Could we stop El Niño by brightening clouds? New study explores how

First, it was news about using cloud seeding to halt hurricanes.

Now, it's global climate troublemaker El Niño that scientists want to stop, this time by "brightening" clouds over the Pacific Ocean.

According to a new study by scientists at the University of California, San Diego, appearing in the peer-reviewed journal Science Advances, "marine cloud brightening" over the southeast Pacific Ocean could weaken an emerging El Niño if deployed at its start and during its growth phase.

El Niño, which brings a potpourri of weather calamities, is the world's most significant climate pattern, costing the global economy trillions of dollars per year, according to a recent study.

Geoengineering to the rescue?

Marine cloud brightening is a type of geoengineering – the altering of climate by making clouds brighter or seeding clouds to make rain – and has been seen as a possible solution to slow the pace of global warming for decades, but is always accompanied by controversy, according to a statement from the UC San Diego.

“One of the biggest social concerns around geoengineering is the fact that if we use it to reduce long-term climate risks, we have to deploy it continuously for an indefinite period of time,” said study lead author Jessica Wan, now a postdoctoral researcher at the University of Chicago who performed the research while she was a graduate student at UC San Diego.

“If we could target natural variability [such as an El Niño event], we could get some of the benefits of geoengineering without having to employ it indefinitely,” Wan said in a statement.

What is marine cloud brightening?

Marine cloud brightening is a solar geoengineering approach that injects aerosols into the lower atmosphere, forming brighter marine clouds that reflect more sunlight back into space. (Aerosols are tiny airborne particles or droplets – such as dust, smoke, sea salt, and pollution – that can affect air quality, weather, and Earth's climate, according to NASA.)

While some researchers have proposed using marine cloud brightening to cool the planet overall, Wan explored the idea of using the technique for regionally and temporally targeted cloud brightening to alter the trajectory of an extreme climate event such as El Niño.

What is El Niño?

El Niño is a natural climate pattern in which surface sea water temperatures in the central and eastern tropical Pacific Ocean are warmer than average.

Its name means the Little Boy, or Christ Child, in Spanish. El Niño was originally recognized by fishermen off the coast of South America in the 1600s with the appearance of unusually warm water in the Pacific Ocean around Christmas.

The entire natural climate cycle is officially known as El Niño-Southern Oscillation, called ENSO by scientists. The cycle swings between warmer and cooler seawater in a region along the equator in the tropical Pacific. La Niña is marked by cooler-than-average ocean water in the region.

How would marine cloud brightening prevent El Niño? Could it actually cool the ocean water?

"Yes, marine cloud brightening would cool the sea-surface temperatures under the region of brightening by reflecting more sunlight back to space before it can be absorbed by the surface of the Earth," said study coauthor Kate Ricke in an e-mail to USA TODAY.

She said that by cooling ocean temperatures in this particular region – which are important to the ocean-atmosphere feedback processes that lead to the growth of an El Niño – the pattern is disrupted and doesn't mature as it typically would.

"By the time that El Niño would typically be reaching its peak in December through February, with cloud brightening, the Pacific is shifting back into its neutral state with cooler ocean temperatures and stronger upwelling in the tropical eastern Pacific," Ricke said.

How would trying marine cloud brightening on El Niño be similar to what happened with the Australian bushfires?

While no scientists have undertaken the marine cloud brightening experiment yet, the catastrophic bushfires (wildfires) that scorched Australia in 2019 and 2020 served as a "natural experiment" for marine cloud brightening, according to a statement from UC San Diego.

The smoke that wafted into the atmosphere from the fires was filled with reflective, cloud-interacting aerosols, contributing to a brightening of low marine clouds over the southeast subtropical Pacific.

Ricke told USA TODAY that "in our study we use a model to isolate the bushfires' low cloud-brightening effects from its other effects on the atmosphere and find that its low cloud brightening effects alone could push the Pacific toward a La Niña state like the one that occurred after the fires in the real world."

Changing El Niño to La Niña

The team modeled what would happen if – instead of “natural” cloud brightening from bushfire smoke during La Niña – deliberate marine cloud brightening were deployed in the Southeast Pacific during major El Niños that originated in 2015 and 1997.

The simulation suggested that the targeted marine cloud brightening would indeed attenuate the effects of El Niño, becoming more effective the earlier in the El Niño event they were introduced. If deployed over the central Pacific Ocean, marine cloud brightening could increase the cooling and drying effects associated with La Niña by more than 40%.

Could such a project ever be undertaken in the real world?

For perspective, USA TODAY asked a pair of outside experts not affiliated with the study about how realistic such a project would be to undertake:

"The practical technology for the sprayers required for marine cloud brightening does not exist," David Keith, a University of Chicago climate systems engineering researcher, said in an email. "Significant innovation would be required to make sprayers that work. There's little effort for this, and it's impossible to say if or when it would become practical."

"Note that other kinds of sunlight reflection, such as putting sulfur air through the stratosphere, could be done with today's technology," Keith said.

Should we even consider it?

"For me, the answer is a clear-cut yes," Keith said. "Broadly, the scientific work on sunlight reflection suggests that the benefits could be large compared to the risks, so in a world where some people, particularly poor people in hotter regions, are suffering from warming, I think it is important to consider these options."

What are the dangers and drawbacks of such geoengineering attempts?

According to Holly Buck at the University at Buffalo, "some geoengineering strategies have consequences that scientists are still learning about. Ecological implications of geoengineering are understudied.

"When it comes to marine cloud brightening, making clouds brighter in one area can impact climate in far-away regions, and there is a lot more to learn about the climate system and impacts of this strategy."

Who would decide to undertake such a project? Who would pay for it?

The researchers said they are not aware of any proposals to test this on the El Niño brewing now, but as research progresses, actual geoengineering schemes could be considered by government-level decision makers in the future.

"We obviously don't address this in the paper, but we believe that if this were ever undertaken, it should be done under a system of global governance," Ricke said. "Because El Niño affects weather all around the world, many would have a stake in the outcomes."

"Ideally, the global governance process would also determine who should be responsible for paying for it as well," she said. "Of course, many things don't happen in an ideal way in the world, so we hope that our research may inspire governance experts to start thinking about how enabling and constraining governance might look under a range of El Niño engineering deployment scenarios."

Do we have the technical ability now to proceed with this project?

In theory, yes, but not in an ideal way, Ricke said. "We also don't know whether the magnitude of cloud brightening we simulate is reproducible in the real world. ... We do need much more research before we can say with confidence that this is a good idea."

Doyle Rice is a national correspondent for USA TODAY, with a focus on weather and climate.