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Monday, 26 May 2014

No way back for West Antarctic glaciers

No way back for West Antarctic glaciers



No way back for West Antarctic glaciers




Tim Radford 26 May 2014, 8:30am 24





Melting Antarctic glaciers


Satellite data analysis reveals the ominous news that the
melting glaciers of West Antarctica have passed the ‘point of no
return’ as the southern hemisphere gets warmer. Tim Radford from Climate News Network reports.




THE GLACIERS OF THE WEST ANTARCTIC may be in irreversible retreat,
according to the evidence of satellite data analysed by scientists at
the US space agency NASA.




The study of 19 years of data, due to be reported in the journal Geophysical Research Letters,
confirms the ominous news that the southern hemisphere is not just
warming  — it is that it is warming in a way that speeds up the melting
of the West Antarctic glaciers.




Long ago, glaciologists began to wonder whether the West Antarctic ice sheet was
inherently unstable. The water locked in the ice sheet in the Amundsen
Sea region – the area the NASA researchers examined – is enough to raise
global sea levels by more than a metre. If the whole West Antarctic ice
sheet turned to water, sea levels would rise by at least five metres.








Steady change



What the latest research has revealed is a steady change in the
glacial grounding line, which is the point in a glacier’s progress
towards the sea where its bottom no longer scrapes on rock but starts to
float on water. It is in the nature of a glacier to flow towards the
sea, and at intervals to calve an iceberg that will then float away and
melt. The puzzle for scientists has been to work out whether this
process has begun to accelerate.




Eric Rignot, a glaciologist at the NASA Jet Propulsion Laboratory and the University of California, Irvine, thinks it has. He and his research partners believe that European Space Agency satellite
data has recorded the points at which the grounding lines can be
identified in a series of West Antarctic glaciers monitored between 1992
and 2011, as the glaciers flexed in response to the movement of tides.




All the grounding lines had retreated upstream, away from the sea
— some by more than 30 kilometres. The grounding lines are all buried
under hundreds of metres of ice, and are difficult to identify.




The shift of ice in response to tidal ebb and flow provides an
important clue. It also signals an acceleration of melting, because it
is the glacier’s slowness that keeps the sea levels static. As it inches
towards the sea, there is time for more snow and ice to pile up behind
it.







Speeds up



But if the water gets under the ice sheet, it reduces friction and
accelerates the passage of frozen water downstream. So the whole glacier
speeds up, and the grounding line moves yet further upstream.




Something similar has been reported from the glaciers of Greenland. And
once the process starts, there is no obvious reason why it would stop.
The melting will still be slow, but the latest evidence indicates that
it seems to be inexorable.




Says Prof Rignot:




We’ve passed the point of no return. At current melt rates, these glaciers will be history within a few hundred years.



The collapse of this sector of West Antarctica appears to be
unstoppable. The fact that the retreat is happening simultaneously over a
large sector suggests it was triggered by a common cause, such as an
increase in the amount of ocean heat beneath the floating sections of
the glaciers. At this point, the end of this sector appears to be
inevitable.





~ Climate News Network



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This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Australia License

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