‘Planetary sunshade’ could strip ozone layer by 76%

New Scientist | Apr 24, 2008

By Catherine Brahic

Planetary engineering projects to cool the planet could backfire quite spectacularly: a new model shows that a “sulphate sunshade” would punch huge holes through the ozone layer above the Arctic.

To make matters worse, it would also delay the full recovery of the Antarctic ozone hole by up to 70 years.

Pumping tiny sulphate particles into the atmosphere to create a sunshield that would keep the planet cool was first suggested as a solution to global warming by Edward Teller, a physicist was best known for his involvement in the development of the hydrogen bomb.

Simone Tilmes of the National Center for Atmospheric Research in Colorado, US, used computer models to see how a sulphate sunshade would affect the ozone layer, which protects us from harmful UV rays. She says it could have “a drastic impact”.

Tilmes modelled two different scenarios: one in which “large” particles measuring 0.43 microns in diameter are used, and one where the particles are two-and-a-half times smaller.

Cooling effect

Sulphate particles catalyse the breakdown of ozone molecules by chlorine atoms. Western economies have almost entirely stopped using chlorine-based coolants called CFCs, thanks to the Montreal Protocol. However, such substances are increasingly being used in Asia and the atmosphere is still full of CFCs emitted during the 20th century.

In January 2008, researchers described how much of each type of sulphate particle would need to be injected into the stratosphere in order to compensate for a doubling in atmospheric carbon dioxide concentrations (Geophysical Research Letters, DOI: 10.1029/2007GL032179). Tilmes used these volumes in her computer models.

She found that injections of small particles over the next 20 years could thin the wintertime ozone layer over the Arctic by between 22 and 76%. Large particles, which would have less of a cooling effect, according to previous research, would still reduce Arctic ozone by 15 to 50% during the winter.

In the Antarctic, the injections would delay the recovery of the existing ozone hole by 30 to 70 years.

Cancer increase

A thinner ozone layer – popularly known as an ozone “hole” – lets more UV rays through, which can cause an increase in the incidence of various cancers. According to NASA, a 1% decrease in the ozone layer can cause an estimated 2% increase in UV-B irradiation, leading to a 4% increase in basal carcinomas – the most common form of skin cancer.

In 2007, Ken Caldeira of the Carnegie Institution of Washington in the US found that if a sulphate sunshield were deployed and then removed – for instance because of a change in governments – the effects of global warming after the removal would be far worse than before the sunshield.

Caldeira has also found that a sunshade could cause severe drought.

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2 responses to “‘Planetary sunshade’ could strip ozone layer by 76%

  1. Since human activity usually backfires in unexpected ways–

    Then there was the one to reflect extra light to dark areas. And at one time the Russians were going to reverse the flow direction of one of their rivers? Guess it was flat there? And the once proposed ground level Panama canal–2 connect two separate biospheres–ew.

  2. Top scientists say revolutionary clean power climate control project will reduce dangerous weather and improve the lives of billions of people.

    Climatologists, biologists and physicists from all corners of the globe agree that U.S. based Gravitational Systems, L.L.C.’s revolutionary clean power climate control project INDRA will improve the lives of billions of people around the world. Concerns have been raised about the projects impact on biodiversity as deserts are terraformed to rainforests.

    Gare Henderson, director of research and development for Gravitational Systems, L.L.C. ( a clean power developer), explains that the INDRA project, a proposed network of specialized evaporation channels moving sea water from the oceans toward the deserts, will convert world deserts into biodiverse rainforests. Deserts which cover 1/3 of all dry land will be terraformed into productive land. The INDRA systems will give mankind control of the weather, ending dangerous storms such as hurricanes, typhoons, tornadoes, and dry heat waves within a decade. Vast rivers can be turned on and off in hours, and reservoirs and salt marshes drained or replenished in days. The increased bio-mass of the terraformed deserts will begin to reverse both global warming and thermal sea level rise. UNFCCC cap and trade certification of the INDRA project will allow individuals and business to fund the plan through carbon offsets. The initial projects will be targeted north American, and north African deserts.

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