Hopes dashed for geo-engineering solutions

Hopes of averting a climate catastrophe by investing in space-age technologies such as mirrors in orbit were dashed yesterday by a Royal Society report that found serious drawbacks with nearly all the methods proposed.

In the first comprehensive report by an influential science academy into the costs and benefits of "geo-engineering" technologies - those intended to compensate for the warming effects of greenhouse gas emissions on the climate by reflecting sunlight or removing carbon from the air - the Royal Society said the ideas were "dangerous and unproven".

John Shepherd, chair of the study group and professor of earth science at Southampton University, said: "We are not advocating geo-engineering. It is not an alternative to emissions reductions."

Nevertheless, the scientists warned, these costly experimental technologies would become necessary if we failed to cut greenhouse gas emissions as deeply as necessary to avert the worst of the warming effect.

"Unless we can succeed in greatly reducing CO 2 emissions, we are headed for a very uncomfortable and challenging future, and geo-engineering will be the only option left to limit further temperature increases," Prof Shepherd said.

Geo-engineering has attracted greater attention in recent months as some scientists have concluded that the world on its current path has little chance of holding global warming to no more than 2°C. They regard that level as the limit of safety, beyond which the effects of climate change become catastrophic and irreversible.

Some scientists have warned that if emissions exceed the level at which such warming becomes probable, the world will need a "plan B". So far, thinking has focused on two ways of cooling the planet: schemes that reflect heat away from the earth's surface; and ways of removing carbon dioxide from the atmosphere once it has been emitted.

Reflecting heat could be achieved by spraying aerosols, such as tiny sulphur particles, into the air, or by whitening clouds with seawater sprayed into the air. But these could have unintended damaging consequences, the panel found.

One much-publicised idea, of painting roofs white to reflect sunlight, espoused by Steven Chu, science adviser to President Barack Obama, was quashed by the Royal Society panel. It found the area of land covered by human habitation too small to make a difference.

The cheapest option studied by the panel was also the most seemingly straightforward: preserving the world's existing forests and regrowing forests that have been cut down. Forestry will be discussed at the Copenhagen climate change talks in December, intended to forge a successor to the Kyoto protocol when its main provisions expire in 2012.

Other ways of removing carbon from the air include encouraging plankton growth in the ocean, but that could result in damaging "dead zones", while seeding the oceans with lime would require vast amounts of energy.

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