Arctic Ozone At Lowest Level Ever - Climate Change Believed Responsible

[hatrack]

"The protective ozone layer over the Arctic has thinned this winter to the lowest levels since records began, alarming scientists who believed it had begun to heal. The increased loss of ozone allows more harmful ultraviolet light to reach the earth's surface, making children and outdoor enthusiasts such as skiers more vulnerable to skin cancer - a disease which is already dramatically increasing.

EDIT

Research by Cambridge University shows that it is not increased pollution but a side effect of climate change that is making ozone depletion worse. At high altitudes, 50% of the protective layer had been destroyed. The research has dashed hopes that the ozone layer was on the mend. Since the winter of 1999-2000, when depletion was almost as bad, scientists had believed an improvement was under way as pollution was reduced. But they now believe it could be another 50 years before the problem is solved.

What appears to have caused the further loss of ozone is the increasing number of stratospheric clouds in the winter, 15 miles above the earth. These clouds, in the middle of the ozone layer, provide a platform which makes it easier for rapid chemical reactions which destroy ozone to take place. This year, for three months from the end of November, there were more clouds for longer periods than ever previously recorded. Cambridge University scientists said yesterday that, in late March, when ozone depletion was at its worst, Arctic air masses drifted over the UK and the rest of Europe as far south as northern Italy, giving significantly higher doses of ultraviolet radiation and sunburn risk.

The results, which were announced at a Geophysical Union meeting in Vienna yesterday, are part of a European venture coordinated by Cambridge University's chemistry department, which has been studying the relationship between the ozone layer and climate change since May 2004. Yesterday, Professor John Pyle, from the university, said: "These were were the lowest levels of ozone recorded since measurements began 40 years ago. We thought things would start to get better because of the phasing out of CFCs and other chemicals because of the Montreal protocol, but this has not happened."

EDIT

http://www.guardian.co.uk/uk_news/story/0,3604,1470944,00.html

[bloom]

1. "more clouds for longer periods than ever previously recorded"

That makes more sense to me as a reason than just the aerosols, etc.

[hatrack]

2. There's also some evidence that w. more heat trapped in the troposphere

Relatively less of it is re-radiating out to space, which means that the stratosphere is cooling, hence greater ozone destruction.

I'm fairly sure the mesosphere is cooling about 10X faster than projected (I've got an article around here somewhere) but it's not a very well-known sliver of the atmosphere, so how that might affect stratospheric ozone depletion I don't know.

[jpak]

3. Positive feedbacks

Tropospheric greenhouse gases absorb upwelling IR that warms the stratosphere. Higher greenhouse gas concentrations in the troposphere cool the stratosphere.

Ozone also warms the stratosphere as well (it's a greenhouse gas).

Polar stratospheric clouds play a central role in the chemistry of stratospheric ozone depletion - they form at temperatures < -78 degrees C.

Deplete ozone and the stratosphere cools even further, which enhances the formation of polar stratospheric clouds, which enhances ozone depletion, which further cools the stratosphere, etc...

Upwelling methane is the primary source of water vapor in the stratosphere - it's photo-oxidized to CO2 and water. As more anthropogenic methane is supplied to the stratosphere, there is more water vapor available to form polar stratospheric clouds (PSC's) further enhancing the probability that ozone depletion will occur etc. etc.

If the Montreal Protocol is adhered to, however, anthropogenic halogens in the stratosphere will decline to insignificant levels in fifty years or so.

But in the meantime, there's going to be some nastiness to contend with...