What if climate change became so intense that one country broke with international protocol to protect its people? In fiction, that scenario has already played out. Kim Stanley Robinson’s 2020 novel Ministry for the Future opens with a catastrophic heatwave in India sparking a climate disaster of unmatched scale: 20 million people die as extreme temperatures take a horrific toll. Unwilling to let such a threat recur, the country’s leaders decide to take drastic action: by unilaterally dimming the Sun. 

Day after day for seven months, fleets of India’s planes pump vast plumes of aerosols into the stratosphere. From there, the mix of sulphur dioxide and other chemical particulates slowly spread across the northern hemisphere and “eventually everywhere”. 

By reflecting sunlight back into space, the particulates act as a planetary parasol, mimicking the effect of large-scale volcanic eruptions. The sky turns whiter, sunsets redder and the planet cools. The contentious move flies in the face of international law, as the book imagines it, and risks disrupting monsoon rains – but it also reduces global temperatures by “one degree, for three years”.

In Robinson’s imagined scenario, India’s rogue deployment of solar geo-engineering turns out to be broadly benign, and buys time to scale-up emissions reductions. But in the real-world, the idea that such a deus ex machina technology could ever be safely deployed remains highly speculative, with many risks and unknowns.

So if one rogue nation did decide to dim the Sun for real, what environmental and geopolitical consequences might unfurl? And is the safe deployment of such a technology even a conceivable goal? 

In Kim Stanley Robinson’s novel, a climate disaster in India prompts the government to go it alone with geoengineering (Credit: Getty Images)

This January, more than 440 scientists signed an open letter calling for a non-use agreement on solar geoengineering – including for small-scale outdoor experiments, like the unauthorised test conducted by a San Francisco start-up in Mexico earlier this year. They argue that the side-effects are unpredictable, the current global governance system is “incapable” of guaranteeing fair and effective control, and that development might encourage “normalisation” of the technology as part of the world’s climate policy. Its cooling effect could create a “moral hazard”, numerous researchers and civil society organisations warn, by taking pressure off efforts to cut the underlying CO2 emissions.

Such concerns have so far resulted in a de-facto moratorium on deployment, while a planned field test over Sweden was cancelled in the wake of objections. “When you’re in a hole, stop digging”, is how Greta Thunberg expressed the fear that solar geoengineering will reinforce a planetary relationship based on extraction and exploitation. “A crisis created by lack of respect for nature will most likely not be solved by taking that lack of respect to the next level.”

Andreas Malm, associate professor of human ecology at Lund University in Sweden and author of How to Blow Up a Pipeline, agrees. “The worst-case scenario for the deployment of geoengineering,” he says, “is that you have it and then business as usual just continues with investment in fossil fuels and their infrastructure – and emissions continue to rise.” You’d then have to keep increasing the injections, he argues, which would only exacerbate the risks.

As Malm wrote in 2021, Robinson’s novel introduces a global armed struggle against fossil fuel capital at the same time as the solar geoengineering experiment. Without this added incentive to decarbonise, Malm fears the world would be too tempted to simply delay emissions cuts. And it’s a fear he still holds today. “The more I’ve read on this, the more I’m convinced this technology has such extraordinary potential for harm and destruction, that I don’t think I will ever personally support or advocate,” he says.

Cooling eclipses

Yet in the three years since the publication of Robinson’s novel, global emissions have continued to rise, exacerbating everything from unprecedented heatwaves to deadly floods. This summer in the Northern hemisphere was the hottest on record, and September’s global temperature jumped again by a huge margin.

Amid these rises, some researchers suggest there could be a case for emergency solar geoengineering as an accompaniment to decarbonisation. In the US, the National Academies of Sciences, Engineering and Medicine last year recommended a national research programme on Solar Radiation Modification [SRM] – as the technology is also known. This year, the White House issued a report that examined what a federally-funded research programme might entail. And in the private sector, money from US tech giants and billionaires is flowing towards further investigation.

This February, dozens of scientists published an alternative open letter, organised by Sarah Doherty, an atmospheric scientist at the University of Washington, arguing more research is needed. And there are growing calls for a clearer international consensus on rules – one way or the other. The UN Environment Program has noted a “dearth of data” on impacts, and the EU has called for international talks about its risks.

As for Robinson, whose novel has helped foment so much discussion, he stressed to BBC Future that his book was not proposing a plan: “I abjure prediction, or even prescriptions”. Yet he also pointed to the need to take “emergency actions” to reduce the damage caused by burning carbon – from finding new ways to pay for decarbonisation, to exploring options for non-solar geoengineering. “I object to anyone saying ‘Oh we can’t try to fix things because it will encourage fossil fuel promoters to keep breaking things!’ We’re past that moment now. The sense of emergency is intensifying year by year.”

So what might it look like in reality?

Alternative methods of solar geoengineering are all now competing for their moment in the spotlight, from marine cloud brightening (which would inject sea salt aerosols into low-lying clouds to increase their reflectivity), to cirrus cloud thinning (which would inject ice nuclei into high clouds, shortening their life-span and allowing more heat to escape into space). But stratospheric sulphate aerosol injection by aeroplane remains the best-studied proposal for global impact. The technology could potentially lower temperatures at speed, and with relatively low finance. One 2013 estimate equates start-up costs to “the price of a Hollywood blockbuster“. A more recent calculation of running costs comes in at around $18bn (£16bn) a year.

Research supports a slightly different technical vision than in Robinson’s novel, however, with scientists suggesting a much slower ramp up, deployment and decline. One paper recommends that if stratospheric injections begin around 2030, they should peak 50 years later before tapering-off over two centuries. Another study has injections starting in 2035 and running at least until 2100; another estimates a duration of 245-315 years.  

One of the key challenges, if we started geoengineering, would be keeping it up for the long-term (Credit: Getty Images)

Particulates fall back to Earth after about 12 months, so too short a run-time could only see minimal cooling effect. But if longer releases end too abruptly, a “termination shock” could also follow – unleashing devastating pent-up warming from emissions whose effects have only been masked and not removed. 

Among the most prominent proponents of further research is David Keith, head of climate systems engineering at the University of Chicago (and founder of a Canadian company developing technologies for carbon removal). Like in the novel, Keith has stressed that solar geoengineering should not substitute mitigation, but instead be used to help the world maintain global temperatures rise below the crucial 1.5C above pre-industrial levels; a threshold the World Meteorological Organization gives a 66% likelihood of overshooting by 2027.

And, as in Robinson’s book, Keith and others have also stressed climate change’s increased threat to the world’s poorest – especially those in the Global South. They note “an obligation” to take steps to reduce such harm and a “moral obligation to conduct research on solar geoengineering”. As the former president of the sinking islands of Kiribati, Anote Tong, this year told the web