Cooling plan may be perilous
2008-04-25 11:35
Washington - Radical proposals to inject sulphur particles into the Earth's stratosphere to cool it down and battle global warming could instead badly damage the ozone layer, a study warned on Thursday.
"Our research indicates that trying to artificially cool off the planet could have perilous side effects," said researcher Simone Tilmes from the National Centre for Atmospheric Research.
"While climate change is a major threat, more research is required before society attempts global geo-engineering solutions."
The study, published on Thursday in Science Express, warns that injecting sulphate particles into the air at an altitude of some 10 to 50km, could lead to a loss of ozone above the Arctic and delay the recovery of the hole in the ozone layer above Antarctica by decades.
In the past few years, scientists have been studying "geoengineering" ways to combat global warming rather than by just reducing emissions of greenhouse gases alone.
One of the ideas put forward and studied by Nobel Chemistry laureate Paul Crutzen draws on the lessons learnt from volcanic explosions, when vast amounts of sulphur particles are unleashed into the air.
The sulphur, which blocks the sun's rays, has in the past led to a cooling of surface temperatures around the volcano site.
Devastating effect
Researchers, led by Tilmes, studied what would happen if regular, large amounts of sulphate particles were artificially injected into the atmosphere with the aim of cooling the surface temperatures.
But in fact the team found that over the next few decades, such large amounts of sulphates would likely destroy between about 25 to 75% of the ozone layer above the Arctic.
This could have a devastating effect on the northern hemisphere, computer simulations showed. The expected recovery of the hole over the Antarctic would also be delayed by 30 to 70 years.
Researchers found that such large amounts of sulphates would enable chlorine gases found in the cold layers of the stratosphere above the two Poles to become active, triggering a chemical reaction harmful to ozone.
Ozone is an unusual molecule. Ground-level ozone produced by pollution, mostly from cars, is harmful to the health. But in the stratosphere, where is it produced naturally, it screens out the sun's dangerous ultra-violet rays, which can cause such things as skin cancer.
"This study highlights another connection between global warming and ozone depletion," said co-author Ross Salawitch of the University of Maryland.
"These traditionally had been thought of as separate problems but are now increasingly recognised to be coupled in subtle, yet profoundly important, manners."
The damaging effects of such sulphate treatments would be lessened in the second half of the century, when international accords on banning the production of ozone-depleting chemicals are due to be fully felt, the study added.