As international efforts to reduce greenhouse gas emissions stall, schemes to slow global warming using fantastical technologies once dismissed as a sideshow are getting serious consideration
“I have seen all kinds of proposals,” said James Fleming, author of “Fixing the Sky: The Checkered History of Weather and Climate Control” and a member of the National Academy geo-engineering committee.
“People are getting more and more desperate about climate change,” he said. “I think it is quite probable we will get the OK to do this.”
So what are these ideas:
Aerosol injection,
Spraying aerosols high up into the stratosphere is currently the most talked-about form of SRM. The technique, which is known as “stratospheric aerosol injection”, could cool the planet in a similar way to a large volcanic eruption.
Marine cloud brightening,
In theory, this could involve using ships to spray saltwater into the clouds above the sea.
Once airborne, the salt particles would act as “cloud condensation nuclei”, meaning they would facilitate the condensation of water vapour into liquid. As more water droplets are created, clouds would appear larger and brighter.
Ocean mirror,
A less well-known option for limiting the effects of sunlight would be to use an “ocean mirror”. In theory, this would involve using a fleet of sea vessels to churn up millions of tiny microbubbles on the ocean surface.
This seafoam would reflect away sunlight, cooling the planet, explains Prof Julian Evans, an emeritus professor in materials science from University College London.
Cloud thinning,
Another less-explored option for reducing the effects of sunlight at the Earth’s surface would be to “remove” cirrus clouds from the atmosphere.
Cirrus clouds are thin, wispy clouds made of ice crystals, which form at high altitudes. The clouds reflect away some sunlight, but also absorb large amounts of long-wave radiation – meaning that, on balance, they warm the planet.
Space sunshades
The final technology discussed by scientists involves sending a giant mirror – or fleet of mirrors – into orbit in order to reflect away more sunlight from the Earth.
The size of the mirror would determine how much sunlight it could reflect back towards space and, therefore, its cooling effect, says Prof Govindasamy Bala, from the Divecha Centre for Climate Change at the Indian Institute of Science.