Severe Arctic Ozone Loss

iONiUM writes "The BBC reports that 'Ozone loss over the Arctic this year was so severe that for the first time it could be called an "ozone hole" like the Antarctic one, scientists report. About 20km (13 miles) above the ground, 80% of the ozone was lost, they say. The cause was an unusually long spell of cold weather at altitude. In cold conditions, the chlorine chemicals that destroy ozone are at their most active.' This is the first time in observational history that the Arctic ozone has been depleted to such extensive levels (abstract). This will mean high UV problems for Russia, Greenland and Norway."

Re:Global warming

[Nulukkhizdin]

Global warming due to CO2 == heat is trapped in the troposphere => less heat lost => colder stratosphere.

If the global warming was due to the Sun, the whole atmosphere would be warming.

On the other hand, Venus has runaway greenhouse effect and its stratosphere is abnormally cold.

Re:Global warming

[gatkinso]

Venus stratosphere ranges between 385C and 75C.

This is abnormally cold to you?

Re:Global warming

[Cimexus]

No, of course he can't. Climate changes due to natural events and cycles. I don't think anyone denies that.

However, he can point out that according to the best figures we have, the climate is currently changing at a far greater rate than has occurred previously (outside of major extinction events), and that that pace of change cannot be explained by natural causes alone. We are seeing changes over decades-to-centuries time frames that would normally take millennia (or longer).

Little more detail

[mps01060]

These aren't traditional clouds that you see in the troposphere (lowest layer of the atmosphere). To get an ozone hole, you need VERY cold temperatures. This happens after during polar night when there is no sunlight for about half the year. The stratosphere is so cold that it can form ice crystals that contain nitric acid. These crystals act as surfaces where ozone destruction takes place. Once the sun rises at the pole (March equinox for the northern hemisphere), the UV light "splits" compounds like CFCs into reactive materials such as Chlorine. The ozone destruction reaction still will not work efficiently without the initial nitric acid/ice crystal surfaces. This is why we don't often see this happening in the Arctic, while the Antarctic shows this signal annually.

http://www.noaa.gov/features/02_monitoring/arctic_thinning.html [noaa.gov]

The "coldness" of the pole is related to the strength of the winds (polar vortex) around the pole in the atmosphere. The south pole generally has strong winds circling it, which works to cut off the south pole's atmosphere from the rest of the world, especially during the southern hemisphere winter. Part of the reason for a stronger vortex is due to ocean surrounding the south pole on all sides, with land masses far away. In addition, the southern hemisphere in general has more ocean compared to land than the northern hemisphere.

In the northern hemisphere, the polar vortex generally has more waves or pertubations in the polar vortex, which help to mix in air from lower latitudes. Some of this is caused by planetary waves that propagate vertically in the atmosphere. These planetary waves are formed generally due to land masses and mountains affecting the atmospheric flow (not this simple but this is the general idea). Generally, the factor that causes the difference in the north and south polar vortices is land mass.

Now relating this all to climate is a bit tricky. It has been seen that as the troposphere warms (lowest layer of the atmosphere), the stratosphere cools. This has been seen in observations in the last 30-50 years (you may argue that 50 years might not be enough to define a long-term trend). The reason for this cooling is basically radiative balance (though I'm oversimplifying it here). If the troposphere warms due to increased greenhouse gasses, then the atmosphere above must cool above it. There cannot be more heat coming in than is leaving the Earth. A good analog to this is Venus. Venus has huge concentrations of greenhouse gasses. We know its surface is very hot (over 400 degrees C), while its upper atmosphere is much cooler than Earth's (gets down below -110 degrees C, compared to about -80 C on Earth).

The tough part is separating the stratospheric cooling due to greenhouse gasses and ozone destruction from CFCs (although we may know this answer once all the CFCs are out of the atmosphere in the future). Increased greenhouse gasses will warm the troposphere and cool the stratosphere. This will lead to more polar stratospheric clouds, leading to more reactions sites for ozone destruction. More ozone destruction means less UV light is absorbed by ozone in the stratosphere. Less UV absorption means a cooler stratosphere which further intensifies the problem.

Re:I call bullshit

[choongiri]

It's mostly true that reactions dependent on kinetics speed up with temperature. Ozone holes, though, are a very very different process. The ozone hole results from surface reactions on polar stratospheric clouds. The colder it gets, the easier it is for those clouds to form, and the more severe the rate of ozone depletion.

Do some homework before calling "bullshit".

(I am an atmospheric chemist, I am not your atmospheric chemist, etc...)