A sunshade for the planet

EVEN with the best will in the world, reducing our carbon emissions is not going to prevent global warming. It has become clear that even if we take the most drastic measures to curb emissions, the uncertainties in our climate models still leave open the possibility of extreme warming and rises in sea level. At the same time, resistance by governments and special interest groups makes it quite possible that the actions advocated by climate scientists might not be implemented soon enough.

Fortunately, if the worst comes to the worst, scientists still have a few tricks up their sleeves. For the most part they have strongly resisted discussing these options for fear of inviting a sense of complacency that might thwart efforts to tackle the root of the problem. Until now, that is.

A growing number of researchers are taking a fresh look at large-scale "geoengineering" projects that might be used to counteract global warming. "I use the analogy of methadone," says Stephen Schneider, a climate researcher at Stanford University in California who was among the first to draw attention to global warming. "If you have a heroin addict, the correct treatment is hospitalisation, therapy and a long rehab. But if they absolutely refuse, methadone is better than heroin."

Basically the idea is to apply "sunscreen" to the whole planet. It's controversial, but recent studies suggest there are ways to deflect just enough of the sunlight reaching the Earth's surface to counteract the warming produced by the greenhouse effect. Global climate models show that blocking just 1.8 per cent of the incident energy in the sun's rays would cancel out the warming effects produced by a doubling of greenhouse gases in the atmosphere. That could be crucial, because even the most stringent emissions-control measures being proposed would leave us with a doubling of carbon dioxide by the end of this century, and that would last for at least a century more.
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