Solar shield a quick-fix for climate change?

PROTECTING EARTH FROM SCALDING

It seems straight out of some sci-fi movie. Scientists have proposed a solar shield to protect humanity — not from some alien attack — but from a threat that’s imminent, global warming.
A solar shield that reflects some of the Sun’s radiation back into space would cool the climate within a decade and could be a quick-fix solution to climate change, reports New Scientist.
Because of their rapid effect, however, they should be deployed only as a last resort when “dangerous” climate change is imminent, the researchers warn. Solar shields are not a new idea — such “geoengineering” schemes to artificially cool the Earth’s climate are receiving growing interest, and include proposals to inject reflective aerosols into the stratosphere, deploying space-based solar reflectors and large-scale cloud seeding.
The shields are inspired by the cooling effects of large volcanic eruptions that blast sulphate particles into the stratosphere. There, the particles reflect part of the Sun’s radiation back into space, reducing the amount of heat that reaches the atmosphere, and so dampening the greenhouse effect. The 1991 eruption of Mount Pinatubo in the Philippines cooled Earth by a few tenths of a degree for several decades.
Ken Caldeira at the Carnegie Institution of Washington, in California, US, and Damon Matthews at Concordia University, Canada, used computer models to simulate the effects that a solar shield would have on the Earth’s climate if greenhouse gas emissions continued to rise along a “business as usual” scenario.
“We have been trying to pinpoint the one really bad thing that argues against geoengineering the climate,” says Caldeira. “But it is really hard to find.” His computer models simulated a gradually deployed shield that would compensate for the greenhouse effect of rising carbon dioxide concentrations. By the time CO₂ levels are double those of pre-industrial times — predicted to be at the end of the 21st century — the shield would need to block 8% of the Sun’s radiation.
The researchers found that a sulphur shield could act very quickly, lowering temperatures to around early 20th-century levels within a decade of being deployed. “The trouble is, the decadal timescale works both ways,” says Caldeira. A sulphate shield would need to be continuously replenished, and the models show that failing to do so would mean the Earth’s climate would suddenly be hit with the full warming effect of the CO₂ that has accumulated in the meantime. AGENCIES