Melting Greenland Ice Sheet Spells More Bad News On Climate Change
Pastor Dale Morgan
Melting Greenland Ice Sheet Spells More Bad News On Climate Change*
Paris (AFP) Sep 21, 2006
The Greenland icesheet, the second largest single store of frozen
freshwater in the world, is melting faster than previous estimates,
according to a study that adds to grim news about global warming. In
2001, the UN's top scientific forum on global warming projected that the
thick slab of ice that covers most of Greenland would melt only slightly
during the 21st century.
But a study published on Thursday in the British weekly journal Nature
calculates that the rate of Greenland ice loss increased by 250 percent
between May 2004 and April 2006 compared with the two years between
April 2002 and April 2004.
Ice is now being lost at around 248 cubic kilometers (59.5 cu. miles)
per year -- equivalent to a global sea level rise of about 0.5mm (0.02
inches) per year.
Taking other accelerating factors into account, such as major losses at
two big glaciers in recent years, Greenland is contributing almost 0.7mm
a year, said Tavi Murray, an environmentalist at Britain's Swansea
University.
This is a significant rise compared to the 2001 estimates by the UN's
Intergovernmental Panel on Climate Change (IPCC).
If averaged out for the 110-year span, those estimates would give
Greenland a contribution of around 0.5mm (0.02 inches) per year of the
planetary rise in sea level. But the nature of global warming means that
the rise would occur especially towards the end of the century -- not
near its start, as the new paper implies.
The new study says the central portion of the icesheet, at altitudes
above 1,500m (4,875 feet), is thickening, thanks to increased snowfall.
But the margins of the icesheet, which are at lower altitudes and are
thinner, are eroding fast, especially in the southeast and northeast of
Greenland, where glaciers are spewing ice into the sea faster than before
The research, which used computer models and satellite measurements made
by NASA's two GRACE satellites, was carried out by Isabella Velicogna
and John Wahr of the University of Colorado.
The pair acknowledge that their work spans observations only four years,
and climate science often needs to look at decades before drawing firm
conclusions about longer trends.
However, it concurs with a separate study on Greenland that was
published in August by the US journal Science.
It also comes less than a week after a paper, also published in Science,
found that year-round sea ice in the Arctic shrank by one seventh
between 2004 and 2005.
Loss of sea ice does not affect global sea levels. Ice that floats in
the water displaces its own volume.
However ice that is on land, as an icesheet, glacier or permanent
snowcap, adds to sea level when it melts and runs off.
Retreating ice cover also creates a vicious circle.
Ice, being white, reflects the Sun's rays. Less ice therefore means the
sea warms, which in turn accelerates the shrinkage.
In addition, melting polar ice sends large volumes of dense water into
the North Atlantic, which slows a conveyor belt of warm water that flows
up from the tropics and gives northwestern Europe its balmy climate.
If this belt were ever stopped or braked, the western part of Europe
could be plunged into a mini-Ice Age, according to some theories.
Greenland is second to Antarctica as a single source of land ice. If the
Greenland icesheet melted entirely, that would boost sea levels by seven
metres (22.75 feet), although this apocalyptic scenario is discounted
unless global warming becomes unstoppable.
The IPCC estimated in 2001 that between 1990 and 2100, the mean global
sea level would rise about 480 millimeters (19.2 inches) in a range from
90mm to 880mm (3.6 to 35.2 inches).
At the bottom of this range, Greenland would not contribute anything to
the increase; at the top of the range, it would contribute around 90mm
(3.6 inches) over the 110 years.
These ranges are based on how fast greenhouse gases, which trap solar
heat, build in the atmosphere and help drive up Earth's surface temperature.
Source: Agence France-Presse