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228 comments on DrumBeat: August 13, 2008

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Black_Dog on August 13, 2008 - 9:26am Permalink | Subthread | Comments top

RE: Human activity, El Nino warming West Antarctic: study

This is an important finding, given that warming in the Antarctic has been somewhat less than that predicted by climate models. The apparent reason is the depletion of the Ozone over the Antarctic, which produced a "Hole" in the ozone layer.

For those interested, the ozone layer is measured in Dobson Units and is typically about 300 Dobson units. At that level, if all the ozone were brought down to the surface as a single layer, it would be only 3 mm thick. If that layer were a liquid with the density of water, instead of a gas, the layer would be thinner than a sheet of plastic food wrap. It's a good thing the world's governments agreed to limit emissions of FREONS, which were destroying the ozone layer, else we'd be headed for extinction.

E. Swanson

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ccpo on August 13, 2008 - 11:38am Permalink | Subthread | Parent | Comments top

Southern Hemisphere sea ice trends in extent

This should interest you. Note that the current year had dropped below BOTH the long-term baseline and last year.

Cheers

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Black_Dog on August 13, 2008 - 2:02pm Permalink | Subthread | Parent | Comments top

This past year, after the astounding melt in the Arctic, the maximum extent was greater than the previous maximum, but somewhat less than that seen in the long term average. The sea-ice situation around the Antarctic looks a bit different, with the minimum being above both last years and the long term average, but (from your link), the maximum extent appears to be heading to a bit less than the long term average. Since the Antarctic ozone hole appears in the spring before the melt season, it would be reasonable to point to the climate impact of ozone for the increase in minimum extent around the Antarctic. One must remember that ozone is a Greenhouse Gas and it's decline could well produce a local cooling. There are also reports that suggest a connection between the strength of the Antarctic Polar Vortex and the decline in the ozone.

E. Swanson

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ccpo on August 14, 2008 - 12:48am Permalink | Subthread | Parent | Comments top

This past year, after the astounding melt in the Arctic, the maximum extent was greater than the previous maximum, but somewhat less than that seen in the long term average.

The important thing is the mass, not just extent. Greater extent is good in that the higher albedo reflects more energy, but it being winter the benefit is mitigated. But we should not discuss extent without discussing concentration and thickness. The ice that grew was thin. (Also, the max extent wasn't "somewhat less" than the baseline, it was significantly less. 1 million sq. miles or more.) Thus, even though we had a larger extent, it melts quickly under any stress, which is why we saw strong melt in early spring and then this August.

The sea-ice situation around the Antarctic looks a bit different, with the minimum being above both last years and the long term average, but (from your link), the maximum extent appears to be heading to a bit less than the long term average.

As of this writing, they are all three tied. What interests me about the large drop in Antarctica is that it 1. was a drop of about 750,000 sq. m in a short time, and that the second large drop after the initial roughly equaled the timing in the Arctic August melt. I don't think the two are considered closely connected, but it is curious. Almost certainly serendipitous, but still...

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enemy of state on August 13, 2008 - 10:01pm Permalink | Subthread | Parent | Comments top

The main effect on the Antarctic weather from the ozone whole is thought to be that it enhances the meridional cirulation (the strong winds that blow around the continent just to the south of it). This tends to bottle up the cold air formed over the continent. The effect of this is that the continent cools, because its exports of cold air are reduced. Presumably as the ozne hole heals, this mode will weaken somewhat.

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Black_Dog on August 13, 2008 - 10:22pm Permalink | Subthread | Parent | Comments top

The winds which make up the Antarctic polar vortex are zonal winds, that is, they flow along the lines of latitude, west to east, AIUI. Meridional winds blow north-south. I don't quite understand the reason for those zonal winds, something to do with the Hadley and Ferrel "cells" and the resulting jet stream. Anyway, as the CFC's (and other ozone destroying chemicals) in the stratosphere continue to decline, it's to be hoped that the "hole" will no longer appear.

E. Swanson

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228 comments on DrumBeat: August 13, 2008

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