Major glacier is long past its tipping point 14 years ago.

22/1/2010 New Scientist  A major Antarctic glacier may have passed its “tipping point” 14 years ago.After   losing more and more ice in recent decades, it is poised to lose enough to raise global sea   levels by 24 centimetres (9.5inches), according to the first study to model changes in an ice sheet in   three dimensions.
  The model, developed by Richard Katz of the University of Oxford and colleagues,   suggests that Pine Island Glacier (PIG) is on a one-way track to losing half its ice in 100   years.

  Katz’s model, which he admits does not reflect all the complexities of ice physics, focuses   on the “grounding line” - the underwater junction where the floating ice sheet butts up   against the rising sea bed. By varying sea levels, and therefore the position of the   grounding line, the team identified a point of no return beyond which the glacier’s   collapse is inevitable.

  As the sea bed rises slowly Up the continental shelf, it makes a dip before rising again to   the shoreline. The point of no return is the crest of a small lip just before the hollow.
  The model shows that once the grounding line progresses into the dip, the glacier loses   ice more quickly and a small change in the climate can cause rapid and irreversible loss of   ice (Proceedings of the Royal Society A. 001:10.1098/rspa.2009.0434).

  PIG’s grounding line probably passed over the lip in 1996, says Katz. Within 100 years, it   could retreat over 200 kilometres, causing the glacier to shed half its ice. That would push   up sea levels by 24 centimetres, says Richard Hindmarsh of the British Antarctic Survey.
  But this prediction, disturbing as it is, assumes that the grounding line will stabilise after   it has passed the dip in the sea bed. In reality, the retreat of a neighbouring glacier -   Thwaite’ s glacier- could cause PIG to disappear entirely, raising sea levels by 52   centimetres (1 foot 8 inches), says Hindmarsh.

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