At his lab in the Florida State University Department of Earth, Ocean and Atmospheric Science in Tallahassee, Michael Diamond researches how the interplay of clouds and tiny atmospheric particles called aerosols could influence the climate.
Diamond studies how such particles, when released from ships as they travel across the oceans, affect clouds — and can cool temperatures in the waters below. If particles released into the air from ships provide local cooling, could they be released purposefully on the large scale like planetary air conditioning?
These are the kinds of questions asked by geoengineering: The science of how to cool the planet to fight climate change. Scientists like Diamond study solutions such as reflecting sunlight back into space. That could entail releasing aerosols into the stratosphere from high-altitude planes or, in the case of Diamond’s research, brightening marine clouds from ship decks.
But the science is contentious. Some critics worry it could be seen as a quick fix for climate change, taking the focus off the need to curb carbon-dioxide emissions. Others denounce the idea of manipulating the climate altogether.
The Florida Legislature passed Senate Bill 56 this spring, which bans weather modification and geoengineering in state airspace. At least 25 other states have seen similar proposals to crackdown on the various technologies, which are still exploratory. Opponents of the laws paint proponents as conspiracists, and some are, having shared debunked atmospheric conspiracies such as "chemtrails" on social media.
But weather modification, or influencing small-scale weather events like rainstorms, has a long history in Florida, which was a key player in early cloud-seeding science before experiments ended in the early 1980s. It's also common in the west, where government and private cloud-seeding programs help increase precipitation during dry times.
Geoengineering refers to broader manipulation of the global climate, but at this point hasn’t been carried out beyond confined experiments.
Diamond regards the science as a way to staunch a bleeding wound while it’s treated, like a tourniquet for Earth while we work to lower carbon emissions.
“It really doesn’t make sense as a standalone,” he said. “[But] if you’re dealing with the underlying issue and it’s just going to take some time, stopping the bleeding is actually a really good idea.”
But he said short-term bans are not a bad idea to prevent premature deployment of an unfinished concept.
But other atmospheric scientists say it’s crucial for the U.S. to fully explore geoengineering research as temperatures continue to rise – and as other nations continue the work.
A volcano sparks an idea
In 1991, Mount Pinatubo, a volcano on the island of Luzon in the Philippines, violently erupted, killing nearly 850 people and sending an enormous plume of ash 28 miles into the sky, according to the U.S. Geological Survey. Nearly 20 million tons of sulfur dioxide particles spewed into the air. Lingering in the stratosphere, those particles redirected sunlight back to space, cooling the planet by almost half a degree Celsius – or a full degree Fahrenheit. The effect lasted nearly two years.
The natural cooling raised an intriguing question: Could researchers replicate the process to divert spiking temperatures caused by climate change?
The eruption advanced an area of geoengineering known as Stratospheric Aerosol Injection. Rather than relying on volcanoes, scientists considered whether high-altitude planes could dispense the particles far above Earth’s surface to alleviate the heat.
Peter Irvine, a University of Chicago research assistant professor of solar geoengineering, believes it’s a very real possibility.
The Paris Agreement, an international pact dedicated to curbing the carbon emissions that cause climate change, set a goal to limit global warming to less than 2 degrees Celsius above pre-industrial temperatures — or 1.5 degrees Celsius as a best-case scenario.
That’s the threshold at which, scientists say, the world will see more severe impacts, including more frequent and worsening droughts, heatwaves and rains. Earth temporarily surpassed the 1.5 degree threshold last year, the world’s hottest on record. That’s why Irvine sees Stratospheric Aerosol Injection as an important part of climate strategy in addition to emissions cuts.
But there's also the matter of unintended consequences: What goes up must come down. Aerosols placed in the sky would have a short-lived effect, Irvine said, lasting a range of months to years before they would need replenishing.
To mimic natural eruptions like Mount Pinatubo, researchers would most likely use sulfuric aerosols. But as those chemicals eventually percolate into the lower atmosphere, Irvine said they could contribute to higher instances of acid rain. Hypothetically, even the planet’s ozone layer, monsoon seasons and jet streams could shift under exposure to Stratospheric Aerosol Injection.
However, Irvine said those systems will also be substantially altered by climate change. To him, the exploratory technology’s beneficial cooling may overshadow the risks.
“It would be hasty to deploy it today because we don’t know enough about the consequences,” he said. “But I think we wouldn’t need to wait until some red line is crossed if we had confidence that it might help to reduce climate risks.”
Once introduced, Irvine likened it to a piece of critical infrastructure: difficult to phase back out. The trajectory for rapid warming would resume quickly if Stratospheric Aerosol Injection were to suddenly stop, introducing a kickback that would drive climate change into an even higher gear, a concept called “termination shock.”
The slight temperature difference instigated by Mount Pinatubo was a shock the global system could absorb, said FSU’s Diamond. But artificially inducing much more cooling without also acting to cut emissions could be a recipe for disaster, he said.
“If you were offsetting four degrees of global warming, yeah, that would keep me up at night,” he said.
Answers above the ocean?
Diamond is fascinated by a different geoengineering approach known as Marine Cloud Brightening.
Similar to how plane contrails line the sky, boats leave streaks over the ocean in the form of long, narrow clouds called ship tracks, which are caused by engine exhaust.
Those clouds are extremely reflective of sunlight and help the ocean absorb less heat. In 2020, United Nations regulations that drastically cut the amount of sulfur in ships’ fuel improved air quality but had the unintended downside of producing fewer ship tracks.
Diamond’s research has helped show that directing natural sea spray into the sky, rather than sulfur or carbon, is a potential tool for producing more the clouds that diminish warming.
In field testing, researchers have used machines similar to mammoth leaf blowers to send sea salt mist off drifting ships and into the lower atmosphere. One such test in the U.S. took place last year in San Francisco Bay but was halted by local government for fears of health or environmental risks, a roadblock for scientists who hoped to understand how sea salt interacts with the atmosphere.
Australia has investigated the prospect of Marine Cloud Brightening since 2020 to protect the Great Barrier Reef from coral bleaching, which stems from marine heat waves.
Diamond said alterations to clouds anywhere on Earth wouldn’t last beyond more than a few days, and the jury’s still out on the feasibility of pulling it off on a larger scale.
Compared to Stratospheric Aerosol Injection, Marine Cloud Brightening also presents a new subset of risks and peculiarities. The science is suited best for clouds above cooled oceans, including off the coast of California where upwelling cycles frigid water from the deep. It wouldn’t be as effective for the thick thunderstorms that swell over the Gulf of Mexico, which is commandeered by the Gulf Stream — upwelling’s warm counterpart.
Those regional singularities could cause uneven cooling patterns from human cloud manipulation, Diamond said, posing a potential threat to atmospheric circulation and weather patterns.
“That’s why we need research,” he said. “To be able to understand this and be able to answer for policymakers … what these consequences would be.”
Cutting atmospheric science
When the Florida Legislature’s geoengineering and weather-modification ban came across his desk last month, Gov. Ron DeSantis said he would support the bill so the state doesn't become “a testing ground for geoengineering.”
“We don’t want to indulge this nonsense in Florida, where we are proud of our sunshine,” DeSantis wrote on X.
The new law will repeal the state’s ability to issue permits for geoengineering or weather modification. It makes atmospheric intervention within the state of Florida a third-degree felony punishable by up to five years in prison and fines reaching $100,000.
Diamond at FSU said precautionary regulations and temporary bans on geoengineering may make sense given the need to research risks before unleashing the technology. What concerns him and other scientists more are cuts at the federal level, to the fundamental science.
The National Oceanic and Atmospheric Administration, or NOAA, currently oversees federal geoengineering research through funding awarded under the Biden Administration, though it may not survive much longer.
Leaked budget memos from early this year show the Trump Administration’s intention to eliminate the NOAA’s Office of Oceanic and Atmospheric Research. Though the cut remains unofficial, it reflects Trump’s endorsement of Project 2025, a plan to reshape the federal government that calls the research branch’s climate work “alarmism.”
“The preponderance of its climate-change research should be disbanded,” the Project 2025 document says of the research branch.
Diamond, a former NOAA employee from 2021 through 2022, said his old division suffered from recent mass layoffs. Even at FSU, he still relies on the agency’s funding for his research, making his future inquiries into Marine Cloud Brightening uncertain.
The National Weather Service was founded in 1870 and was later wrapped into NOAA when Richard Nixon, a Republican president, organized the agency a century later. Since then, NOAA research has formed the basis of everyday weather forecasting, preparation for natural disasters, predictions for climate change and more.
“I don’t entirely see how we’re going to recover some of the federal expertise that’s already been lost,” Diamond said. “You really can’t just hit one side of the field without having consequences for the others, and that’s going to have big consequences for society.”
A need for cooperation
Though geoengineering science is still in an “incubation state,” cuts to NOAA climate change programs writ large endanger the country, said Jeff Goodell, author of the geoengineering book “How to Cool the Planet.”
“That’s what’s kind of scary,” he said. “The bigger goal of learning more about how the climate system works is just getting destroyed.”
Goodell said while geoengineering shouldn’t be dismissed as “Frankenstein technology,” its potential to further alter the climate at the hand of a government or individual calls for both careful research into impacts and international cooperation.
“The technology is very simple. It’s not complicated at all,” Goodell said. “It’s the politics of it.”
Since the science is relatively straightforward, Goodell fears it could be deployed by amateurs who could inadvertently wreak havoc or other agencies vying for some sort of global control. That’s the vital question: “Whose hand is on the thermostat?”
He likened it to the need for international governance of nuclear weaponry, as geoengineering has the potential to become another tool of war beyond its applications in global cooling, he said.
University of Pennsylvania political science professor Scott Moore, who also directs the university’s Climate Security and Geopolitics Project, suggests a system similar to the United Nations Framework Convention on Climate Change. Enacted in 1994, the treaty of 198 member countries has since served as the foundation of modern climate negotiations like the Paris Agreement, which the U.S. has withdrawn from for the second time after a brief reentry between Trump’s presidencies.
“It’s not perfect, but I think it’s probably the best forum for this kind of discussion,” Moore said.
To him, U.S. vigor for tackling emissions has been “woefully insufficient,” but solar geoengineering could remedy that, though he prefers to call it “climate intervention.” However, he said the likelihood of striking a perfect international agreement before inevitable real-world testing is low.
As the U.S. rolls back research funding, the United Kingdom has ramped up. Its advanced research funding agency — Aria — is investing the equivalent of about $76 million for 21 climate cooling research teams, including some on Marine Cloud Brightening and Stratospheric Aerosol Injection.
At Cornell University, climate engineering researcher Douglas MacMartin said the choices shouldn’t be either, or: either to work toward lower emissions or to deploy geoengineering: either to hastily block the sun, or outlaw all the experiments.
“I do not get into my car in the morning and think, ‘Should I drive safely, or should I wear a seat belt?’” he said. “I do both.”
