Some academics worry research into solar geoengineering will normalise a risky and little understood technology. But advocates say any tool that can mitigate climate change deserves more investigation
The year is 2025. A heatwave like no other has swept over northern India, pushing temperatures into the 40s and raising humidity to such stifling levels that humans cannot sweat enough to cool down.
Too poor for air conditioning, people desperately jump into lakes to escape the heat, but for most, it is no use. Around 20 million people die. In a matter of weeks, climate change has killed more than the First World War.
This is the notoriously harrowing opening to The Ministry for the Future, a 2020 novel by the American sci-fi writer Kim Stanley Robinson which imagines the fraught choices mankind faces as it struggles with a warming planet.
But the book is not merely a chronicle of disaster, but of controversial solutions too.
India, willing to try anything to avoid another deadly heatwave, sends a fleet of planes to spray the atmosphere with sulphur dioxide to block some of the sun’s rays, replicating the cooling effect of an erupting volcano.
Delhi takes such unilateral action despite a United Nations ban on solar geoengineering. It risks international condemnation as the sulphur particles waft into the skies of other countries.
But, on the whole, India’s gambit works, cooling the country and helping to stave off future heatwaves.
There is now a fierce debate among academics over research into this most controversial of technologies. Some researchers want modelling and field experiments banned, arguing that solar geoengineering could never be deployed fairly, and distracts from efforts to cut carbon emissions.
Supporters still think cutting emissions should be priority number one, and admit the idea of spraying things into the sky to cool the earth sounds a little out there.
But the evidence is that solar geoengineering should work and it could be a method of last resort to avoid disaster as the century progresses, and so it at least needs to be investigated. Yet it is hard to win grants because the technology is so controversial. One recent high profile outdoor experiment was cancelled due to local objections.
“The argument is that we want to be researching it so that if we ever get to the point where we need to use it, we know how to do it as well as we can,” said Rob Bellamy, a climate and society researcher at Manchester University.
How would it work?
There are several types of solar geoengineering, all of which aim to reflect sunlight. They include spraying sea salt to brighten marine clouds, or bioengineering crops to make them more reflective.
But the best understood and most feasible technology is stratospheric aerosol injection (SAI), where the aim is to mimic the aftermath of a volcanic eruption. 1816 was famously the “year without a summer”, after Mount Tamboro in Indonesia erupted in April 1815, spreading volcanic particles around the world and causing such miserable weather in Europe that a young Mary Shelley stayed cooped up inside writing Frankenstein.
More recently, when Mount Pinatubo in the Philippines erupted in 1991, it spewed 15 million tons of sulphur dioxide into the atmosphere, cooling global temperatures by 0.6 degrees centigrade.
“It was a real global impact for a couple of years that was absolutely measurable,” said Adrien Abécassis an expert on climate policy at the Paris Peace Forum, a French nonprofit. “That solar geoengineering would work in cooling down the atmosphere is not in question. But it could also introduce new risks.”
SAI is seen as relatively straightforward to deploy, requiring a fleet of specially adapted planes and readily available compounds like sulphur dioxide or calcium carbonate, meaning that most countries have the technical – if perhaps not the diplomatic – ability to deploy it in a climate emergency.
“On the face of it seems relatively easy to do,” said Bellamy. “There's different ways in which you could do it: planes, balloons, missiles, various other kinds of delivery mechanisms.” This ease of use makes it an option not just for countries, but potentially even a “rogue billionaire” to unilaterally deploy, he said.
This ease of deployment is a “very strong” argument against stopping research, argues Abécassis. The means is already at hand, so unlike with other potentially risky technologies, more research will not make it that much more accessible, but will instead help better understand the impact.
The Intergovernmental Panel on Climate Change has repeatedly looked into solar geoengineering, and struck a balance between acknowledging it could work while warning of unknown side effects.
In the draft of its most recent report on mitigation, released on Monday, IPCC continues to sit on the fence, saying that modelling studies indicate SAI could reduce surface temperatures and some climate change risks, but at the same time it could also introduce a range of new risks.
Winners and losers
This points to the fundamental uncertainties around deployment. For example, would the clouds of particles unleashed by SAI have a uniform cooling impact across the globe, or could they exacerbate problems in certain areas, by disrupting the monsoon season or reducing rainfall, even if average temperatures fell?
“As soon as you start unpacking in the discussion about the impacts on various dimensions – not only on temperature and precipitations, but also on human health and wellbeing, food security, biodiversity – and the granular impact on different places of the globe, it gets very, very, very complicated,” said Abécassis.
“You could get one country saying, oh, you've screwed up my potato crop this year,” said Bellamy. “And then you start entering into the realms of compensation and liability.”
There are other side effect risks of SAI. It could deplete the ozone layer or contribute to acid rain and there’s a chance it will make the sky look slightly more hazy.
Countries that profit from climate change might also object. Melting Artic sea ice is set to allow Russia to fully exploit the northern sea route, a shipping lane from Asia to Europe that would cut weeks off the journey via the Suez Canal.
Some of the literature on solar geoengineering warns darkly of countries engaging in “counter-geoengineering” by releasing warming gasses, or even shooting down aerosol aircraft as they try to wrest back control over the planet’s thermostat.
This problem of governance is the chief argument of a campaign, now backed by more than 300 academics, to ban funding for research into solar geoengineering, prohibit outdoor experiments, and forbid patents on enabling technologies, such as aircraft fitted out to deliver aerosols.
“What I honestly can't see is any way, shape or form of governance that works in a fair and effective way,” said Jeroen Oomen, a postdoctoral researcher at Utrecht University focused on geoengineering, and one of the authors of an article published in January setting out objections to the technology. “And we shouldn't act like that is the inevitable future.”
Their argument is that powerful, industrialised countries would never agree to give poorer states sufficient say over when and how to deploy SAI.
But not everyone agrees. “How would they be able to determine, with their crystal balls, that it's impossible to govern?” said Peter Irvine, a climate change and solar geoengineering lecturer at University College London.
And far from excluding the global south, some advocates of SAI argue it will help developing countries the most, given that they are most likely to bear the brunt of climate change.
The IPCC’s recent draft finds some evidence that people in developing countries are actually more open to SAI than those in the rich world, “perhaps because they experience climate change more directly.”
In the west meanwhile, the public, insofar as it is even aware of solar geoengineering, is “very cautious” about it because of potential side effects and governance concerns. But there is “reluctant and conditional” support for research and field experiments.
The January manifesto against solar geoengineering research also argues that “proliferating calls” for its study are a cause for “alarm”, as they “risk the normalisation of these technologies as a future policy option.”
Again, some researchers remain unconvinced. “Patent offices are the graveyards of dreams,” says Bellamy, quoting a former boss. “Many more ideas have been researched, and technologies developed in human history, than have gone on to be deployed,” he said. There are plenty of reasons to be concerned about the side effects of SAI, “But the slippery slope argument is not one of them.”
Martin Quaas, a researcher at the German Centre for Integrative Biodiversity Research, makes the point that research would only raise the chances of SAI being used if it found the benefits outweighed the costs. “If that's conceivable at all, then this kind of slippery slope isn't the problem, right?”
Conversely, supporters of research argue that further study would actually make deployment less likely if experiments and modelling confirmed that SAI came with serious risks. In other words, a desperate country stricken by climate change would think twice about gambling on SAI if its dangers are clearly mapped out.
Another long-standing worry is that research into geoengineering creates a moral hazard, that is, the comforting illusion that it can be pulled out of the hat, mid-century, to “solve” climate change, meaning we can all keep on driving petrol SUVs and flying long-haul today.
“I would be afraid that it would give countries an out in terms of making the really hard choices that need to be made,” said Oomen.
He is worried about solar geoengineering sneaking, undiscussed, into policy projections for how to get to net zero by mid-century, just as untested technology for capturing carbon directly from the air has wormed its way into US plans for carbon neutrality, for example. “What we're aiming for is for this not to happen without politicisation,” he said.
But for its part, the IPCC’s latest report says there is “limited” empirical evidence for this moral hazard argument, and it is “mostly at the individual, not societal, level.”
It is true that in the 1990s and 2000s, interest in solar geoengineer in the US was often led by those who wanted business as usual: conservative think tanks and fossil-fuel backed politicians, according to Kevin Surprise, a visiting lecturer in environmental studies at Mount Holyoke College in Massachusetts.
But now, fossil fuel firms and climate-deniers are “largely absent” from the conversation about the technology, and certainly not its primary research funders, according to a forthcoming paper currently going through peer review investigating into who is backing such research.
Instead, it is a coalition of, “climate scientists, environmental NGOs, ‘green’ philanthropists, and Silicon Valley ecomodernists” driving research.
This still concerns Surprise, who sees solar geoengineering as a way for an ecologically unsustainable system to “buy time” in the face of demands for more radical change.
But solar geoengineering’s cheerleaders are not now, on the whole, those who have a direct interest in avoiding emissions cuts.
Instead, financial support is increasingly coming from billionaires like Bill Gates via their philanthropic organisations.
Harvard’s Solar Geoengineering Research Programme, by some way the best funded of all current initiatives, has backing from Gates as well as $2.5 million from the Open Philanthropy project set up by Facebook co-founder Dustin Moskovitz, plus a string of other investors and philanthropists.
Moskovitz, worth an estimated $13.9 billion, personally wades into geoengineering debates on Twitter, and has funded research into the technology’s governance precisely because he is worried about deployment by one country leading to droughts in another.
But this isn’t to say governments are not funding any research. Public funding agencies in Japan, the US, UK, France, India, Sweden, China, Germany, Norway and Finland, plus the EU under the predecessor to Horizon 2020, have all backed research projects in the past, according to a Harvard survey that tracks spending up to 2018.
Europe was actually the centre of solar geoengineering research in the mid-2010s, with more than $4 million a year invested in 2014, largely from government sources. Since then it has trailed off, but US philanthropists have taken up the slack and become the biggest source of funding.
Although research is going on – the IPCC counts hundreds of modelling studies since 2014 – it does still fall foul of objections.
The test flight of a balloon in Sweden, organised by the Harvard project, was suspended in 2021 after objections from environmentalists and the indigenous Saami people, who worry it will help normalise the technology.
In 2012, another balloon test flight was called off in the UK after concerns emerged over a commercial conflict of interest, and the lack of a governance architecture regulating such experiments.
There is still a certain stigma around geoengineering research, said Irvine, who recently had a grant rejected because it was deemed “very high risk”. “I think a lot of people in the community don't want to have anything to do with it,” he said. “Anecdotally, from my experience, and from others’ experience, it's hard to get this research funded.”
Recently, there have been several heavyweight calls for more solar geoengineering research. Last year, a report from the US National Academies of Sciences, Engineering, and Medicine concluded that a “strategic investment in research is needed to enhance policymakers' understanding of climate response options.”
Supporters of research are also sceptical that it could ever be cleanly banned. For a start, says Abécassis, improvements in generic climate modelling will also make SAI modelling more accurate.
“If you're going to start interfering with the funding or governance of scientific research in certain areas, where do you draw the line?” said Bellamy. If it were banned, scientists interested in solar geoengineering might just present it as more general, innocuous research. A ban on such research creates “the risk of driving scientists doing this research underground,” he fears.
There are currently no global bodies that regulate the research, development and deployment of solar geoengineering. The world effectively has no forum to decide if and how to use the technology.
But efforts are underway to create one. At the Paris Peace Forum, Abécassis is steering efforts to set up a Global Commission on Governing Risks from Climate Overshoot.
Composed of former heads of state and ministers, names as yet unannounced, but at least half of whom should come from the global south, and chaired by former EU commissioner Pascal Lamy, it will review the gaps in global governance options to stop the world overshooting the 1.5 centigrade of warming set down by the Paris Agreement in 2015, including looking at the cost-benefits of solar geoengineering. The governance gap for solar geoengineering is most acute, it says.
“There's a high probability that we overshoot even if we finally come back at 1.5C at the end of the century” Abécassis said. Cutting emissions “must remain the central tool,” but it is necessary, “explore whether [SAI], among others, could be an option”.
The commission should launch later this year, but will only report its findings in early 2024.