2006-12-05
Down under, where the carbon is.
Today's little tidbit is a short news story about a Journal of Climate paper [LINK]. The paper is about a climate simulation that includes an ocean (and presumably a carbon cycle model). The bottom line is that they think they have a credible southern hemisphere atmospheric circulation, with then drives a realistic Antarctic circumpolar current. If you have never done so, go get a globe and look at it from the "bottom," so you are looking right at the south pole; notice that there is a ring of water around Antarctica. That's the only place where that happens, and it makes a big difference to the world's climate. Anyway, they say that as the winds around Antarctica move south, they change the uptake of carbon dioxide into the ocean, which partially offsets the climate change associated with the anthropogenic greenhouse effect. That's good! Unfortunately, it also accelerates sea level rise (by pumping heat into the ocean, raising the temperature faster) and ocean acidification (which might feed back onto the carbon cycle if critters start dying off). So there you go. Maybe I'll try to tap Nikki for more nuianced insight, since this is closely related to her work.
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Over the past 50 years, we have observed a southward shift in the winds around Antarctica, so it makes sense that this trend will continue in the future. However, according to ocean models and atmopsheric observations, we have NOT observed an increased oceanic uptake of carbon dioxide. We have observed the opposite effect: less uptake of carbon dioxide in the Southern Ocean over the past 50 years.
http://quercus.igpp.ucla.edu/~lovenduski/lovenduski_2006_gbc.pdf
http://www.atmos.colostate.edu/ao/other_papers/ButlerThompsonGurney2006.pdf
So if uptake of CO2 is decreasing, then the southern ocean is amplifying anthropogenic climate change. I wonder if there is some compensating effect elsewhere in the system then, since temperatures are not rising faster than expected. One possibility is that the terrestrial biosphere is taking up the extra CO2. The other obvious one would be some kind of cloud feedback, but I don't think there's any evidence for that at this time.
My understanding is that without this ring of ocean Antarctica would be a much more verdant place, and that the formation of this ring is considered greatly responsible for our general cool temperatures?
This is the kind of post of yours when I wish we had a blackboard for you to blog on.
I guess Antarctica would be somewhat more "verdant" if the ACC weren't there... though I wonder if the super cold temperatures of the interior of the continent are more closely related to the circulation in the upper troposphere/lower stratosphere (maybe Nikki can comment on that). Of course because of the ring of ocean, the lower and upper level winds are more directly connected than in most places, and probably the upper level wind is stronger, which strengthens the polar vortex (related to the ozone hole). Hmmm.... I'll have to take a look at my "Meteorology of the southern hemisphere" monograph and see if there's any good explanations of the climatic impact of the circumpolar ocean.....
Also, Nikki has some interesting ideas about the carbon in the southern ocean, but they are being put into a proposal right now, so I probably shouldn't divulge them yet. Stay tuned for that.
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