In the 1600s, fishers in Peru saw that every few years around Christmastime, the waters there warmed, and they caught fewer anchovies. They called this “El Niño” – the boy – after the Christ child.

In the early 20th century, the physicist Gilbert Walker noticed that the prevailing low atmospheric pressure and rainy weather over the western Pacific and dry, high pressure over the eastern Pacific periodically flipped. But it wasn’t until 1969 that meteorologist Jacob Bjerknes linked the two, showing that swells of warm water in the Pacific Ocean end up wreaking havoc on weather across the globe.

Under normal conditions, the sun’s heat and Earth’s spin fuel east-to-west trade winds around the tropics, which blow water into a “warm pool” near Indonesia. As this warm pool grows, it builds up energy. “It could be a bit like a coiled spring waiting to emerge,” says at the University of Reading, UK.

Every two to seven years, natural chaotic disturbances release that spring. Bursts of westerly winds can blow against and slow the easterly trade winds, allowing swells of warm water to across the Pacific Ocean, raising sea levels along the coasts of Peru, Colombia and Ecuador. These so-called Kelvin waves indicate that El Niño is coming.

A self-reinforcing cycle called the kicks in. The blob of warm water suppresses the upwelling of cold, nutrient-rich deep water that normally makes Peru’s anchovy fishery so rich, further warming the surface water. The warm sea heats the air above it and causes it to expand. The resulting fall in atmospheric pressure slows the trade winds down even more, since winds flow from high to low pressure. This allows still more warm water to slosh back into the eastern Pacific.

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The swathe of warm water stretching across the tropical Pacific releases trillions of joules of heat energy into the atmosphere, raising worldwide temperatures on top of global warming. This is why scientists expect 2027 to be the hottest year on record. But it also drastically alters weather patterns, bringing drought and wildfires to some areas and storms and flooding to others.

Normally, warm air rises over the warm pool, carrying moisture that falls out in thunderstorms, which is why rainforests flourish in places like Indonesia. Denuded of moisture, this warm, dry air then reaches the top of the troposphere and spreads out to the east and west. It descends over the eastern Pacific and the Horn of Africa, fuelling a belt of such air loops around the tropics called the Walker circulation.

During El Niño, however, the warming of the eastern Pacific moves this upward convection eastward, shifting the entire Walker circulation. Now dry, warm air that was sinking over the Horn of Africa and the eastern Pacific is sinking over Indonesia and the Amazon, encouraging drought and wildfires there. Over eastern Africa, warm air is rising, increasing rainfall and the risk of flooding.

Meanwhile, the warming waters also create a stronger temperature contrast between the tropical and northern Pacific, strengthening the jet stream and bringing more storms and wet weather to the southern US. It can bring storms and rain to the UK as well, in certain circumstances.

“If this deep convection in the atmosphere moves around, it changes things locally, but it also then starts to change the whole circulation of the atmosphere,” says at the European Centre for Medium-Range Weather Forecasts. “That’s why El Niño is a big deal, not just some local process.”

August was the joint hottest month ever observed, tying with July 2023, as the most severe super El Niño on record amplified temperatures already heightened by global warming.

The monthly mean temperature was 1.65°C above pre-industrial levels, according to the European Union’s Copernicus Climate Change Service. Humans have not experienced temperatures warmer than this summer in the past 100,000 years, according to at Copernicus.

August was also a record-warm month for the extra-polar ocean – the regions lying just outside the Arctic and Antarctic circles – peaking at 21.1°C, the hottest temperature ever observed in the sea surface. That included unprecedented temperatures in the tropical Pacific, where winds have slackened and warm waters have been sloshing back towards the eastern Pacific, creating the strong El Niño.

“August 2026 is remarkable not simply because it’s yet another temperature record that’s been broken but because multiple parts of the climate system have reached unprecedented levels at the same time,” she says.

The records will keep being broken as the El Niño intensifies through December, she predicts, with some months likely to be as much as 2°C above average.

The record August temperature caps off western Europe’s hottest summer on record. That warmth drives extreme weather and climate catastrophes. It makes heatwaves more likely and allows the atmosphere to hold more moisture, worsening storms.

Four major heatwaves in Europe, as well as severe drought, fuelled massive wildfires near cities like Bordeaux in France and Madrid in Spain and lowered water levels in major rivers to reveal everything from long-lost woolly mammoth bones to Nazi boats.

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At least in Europe during the heatwaves than would be statistically expected, and including wheat are expected to be lower than usual.

The heat in August was also linked to a glacier collapse that destroyed several towns in Nepal and Tibet, with at least 1300 people dead and more than 5500 still missing.

“For every degree of warming, the extreme events… intensify, so in summer we get more frequent, more intense, more longer-lasting heatwaves,” Burgess says. “This obviously has a direct impact on our food security.”

In light of the temperature record, the Energy and Climate Intelligence Unit (ECIU) – a UK-based think tank – called on leaders meeting in November for the COP31 climate summit to both reverse the rise in greenhouse gas emissions and also invest more in adapting to the current impacts.

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“The task now is to match the scale of the science with the scale of action… accelerating the transition away from coal, oil and gas to bring our climate back into balance,” , international lead at the ECIU, said in a statement.

The United Nations Environment Programme said this month that the world will “overshoot” the Paris Agreement goal of preventing warming of more than 1.5°C and should now focus on reversing this warming at a later date, including with approaches like carbon dioxide removal.  

“The sooner we can bring temperatures back down, the less time we overshoot, the better it will be for our climate system,” says Burgess.

“I often get asked whether this is the ‘new normal’. The simple answer is no,” at Imperial College London said in a statement. “Until we stop burning fossil fuels, these records will continue to tumble, and the extremes will worsen faster than we are able to adapt.”

Growing seaweed has long been as a way to slow climate change. But this approach is mistaken, a new study argues, as the loss of seaweed emits far more carbon than what is being absorbed by attempts to grow it.

Seaweeds absorb an estimated 3.7 billion tonnes of carbon dioxide through photosynthesis every year, drawing it from seawater, which then draws more CO2 from the air above. They mostly grow near the coast, where they are eventually digested or decomposed, emitting carbon. But fragments of fronds, as well as from the seaweeds that dissolve in seawater, can sink into the deep sea, sequestering a of the CO2 as “” for thousands of years.

Scientists and start-ups have suggested that seaweed growth, especially kelp, could be expanded to take up more CO2, something the UN has said we will need to do on a massive scale to eventually reverse dangerous levels of global warming.

But there are concerns that cultivating huge amounts of seaweed could backfire and diminish growth of phytoplankton, another important carbon sink. And even the kelp forests we currently have, which are estimated to cover around 640,000 square kilometres worldwide – an area slightly larger than France – are dying off as ocean temperatures reach record highs.

Now, at the University of Western Australia and her colleagues have concluded that, with some 60 per cent of kelp forests in decline, these ecosystems could eventually begin emitting more CO2 than they absorb. Researchers, as well as governments and companies trying to offset their emissions, need to focus on preserving rather than growing seaweed, they suggest.

“Instead of asking how much carbon we can remove with seaweeds, we should be asking how much carbon we can stop from being released as these ecosystems are damaged by climate change,” says Filbee-Dexter.

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Some studies have the possibility of removing a billion tonnes of carbon per year with seaweed, but there are already signs that this may not be feasible. For instance, the US carbon removal start-up Running Tide, which raised $70 million to cultivate kelp on wooden buoys that would gradually sink into the deep sea, in the open ocean and shut down last year.

Other projects have tried to bring back lost kelp forests. An experiment in northern Norway of kelp by poisoning seaweed-eating sea urchins, which can multiply when overfishing and hunting remove their predators.

While kelp restoration like this is a win for biodiversity, it only draws down about 50,000 tonnes of CO2 per year. Meanwhile, global kelp loss is emitting an estimated 14 million tonnes of CO2 per year.

The study by Filbee-Dexter and her colleagues also notes that preserving kelp ecosystems is at least eight times cheaper per hectare than restoring them, yet only 2 per cent of kelp forests lie in protected areas.

Firms are also cultivating seaweed to make nori for sushi, animal feed and thickeners for products like ice cream and toothpaste. Fragments of seaweed still drift away and sink into the deep sea, and aquaculture companies like Kelp Blue have to eventually sequester and offset hundreds of millions of tonnes of CO2.

Seaweed farming now takes up 4000 square kilometres of ocean. But that’s only about a third of the kelp forest cover lost each year. And after factoring in emissions associated with farming operations – like boat fuel and plastic lines – nine out of 11 seaweed farms were found to emit more CO2 than they sequestered in a .

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“Seaweed restoration and farming is unlikely to be a major climate change solution,” Filbee-Dexter says. “But that doesn’t mean it isn’t worthwhile.”

Restoration can improve biodiversity, and farming can make low-carbon alternatives to fossil-fuel products like fertiliser, she notes.

at Queen’s University Belfast in the UK, however, says scientists don’t have a solid enough understanding of how much carbon seaweed sequesters to write it off yet. Macroalgae restoration, conservation and farming can all still be climate solutions, even if their impact has often been exaggerated in the past, she argues.

“Blue carbon is part of the puzzle,” she says. “It can make a contribution. The question is how that is determined and validated.”

Short-term geoengineering to brighten clouds over the eastern Pacific Ocean could limit the damage caused by El Niño and save the global economy trillions of dollars, although there could be winners and losers from the disruption of natural cycles.

The El Niño climate phase occurs when easterly winds weaken, allowing warm water built up in the western Pacific to slosh back across the central and eastern parts of the ocean. That heats the atmosphere and raises global temperatures, with losses to economic growth estimated in the trillions of dollars.

What could become a very strong or “super” El Niño is now developing in the eastern Pacific. But climate modelling has suggested that, in the future, a geoengineering method called marine cloud brightening might be able to cut this warming short.

The technique involves spraying tiny droplets of seawater into the air below low-lying stratocumulus clouds, where moisture condenses onto them. The clouds become whiter thanks to the increase in the number of droplets, reflecting more sunlight back to space.

Shading part of the eastern Pacific called the Niño 3.4 region via cloud brightening could interrupt the feedback loops that cause an El Niño to develop. Cooler sea surface temperatures would strengthen the trade winds to again blow warm water back into the western Pacific. More cool water would then well up from the depths of the eastern Pacific, further cooling surface temperatures, and so on.

“You can basically stop the dominoes from falling early when you do marine cloud brightening,” says at the University of California, San Diego, who worked on the study. “We’re kicking the cycle in the other direction.”

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Wan and her colleagues got the idea from the “black summer” of catastrophic bush fires in Australia in 2019-2020, which were followed by La Niña, the opposite phase of El Niño that lowers global temperatures. Research has that drifting smoke particles brightened clouds and cooled the eastern Pacific, intensifying and prolonging the “triple dip” La Niña that began in 2020 and persisted through three winters, rather than just one or two.

The study modelled what cloud brightening could have done to the super El Niño events of 1997-1998 and 2015-2016. It found that nine months of spraying seawater would have nearly halved warming of the Niño 3.4 region, from 2°C or more to a little over 1°C. It would have ended the El Niño by January, shaving several months off the events.

The hypothetical cloud-brightening mission would have been massive, involving an estimated 2400 ships and delivering an amount of seawater spray that isn’t possible with current nozzle technology. But it would have turned a super El Niño into a moderate one.

Wan says she was surprised how well it seemed to work, given that it could only be started in June, once El Niño had clearly begun developing.

at the University of Exeter, UK, warns that these results might not translate to the real world, where warming seas typically start dissipating low-level clouds, leading to further warming and dissipation through a feedback loop.

“In a model with a stronger cloud feedback, you would have to do more aerosol injection,” he says. “The experiments seem to be at the limit of what can be done.”

Wan admits this approach could have unexpected consequences, since the model only projected the impact over two-year periods. In both simulations, La Niña started earlier after El Niño subsided, and in the 2015-2016 case, this subsequent cooler phase became stronger. That could be bad news for regions like the Horn of Africa, where strong La Niñas have, in the past, disrupted rainfall and .

But she says the idea is worth further research. Unlike geoengineering aimed at reducing global temperatures for the long term, short-term geoengineering like this could avoid the risk of “termination shock”, where any disruption to the spraying of low-level seawater or stratospheric aerosols could allow years of pent-up warming to come roaring back.

“This study is opening up doors for a completely new target for geoengineering research, which is climate variability and things like El Niño,” says Wan. “It’s potentially very powerful, because you’re not locked into these long-term risks.”