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.”

El Niño has officially begun, and it’s more likely than not that it will develop into a “super” El Niño. Either way, it will amplify temperatures and extreme weather around the world.

El Niño is a natural climate phase that occurs when east-to-west winds weaken in the tropical Pacific, allowing water concentrated in the “warm pool” on the western side of the Pacific to wash back towards the eastern side. This broad smear of warm water heats the atmosphere, raising the global temperature.

The US National Oceanic and Atmospheric Administration (NOAA) has now declared the onset of El Niño because sea surface temperatures in the central-eastern Pacific have been more than 0.5°C above normal for the past month, and climate models project they will remain there for at least the next six months. The Japan Meteorological Agency has also declared that El Niño has begun.

“We are seeing westerly wind anomalies from the dateline almost all the way to about 130° west, so basically the entire area south of Hawaii,” says at NOAA’s National Weather Service. “What that means is significantly reduced trade winds there, so it’s allowing the atmosphere and the ocean to slosh to the east and bring that warm water with it.”

NOAA also said there is a 63 per cent chance this El Niño will become a very strong or “super” El Niño, when sea surface temperatures in the equatorial Pacific breach 2°C above average. It could be the hottest El Niño ever seen.

“This latest El Niño is likely to be a significant event, perhaps one of the most intense on record,” said at the Met Office, the UK’s weather service, in a statement.

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Out of 200 model simulations, none show sea surface temperatures in the central-eastern Pacific going back below 1°C above normal this year once El Niño gets going, according Rosencrans. Several models project sea surface temperatures could reach 2.6°C higher than usual, and one Canadian model says they could even hit 3°C, which would smash the 2.5°C record set during the super El Niño of 1982-83. During that event, flooding killed an 1300 to 2000 people in Peru.

Temperatures will likely peak by the end of the year and simmer well into 2027. This rush of heat comes on top of global warming of 1.36°C, leading scientists to predict that next year will be the hottest ever observed. The boost in temperatures will worsen extreme weather, since a warmer atmosphere holds more energy and moisture. El Niño also tends to bring abnormally wet or dry weather to different regions.

“What it does is change the odds of those rainfalls��or heatwaves or cold snaps happening in certain places,” says Rosencrans. “The atmosphere [is] throwing loaded dice in a way, so you’re more likely to get rainfall in southern California, you’re more likely to get drying in the maritime continent, and potentially even into India [and] the northern parts of Australia.”

The southern US is more likely to see reduced rainfall this summer, followed by cool, wet, stormy weather this winter, with cold snaps possible as far south as Mexico. South-East Asia and south-east Africa could face heat and drought this summer and winter, raising the risk of wildfires.

El Niño can tend to bring colder winters to the UK, but it can also bring warmer, wetter conditions, said independent climate scientist at a briefing. Many other climate factors affect Europe, meaning El Niño impacts are less certain. “It tends to change the storm tracks, and you often get these warmer, wetter conditions,” says Gilbert. “In the past, for the UK, you’ve seen more storm incidents than otherwise… but the direct connection in the UK is less obvious than in the US or Australia.”

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Heat or drought could impact commodities like rice, coffee and chocolate, and disrupt food supplies around the world. If rice yields decline, India – a major producer – could limit exports and cause rice to become scarcer and more expensive in other countries, says at the University of Maryland.

“The impacts… ripple through the food system,” he says. “We think about a commodity like rice, which is important for food security for many people, and we do have concerns about potential monsoon deficits leading to lower rice production.”

El Niño may be getting more frequent, and global warming will regardless exacerbate its consequences, which could compound issues like migration, says at the University of Oxford. “We need long-term preparedness and planning as we continue with climate change and we also continue with El Niño amplifying that.”

In the winter of 2013-2014, the strong winds of the jet stream shifted north, allowing a mass of warm water dubbed “the blob” to across more than 1500 kilometres of the north Pacific Ocean.

Floating instruments moored to the seabed off Alaska, Washington and Oregon alerted scientists and the fishing industry to the arrival of this water, which was up to 4°C hotter than normal.

They were part of the Ocean Observatories Initiative (OOI), five mooring off the US west and east coasts and Greenland. Announcing $220 million in funding for the programme in 2023, the US National Science Foundation (NSF) the OOI was needed to monitor “critical organs of the Earth”. But last month the NSF from the water following funding cuts by the administration of US President Donald Trump.

As a planet-warming El Niño climate phase warmed the water further in 2015-2016, sensors running up and down OOI mooring wires revealed the blob was into the deep sea below 250 metres. The mooring data helped show the blob, which repeated in 2019 and may be happening more frequently due to climate change, spurred toxic algal blooms that California’s $60 million Dungeness crab fishery for the season.

The removal of most OOI moorings will diminish the accuracy of weather forecasting, including precipitation patterns influencing the record drought in the western US. It will also hinder efforts to monitor a possible weakening in the Atlantic Meridional Overturning Circulation (AMOC) that keeps Europe temperate, as well as the effects of an imminent El Niño.

“We’re flying blind, and it will end up costing us more,” says at the University of St. Thomas in Minnesota.

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While the OOI costs $56 million a year to run, the US commercial fishing industry, which relies in part on OOI data, billions of dollars each year. Weather and climate disasters did $183 billion of in 2024. (The US government discontinued this tally in 2025.)

Without the OOI, fleets won’t know which fishing areas might be less impacted by the coming El Niño, which some models say could be the strongest on record, says at Oregon State University. Oyster, clam and shellfish farms won’t be able to prepare for heating and reduced nutrients the El Niño could bring, and scientists will lose their view of harms to marine ecosystems. In the past, the OOI has also alerted scientists to the formation of low-oxygen “dead zones” on the seafloor.

“That is going to be lost at exactly the worst time,” says at Boston College in Massachussetts.

Because satellites can’t see beneath the surface of the sea, measurements by underwater floats, gliders and moorings are crucial to understand what’s happening in the 70 per cent of the planet covered by ocean.

While these mostly measure temperature, salinity and flow rate, the OOI moorings also have sensors for parameters like pH, oxygen and CO2 for understanding the biology and chemistry of the ocean. And they do so in remote, little-monitored places where the movement of water masses affects the climate.

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The loss of these sensors will impact the rest of the world, especially by reducing observations of the AMOC. The OOI array in the Irminger Sea, east of Greenland, is part of OSNAP, a line of moorings, gliders and floats stretching from Canada to Greenland to Scotland. It monitors warm, salty water flowing from the tropics to the north Atlantic, where it cools and sinks, driving the AMOC. A collapse in this system could plunge Europe into “ice age” winters and disrupt monsoon rains critical for agriculture in Africa and Asia.

“OSNAP has taught us that most of the actual overturning takes place east of Greenland and that the Irminger Sea is key in understanding the overturning variability,” says at the Royal Netherlands Institute for Sea Research.

Removing OOI will create a data gap that will limit understanding of the AMOC, even if it’s someday replaced, Palevsky adds.

Scientists fear the dismantling of OOI is the start of a massive rollback of US ocean research funding that could see the discontinuation of OSNAP. Some worry it could even undercut Argo, a vital network of almost 4000 descending instrument floats across the global ocean, of which are provided by the US.

In a statement to 91av, the NSF said the OOI removal was to “prioritize support for evolving scientific priorities”. But it comes as the Trump administration wages what at the Union of Concerned Scientists calls an “attack on science”. The administration has or suspended thousands of research grants, and it has proposed slashing the NSF’s budget by 55 per cent in 2027.

This week, the administration proposed a rule that would cancel peer review of research grant applications, allowing political appointees rather than independent experts to decide the fate of federally funded research. It would also ban international collaborations and research on gender and diversity.

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at the Oregon State University, who manages the OOI array off the coast of Washington and Oregon, says the dismantling of OOI and the proposed grant rule are both part of sweeping changes that would “weaken peer review and politicise NSF-funded science”.

A last month found that dismantling even one-fifth of the Global Ocean Observing System, a network of instruments that includes the OOI arrays and the Argo floats, would increase the error in the annual rate of ocean heating by 33 per cent. That would be like going from predicting an unemployment rate of 3 per cent this year to only being able to give a range of 2 to 4 per cent, says Abraham, who was part of the team behind the research.

“This is purposeful to try and remove our eyes and ears in the ocean,” he says of the OOI dismantling. “Because if we don’t measure something, how do we know we have a problem?”