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View Diary: Top Climate Scientist: "The Arctic Is Screaming" (161 comments)

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  •  Melting of sea ice (6+ / 0-)

    should yield a rise of zero.

    •  Not when the warming potential (4+ / 0-)

      is factored in. Then the rest of the sea warming up will produce substantial level rises.

      This is not a sig-line.

      by Joffan on Tue Dec 11, 2007 at 07:47:10 PM PST

      [ Parent ]

    •  But Greenland isn't sea ice (0+ / 0-)

      And then on the other side of the world is Antarctica.

      Obama '08

    •  Not quite zero (2+ / 0-)
      Recommended by:
      dotdot, Justanothernyer

      if I may link to my dad's site, since he studies these things for a living:

      In terms of the ice, there are five identifiable reservoirs, only one
      of which is expected to be able to have catastrophic effects on sea
      level.  They are sea ice, mountain glaciers, the Greenland ice sheet,
      the East Antarctic ice sheet, and the West Antarctic ice sheet.  The one
      expected to be potentially catastrophic is West Antarctica.
      Catastrophic is taken to mean meters of sea level in a few hundred years
      or less.

       First, why can't the other four be catastrophic?  Sea ice cannot
      change sea level much.  That it can do so at all is because sea ice is
      not made of quite the same material as the ocean.  Sea ice is much
      fresher than sea water (5 parts per thousand instead of about 35).  When
      the ice melts (pretend for the moment that it does so instantly and
      retains its shape), the resultant melt water is still slightly less
      dense than the original sea water.  So the meltwater still 'stands' a
      little higher than the local sea level.  The amount of extra height
      depends on the salinity difference between ice and ocean, and
      corresponds to about 2% of the thickness of the original ice floe.  For
      30 million square kilometers of ice (global maximum extent) and average
      thickness of 2 meters (the Arctic ice is about 3 meters, the Antarctic
      is about 1), the corresponding change in global sea level would be 2
      (meters) * 0.02 (salinity effect) * 0.10 (fraction of ocean covered by
      ice), or 4 mm.  Not a large figure, but not zero either.

      4mm isn't very much, honestly, but it's not quite zero either.

      He goes on to explain why Greenland and East Antarctica seem likely to essentially balance each other out; Greenland will melt slowly because the ice sheet is largely retained by surrounding mountains, and East Antarctica is too cold to experience any significant degree of melting and will respond to warming with increased precipitation.

      Here's the problem with West Antarctica: it's not the sea ice, but the ice sheet that the sea ice is holding.

      West Antarctica is the joker in the deck.  Sea ice we can ignore (for
      sea level that is).  Greenland and East Antarctica seem to be inclined
      to balance each other's effects.  But West Antarctica represents 6
      meters of sea level that can collapse rapidly as glaciologists
      measure things.

       The collapse mechanisms rely on the peculiar geometry of the West
      Antarctic ice sheet.  The first major feature of West Antarctica is
      that it includes two large ice shelves.  These are masses of ice
      approximately the size of France, approximately 500 meters thick.  They
      float on the ocean, so cannot directly change sea level if they were
      lost.  The peculiarity of having ice shelves is that ice shelves are
      dynamically unstable.  The stable configurations are for the ice sheet
      to advance all the way to the edge of the continental shelf, or to
      collapse to include no ice shelf.

       Why should we worry about the presence or absence of the ice shelves?
      They can't change sea level if they disappeared.  But the ice shelves
      serve another role in West Antarctica.  The Filchner-Ronne (in the
      Weddell Sea) and the Ross Ice shelf (in the Ross Sea) act as buttresses
      to the West Antarctic ice sheet.  Without these buttresses, the West
      Antarctic ice sheet will collapse into the ocean on a time scale of
      several decades to a few centuries.

       The ice shelves contribute to ablation both through melting (at their
      bases more than the surface) and through iceberg calving.  Some notably
      large bergs have calved in the last few years, including a couple
      larger than the state of Rhode Island.  So through either a warmer
      ocean providing more ablation or through an increase in calving
      (arguably observed), the West Antarctic ice shelves could collapse.

      To anyone interested in the effects of warming on ice melt and sea level rise, the above link is a good read. There's a whole lot more in there than I can reasonably summarize.

      During times of universal deceit, telling the truth becomes a revolutionary act. - George Orwell

      by kyril on Wed Dec 12, 2007 at 06:49:12 AM PST

      [ Parent ]

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