Luke Iseman got tired of waiting for the world to stop climate change so he decided to try it himself. The founder of a controversial two-person startup called Make Sunsets has begun launching balloons filled with sulfur dioxide high into the sky with the intention of imitating the effects of volcanic eruptions. The molecules are meant to act like little mirrors, cooling the planet by reflecting sunlight back into space before it reaches the Earth’s lower atmosphere.
Iseman’s venture into the relatively new arena known as solar geoengineering is drawing its own heat in the form of criticism from scientists amid an intensifying debate over whether the world should explore once-unthinkable measures some say might buy time to address climate change.
The window to keep warming under 1.5 degrees Celsius (2.7 degrees Fahrenheit) in order to prevent dramatically more severe global impacts is closing fast. Earth is on track to hit that threshold “in the first half of the 2030s,” according to an Intergovernmental Panel on Climate Change (IPCC) report released last month.
Many scientists oppose geoengineering strategies, defined as interventions in the earth’s oceans, soils and atmosphere that reduce climate impacts such as extreme temperatures, variability in water availability, and the severity of storm systems. Solar engineering specifically focuses on masking the effects of climate change caused by greenhouse gases, although it isn’t a permanent fix since it doesn’t actually get rid of these gases.
Critics say further tinkering with Earth’s climate using new technologies could have dire unintended consequences such as acid rain and health problems, as well as rapid global temperature rises if such interventions were stopped without fixing the problem at its root. Some fear that investing research into such drastic avenues could create illusions of a cheap fix at a moment when there is no time to spare.
Even those in favor of studying solar geoengineering say they still have no idea if it should actually ever be used –the research is too early and the risks and effectiveness of such strategies are not well understood.
But Iseman, who has a history of launching startups and holds an economics degree from the Wharton Business School, says it’s past time to begin deploying and scaling up the untested technology.
“The ugly truth behind this is we need to do crazy ideas because we’re not going to just suddenly stop emitting,” said Iseman. “We invented our way into this, and we’ll invent our way through this, clumsily as we always do.”
Iseman said that he and co-founder Andrew Song have deployed 10 balloons so far, in Baja California, Mexico and Nevada. As of April 6, Iseman said 72 customers have purchased “cooling credits” – promises from the company to release one gram of sulfur dioxide (via balloon), which Iseman said offsets the warming caused by one ton of carbon dioxide for one year if it does, in fact, make it to the stratosphere (he claimed he has only been able to confirm this once so far).
“Obviously launching a couple of balloons is not going to show a measurable global impact on temperature,” said Iseman. “Frankly, I hope that one way this creates urgency is that many academics and governments, whoever, can be like, ‘look, I told you we had to research this or some idiot was just going to do it on his own.’”
Like a “taxi service”
For the most part, solar geoengineering research focuses on three strategies: releasing aerosols into the stratosphere to scatter light back into space (stratospheric aerosol injection), adding aerosols to clouds over the ocean to make them reflect more light (marine cloud brightening), or seeding cirrus clouds with dust particles to make them act like a thinner blanket, allowing more heat to escape through the atmosphere (cirrus cloud thinning).
“Stratospheric aerosol [injection] is the technique that has the most potential to allow us to effectively produce cooling at the global scale at some kind of affordable price point,” said Chris Field, a climate change researcher at Stanford University and a science advisor for the Climate Overshoot Commission.
Field says that deploying this technique at scale would require specially designed aircraft to act like a “taxi service,” popping briefly into the stratosphere to release their aerosol cargo.
“The need for cooling the climate by something like half a degree to a degree looks like it would be on the order of several hundred airplane flights per year,” said Field.
There is “good evidence” that marine cloud brightening could result in at least regional cooling, said Field, although it is less clear if the technique would have meaningfully buffer climate warming at a global scale.
Scientists who study cirrus cloud thinning are still debating whether it could be done, but if the technique is viable it would work best in the Arctic or Antarctic and could produce a global cooling effect, said David Mitchell, a scientist who studies cirrus cloud thinning at the Desert Research Institute in Reno, Nevada.
A crutch for polluters?
Even if solar geoengineering worked, scientists who study it acknowledge that the technology couldn’t “solve” climate change. While spraying the stratosphere with aerosols, for example, could mask some of climate change’s effects, it wouldn’t get rid of excess greenhouse gases and it wouldn’t prevent the ocean from becoming abnormally acidic (one side effect of all that carbon dioxide in the air).
But the idea of at least looking into solar geoengineering has become increasingly mainstream in the US, with the White House Office of Science and Technology Policy coordinating a five-year plan to assess solar engineering research.
It’s better to do the research now rather than later in order to “know what we’re dealing with” in the event that such technology is ever needed, said Mitchell, who is one of over 100 scientists to recently sign an open letter calling for solar geoengineering research to proceed.
However, many scientists oppose not only the actions of a lone startup but research into solar geoengineering altogether – let alone any possibility of deploying it in the future.
“Solar radiation modification approaches, if they were to be implemented, introduce a widespread range of new risks to people and ecosystems, which are not well understood,” says a 2022 IPCC report.
Hundreds of scientists around the world have signed an open letter calling for an international non-use agreement on solar geoengineering, and activists including Bill McKibben, Naomi Klein, and Greta Thunberg have spoken out against it.
The Saami Council, a group representing indigenous peoples in Sweden, wrote an open letter in 2021 opposing solar geoengineering that led to the cancellation of a planned flight by the Harvard SCoPEx project, which studies how aerosols behave in the stratosphere to advance research on geoengineering techniques.
In a 2021 National Academies of Sciences, Engineering, and Medicine report led by Field, “The authors are basically arguing that because carbon reductions haven’t been great enough (thanks to successful opposition by polluters and their advocates) we should consider geoengineering,” writes Michael Mann, director of the Earth System Science Center at Pennsylvania State University. “That framing (unintentionally, I realize) provides precisely the crutch that polluters are looking for.”
“We see Make Sunsets as a symptom of the Silicon Valley mindset that every problem has to have a technology fix,” said Lili Fuhr, the deputy director of the Center for International Environmental Law (CIEL)’s climate and energy program. “Then we have the fossil fuel industry and big polluters who are very happy to see us discussing potential future techno fixes.”
The fossil fuel industry has long been developing, patenting, and promoting geoengineering technologies, according to a 2019 CIEL report.
“Maybe by chance, some of the very materials you would need for [stratospheric aerosol injection] like sulfur dioxide happen to be a waste product of the oil and gas industry,” noted Fuhr.
In her view, researching solar geoengineering technologies brings the world dangerously closer to deploying them.
“There’s a very small group of people, mostly from the US and from the UK – we call them the ‘geo clique’ – who have been pushing this for probably almost two decades now, [but] the broad consensus is to stop this research” she said. “Just because we’re desperate doesn’t mean that a bad idea is suddenly a good idea.”
Disrupted weather patterns and “termination shock”
Even scientists who support solar geoengineering research think there could be plenty of cause for concern if it were someday deployed at scale.
If sulfur dioxide were used for stratospheric aerosol injection, the amount of the pollutant in the atmosphere could increase by as much as 10%, said Field, potentially damaging the ozone, causing acid rain, and increasing health problems like skin cancer. It might also make the sky look hazier, he added.
Solar geoengineering could even exacerbate malaria in developing countries, increasing transmission in lowland sub-Saharan Africa and southern Asia, according to a study published last year.
Computer models suggest that stratospheric aerosol injection would modify precipitation patterns across the globe, jeopardizing lives by potentially interfering with regional weather patterns like the monsoon, said Fuhr.
Fuhr worries there may be other serious unknown effects, since the technology is “basically untestable” unless it is deployed on a global scale. At that point, we would have to keep going or face the effects of “termination shock,” she said, since sun-dimming particles that mask the effects of carbon in the atmosphere only stay put for a year or two.
“Temperatures would suddenly rise rapidly, which wouldn’t allow for humans or any life on Earth to adapt to it,” said Fuhr.
“There are scenarios where [solar geoengineering] could be weaponized and lead to conflict and war,” she added. “Or you might just have a regime change in a powerful country that’s involved in geoengineering.”
Some also worry that lone actors may take it upon themselves to implement the technology – on a large scale – before the rest of the world is ready.
Scientists fear that rogue governments could, potentially, strong-arm the world into a solar geoengineering future. Another concern is that more groups will emerge who hope to profit off lone solar geoengineering efforts, said Shuchi Talati, a former Department of Energy chief of staff who is building a nonprofit focused on the intersections of solar geoengineering, governance and justice. With no governance infrastructure in place yet, there would be no consequences for those with less-than-altruistic motivations.
“It’s incredibly dangerous to see some of the momentum growing in that space and I hope it motivates a lot more movement around building good governance infrastructure,” said Talati.
Part of developing good governance means engaging with climate-vulnerable communities, said Sikina Jinnah, a professor who studies climate governance at the University of California, Santa Cruz.
“The environmental justice discourse surrounding solar geoengineering is dominated largely by scholars in the Global North who make claims about what’s best for communities in the Global South,” she said.
The Degrees Initiative, a nonprofit that awards solar engineering research grants to countries in the Global South, says it “empowers scientists in the Global South to ask their own questions.” In February, the initiative granted $900,000 to research teams in 14 developing countries.
Transparency in funding is a critically important aspect of governing solar geoengineering research, said Jinnah.
“I think the only way you get that is through public funding,” she said. “One of my main concerns with the non-use agreement is they’re calling for a ban of all public finance of this work, which I think is quite dangerous and irresponsible.”
Models for solar geoengineering governance are emerging. The Carnegie Climate Governance Initiative (C2G), for example, is working to “catalyse the creation of effective governance for climate-altering technologies,” including solar geoengineering. C2G aims to encourage discussions about the risks, trade-offs, and potential benefits of such technologies, according to its website.
The recent National Academies report suggests that UNEP could be asked to conduct an assessment of geoengineering technologies and offer options for governance frameworks, although it notes that a 2019 discussion about this role for the UN group did not pan out.
But for some, the past portends that solar geoengineering, if deployed, would be ungovernable.
“Solar geoengineering imposes a long-term obligation on human society of a sort that humanity has never been able to pull off in its entire existence, and that is what makes the idea crazy,” said Raymond Pierrehumbert, a physics professor at the University of Oxford. “[It] is not a way of ‘buying time’ and cannot be viewed as just a temporary fix until something better comes along.”
To limit global warming to 1.5°C, the world needs to focus its efforts on rapidly phasing out fossil fuels and protecting and restoring ecosystems, said Fuhr.
“The proven and reliable technologies needed for that exist and are readily available,” she said. “What is missing is political will.”
Scientists who support solar geoengineering research largely oppose Make Sunsets’ dash to deploy such technology, saying it has already done political damage – Mexico is now banning solar geoengineering – and citing a lack of research and the absence of any global consensus.
“There can be no room for selling snake oil,” wrote SilverLining, a nonprofit that provides grants for solar geoengineering research, in a statement condemning Make Sunsets’ “rogue releases of material into the atmosphere and its efforts to market unsubstantiated ‘cooling credits’.”
The group says that while Make Sunsets’ activities are “too small and ineffectual” to cause much harm, “if these activities were to scale, the risks could be substantial, and any benefits unclear.”
“They are deeply damaging the legitimacy of solar geoengineering as a field,” said Talati.
Even Iseman doesn’t really think he should be allowed to send air pollution-filled balloons into the stratosphere.
“Some internationally-governed, equitably-represented [group] would be best to manage this,” said Iseman. “Get ready for far more extreme actors than me. That somehow I’m the only person that will do this is not likely, to put it mildly.”