This October, to challenge the US National Academies report, a Manifesto Against Geoengineering was signed by over 100 civil society and indigenous peoples groups, calling for a ban on all geoengineering experiments due to “risks that geoengineering poses to biodiversity, the environment and livelihoods”.

Surprisingly, Burns has a lot of sympathy for that view: “It would be dangerous to deploy solar geoengineering and stop emissions reduction efforts – because if greenhouse gases were to continue to rise, you would need more and more solar geoengineering every year to offset that… basically pushing the Earth’s system even harder, in an experimental way that hasn’t been done before.” Burns likens it to taking morphine to undergo lifesaving surgery; to do solar geoengineering without reducing emissions would be like taking the morphine, but then not undergoing the surgery.

Burns is less sympathetic about the allegation that the research is backed by fossil fuel giants and billionaires. Geoengineering Monitor, the group behind October’s Manifesto, names David Keith and SCoPEx as being backed by “a multimillion geoengineering fund provided by Bill Gates” and highlights ExxonMobil and Shell as “key players”. But Harvard's Solar Geoengineering Research Program “have not and will not accept funding from the fossil fuel industry”, responds Burns. (A full list of funders is published on its website.)

There are many preferable ways to reduce climate change than solar geoengineering. Planting trees – reforesting – is a proven, conservation-friendly method of taking carbon out of the atmosphere. A rapid transition from fossil fuels to renewable energy would tackle the source of emissions. But neither are happening fast enough. Perhaps, if nothing else, even contemplating solar geoengineering may be enough to shock governments into rapid emissions reduction.

If the world says “no” to solar geo-engineering, that “is totally fine with me”, says Burns. “Truthfully this is scary, I hope we don’t have to do it.” But she, and academics such as Salter and Keith, at least want that “no” to be based on scientific evidence.

“We are doing an intervention [already] into our atmosphere in an unprecedented way [through fossil fuel and CO2 emissions],” continues Burns. “We have something that could potentially help with some of the symptoms, albeit not the cure… it is such an important topic globally that we need to start thinking about it.”

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Tim Smedley is a sustainability writer, based in the UK. His first book, Clearing the Air: The Beginning and the End of Air Pollution, will be published by Bloomsbury in March, 2019.

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