Anthropogenic influence on recent circulation-driven Antarctic sea ice changes

Oh good grief I hear you cry, not more science. Yes. Sorry. And its even about sea ice, but the Antarctic kind. This is in the trail of Holland and Kwok and so on.

Observations reveal an increase of Antarctic sea ice over the past three decades, yet global climate models tend to simulate a sea ice decrease for that period. Here we combine observations with model experiments (MPI-ESM) to investigate causes for this discrepancy and for the observed sea ice increase. Based on observations and atmospheric reanalysis, we show that on multidecadal time scales Antarctic sea ice changes are linked to intensified meridional winds that are caused by a zonally asymmetric lowering of the high-latitude surface pressure. In our simulations, this surface pressure lowering is a response to a combination of anthropogenic stratospheric ozone depletion and greenhouse gas increase. Combining these two lines of argument, we infer a possible anthropogenic influence on the observed sea ice changes. However, similar to other models, MPI-ESM simulates a surface-pressure response that is rather zonally symmetric, which explains why the simulated sea ice response differs from observations.

So, maybe the GCMs wind-pattern response, aka MSLP, around Antarctica is a bit off?

4 thoughts on “Anthropogenic influence on recent circulation-driven Antarctic sea ice changes”

  1. William,

    MSLP = Mean Sea Level Pressure ?

    [Yes -W]

    Tangent.

    As to the suite of AOGCM’s, I’d like to (at least) understand the convective parametrizations (atmospheric and ocean), which is my current rather retarded level of understanding (i. e. that there are parametrizations).

    [Yes, there are, because the model scale can’t resolve them. At the simplest, the models simply overturn a column of air (or water) that has become statically unstable. That however doesn’t mimic reality terribly well, so you then get into a long trail of how to do it better: entrainment, detrainment, etc. http://www.met.rdg.ac.uk/~sws00rsp/research/param/cambridge.pdf discusses some of the issues -W]

    I also wonder about about the pace of inclusion of additional parametrizations (e. g. process based ice sheet models) versus the pace of computational resources.

    [Typically, ice sheet models only need updating very slowly (well, that’s true for Antarctica) so hardly need including in century-type simulations. You could throw one into a GCM, resource-wise it wouldn’t be a problem -W]

    It seem as there are papers released on a weekly-to-monthly basis suggesting either the need to improve current parametrizations and/or add additional parametrizations to include processes that are not currently in the AOGCM’s.

    Finally, given the spatial scope and temporal time scales of the problem, parametrizations are a necessary requirement for solving many (if not all) complex problems.

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  2. So I guess the obvious question is ‘What have the meriodonal winds been doing? Wouldn’t variations that create a low pressure imply that other areas have high pressure? Does the tropopause boundary change with with meriodonal wind changes?

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  3. Wiliam, I would say your paper with Tom B. looking at the AR4 models’ temperature responses in Antarctica already effectively showed that the sea ice was wrong because the winds were wrong. My educated guess is that the ‘overly symmetric’ nature of the models is that they are not doing the tropics right. But that’s just me.

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