A little "light" reading... ;-) 
Joe 

Plan B for global warming?
Mar 8th 2007
From The Economist print edition 
Environment: “Geo-engineering” is the direct use of technology  to 
counteract climate change. The idea is highly controversial
IF MAN is inadvertently capable of heating the entire planet, surely it is  
not beyond his wit to cool it down as well? Although most climate scientists do 
 not like to talk about it, cutting greenhouse-gas emissions is not, strictly 
 speaking, the only way to solve the problem of climate change. Just as  
technology caused the problem, it might also be able to help reverse it. The use  
of planetary-scale engineering to counteract climate change is known as  “
geo-engineering”. 
The idea has been around for years. When a report on climate change was  
submitted to President Lyndon Johnson in 1965, the authors did not even bother  to 
consider the idea of reducing carbon-dioxide emissions. Instead, the report  
suggested spreading “very small reflecting particles” across the ocean 
surface  to reflect light and heat back into space.  
Since then most campaigners and policymakers have focused on cutting  
emissions, but the idea of deliberately cooling the Earth has never gone away.  Most 
people think cutting emissions is the more sensible path. But global  
emissions are still rising, and seem likely to do so for years to come, so some  
scientists believe it might be worth thinking about a second line of defence, if  
only as an insurance policy. 
The idea has gained new currency in recent months. Climate Change, a  
scientific journal, published a series of papers on geo-engineering last August,  
including one by Paul Crutzen, a Nobel prize-winning atmospheric chemist. In  
November the Carnegie Institution and America's space agency, NASA, held a 
conference on the topic. And American officials  have lobbied for geo-engineering 
research to be included among the  recommendations of the Intergovernmental 
Panel on Climate Change's latest report  on climate-change mitigation. 
Of all the schemes proposed, the most ambitious (and expensive) idea would be 
 to place a giant sunshade in space at the inner Lagrange point, the position 
on  the line between the Earth and the sun where the combination of 
centripetal and  gravitational forces allows an object to maintain a constant position 
between  the two. If the object is big enough, it could block out enough of 
the sun's  rays to cool the Earth. Roger Angel, an astronomer at the University 
of Arizona,  has suggested assembling a cloud of millions of small, reflecting 
spacecraft  less than a metre across at this point, where together they would 
block out 1.8%  of the sun's rays. 
Dr Angel estimates that the total mass of the sunshade required would be  
around 20m tonnes. The shade would consist of individual craft around one metre  
across, put into position using a combination of magnetic launchers and ion  
propulsion. He believes the total cost of the project would be a few trillion  
dollars, or less than 0.5% of world GDP. Dr Angel  admits that this is a 
somewhat far-fetched solution, and does not believe it  would be attempted unless 
all other options had failed. But he has been given a  small grant by NASA to 
explore the idea. 
A less exotic approach, endorsed by Dr Crutzen, would be to spread tiny  
particles in the upper atmosphere to reflect the sun's rays. This effect has  
already been shown to work in nature: fine sulphate particles, called aerosols,  
ejected by large volcanic eruptions like that of Mount Pinatubo in 1991, have  
produced periods of global cooling. And sulphate pollution from industry had  
similar consequences, helping to balance the warming effects of carbon dioxide 
 until the 1990s, when pollution controls in many regions had the perverse 
effect  of increasing warming. 
Ken Caldeira, a scientist at the Carnegie Institution, suggests that this  
idea might be more suited to local rather than global application, at least at  
first. The Arctic, for example, is among the regions most affected by global  
warming, and keeping the polar sea-ice frozen would be a good thing: white ice 
 reflects more heat back into space than dark ocean, and the scheme would 
also  save a few polar bears from drowning. 
The most down-to-earth idea is that proposed by John Latham, a scientist at  
the National Centre for Atmospheric Research in Colorado. He suggests that  
blasting tiny droplets of seawater into the air would stimulate the formation of 
 highly reflective, low-lying marine cloud. Simulations suggest this would 
have a  substantial cooling effect. The question is how to do it economically. 
Stephen  Salter of the University of Edinburgh has designed an unmanned vessel 
which  would produce these clouds using wind power. Just 50 vessels, he 
reckons, each  costing a few million dollars and spraying around 10kg (22lb) of 
water per  second, could cancel out a year's worth of global carbon-dioxide  
emissions—though another 50 vessels would be needed every year until  
carbon-dioxide emissions were under control. 
Dr Salter's ships would be much more precise than other geo-engineering  
schemes—“like an artist's paintbrush”, as he puts it. They could be deployed to  
the North Atlantic to cool the Greenland ice sheet during the northern summer  
and then migrate to Antarctica for the southern summer. Dr Caldeira even  
suggests that by cooling the sea, these ships could be used to combat  
hurricanes, since high sea-surface temperatures are linked to hurricane  formation. 
Other proposals include seeding the oceans to get them to absorb more carbon  
dioxide and building huge reflectors in desert regions to reflect sunlight 
back  into space. This latter idea is impractical, says Dr Caldeira, who reckons 
that  half the world's deserts would have to be covered. Indeed, most 
geo-engineering  schemes sound half-crazy and tend to have both technical and 
aesthetic  complications. Deliberately polluting the stratosphere would make the sky 
less  blue, although sunsets would probably be prettier. Blocking out the sun 
would  help to cool the planet, but it would do little to address other nasty  
side-effects of high carbon-dioxide levels, such as the acidification of the  
oceans. 
Many greens oppose the whole idea in principle. Ralph Cicerone, president of  
America's National Academy of Sciences, has said that geo-engineering 
inspires  opposition for “various and sincere reasons that are not wholly scientific”
. But  it does seem reasonable to worry that the illusory hope of a 
scientific fix  might undermine the adoption of policy solutions, such as carbon caps 
and carbon  quotas, designed to address the underlying cause of the problem. 
And then there  is the danger of unintended consequences. Climate change is 
arguably an  experiment which mankind has unwittingly found itself performing on 
the planet.  To start a second experiment in the hopes of counteracting the 
first would be  risky, to put it mildly. 
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