Satellite shows Greenland's ice sheets getting thicker
All down to more snow falling, it seems
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While the edges of the glaciers are melting, the ice
sheets in Greenland's interior are getting thicker, according to
satellite data collected over the last 11 years. On average the ice
sheets have got thicker by about six centimetres each year, the
researchers say.
The researchers, based at Norway's Nansen Environmental and Remote
Sensing Center (NERSC), say that this is probably because snowfall in
the region has increased, due to a weather pattern known as the North
Atlantic Oscillation (NAO).
The research was conducted using the European Space Agency's ERS
satellites. These carry radar altimeters that send 1800 radar pulses to
Earth each second, and record how long they take to return to the
satellite. The sensor can time this journey down to the nanosecond, ESA
says, meaning that the instrument is accurate to within two centimetres.
In total tens of millions of data points were collected. The results
were then compared to the known fluctuations in the NAO over the
period. The researchers found a strong relationship between changes in
the height of the ice sheet and the strong positive and negative phases
of the NAO.
Professor Ola Johannessen of NERSC says that the results suggest
that the role of the NAO in ice thickness is more significant than
previously thought, making it something of a wildcard in climate
modelling.
"There is clearly a need for continued monitoring using new
satellite altimeters and other observations, together with numerical
models to calculate the Greenland Ice Sheet mass budget," Johannessen
commented.
It is just the kind of work that the CryoSat mission would have taken on, had it not been lost during its launch.
The NAO was first identified in the 1920's, and is an imbalance in
atmospheric masses between the high pressure of the subtropicals the
low pressure of the northern polar regions. The size of the difference
influences the weather across the whole of the northern hemisphere, and
is much more important in the winter months.
Finding out whether or not the Greenland ice sheet is shrinking
overall is important because it is so large. While plenty of data has
been collected on the retreating glaciers and thinning edges of the ice
sheets, much less in known about the interior.
If the Greenland ice sheet were to melt entirely, it would raise
global sea levels by seven metres. The addition of such a large
quantity of fresh water to the oceans would also disrupt familiar ocean
currents, such as the gulf stream, which could have a huge knock on
effect on weather systems.
The research was published in Science Express late last month. ®
