[Mb-civic] An article for you from an Economist.com reader.

Mon Feb 20 19:38:23 PST 2006

- AN ARTICLE FOR YOU, FROM ECONOMIST.COM -

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Michael Butler (michael at intrafi.com) wants you to see this article on Economist.com.

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GREENLAND'S LESS-ICY MOUNTAINS
Feb 16th 2006  

Evidence that sea levels will rise more rapidly than previously thought

THE biggest unknown factor in making predictions of rising sea levels
in response to global warming is the role played by the massive ice
sheets that cover Antarctica and Greenland. If parts of these were to
melt, the sea level would rise far more rapidly than in the past (when
much of the rise has been because water expands as it warms). Until
recently, it was thought that any melting going on in the ice caps was
fairly gentle. But four years ago a small Antarctic ice shelf suddenly
disintegrated, leading many people to think again. This week brings
further pause for thought, with alarming news from the other end of the
world.

In the past, researchers have used data from planes that fly
criss-crossing paths over Greenland to assess the extent of its ice
sheets. It is a mammoth undertaking. The Greenland ice sheets cover
1.7m square km--an area only a little smaller than Mexico--and the
surface of the ice rises to an altitude of 3km. Not surprisingly, the
flights leave some areas unmonitored, and so computer models have been
used to fill in the blanks and to estimate the role played by these
patches. The conclusion, combining data and models, was that the
Greenland ice sheet is relatively stable in the centre, but thinning
slowly at the edges.

That conclusion, however, has been questioned by Eric Rignot of the
California Institute of Technology and Pannir Kanagaratnam of the
University of Kansas. They used satellite data concentrating on
Greenland's coastline to examine how fast the thinning is happening,
and they have found that the flow-speed of 12 glaciers, which together
account for about half the discharge of water from the ice sheet, is
increasing--and fast. 

According to their calculations, published in this week's SCIENCE and
to be presented in more detail on February 18th at a meeting of the
American Association for the Advancement of Science, SCIENCE's
publisher, the speed at which the glaciers flow has doubled to 12km a
year. As a result, the volume of ice falling into the sea from
Greenland has also doubled over the past decade.

That is worrying enough. But Dr Rignot and Dr Kanagaratnam also found
that the Greenland ice sheet experienced a greater area of surface
melting in 2002 and 2005 than at any previous time since records began
in 1979. Most of this has been in the south of the island, which is
where the accelerating glaciers lie. Water flowing from the surface
could ease the passage of the glaciers into the sea. Taking both
factors into account, the contribution made by the Greenland ice sheet
to the rise in global sea levels has increased from 0.23mm a year in
1996 to 0.57mm in 2005. 

On top of this, since glacial ice contains no salt, the water formed
when it melts is fresh. Such an increased flow of fresh water from
Greenland could, according to the best available models of ocean
circulation, change the way that currents flow in the North Atlantic,
to the detriment of the Gulf Stream, the current that keeps north-west
Europe warmer than its latitude suggests it should be. In the context
of a report late last year that the Gulf Stream may, indeed, be
weakening, the news from Greenland is doubly disturbing.

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