continues to develop and that’s one of the reasons that we have increased confidence that this will be a record-setting event,” said Dr Zeke Hausfather, a climate scientist at Berkeley Earth, a US research group.

Some other climate groups have projected something even stronger than the Met Office’s forecast, perhaps even 4C above average.

If that came to pass, “It’s not beyond the realm of possibility to say this might be the strongest El Niño event in 500 or even 1,000 years,” Hausfather said, although it is impossible to say for sure that far back in time.

The change in the distribution of heat across the ocean – and shifts in the wind patterns in the atmosphere above – can have wide ranging effects on the weather right across the globe.

No two El Niño events are the same and the impacts on weather patterns can vary. However, there is evidence that the effects are already being felt.

For example, in El Niño years the southwest monsoon can deliver suppressed rainfall in South Asia – and so far in 2026 it is running well below normal.

Changes in wind patterns in the Caribbean and tropical Atlantic can reduce hurricane activity.

So far this season there have been only three named storms.

In areas close to the tropical Pacific the influence of El Niño can be profound, with the risk of drought and bushfires in Australia and the increased threat of flooding in Peru, Ecuador and the southern United States.

El Niño is not thought to have been a major driver of the record-breaking heatwaves that have dominated this summer.

However it could have a greater impact on the weather during autumn and early winter, with the increased potential for wet and stormy conditions across north-west Europe, including the UK.

Perhaps counter-intuitively, El Niño can also increase the odds of cold weather late in the winter, although the links are rather loose.

During El Niño events, significant heat is released from the ocean to the atmosphere.

Met Office climate scientist Dr Nick Dunstone says this can lead to “an increase in global average temperature, particularly in the calendar year following the winter peak of the El Niño.

“Hence, 2027 is very likely to replace 2024 as the warmest year on record.”

Earlier this month, the UN’s Food and Agriculture Organization warned that El Niño could threaten tens of millions of people in at-risk countries with crisis-level acute food insecurity.