Forty-seven scientists funded by two space organisations have analysed data from ten satellites to conclude that both Greenland and Antarctica are losing ice at an accelerating rate. Science magazine published their findings today.
The consensus is that the loss of ice sheets on Greenland and Antarctica has contributed to an 11 millimetre sea level rise over the past 20 years. This is roughly one fifth of the global sea level rise, the rest results from thermal expansion of the oceans and contributions from other melting glaciers on the continents.
About two thirds of the ice loss is attributed to Greenland (-169 +/- 54 cubic kilometre per year) and one third to Antarctica (-79 +/- 58 km3/year) between 1992 and 2011.
The study also shows that ice sheet loss is accelerating. Both land ice masses together are currently losing mass at three times the rate they did in 1992. Combined, they contribute to approximately 1 millimetre of sea level rise every year.
Of the two, the Greenland ice loss has accelerated the most. The rate of ice loss is now five times that of the mid 1990’s.
Ice sheet loss on Antarctica has been less clear. Different methods of tracking ice sheet loss have produced dissimilar results. Space organisations ESA and NASA have taken the initiative to assemble 47 researchers from 26 institutions to analyse the outcome of ten different satellites to find out if a consistent estimation of the mass loss on Antarctica could be reached.
The result of this Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) with main author Professor Andrew Shepherd of the University of Leeds, has been published* in Science today.
Dutch contributionDutch contribution
Dutch contribution
Dr. Ernst Schrama (Aerospace Engineering) is one of the authors. The study compared satellite data on meteorology, gravity change and volume to determine ice sheet loss.
Schrama himself worked on the gravity data from the GRACE satellites. “Until recently we couldn’t disentangle the influence of ice sheet mass loss and geological uplifting on Antarctica.” he says. ‘Uplifting’ is the very slow rebound of the earth’s surface after the thawing of the ice masses from the last Ice Age.
“Uplifting and ice sheet loss both influence the local gravity change as well as the height of the ice sheet. We’ve used new geophysical models describing the uplifting in order to evaluate the mass balance. This led to a melting rate half the previous estimate for Antarctica. Not 180 but 80 to 90 cubic kilometres per year for Antarctica.” says Schrama.
The new estimates for ice sheet mass balance will be included in the next UN climate council (IPCC) Assessment Report number 5 (AR5) due out next year.
The other Dutch group involved in the IMBIE project is that of Professor Michiel van den Broeke from the Institute for Marine and Atmospheric Research (IMAO) from Utrecht University who studied the meteorological data to assess the ice sheet mass balances.
Researchers are worried that future monitoring the ice sheet loss will be hampered by upcoming shortage in satellite data. The GRACE mission, for example, is on its last legs, but will hopefully be succeeded in 2017.
* A reconciled estimate of ice sheet mass balance, Prof. Andrew Shepherd et al, Science, 30 November 2012, doi:10.1126/science.1228102
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