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. ®
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