Jan 29th 2026|6 min read
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Donald Trump says he sees in the thawing of the Arctic a serious threat, allowing as it does the Russians and Chinese to spread their influence further and wider. There is a bevy of reasons to see this professed belief as a pretext, rather than a true concern. One does not need to add to them the revealed preference of not doing anything to stop the great thaw.
But others think it is beyond time for such efforts. In 2023 Operaatio Arktis, a group of young Finnish climate activists, published a manifesto for what they called “climate repair”: research aimed at finding ways to stabilise glaciers and ice sheets, to pull carbon dioxide out of the atmosphere, and to cool the surface by reducing incoming sunlight. They pointed to the intrinsic value of sublime landscapes and the ways of life they support. They expanded on the threats posed by “tipping points” which would see sea ice vanish completely, or ocean circulation change catastrophically. They called on their fellow activists, and the world at large, to take on a new attitude to such climate interventions, rooted in a refusal to accept the damage being done by greenhouse gases already emitted.
Among those who gathered in Helsinki to discuss the group’s “Arctic Endgame” document was Matthew Henry of Exeter University. He noticed that when talk turned to solar geoengineering—the reduction of incoming sunlight at the surface—it focused on the idea of spraying sulphur dioxide, a gas, into the stratosphere, where it goes on to form small, reflective particles. He also noticed that many people had strong and understandable misgivings about such “stratospheric aerosol injection” (SAI), which depends on creating sulphuric acid that will eventually return to the surface.
There is another form of solar geoengineering that feels more benign: “marine-cloud brightening” (MCB). It would add tiny particles of sea salt to the lower part of the atmosphere—the troposphere—perhaps from aircraft, but more probably from the decks of ships or barges. These would form reflective hazes and make the water droplets in clouds smaller and more numerous, rendering those clouds longer-lived and more reflective. That means less sunlight reaching the sea below. No one has yet created hardware capable of delivering the ultrafine saltiness needed. But this does not matter to computer models.
Chart: The Economist
Inspired by the meeting in Helsinki, Dr Henry and his colleagues asked three models of Earth’s natural systems whether MCB could, in principle, preserve the Arctic’s sea ice. Virtual sea-salt aerosols were sprayed into the air above all the open water in the Arctic at the same time as greenhouse-gas levels increased in a reasonably realistic way. In all three models it worked (see chart) and ice cover persisted.
What is more, effects outside the area were minimal. One drawback of MCB at a whole-planet level is that to cool everywhere a bit means cooling the places most susceptible to it a lot. But when it comes to limiting side-effects attendant on an Arctic cooling, this regionality feels like a plus.
The MCB results are in striking contrast to the drastic changes suggested by models that simulate Arctic cooling by means of SAI. Spraying sulphur dioxide into the stratosphere at 60°N also lowers Arctic temperatures. But at the same time it damages the ozone layer—probably not catastrophically, but almost surely significantly—and deposits a fair amount of sulphate on people and ecosystems in high and mid latitudes. It also cools the northern hemisphere enough to move the “intertropical convergence zone” (ITCZ), the rippling border between the northern hemisphere’s weather and that of the southern hemisphere. That changes patterns of rainfall and drought throughout the tropics.
The models offer a fix for this: cool the south, too, using counterbalancing injections of sulphur at 60°S. Doubling the level of effort this way seems to keep the ITCZ in place. If the geophysical status quo is thus maintained, though, the geopolitical one is not. The position of the ITCZ stops being just an aspect of the way the planet is and starts being something for which someone, somewhere is responsible.
Given all this, why even look at polar SAI? One answer is that, unlike MCB, for which there is no hardware, from a technical point of view injecting aerosols into the atmosphere around the poles looks almost indecently feasible. At high latitudes you can get sulphur into the stratosphere using everyday planes.
In the tropics, the border between troposphere and stratosphere—the tropopause—sits at around 20km, far above any normal aircraft’s ceiling. But its height drops as you move away from the equator. By the time you get to 60°N and 60°S it is low enough for airliners to rise above it.
It is widely accepted among those who study solar geoengineering that the best approach to SAI would be to spread aerosols at both low and high latitudes, thus covering the planet more or less evenly. But this would require planes that could carry sulphur dioxide to altitudes not now reachable. Designing and building even a few such aircraft would cost hundreds of millions of dollars, maybe billions. And they would have no uses other than exploring the possibility of SAI.
In their absence, might polar-only SAI be better than nothing? It would probably save the sea ice and it might reduce the risk that further warming will weaken a crucial bit of the ocean’s circulation. At the same time it would be vigorously opposed by countries and companies with an interest in the new fisheries, trade routes and access to raw materials the great thaw could provide. And as Ted Parson, a professor of law at the University of California, Los Angeles, points out, it also looks illegal. All countries in and near the Arctic have signed the Convention on Long-Range Transboundary Air Pollution (CLRTAP). The convention’s Gothenburg protocol limits sulphur emissions from their territories to levels far below what SAI requires.
Chart: The Economist
What of the world beyond the poles? You would get some cooling there, too, which seems at least a potential benefit. Recent work led by Alistair Duffey, a researcher at University College, London who now works for Reflective, an NGO focused on solar geoengineering, suggests that SAI using jets flying at 13km to inject 12m tonnes of sulphur dioxide a year, half at 60°N and half at 60°S, could lower the global average temperature by 0.6°C.
But you could get the same effect with half that sulphur—and thus less pollution and risk to ozone—if you had the means to insert it at 30°N and 30°S (which are also, as it happens, largely beyond the scope of CLRTAP). That would also result in more cooling of the tropics, home to the people most vulnerable to warming.
Solar geoengineering is on no one’s near-term agenda. To put it there would take not just some nifty new aircraft, but a widespread move towards the refuse-to-accept-the-harm stance of Operaatio Arktis. But if that happens, it looks as if the argument should be over cooling the world as a whole, not just a part of it, however special that part may be. ■
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This article appeared in the Science & technology section of the print edition under the headline “Refreezing the Arctic”
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