The World Meteorological Organization (WMO) says a potentially exceptional El Niño warming event is now firmly established in the tropical Pacific and is expected to strengthen significantly into a “very strong” El Niño over the coming months.

The event could reshape rainfall and temperature patterns across large parts of the planet, increasing the risk of floods in some places, drought in others and additional extreme heat.

The WMO says almost all land areas are likely to experience above-normal temperatures during the coming months.

WMO forecasting centres put the probability of El Niño persisting through February 2027 at nearly 100%, a remarkable degree of certainty.

It is the first time that an El Niño/La Niña update has been so unequivocal.

The event is expected to continue intensifying through the autumn and peak towards the end of 2026, although its climatic effects are expected to continue well into 2027.

The Head of Long-Range Forecasting at the UK Met Office, Professor Adam Scaife, described the unfolding event as potentially the largest El Niño in living memory and perhaps the most significant since the 19th century.

As a result, he said next year, 2027, is “very likely” to replace 2024 as the warmest year ever recorded.

Although a very strong El Niño can cause major shifts in atmospheric circulation, rainfall and temperatures around the world, the consequences vary greatly according to location.

Not every region will experience extreme weather and its influence on Ireland and Europe is much less predictable.

El Niño typically peaks between November and February, but its influence on global average temperature can continue afterwards and can be most pronounced during the year following its development.

The WMO says the underlying warming of surface waters that has already occurred in the Pacific is exceptional with average temperatures as much as 2.6°C above normal in recent weeks.

Even more striking is the amount of heat stored beneath the surface of the Pacific, which was more than 8°C above average in some areas during July and early August.

This is an extraordinary amount of excess heat and helps explain why the WMO is so sure that this El Niño will strengthen further.

The WMO is therefore mounting an unusually large international preparedness and early-warning effort, working with national meteorological agencies, UN organisations and humanitarian agencies.

It is particularly concerned about agriculture, food security, water resources, health and energy, as well as the humanitarian consequences of floods, droughts and extreme heat.

The WMO stresses that El Niño itself is a naturally occurring climate phenomenon and is not caused by human-induced climate change.

However, this El Niño is occurring against the background of an already much warmer planet and unusually warm oceans.