The writer is a science commentator

When UK temperatures hit a record 40C last year, Imperial College climatologist Friederike Otto responded to comparisons with the 1976 heatwave by observing: “Unprecedented by definition means it hasn’t happened before.”

Get ready for more of the same. Last week, the U.S. National Oceanic and Atmospheric Administration announced the official arrival of the El Niño weather phenomenon — which happens about every two to seven years, but is not predictable. The change associated with rising sea surface temperatures will push more heat into an already warming atmosphere: some scientists predict that the symbolic 1.5C ceiling on global warming may soon be temporarily exceeded.

Whether it happens or not, the arrival of El Niño heralds a new period of climate uncertainty—and one that brings with it the risk extreme weatherEconomists and politicians ignore at their peril. Even the best-laid plans to deal with the rising cost of living will have to factor in crop failures and spiraling commodity prices. It also offers a preview of what could be coming down the track.

El Niño can be thought of as the “warming” phase of the naturally occurring climate cycle in the equatorial Pacific Ocean. Its opposite, cooling phase is called La Niña. Together they form the El Niño (Enso) Southern Oscillation cycle, or the weakening and strengthening of the trade winds. These changes affect the jet streams that drive storms around the world.

Last week’s NOAA statement means, according to Richard Allan, a professor of climate science at the University of Reading, that three criteria have been met: a defined area of ​​the tropical eastern Pacific is more than 0.5°C warmer than the long-term average; warming is expected to continue; and the atmosphere is showing signs of responding to this warming.

The atmospheric response to El Niño, which is expected to intensify in the fall and winter in the Northern Hemisphere, is essentially an altered pattern of wind and precipitation: researchers expect the southern US to be wetter; and warmer and drier in northern South America, southern Africa, southern Asia, and southern Australia. Beyond that, however, there is uncertainty, including when El Niño may peak.

That could happen this year or next year; or it might go out. “It’s too early to tell how the current El Niño storyline will play out,” says Allan. “But if it unleashes its full power in 2024, then it is very likely that another global temperature record will be broken.” Earlier this year, the World Meteorological Organization said temperatures could move into “uncharted territory” with impacts on health, food security, water management and the environment. The mood among climatologists seems to be one of uncertainty laced with fear.

One of the challenges is predicting how countries should prepare: while climate models work relatively well on a global scale, they are less effective at making long-term predictions at the level of individual countries, according to Professor Tim Palmer, a climate physicist at the University of Oxford. This will matter in the coming years as nations invest in adaptation, such as building flood defenses. Palmer is among those advocating for “Cern for Climate Change,” a massive multinational supercomputer effort to produce higher-resolution forecasts and examine how the Enso cycle itself might change in a warming world.

For many countries directly affected El NinoPalmer says that’s the “trillion dollar question”: how might climate change affect the frequency and strength of El Niño and La Niña events in the future? “It’s a phenomenally complex question that can’t be tackled at a national level,” he says, suggesting it should be modeled after the international particle physics effort at Cern in Geneva that discovered the Higgs boson.

The reality for now is that the mercury keeps rising and the climate keeps changing. The global average temperature is now at least 1.1 C above pre-industrial levels; the El Niño warming effect, which limits the oceans’ ability to remove heat from the atmosphere, pushes it within 1.5°C of the Paris Agreement limit.

Any rise should be temporary – but it still represents a new extreme. Twenty-eight countries, including the UK and China, experienced their warmest years in 2022. It could have been worse: those temperatures were kept in check by the cooling effects of La Niña.

This year, meanwhile, brought record-breaking April heat to Spain, massive wildfires to Canada, and, as a result, unbreathable skies over New York. This is the critical message: the unprecedented becomes the norm.

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