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 globally.
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 with signs of a very unsettled spell already showing up in long-range forecasts.
“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.”
There is no clear evidence that climate change is making El Niño events worse, but its weather impacts are more extreme in a warming world.
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.
Is climate change making El Niño worse?
The World Meteorological Organisation (WMO) says there is “no evidence that climate change increases the frequency or intensity of El Niño events.”
However this is an ongoing area of research and debate for scientists.
The 2021 report from Intergovernmental Panel on Climate Change (IPCC) said that the intensity of El Niño has increased since 1950, when compared with the period dating back to around 1400.
The strongest El Niño events are also happening more frequently.
However, historical records show that El Niño has fluctuated significantly in its strength over past millenia so it is difficult to link this recent strengthening to global warming.
What is clear is that El Niño is now happening against the background of a warmer world – making its impacts on the weather more extreme.
