The writer is a science commentator
When UK temperatures hit a record 40C last year, Imperial College climate scientist Friederike Otto responded to comparisons with the 1976 heatwave by observing: “By definition unprecedented means it hasn’t happened before.”
Prepare for more of the same. Last week, the US National Oceanic and Atmospheric Administration announced the official arrival of the El Niño weather phenomenon — which occurs about every two to seven years but not predictably. The change, linked to rising sea surface temperatures, will push more heat into an already-warming atmosphere: some scientists predict the symbolic 1.5C cap on global heating may soon be temporarily exceeded.
Whether or not that happens, El Niño’s arrival heralds a new period of climate uncertainty — and one that, with its associated risk of extreme weather, economists and politicians ignore at their peril. Even the best-laid plans to tackle the escalating cost of living will need to factor in crop failures and spiralling commodity prices. It also offers a preview of what might be coming down the track.
El Niño can be seen as the “heating” phase of a naturally occurring climate cycle in the equatorial Pacific Ocean. Its opposing, cooling phase is called La Niña. Together, they make up the El Niño Southern Oscillation (Enso) cycle, respectively weakening and strengthening trade winds. Those changes influence the jet streams that steer storms around the globe.
Last week’s NOAA declaration means, according to Richard Allan, 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 0.5C warmer than the long-term average; the warming is expected to continue; and the atmosphere is showing signs of responding to that warming.
The atmospheric response to El Niño, which is expected to strengthen throughout the northern hemisphere autumn and winter, is essentially altered wind and rainfall patterns: researchers expect it to become wetter in the southern US; and hotter and drier in northern South America, southern Africa, South Asia and southern Australia. But beyond that, uncertainty abounds, including on when El Niño might peak.
This could happen this year or next; or it could fizzle out. “It’s too early to say how the current El Niño storyline will unfold,” Allan says. “But if it does unleash its full power in 2024 then it’s very likely that yet another record global temperature will be breached.” 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 uncertainty spiked with trepidation.
One challenge is forecasting how countries should prepare: while climate models work reasonably well at the global scale, according to Professor Tim Palmer, a climate physicist at the University of Oxford, they are less effective for making long-term, country-level forecasts. That will matter in the coming years as nations invest in adaptation, such as building flood defences. Palmer is among those advocating for a “Cern for climate change”, a massive, multinational supercomputing effort to make higher-resolution forecasts, and to explore how the Enso cycle might itself alter in a warming world.
For the many countries directly affected by El Niño, Palmer 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 which can’t be tackled at the national level,” he says, suggesting it should be modelled on the international particle physics effort at Cern in Geneva that found the Higgs boson.
For now, the reality is that the mercury is still rising and the climate is still changing. Global mean temperature now stands at least 1.1C above pre-industrial levels; the warming effect of El Niño, which limits the ability of the oceans to draw down heat from the atmosphere, pushes it to within striking distance of the 1.5C limit set out in the Paris agreement.
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, has brought record-breaking April heat to Spain, extensive wildfires to Canada and, as a result of those, unbreathable skies over New York. That is the critical message: the unprecedented is becoming the norm.
