The great geoengineering gamble

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The writer is a science commentator

Amid rising global temperatures and widespread heatwaves, metaphorical storm clouds are gathering. Last month, a city council in California voted unanimously to halt an experiment into a potential climate-fixing technology.

The trial, which university researchers had already begun, involved spraying sea salt particles into the clouds above San Francisco Bay. The experiment was meant to test whether making clouds brighter could reflect more sunlight back into space, and thereby cool the local climate. The clampdown by Alameda City Council follows the scrapping earlier this year of a Harvard University project to release sulphur particles into the stratosphere above Sweden. 

There are good reasons why geoengineering experiments like these raise hackles: the climate is complex and there could be unintended consequences; the prospect of quick and dirty fixes distracts from cutting emissions; public opinion is rarely courted; governance and accountability appears opaque. 

But the failure to conduct experiments is not cost-free either, given the clear trajectory of climate change and real prospect of overshooting the 1.5C/2C threshold in the Paris Agreement. Current temperatures are already linked to more intense heatwaves globally, according to the World Weather Attribution research project, with corresponding losses in life, health, crops, productivity and education. If the world is prepared to neither slash emissions nor to collect evidence on climate interventions, then the only rational conclusion is that we are in denial about a sweltering future.

The Marine Cloud Brightening Project was co-ordinated by the University of Washington and the rationale was simple: clouds containing fewer, large particles tend to be less reflective than clouds with higher concentrations of fine particles. Accordingly, the plan involved spraying fine sea salt particles into clouds from the USS Hornet, a decommissioned aircraft carrier, and trying to measure the cooling effect.

The city council voiced justified concerns: the research team had not obtained prior permission; transparency and accountability were found wanting. Civil society groups warned that salt could rain down unpredictably, threatening ecosystems, and that removing large volumes of seawater could damage marine life, with cascading effects on food chains, fisheries and communities. 

And, of course, nobody knew whether it would work. Last week, the Scripps Institution of Oceanography in San Diego published modelling research suggesting that cloud brightening might work short-term but backfire long-term, ultimately increasing heat stress.

This is one example of “solar radiation management”, an approach that includes such schemes as painting roofs white and larger-scale plans to shoot sulphates into the stratosphere to mimic the global cooling caused by volcanic eruptions. The finances behind such projects also invite suspicion: some backers of geoengineering have fortunes that can be traced back in part to fossil fuel investments.  

One thing is clear: climate fixes cannot substitute for cutting emissions. But we remain in a quandary: emissions are not falling and the atmosphere is still warming. That is why Pascal Lamy, chair of the Climate Overshoot Commission, says governments should “‘open the box” of solar radiation management. 

That does not mean championing climate engineering or using it globally. Packing the stratosphere with sulphates could be catastrophic — testing is tantamount to deployment, carrying the risk of sudden warming when the particles dissipate. 

But we do have a duty to at least think about geoengineering, including on a regional scale, and to put together a governance framework — as well as prepare for the possibility that a nation, or a zealous individual, might covertly deploy the tech for their own interests.

Such a scenario, carrying the risk of unquantified fallout in neighbouring territories, is the stuff of geopolitical nightmares. Last year, the US National Oceanic and Atmospheric Administration began the Sabre project to characterise particles in the stratosphere. It will inform any future geoengineering efforts — and should pick up signs of rogue deployment. 

In contrast, there is some merit in the idea of a small-scale, well-monitored, controlled experiment, with results shared openly, globally and equitably. We especially need to know if geoengineering is a dud, a last resort that should be taken off the table. That would feel like a useful gambit given the current stalemate.