* Sun-dimming schemes may cause threats to rainfall
* U.N. climate panel to review geo-engineering-Stocker
Alister Doyle, Reuters AlertNet 28 Oct 10;
OSLO, Oct 27 (Reuters) - Futuristic schemes for slowing climate change such as dimming sunlight are fraught with risks but will get a serious hearing from the U.N. panel of climate scientists, a leader of the panel said on Wednesday.
Thomas Stocker, co-chair of the panel's working group examining climate science, said some so-called geo-engineering solutions could disrupt world rainfall and might backfire by causing abrupt temperature rises if they go wrong.
He told Reuters his group will hold meetings of experts in 2011 to focus on geo-engineering and ocean acidification, blamed on rising concentrations of carbon dioxide, to help prepare the next U.N. review of climate science, due for completion in 2014.
Stocker said proposals for imitating the effect of volcanoes by frequently pumping sun-dimming sulphur gases into the upper atmosphere would have knock-on effects on world rainfall.
"You will have additional effects of drying or moistening in various regions of the world that may be unwanted and even surprises," Stocker, a professor at the University of Bern in Switzerland, said in a telephone interview.
Proposals for geo-engineering include mirrors in space as planetary sunshades, sun-blocking gases injected into the upper atmosphere, fertilisation of the oceans to grow carbon-absorbing algae or methods to produce more clouds.
The last report by the Intergovernmental Panel on Climate Change (IPCC) in 2007 was dismissive, saying geo-engineering was so far "largely speculative and unproven" with "risks of unknown side effects".
"TERMINATION PROBLEM"
Among geo-engineering proponents are 1995 Nobel Chemistry laureate Paul Crutzen, who has proposed spewing sulphates into the upper atmosphere.
Geo-engineering "is a young and emerging branch of the physical science," Stocker said. "It's natural that additional ideas and options are being discussed."
But, he cautioned that there was also a "termination problem" if the world adopted such geo-engineering projects for several years but then found that damaging side-effects, for instance on world food output, outweighed the benefits.
In one scenario, abruptly stopping injection of sun-dimming sulphates could cause an annual temperature rise 10 times faster than the current rate from global warming if greenhouse gases kept on building up, he said.
Stocker denied suggestions that the panel's focus on geo-engineering was caused by the failure of world leaders to agree a new U.N. treaty to curb emissions of greenhouse gases at a summit in Copenhagen in December 2009.
"I have seen increasing interest significantly earlier" than Copenhagen, he said. And he said that global warming, blamed on a build-up of greenhouse gases, could not be solved by geo-engineering alone but would also need cuts in emissions.
The IPCC is trying to restore credibility after errors including its exaggeration of the thaw of the Himalayan glaciers in the 2007 report. It says the mistakes do not affect its conclusion that it is at least 90 percent certain global warming is manmade. (For Reuters latest environment blogs, click on: http://blogs.reuters.com/environment/ )
(Editing by Elizabeth Fullerton)
