Modelling suggests it would cost billions of dollars to maintain a fleet of aircraft to mimic that effect – yet that is small change compared with the sums typically bandied about in climate debates.
The arguments against the process are compelling too.
Nicholson notes that many of those engaged in the climate movement want to educate humans to live within natural limitations. “Anything that seems to smack of the type of hubris that got us into this mess in the first place, like heavily industrial, highly capitalist types of pathways forward, tend to be viewed sceptically.”
A second concern is the “moral hazard” such technologies may present by diverting research and attention from efforts to curb emissions and present industry with a continued licence to pollute the planet.
Opponents also point out that if such technology was deployed the world may become dependent on it, meaning we would need to keep feeding the atmosphere with cooling particles without fully understanding the long-term effects.
Michael Mann, one of the world’s leading climate scientists and communicators, and Oxford physicist Ray Pierrehumbert, likened the process to “climate methadone” in a recent column in The Guardian newspaper.
“When it comes to a system we don’t understand perfectly, the principle of unintended consequences reigns supreme,” wrote Mann in his recent book The New Climate War. “If we screw up the planet with botched geoengineering attempts, there is no ‘do-over’.”
Nicholson believes the new climate report suggests we no longer have the luxury of not investigating geoengineering. “We’re in a position now where it’s not just the risks of solar geoengineering versus a world where climate change has been dealt with in other ways,” he says.
“That’s not what the [Intergovernmental Panel on Climate Change] report is putting on the table for us. Instead what the IPCC is saying is climate risk is going to get worse moving forward, even if we do everything that the IPCC is recommending to reduce emissions.
“I think we may reach a point down the road where solar geoengineering is going to be one of the most just things that can be done to help those who are most vulnerable to climate change.”
Given that, he believes proper research and protocols should be developed now when it can be controlled, before the climate crisis escalates.
He believes the argument that existing international law makes the research illegal is a misreading of the relevant treaties. “I’m in the group of people who thinks that the time has come to stop the fighting over whether small-scale investigation into solar geoengineering is necessary. I think it actually is required at this point.”
In March this year, before the Harvard team abandoned its test flight, Dr Dan Harrison of Southern Cross University led a team of scientists on a live-aboard barge onto a section of the Great Barrier Reef off the coast of Townsville to test specialised new equipment that might one day help cool the reef and avert coral bleaching.
Harrison’s team is exploring a process known as cloud brightening, technically a form of solar geoengineering, though on a far smaller and less controversial scale.
It involves blasting seawater high into the air using specialised pumps and nozzles to create a mist of ultra-fine particles. Once airborne the droplets evaporate, leaving behind billions of salt crystals that can form the nuclei of cloud droplets.
These in turn would make clouds brighter and more dense, cooling the reef below by reflecting more of the sun’s rays and through evaporation.
Harrison’s hope is that one day equipment like this could be moored at key points along the reef and deployed on what he calls “ships of opportunity” – vessels that already ply the reef, as well as carefully placed barges – to cool the reef as heat waves approach, sparing the delicate coral below.
As with the Harvard team’s stratospheric aerosol injection, cloud brightening has already been observed in the field by chance, caused by the wakes of ships tracking across the ocean.
So far, he says, the group’s two field trials – the first in which such technology has been deployed outside a laboratory – suggest it could work.
In March the team showed that each of the 300 nozzles it deployed produced around 3 trillion droplets per second and drones detected the plume created 12 kilometres from the blasters.
Harrison doubts a process like this is viable to cool the Earth, but the team’s results suggest it may help protect the reef. “I view it as life support or something, treating the symptoms while hopefully the cause is taken care of,” he says.
“Emissions reductions to reduce climate change aren’t going to happen quickly enough to save the reef, which is why we have this whole program now.”
Harrison believes the argument that such technologies might distract from efforts to combat climate change is “nonsense”: “We haven’t had these geoengineering solutions to hand with any real chance of working or any proof of their efficacy, and yet we’ve done very little to reduce our carbon emissions or change the trajectory of climate change.”
In the face of the speed of climate change, he says, scientists have a responsibility to explore all the options we have that might help us fight it. “It’s now a risk versus risk equation,” he says.
“The question of whether we should implement any of these ideas is one for wider society, but the scientists need to do the research to be able to provide the right information to allow that debate to occur.
“You need knowledge as a foundation, instead of speculation.”