Pretty dangerous: Polar stratospheric clouds can be beautiful, but reactions occurring on their surfaces convert chlorine to a form highly reactive with ozone. A proposed geoengineering scheme to mitigate climate change involves the injection of sulphur into the stratosphere, resulting in aerosol surfaces that could enhance polar ozone depletion

Credit: Ross J. Salawitch

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SYDNEY: A plan to inject sulphate aerosols into the stratosphere, as a quick fix to counteract global warming, may drastically increase Arctic ozone depletion and slow the recovery of the Antarctic ozone hole, researchers warn.

A number of 'geoengineering' schemes have been proposed in recent years as possible ways for us to deflect the Sun's heat or reduce the amount of carbon dioxide in the atmosphere.

Infeasible and costly

Examples include positioning giant mirrors in orbit around the Earth in order to deflect sunlight, seeding clouds with seawater to increase their whiteness and therefore reflectivity, and 'ocean fertilisation', whereby algal blooms are stimulated to encourage the capture of CO₂ from the atmosphere.

None of these plans have been proven on a large scale, and most are infeasible due to high costs or potentially dangerous side effects.

One scheme proposes that the sulphate aerosols could be used to whiten clouds and cool the planet (See, Fake volcanoes could combat global warming, Cosmos Online). The idea is based around a cooling effect detected after the 1991 eruption of Mt. Pinatubo, a Filipino volcano that pumped sulphates into the atmosphere.

To probe the idea further, researchers in Germany and the U.S., led by Simone Tilmes at the National Centre for Atmospheric Research in Boulder, Colorado, analysed atmospheric data following the eruption. But what they found suggested that the sulphates would also react with chlorine in the cold conditions of the Arctic and Antarctic to deplete atmospheric ozone.

Her team publish their results today in the U.S. journal Science.

According to Tilmes, pumping sulphate aerosols into the upper atmosphere would thin the ozone layer, which protects us from the Sun's dangerous ultraviolet (UV) rays. This is because sulphates catalyse the creation of reactive chlorine compounds in the stratosphere, similar to the chlorofluorocarbons (CFCs) that were phased out starting with the Montreal Protocol in 1989.

Dangerous and unintended effects

Up to half of the ozone layer could be destroyed, the researchers said, which would particularly impact the northern hemisphere. The recovery of the existing ozone hole over the Antarctic continent (which is currently predicted to heal over by the mid-21^st century) could be delayed by a further 30 to 70 years.

"Our study shows that trying to artificially cool off the planet by
global geoengineering solutions might have dangerous side effects on our society and all life on earth," Tilmes told Cosmos Online. "Geoengineering schemes that cool the climate, only cure the symptoms but do not heal the real problem, which is the large amount of climate gases in the atmosphere that need to be reduced."

Barry Brook, director of the Research Institute for Climate Change and Sustainability at the University of Adelaide in South Australia, said that the sulphate aerosol scheme might also lead to acid rain and droughts.

"[This study] points out another mechanism by which these geoengineering schemes can go wrong," said Brook, who was not one of the study's authors. "There is always a chance of unintended side effects."