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Quick Fix for Global
Warming? 15:35 05 June 2007 NewScientist.com news service Catherine Brahic http://environment.newscientist.com/article.ns?id=dn11993 - - - Excerpts [with inserts, not part of orig- inating article, in brackets]: 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, researchers say. Because of their rapid effect, however, they should be deployed only as a last resort when "dangerous" climate change is imminent, they 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 stra- tosphere, 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 stratos- phere. 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. ... Quick-acting Ken Caldeira at the Carnegie Institution of Washington, in California, US, and Damon Matthews at Concordia Univer- sity, 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" sce- nario. - - - [of note, many measures can be taken to reduce greenhouse emissions, and hopefully, those measures will be taken and will reduce emissions, rather than doing nothing and allowing emissions to rise as they have been] - - - "We have been trying to pinpoint the one really bad thing that argues against geoengineering the climate," says Cal- deira. "But it is really hard to find." His computer models simulated a gra- dually deployed shield that would com- pensate for the greenhouse effect of rising carbon dioxide concentrations. By the time CO2 levels are double those of pre-industrial times - predict- ed to be at the end of the 21st century - the shield would need to block 8% of the Sun's radiation. - - - [of note, many scientists warn that with a 'business as usual' approach, CO2 levels will be far greather than double far sooner than the end of the 21st cen- tury] - - - The researchers found that a sulphur shield could act very quickly, lowering temperatures to around early 20th-cen- tury levels within a decade of being deployed. "The trouble is, the decadal timescale works both ways," says Caldeira. A sul- phate shield would need to be contin- uously 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 mean- time. "So if you have the shield up there and it fails ... then you effectively compress into a decade or two the warming that would have happened while the shield was up," Caldeira explains. ... "Personally, as a citizen not a scientist, I don't like geo-engineering because of the high environmental risk," Caldeira told New Scientist. "It's toying with poorly understood complex systems." And the ease with which they could work is also risky, he says: "These schemes are almost too cheap and easy. Just one fire hose spraying sulphur dioxide into the atmosphere would do the job for a century. That would cost about $100 million - nothing in comparison to the hundreds of billions it would take to transform our energy supply." But he also believes it is time to consider solar shields seriously. On 1 June, James Hansen, head of NASA's Institute for Space Studies in the US, published a paper stating that Earths' climate system has reached a tipping point. http://www.atmos-chem-phys.net/7/2287/2007/acp-7-2287-2007.html ... Hansen's study suggests that only mod- erate additional warming is likely to trig- ger the disintegration of the west Ant- arctic and Arctic ice sheets - events which would be near-impossible to re- verse. ... He says that if forced to consider deploy- ing a solar shield, "we would need to be confident that we would not be creating bigger problems than we are solving." ... Climate Change - Want to know more about global warming: the science, im- pacts and political debate? Visit our continually updated special report. http://www.newscientist.com/section/environment - - - end excerpts - - -
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