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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