Plan B for global warming?
From: Lloyd Wright [mailto:lwright@...]
Hi Eric, I thought this article from today's Economist might be of interest to you, in a depressing sort of way.
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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