Ozone Depletion Three Times Worse Than Predicted

By Roland Piquepaille

Before going further, here is where these arctic polar clouds live (Credit: NASA).

If the upper reaches of the Arctic atmosphere get colder -- a predicted consequence of climate change -- then the rate of ozone depletion could be three times greater than currently forecast, according to Markus Rex of the Alfred Wegener Institute for Polar and Marine Research in Potsdam, Germany, and his co-workers.

"I was surprised to see these results," says Drew Shindell, an atmospheric scientist at NASA's Goddard Institute for Space Studies, New York. "We never suspected the models were this far out of whack," he says.

It seems that the previous models largely ignored the presence of these artcic clouds.

Rex and his colleagues studied climate conditions in the Arctic over the past ten winters to calculate how ozone destruction depends on the weather. They found a surprisingly strong relationship between ozone loss and the amount of polar stratospheric clouds.

These clouds form 20 kilometres above the ground in winter-time, and are sometimes called 'mother-of-pearl clouds' because of their shimmering appearance.

It's true that these clouds can be beautiful. Here is how they look from the ground (Credit: NASA).

But they are not harmless things of beauty: the clouds provide reaction surfaces for chemicals eating away the Earth's protective ozone. Chemical reactions in the clouds convert chlorine from industrially produced compounds, such as the chlorofluorocarbons (CFCs) found in old refrigerators, into a reactive form that breaks apart ozone molecules.

The destruction of ozone allows more ultraviolet rays from the sun through to the surface of the planet, harming humans and the ecosystem close to the poles.

It remains to be seen if this new model is more accurate than previous ones. However, even if we reduce the emission of CFCs in a near future, another big unknown, the ozone layer will continue to shrink for decades to come.

This research has been published by Geophysical Research Letters. Here is the abstract of this report, called "Arctic ozone loss and climate change."

We report the first empirical quantification of the relation between winter-spring loss of Arctic ozone and changes in stratospheric climate. Our observations show that ~15 DU additional loss of column ozone can be expected per Kelvin cooling of the Arctic lower stratosphere, an impact nearly three times larger than current model simulations suggest. We show that stratospheric climate conditions became significantly more favorable for large Arctic ozone losses over the past four decades; i.e., the maximum potential for formation of polar stratospheric clouds increased steadily by a factor of three. Severe Arctic ozone loss during the past decade occurred as a result of the combined effect of this long-term climate change and the anthropogenic increase in stratospheric halogens.

For more information about the research on the subject, you can visit this Atmospheric Research: Ozone and Climate Change page.

Sources: Philip Ball, Nature, March 3, 2004; Geophysical Research Letters, Vol. 31, L04116, February 28, 2004