Ice melt picture ‘bleak’
The melting of ice on Greenland will result in 27cm of sea-level rise around the world irrespective of our response to the threat posed by climate change, a study suggests.
The findings, which have been drawn from an assessment of the yearly balance between thawing and freezing on the ice cap, imply that on the basis of the present rate of warming alone, more than 3% of the ice is destined to melt.
The estimate, published in the journal Nature Climate Change, paints a bleaker picture than that predicted by the Intergovernmental Panel on Climate Change by the end of the century.
Professor Jason Box, from the National Geological Survey of Denmark and Greenland, said that in his view it was a lower limit of what could be expected. ‘‘It is a very conservative, rockbottom minimum. Realistically, we will see this figure more than double within this century,’’ he said.
‘‘In the foreseeable scenario that global warming will only continue, the contribution of the Greenland ice sheet to sea-level rise will only continue increasing.’’
To come up with the estimate, he and his colleagues used a different method from the modelling applied previously. Instead of trying to understand the complex dynamics of ice flow, they looked at 20 years of data on the snow line, the zone between the area that is always frozen and the area that melts in summer.
During the winter the ice cap gains mass and during the summer it loses it. If temperatures are completely stable, then it settles into an equilibrium where the two match each other over a 12-month period.
Since the 1980s, with changing temperatures it has been losing more mass in summer than it gains in winter. This response is lagged, though: it takes many years to adjust to fluctuations in temperature.
This means that even if today’s warming of more than 1C stabilised, the ice cap would take decades to catch up.
The new work looked at real data on the lowest point where snow that landed in the winter was able to survive the summer. From this, the researchers calculated the ‘‘disequilibrium’’, and from that how much ice needed to be lost before the annual thaw and freeze would be in balance again. Given that the findings were at a lower limit of their estimates, they were, the scientists wrote, ‘‘ an ominous prognosis for Greenland’s trajectory through a 21st century of warming’’.
‘‘It is a very conservative, rockbottom minimum. Realistically, we will see this figure more than double within this century.’’ Professor Jason Box National Geological Survey of Denmark and Greenland