Scientists debate man's cooling Earth

DURBAN, South Africa - Brighten clouds with sea water? Spray aerosols high in the stratosphere? Paint roofs white and plant light-colored crops? How about positioning "sun shades" over the Earth?

At a time of deep concern over global warming, a group of scientists, philosophers and legal scholars examined whether human intervention could artificially cool the Earth - and what would happen if it did.

A report released late Thursday in London and discussed Friday at the U.N. climate conference in South Africa said that - in theory - reflecting a small amount of sunlight back into space before it struck the Earth's surface would have an immediate and dramatic effect.

Within a few years, global temperatures would return to levels of 250 years ago, before the industrial revolution began dumping carbon dioxide into the air, trapping heat and causing temperatures to rise.

But no one knows what the side-effects would be.

They could be physical - unintentionally changing weather patterns and rainfall. Even more difficult, it could be political - spurring conflict among nations unable to agree on how such intervention, or geoengineering, will be controlled.

The idea of solar radiation management "has the potential to be either very useful or very harmful," said the study led by Britain's Royal Society, the Washington-based Environmental Defense Fund and TWAS, the academy of sciences for the developing world based in Trieste, Italy.

Environmentalist Silvia Ribeiro, of the Canada-based ETC-Group, said geoengineering should be outlawed before it gets off the ground.

"Solar radiation management technologies are high-risk and extremely dangerous, and they should be treated under international law like nuclear weapons - except, unlike nuclear weapons, we have an opportunity to ban their testing and their proliferation before the technology is fully developed, rather than trying to prevent their proliferation after the fact," she said.

The final report grew out of three days of talks in a quiet country retreat last March, the climax of a yearlong dialogue spanning experts in 22 countries.

It was prompted in part by the failure of a 20-year U.N. negotiating process to take decisive action to curb greenhouse gas emissions, mainly from burning fossil fuels, responsible for climate change.

"The slow progress of international climate negotiations has led to increased concerns that sufficient cuts in greenhouse gas emissions may not be achieved in time to avoid unacceptable levels of climate change," the report said.

But geoengineering is not an alternative to climate action, said John Shepherd, a British oceanographer from the University of Southampton who was a lead author of the report.

"Nobody thought this provides a justification for not reducing carbon emissions," Shepherd said in a telephone interview from London.

"We have to stick with Plan A for the time being, and that could be a very long time indeed," he said. "This would buy time for people to make the transition to a low-carbon economy."

The Intergovernmental Panel on Climate Change foresees temperatures rising as much as 6.4 degrees Celsius (11.5 degrees Fahrenheit) by 2100, swelling the seas with melted glacial water and disrupting climate conditions around the globe.

Releasing millions of tons of sulfur dioxide in the upper atmosphere would mimic the cooling effects of a volcanic eruption, lowering global temperature about 0.5 Centigrade (0.9 Fahrenheit), which can last for a year or two when it occurs naturally.

But deliberately tinkering with nature to counter global warming can only be a stopgap measure, and is fraught with danger, the report said.