Fighting Climate Change Through Solar Geoengineering Is a Bad Idea, Scientists Warn

A group of these scientists and scholars launched an open letter calling it frightening.

Sky with sun

Manuel Breva Colmeiro / Getty Images

Should we dim the sun in order to fight the climate crisis? 

The idea has been gaining traction with some scientists and policymakers in recent years, leading others to respond with concern. At the beginning of 2022, a group of these scientists and scholars launched an open letter calling for an international non-use agreement on solar geoengineering

“It is an experiment on a planetary scale,” letter signatory and professor of global sustainability governance at Utrecht University Frank Biermann tells Treehugger. “And this is frightening.” 

There is the concern that wealthier countries would simply end up deploying it after only a token consultation with poorer countries that are among the most vulnerable to climate change. 

What Is Solar Geoengineering? 

Solar geoengineering is the idea that we could lower the Earth’s temperature by reducing the amount of sunlight that reaches the planet. The idea has been discussed in theory for decades but was not really taken seriously. 

“It sounded a bit like crazy science fiction,” Biermann says. 

Types of Geoengineering

There are two primary types of geoengineering: solar geoengineering and carbon dioxide geoengineering. Solar geoengineering would manipulate the radiation the Earth receives from the sun, while carbon dioxide geoengineering would remove carbon dioxide from the atmosphere.

However, in the past few years mainstream scientists, especially in the U.S., have begun to express more interest in the idea, according to a longer article published in tandem with the open letter published in WIREs Climate Change. In March of 2021, for example, the National Academy of Sciences published a report calling for more research into the prospect of solar geoengineering as one part of the solution to the climate crisis. The report considered three strategies:

  1. Injecting aerosols into the stratosphere in order to reflect more sunlight back into space. This is the strategy the open letter is especially concerned with.
  2. Adding particles to the lower atmosphere to make clouds brighter and reflect more light away from certain regions.
  3. Thinning high-altitude ice clouds so they absorb less of Earth’s heat.

Harvard University has gone so far as to set up a Solar Geoengineering Research Program. Like the National Academy of Sciences, Harvard positions its efforts as a potential climate solution to be deployed alongside emissions cuts. 

“Solar geoengineering in particular could not be a replacement for reducing emissions (mitigation) or coping with a changing climate (adaptation); yet, it could supplement these efforts,” the website reads. 

However, not everyone agrees that dimming the sun is a reasonable card in the climate solutions deck. 

“To us, these proliferating calls for solar geoengineering research and development are cause for alarm, as they risk the normalization of these technologies as a future policy option,” Biermann and his colleagues wrote in WIREs Climate Change.

An International Non-Use Agreement 

The scientists calling for an international non-use agreement oppose solar geoengineering for three reasons, according to the open letter. 

  1. It's uncertain: It is impossible to fully know the risks of injecting aerosols into the atmosphere, and these risks will vary from region to region.
  2. It’s a distraction: The thought that we could reduce global temperatures without curbing greenhouse gas emissions might make businesses or governments less likely to work on achieving carbon neutrality as soon as possible. 
  3. It’s ungovernable: There simply isn’t an international framework that could decide on how to use solar geoengineering in a fair and democratic way. 
Graphic of solar geoengineering non-use agreement

Frank Biermann / CC BY-NC-ND 4.0

As Biermann tells Treehugger, ideally all seven billion people on Earth would need to weigh in on how many degrees cooler scientists wanted to aim for, how long the solar geoengineering would last, and where it would be deployed. 

“We have no institutions that are able to deal with these issues,” he says.

Further, there is the concern that wealthier countries would simply end up deploying it after only a token consultation with poorer countries that are among the most vulnerable to climate change. 

“Because of the high vulnerability of the least developed countries and many other countries in the Global South, their governments would need to have decisive control over whether and how to deploy solar geoengineering technologies,” Biermann and his co-authors argue in WIREs Climate Change. “Yet there is little evidence to suggest that countries most able to develop technologies for solar geoengineering would be willing to transfer effective control of such geopolitically important technologies to the most vulnerable countries in the global South.

An example of the inherent difficulties of making a fair international decision about solar geoengineering occurred when the Harvard research group attempted a field test in Sweden. Indigenous and environmental groups opposed the test, however, and, in this instance, their concerns won the day.

The open letter signatories want to resolve these difficulties by persuading countries to agree not to use the technology at all. Their proposed International Non-Use Agreement on Solar Geoengineering would include five components: 

  1. A ban on publicly-funded research.
  2. A ban on outdoor experiments.
  3. A ban on granting patents for technologies that would facilitate solar geoengineering.
  4. An agreement not to deploy solar geoengineering technology developed by third parties.
  5. An agreement to protest the normalization of the technology in international institutions like the Intergovernmental Panel on Climate Change [IPCC].

“Decarbonization of our economies is feasible if the right steps are taken,” the open letter states towards its conclusion. “Solar geoengineering is not necessary. Neither is it desirable, ethical, or politically governable in the current context.”

A Movement 

Biermann tells Treehugger the initiative behind the open letter is building “a stronger movement to get this thing stopped.” 

The letter started with 63 experts from an intentionally diverse array of academic backgrounds—including environmental policy, international relations, and natural and social sciences, and national origins.

“That's how we kind of built it up to show that, from different communities and different perspectives, many people are against this idea,” Biermann says.

Since the letter went live, even more scientists have signed on, for a current total of more than 340 academics from 50 countries, according to the website. The letter has also been endorsed by 25 organizations. An accompanying petition has gained nearly 800 signatures from concerned citizens. 

However, not every scientist agrees with this position. 

David Keith is a professor of both applied physics and public policy who led the development of the Harvard research program. He tells Treehugger he understands the other scientists' concerns about the morality of deployment and the issue of governance. In 2013, he argued for a moratorium on large-scale deployment of solar geoengineering and agreement on a small-scale threshold below which research could move forward. However, he thinks it would be a mistake to dismiss outright technology that might help mitigate the impacts of the climate crisis. 

“While the authors say they are not against research[,] a ban on public funding and on assessment by IPCC is tantamount to prohibition of research,” he tells Treehugger in an email. 

Further, he thought the letter signers’ goals for democratic and equitable global governance of new technology were admirable, but would ultimately exclude many other technologies used today that are not always governed to that standard.

“The mRNA technology at the heart of the COVID vaccines has a host of implications that are not governed with ‘global participation, inclusiveness, and justice,’” he tells Treehugger. “Nor is the Internet. Yet the authors do not advocate a global non-use agreement on mRNA or the Internet.”

But how likely is it that governments would even sign on to the non-use agreement? Biermann thought it was not likely in the immediate future, but that the idea could gain traction. And he thought the agreement would be effective at decreasing investment in the idea even if the U.S.—where solar geoengineering is more accepted than in many other countries—does not join.  

“Why should you invest a lot of money and time and effort in developing technology, of which you know that 100 countries don't want to have it in the first place?” he points out. “You could still do it, but it's a little bit of [a] waste of effort and you won't get the Nobel Prize.”

View Article Sources
  1. "Reflecting Sunlight: Recommendations for Solar Geoengineering Research and Research Governance." National Academies, 2021.

  2. "What Is Geoengineering?" Harvard's Solar Geoengineering Research Program.

  3. Biermann, Frank et al. "Solar geoengineering: The case for an international non-use agreement." WIREs Climate Change, 17 Jan 2022. doi:10.1002/wcc.754

  4. "Open Letter." Solar Geoengineering Non-Use Agreement.

  5. "Non-Use Agreement." Solar Geoengineering Non-Use Agreement.