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Sunshade World – a global warming solution?

Press release issued: 22 May 2008

Recent research at the University of Bristol indicates that contrary to popular conception, 'Sunshade' geoengineering would not re-establish a ‘natural’ pre-industrial climate.

Placing a ‘sunshade’ in space in order to counteract global warming was first proposed in 1989. More recent  studies concluded that such a scheme could be developed and deployed in about 25 years time at a cost of several trillion dollars.

Recent research at the University of Bristol indicates that contrary to popular conception, this kind of geoengineering would not re-establish a ‘natural’ pre-industrial climate. The results are published online in Geophysical Research Letters.

For the first time, Dr Dan Lunt and the team at Bristol investigated the magnitude and nature of climate change in a Sunshade World using a climate model capable of simulating changes to both atmosphere and ocean circulation, developed at the UK Met Office.

Using this climate modelling approach, they exactly cancelled out the global warming caused by increased atmospheric carbon dioxide, by decreasing the amount of sunlight reaching Earth from the sun. They then examined the regional effects this would have on other aspects of the climate.

“We found significant cooling of the Tropics, a warming of the polar regions and related sea ice reduction,” said Lunt. “We also found important differences in the hydrological cycle, with Sunshade World being generally drier than the pre-industrial ‘natural’ world. Average precipitation decreased by five percent with the largest decreases being in the Tropics.”

Despite these problems, when compared to possible scenarios of ‘uncontrolled’ future climate change, the predicted changes are relatively small. In this respect, the research found sunshade geoengineering to be highly successful.

Other problems, however, remain unsolved by this form of geoengineering. In particular, the potential effects of ocean acidification on certain types of plankton – the base of the ocean food chain – could lead to an unforeseen impact on ecosystems in Sunshade World.

As a result, the team could not recommend sunshade geoengineering as an alternative to the reduction of carbon emissions. This is even before the high cost and possible ethical considerations of a sunshade geoengineering scheme have been considered.

Further information

The paper: D. J. Lunt, A. Ridgwell, P. J. Valdes, and A. Seale (2008), 'Sunshade World': a fully coupled GCM evaluation of the climatic impacts of geoengineering, Geophysical Research Letters, doi:10.1029/2008GL033674.