August 7, 2009 3:00 am

Study calls for cheaper options to cut emissions

Engineering techniques to deflect sunlight from the face of the earth could reduce global warming for just 5 per cent of the cost of cutting carbon emissions, according to a paper published today by two climate change economists.

The paper comes ahead of a meeting in Copenhagen in December, where governments will discuss cutting carbon emissions to fight climate change. It concludes that using the lowest cost technologies, such as making clouds whiter to reflect sunlight, could achieve the same cooling effect as emissions cuts being discussed by the United Nations for only about $9bn (€6bn, £5bn).

This compares with $250bn a year authors of the paper calculate would be the probable cost of cutting emissions, although many other economists contend the real cost of cutting emissions will be far lower.

For instance, McKinsey has found that much of the emissions reduction necessary in large economies such as the US could be achieved at little or no cost, because of the vast potential for efficiencies.

"The benefits include both avoided climate damage and the savings made possible by more gradual, and hence less costly, greenhouse gas controls," said Lee Lane, coauthor and fellow of the American Enterprise Institute, the conservative think-tank.

But the conclusions are likely to be controversial as the technologies in question are untested.

The source of the paper - the Copenhagen Consensus, a group of economists brought together by Bjorn Lomborg, a prominent critic of current approaches to global warming - is also likely to attract controversy.

Scientific debate on "geo-engineering" - ways to change the earth's climate to counteract the effect of greenhouse gas emissions on temperatures - has gathered pace following concerns that it is now too late to hold global warming to 2°C, regarded by scientists as the limit of safety.

Some of the techniques under consideration include sending ships out to sea with equipment to spray fine droplets of seawater into the air.

This would create lighter, whiter clouds to increase the reflectivity of the earth and deflect more sunlight into space.

Other more space-age and costly solutions include erecting a giant sunscreen in space.

But in a separate paper published today in the peer-review journal Science, two prominent climate change scientists call for caution on geo-engineering techniques.

Studies have shown that while cloud whitening could lower temperatures. It might also lead to changes in rainfall in vulnerable parts of the world such as the Amazon. If this area dried out, it would cause much greater climate change than anything yet seen.

"Very large risks are associated with any such geo-engineering scheme," found the study by Gabriele Hegerl of Edinburgh university and Susan Solomon of the US National Oceanic and Atmospheric Administration.

Changing rainfall patterns could create big droughts, conflicts over water resources and refugee movements, they said.

However, proponents of the seawater spraying technology say that if adverse effects are discovered, the technology could be swiftly turned off.

Mr Lane agrees that much more research must be put into geo-engineering techniques, which are almost entirely untested.

He also warned that such technologies could not be regarded as a way of avoiding cutting emissions.

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