Greenland ice sheet begins melting again

(18 Nov 2015) LEAD IN:
The annual summer melting of the Greenland ice sheet has once again resulted in a greater-than-average melt, according to scientists monitoring man-made climate change.
Although the ice sheet isn't in danger of completely disappearing in the coming centuries, scientists warn that even minor increases in melting can cause devastating sea level rises.
The Greenland ice sheet, huge mountains of ice and snow reaching 3,000 metres (9843 feet) at its peak.
It's the second largest mass of ice on the planet - after the Antarctica ice sheet - covering 80 percent of the island of Greenland.
The numbers are so large they almost seem to lose meaning - the total mass of the ice is estimated to be 2,900,000 cubic kilometres.
But the ice sheet is shrinking, albeit very slowly.
This is partly due to melting and partly to the glacier's calving into the ocean, a natural process that's happening faster than before. Calving is where huge chunks of ice break off and form icebergs.
Scientists from the Danish Meteorological Institute (DMI) collect data from satellites and research stations around Greenland to produce daily estimates of whether the Greenland ice sheet is losing or gaining mass.
This year their data has shown that overall, the 2015 season has been close to average with some slightly unusual features.
In just one week in early July, the ice sheet lost about 30% of what is normally melted off in an entire melt season.
A cold period in August accompanied by an early snowfall ended melting in many parts of Greenland.
The US-based National Snow and Ice Data Centre (NSIDC) also run models estimating the Greenland ice sheet melting and mass.
Their data indicates that melt extent across the whole of Greenland was above average in 2015 and that in July over 50% of the ice sheet experienced surface melting.
DMI has estimated that since 1840, melting has increased by 60 percent and glacier calving by about 40 percent.
At the same time, snow fall has increased by 12-20 percent, offsetting some - but not all - of the loss.
Most of the melting increase has occurred in the last decade, with 2012 being the most extreme melting year so far.
NSIDC figures show that the rapid increase in total melt area across the country in July 2015, was at a rate comparable to the record melt year 2012.
Ruth Mottram, is a climate scientist at DMI, specialising in running the Greenland ice sheet models.
"Sometimes only for short periods, but that short period - if it happens in the middle of July or beginning of August - can be extremely significant for the whole ice sheet. So we can see a large amount of melt happening during a short period of time and that just changes the entire surface of the ice sheet," she explains.
According to the Intergovernmental Panel on Climate Change (IPCC), if the whole of Greenland's ice sheet were to melt, global sea levels would rise around seven metres (23 feet).
If current melting continues, the ice sheet will eventually be lost. But it will take a long time, according to Mottram.
"I would say that we have observations from satellites that show that the ice sheet in general is losing more ice every year than it is gaining, it is not in a state where it's going to grow, it's in a state where it's going to gradually shrink," she says.
"If those rates continue and if those rates start to accelerate, then we could see the ice sheet being lost. But it will still take hundreds of years, if not thousands of years, for the entire ice sheet to disappear. It's not just going to vanish overnight."
"Yes, currently the ice sheet is getting smaller. So, it's not just getting smaller because it's melting more, but also because it's flowing faster," he says.

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