Aboard the deck of a World War II-era aircraft carrier, University of Washington scientists flicked the switch on a glorified snow-making machine, blasting a plume of saline spray off the coast of Alameda, Calif.
They’re trying to perfect a shot of salty particles that would make clouds better at reflecting sunlight back toward space, and help cool the Earth. It’s called marine cloud brightening. The outdoor studies began this month, but the UW scientists are far from a real attempt to change how much sun a cloud reflects.
Even taking this first step has renewed questions about how to appropriately study methods of reeling in climate change’s effects that could potentially impact ecosystems and humans in ways that aren’t yet understood.
Some scientists warn that human influence on natural phenomena has rarely yielded the desired outcome, and often comes with unintended consequences. But, as the fossil-fueled world hurtles toward the internationally approved global warming limit to avoid the worst impacts of climate change, some argue there’s a need to study backup plans.
“When I started graduate school in 1995, climate change, global warming was on the horizon, but there was still time to do something like reduce emissions at a scale that would allow us to avoid serious climate disruption,” program manager Sarah Doherty said in an interview. “I think it’s come to the point where the science community recognizes that a fairly significant degree of climate disruption and damage and suffering is pretty inevitable.”
The University of Washington is a funder of The Seattle Times’ Climate Lab.
Doherty and the team are not advocating that anyone try cloud brightening now, but instead are hoping to develop a foundation for research that future decision-makers could rely on if they are evaluating geoengineering as a means of reducing suffering.
A climate intervention
Last Tuesday was the first outdoor test of equipment Doherty and Robert Wood, aerosol-cloud scientists with UW’s Department of Atmospheric Sciences, and others spent years trying to get right.
Compressed air was pumped at hundreds of pounds per square inch through a nozzle full of a salty mix with a similar composition to seawater housed in an apparatus similar to a snow-making machine. The New York Times reported the machine produced a deafening hiss, releasing a fine mist that traveled hundreds of feet through the air.
The scientists wanted to see if the machine could generate a consistent spray of the right size salt aerosols, taking samples downwind with instruments mounted on scissor lifts, commonly used in construction.
This study is not yet large enough to affect local weather. The machine is run for periods of 30 minutes or less, and the overall amount of salt produced by the UW scientists’ system is relatively small compared to the natural salt production of the ocean.
Scientists hope the results will inform the next steps. For example, if they were to study this on a barge over the open ocean, how quickly would a cloud take in those particles, and is it enough to brighten a cloud?
Only later would they go out to the ocean and aim the spray toward the clouds.
Marine cloud brightening is one of several climate interventions scientists are evaluating under the umbrella of solar radiation management or modification.
“It’s kind of an insurance policy in case there’s an emergency that we feel like we have to do something,” said Nick Bond, emeritus state climatologist. “It would seem prudent to put in some effort there to kind of understand what could possibly be done.”
And scientists have already determined how particulate pollution from humans burning things has led to cloud brightening around the globe. This is most visually obvious in brightened streaks of clouds produced by sulfate emissions from ships as they traverse the ocean.
In 2020, the International Maritime Organization put new limits on the amount of sulfur in ship fuels. Atmospheric scientists have since tracked a decline in brightened clouds. The UW scientists think sea salt particles could brighten clouds the same way the ship’s sulfate emissions have, but without adding sulfur pollution to the atmosphere.
But before any intervention like this can be seriously considered, researchers need to understand how it would affect the climate system, our oceans and marine and land-based ecosystems.
Concerns about human interventions
John Latham, a British microphysicist, first had the idea for marine cloud brightening in the early 1990s.
It took another decade or more for the idea to become more mainstream, said Graham Feingold, lead for the cloud, aerosol and climate program at the National Oceanic and Atmospheric Administration’s Chemical Sciences Laboratory. In the early days, a lot of people were concerned about climate interventions, and more interested in reducing carbon dioxide emissions, the primary source of climate change. That is still largely true today.
But some things have changed since Latham first proposed the idea.
Last year was the hottest in recorded history and some experts project this year could also top the charts. As the frequency of extreme weather events has accelerated, elected leaders have directed federal agencies to take a closer look at more drastic options to defer the worst climate impacts.
Feingold was the lead author on a study published last month evaluating the research needed to understand the viability and risks of marine cloud brightening.
“The way I usually sum it up is, every time this subject comes up, I simply ask people to tell me of a large-scale human modification of the environment that’s ever gone well,” said Andrew Gettelman, a scientist specializing in clouds and climate change at the Pacific Northwest National Laboratory, and a co-author on the paper. “Nobody’s come up with a good example for me. It may have gone well for us, but not for the environment.”
On one end of the research spectrum, UW researchers are studying how to get the right concentration and size distributions of particles that might be more likely to brighten clouds. These are just the first steps.
On the other end are questions about how marine cloud brightening might have impacts on a global scale. The unintended consequences have yet to be understood.
There needs to be an international governance program in place, because brightening clouds off the U.S. could have ramifications across the world, Feingold said. It’s also unknown how marine cloud brightening might influence marine and terrestrial ecosystems, the economies that depend on them, and people’s lives.
“If we think we can cool the planet by half a degree centigrade, just as an example, on average, what does that mean for somebody living in the Amazon or in the United States or in Africa?” Feingold said. “There’s a potentially big difference in how this might play out in different parts of the world.”
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