Averting climate disaster: is there a role for solar engineering?

Forecasts indicate that we’re heading for disastrous levels of global warming. It might be time to accept that controversial solar engineering methods to tackle the problem are a necessary evil


Most people recognise that we need to cut our greenhouse gas emissions to decelerate global warming. The UN’s Intergovernmental Panel on Climate Change (IPCC) recommends that the world’s temperature increase be kept to 1.5ºC above pre-industrial levels, yet we’re currently on course for a much warmer future.

A projection published in July by Our World in Data indicates that the planet is likely to heat up by between 2.7ºC and 3.1ºC by the end of the century if existing climate policies remain in place. If countries honour their latest pledges on cutting emissions, the figure could be reduced to 2.4ºC, scientists predict, but this is clearly still far higher than the IPCC’s recommendation.

This is where geoengineering comes in. Many people see this large-scale manipulation of the Earth’s climate systems as the only effective solution to the global warming problem, yet it comes with huge problems of its own.

Tim Kruger is manager of the University of Oxford’s geoengineering programme. He notes that Eli Kintisch, author of the 2010 book Hack the Planet: science’s best hope – or worst nightmare – for averting climate catastrophe “called geoengineering a bad idea whose time has come. It’s not something that people would want to reach for immediately. It has all sorts of potential side effects, but it is something we need to consider. If we don’t, we’re not taking climate change seriously.”

One of the main categories of geoengineering is solar engineering, also known as solar radiation modification (SRM). This involves reflecting sunlight away from the Earth, usually by spraying chemicals into the atmosphere in aerosol form.

There has been little field research into SRM so far. In 2009, Russian scientists conducted what’s thought to be the first experiment when they mounted aerosol generators on a helicopter and sprayed particles 200m into the air. They claim that this reduced the amount of sunlight reaching ground level. There was another test in 2011, but several have since failed to make it off the launchpad. 

For instance, the UK’s stratospheric particle injection for climate engineering (Spice) project aimed to pump particles up a pipe to a high-altitude balloon that would then scatter these into the atmosphere. But it was scrapped in 2012 after a public backlash. 

In March 2021, researchers from Harvard University were forced to postpone an experiment in northern Sweden that would have launched a balloon into the stratosphere to test the so-called Pinatubo option, named after a volcano in the Philippines whose 1991 eruption reduced global temperatures by 0.5°C within 15 months. If ever deployed at scale, this method would involve putting thousands of tonnes of sulphates into the stratosphere.

Geoengineering solutions are tools in our toolbox. As every week passes, we get closer to the inevitability of having to use them

The Harvard scientists’ plans were more modest: when their balloon reached an altitude of 20km, it would spray out less than 2kg of chalk dust and the researchers would monitor the particles’ interactions with the atmosphere. But they didn’t get the chance. The flight, which had faced vehement opposition from environmentalists, was cancelled because the academics had failed to seek consent from the region’s indigenous Sámi people.

George Monbiot, one of the UK’s most prominent climate campaigners, classifies geoengineering proposals into two groups: those (such as carbon-capture technologies) that he believes are “safe, expensive and totally useless; and those that are cheap, effective and extremely dangerous. At this end is pouring sulphur compounds into the atmosphere. It makes a lot more sense to be growing trees.”

Such opposition has left most policy-makers reluctant to publicly voice their support for any kind of SRM activity, which encompasses methods other than the Pinatubo option. These include cloud thinning, which modifies high-altitude clouds to allow more heat to escape, and brightening, which adds a fine salt mist to low clouds over the sea to make them more reflective. And, back down at sea level, it has even been proposed that a thin layer of reflective glass powder could be poured over Arctic ice to protect it from the sun’s rays.

Yet solar engineering will be necessary, according to Hugh Hunt, professor of engineering dynamics and vibration at the University of Cambridge and a co-investigator on the ill-fated Spice project. 

“Geoengineering solutions – whether they’re capturing carbon dioxide or reflecting sunlight – are tools in our toolbox. As every week passes, we get closer to the inevitability of having to use them,” he argues.

Research into solar engineering is ongoing. In March, the US National Academies of Sciences, Engineering and Medicine (NASEM) surprised many observers by recommending that the White House spend up to $200m (£145m) on a new SRM programme. While there are no signs yet of such an investment, this development has heightened activists’ fears that the technology’s use will be normalised – and that its early adoption by one country could even stoke up geopolitical tensions. 

“The risk is that the research they’re doing and the experiments they want to run, especially under the vastly expanded programme proposed by the NASEM, will inevitably develop the technology for deployment,” says Raymond Pierrehumbert, professor of physics at the University of Oxford. “As we did with the hydrogen bomb, we know that the technology is feasible, but many of our questions about it can be answered only through deploying it on a near-full scale. That is why the research is dangerous.”

There are also legitimate concerns about the motives of some of the groups seeking to push geoengineering up the agenda. “It’s certainly true that there are people on the right of the political spectrum who believe that SRM is the way to avoid having to decarbonise the economy,” Kruger notes. 

Indeed, Newt Gingrich, a former Republican speaker of the House of Representatives and confidant of Donald Trump, proclaimed in 2008: “We would have an option to address global warming by rewarding scientific innovation. Bring on American ingenuity. Stop the green pig.”

Ultimately, even though geoengineering poses several risks, business leaders need to ensure that there’s further research in this field. But such investments need to act in conjunction with rapid emission reductions. Otherwise, there might not be much of an economy left to save.