UN warms to idea of using giant mirrors in fight against climate change effects

Putting giant mirrors in space or salting clouds to make them brighter may sound more like science fiction than reality.

But these and a raft of other futuristic ploys have made it into the pages of a landmark UN report that concludes some have the potential to "substantially" curb global warming, according to a final draft seen by the Financial Times.

Scientists have been working on so-called geo-engineering ideas for years but the UN's Intergovernmental Panel on Climate Change has largely confined its analysis of it to less closely-watched volumes of the extensive assessments it produces every six or so years.

This year, as atmospheric concentrations of carbon dioxide have reached record levels, the panel has elevated the issue to the most carefully scrutinised volume of its report, on the physical basis of climate science, which is due to be finalised in Stockholm next week.

The report assesses the two main types of geo-engineering that have emerged as global temperatures have risen: carbon dioxide removal and solar radiation management.

Carbon dioxide removal includes measures such as fertilising the ocean with iron to spur the growth of plankton that would absorb carbon, or using chemicals to capture C02 directly from the air, then storing it under the sea or ground.

Solar radiation management covers a range of measures to reflect sunlight, from giant reflectors in space to injecting sulphate particles, or aerosols, into the stratosphere, or salting clouds to produce more droplets of water so the clouds appear whiter and brighter.

The panel's draft conclusions say computer modelling has shown some solar management methods could sharply reduce global temperature rises, but both types of geo-engineering risk "unintended side-effects and long-term consequences on a global scale".

Scientists whose research contributes to the new report have previously warned that tinkering with the oceans' fertility could have many unknown effects on complex marine ecosystems, and that using aerosols to reflect sunlight could cause stratospheric ozone depletion.

In addition, because high carbon dioxide concentrations would stay in the atmosphere for thousands of years unless curbed, there could be problems if solar management started then ended, the IPCC draft says.

"If solar radiation management were terminated for any reason, there is high confidence that global surface temperatures would rise very rapidly," the report.

The uncertain effects of artificially manipulating the climate is only one reason geo-engineering is seen as contentious. Many methods would also be extremely expensive. A study by US researchers last year found shooting aerosols into the sky could cost between $1bn and $8bn a year.

The draft report summarising the IPCC's lengthy assessment must be approved by governments this week before its release and some wording may change in the process.

The central findings of the broader assessment are unlikely to change, however.

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