When Prof Adam Scaife, the Met Office's head of long-range forecasting, reviewed his models earlier this year, he found something he had never encountered before: an El Niño signal so intense that it fell outside the range of modern climate records. The UK's national weather service now believes the developing Pacific event will be the most powerful since the nineteenth century — a conclusion that carries consequences measured not in degrees alone, but in droughts, storms and disrupted harvests across multiple continents. A typical El Niño raises Pacific sea surface temperatures by more than 1°C; a rise of 2°C is already considered a major event. The current cycle is projected to push those temperatures up by 3°C, a figure that the Met Office describes as unprecedented.

That additional heat pulse is expected to drive global average temperatures temporarily above 1.5°C over the pre-industrial baseline during 2027 — the threshold that negotiators at successive climate summits have fought to hold as an upper limit. Some scientists place the likely peak even higher, at around 1.7°C.

The regional effects are already being mapped. Patagonia in Argentina faces severe drought, as do parts of southern Africa and north-eastern Australia, where agricultural and water systems are particularly exposed. In the western Pacific, island communities that depend on rainfall patterns built up over centuries may face acute shortfalls. Meanwhile, north-western Europe — including the United Kingdom — is forecast to see heightened rainfall and storminess, particularly around November, as wave-like disturbances propagate outward from the overheated tropics.

What makes these projections especially arresting is that the Met Office is, by its own account, among the more cautious voices. The US National Oceanic and Atmospheric Administration has placed the probability of a very strong event above 90%, and some independent researchers regard even the 3°C projection as a conservative floor rather than a ceiling.