Another ‘Super El Niño’ is brewing. Scientists are looking at a controversial solution to squash them

By Laura Paddison, CNN

(CNN) — A Super El Niño is brewing and it could be the most intense in decades, threatening a dramatic increase in deadly extreme weather. But what if there was a way humans could dial down the ferocious impacts of the most severe El Niños by temporarily dimming the sun?

That’s the question a group of scientists has investigated in a new study published Wednesday in the journal Science Advances.

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El Niño is a natural climate pattern originating in the tropical Pacific Ocean, which typically boosts global temperatures and fuels extreme weather. It’s being compounded by human-driven climate change, which is ramping up the planet’s background temperature, pushing El Niño years into increasingly extreme territory — with devastating impacts on human lives and global economies.

The study, led by scientists at Scripps Institution of Oceanography, focused on whether a highly controversial technique called solar geoengineering could be used as a tool to tamp down the severe heat, fires and other impacts El Niño brings.

Specifically, they looked at “marine cloud brightening,” which involves spraying particles into ocean clouds in order to reflect sunlight away from the Earth and back into space.

The researchers couldn’t conduct real-world geoengineering experiments to test the idea for fear of “disastrous unintended consequences,” so instead they turned to a “natural experiment,” they wrote in a statement accompanying the report.

Australia’s “Black Summer” bushfires in 2019 and 2020 incinerated tens of millions of acres and contributed to the deaths of hundreds of people. They also produced plumes of smoke filled with sun-reflecting particles, which mixed with clouds over the Pacific Ocean.

Previous research has found these ultra-reflective clouds bounced more of the sun’s energy back into space and cooled the Pacific, contributing to a subsequent La Niña event, El Niño’s counterpart, which tends bring down global temperatures.

The scientists isolated the cloud brightening impacts of the Australian fires and used climate models to simulate the effect of a similar event happening before two historically strong El Niño events, one that started in 1997 and another in 2015.

They found targeted marine cloud brightening could weaken El Niño’s impacts and increase the cooling and drying effects associated with La Niña by 40%. The earlier in the El Niño event the technique is deployed, the more effective it would be, the study concluded.

Geoengineering is a hotly debated topic. Some experts are of the view that it is too dangerous to even consider, with a near infinite number of unintended consequences. They also fear it would need to be continued indefinitely to prevent possible “termination shock” — a catastrophic rise in temperatures if geoengineering is started then halted.

But what the scientists are considering here is different, said Kate Ricke, a study author and a climate scientist at Scripps Oceanography and UC San Diego’s School of Global Policy and Strategy. The idea is to deploy geoengineering as a temporary tool to target a specific seasonal or multi-year event all but guaranteed to bring significant damage, she said, “it’s not something that you’re locking yourself into.”

Ricke stressed that the paper is not advocating for geoengineering. “This is just a proof of concept … the only thing we’ve shown is that it’s worth further study,” she said.

The researchers acknowledges several potential drawbacks. El Niño is a very complex phenomenon; while it causes trillions in global economic losses, not every region loses out. Some are adapted to its impacts — for example, California relies on the heavy rain El Niño typically brings to replenish water reservoirs, even if it can be dangerous.

It will also be important to understand how this technique would affect the timing, frequency and magnitude of a subsequent La Niña event, and what the impact would be on specific regions, Ricke said.

“You have to think very carefully about trade-offs,” she said. Geoengineering “is probably best to think about for now in terms of super El Niños, where most people, most places are losers and really extreme, damaging events are most possible,” she added.

James Haywood, a professor of atmospheric science at the University of Exeter, who was not involved in the research, said there remain “many, many unanswered questions and uncertainties as to the viability of marine cloud brightening” in terms of controling its cooling impact.

There’s the technical challenge of generating particles of the right size and quantity to produce the desired amount of cooling, he said. “Then there is the question of what if we overdo it?” he added, referring to the possibility of a mega La Niña “many, many times stronger than we’ve experienced before.” La Niñas can bring extreme weather, too, including increased rainfall and flooding in parts of Asia and Australia, and drier-than-normal conditions in parts of South America and the US.

“We are a long way away from being able to deploy such technologies and knowing whether they would work as intended,” he said.

David Keith, a geophysical sciences professor at the University of Chicago, also pointed to the engineering challenges. “Almost two decades after research started, marine cloud brightening sprayers have spray rates… that are at least factor of a hundred too small for practical use,” said Keith, who was also not involved in the study. The technique may be physically possible, he added, but currently “the technology simply doesn’t exist.”

Beyond the technical problems lie ethical quandries, said Haywood, such as who gets to decide if the world opts for this technique and whether geoengineering would distract from efforts to cut planet-heating pollution.

These questions are beyond the scope of this research but Ricke acknowledged there is much more work to be done. “We need to understand a lot more,” she said, “but if there is a way to use this… to mitigate El Niños, why wouldn’t we consider it?”

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