A new study has come up with the most accurate estimate yet for the melting of the polar ice sheets, possibly ending decades of uncertainty about whether the sheets will melt further or actually gain mass in the face of climate change.
The scientists published their findings in the journal Science. The ice sheets in Antarctica and Greenland have been melting at an ever-quickening pace. The melting has contributed to an 11-millimeter rise in the oceans. The two polar regions are losing mass three times faster than 20 years ago and Greenland is shedding ice at five times the rate observed in the early 1990s.
This latest study uses data from 32 years of ice-sheet simulations and 20 years of satellite data. Some scientists had expected that warmer air would increase the snowfall over Antarctica, which would offset the increased ice loss from Greenland caused by warmer seas. However, both of these ice sheets are losing mass at an alarming rate, as ice streams speed up and bigger icebergs are discharged in to the ocean.
Previous estimates have not always been consistent. In this study, scientists used four techniques to determine whether the ice caps are gaining or losing mass. Two techniques involve lasers and radars on satellites to measure changes in the surface elevation of the ice. Another method uses input-output modeling to represent regional changes in snowfall and ice melt. The last measures changes in the ice-sheet mass from space using the Gravity Recovery and Climate Experiment (GRACE) satellites.
The team of 47 international experts analyzed the data from almost 30 previous ice-sheet studies, including 20 years of data from 10 different satellite missions and 32 years of model data on surface mass balance. This means that the results are supposed to be two to three times more accurate than the last IPCC report.
There are still some uncertainties for Antarctica, which isn’t losing ice as rapidly as indicated by many recent studies. Snowfall in east Antarctica is also compensating for some of the melting in Antarctica, but not all of it.
It’s not yet clear how these trends will evolve in the future, whether such losses will continue to decline, whether they will level off or accelerate.
Reference: “A Reconciled Estimate of Ice-Sheet Mass Balance” by Andrew Shepherd, Erik R. Ivins, Geruo A, Valentina R. Barletta, Mike J. Bentley, Srinivas Bettadpur, Kate H. Briggs, David H. Bromwich, René Forsberg, Natalia Galin, Martin Horwath, Stan Jacobs, Ian Joughin, Matt A. King, Jan T. M. Lenaerts, Jilu Li, Stefan R. M. Ligtenberg, Adrian Luckman, Scott B. Luthcke, Malcolm McMillan, Rakia Meister, Glenn Milne, Jeremie Mouginot, Alan Muir, Julien P. Nicolas, John Paden, Antony J. Payne, Hamish Pritchard, Eric Rignot, Helmut Rott, Louise Sandberg Sørensen, Ted A. Scambos, Bernd Scheuchl, Ernst J. O. Schrama, Ben Smith, Aud V. Sundal, Jan H. van Angelen, Willem J. van de Berg, Michiel R. van den Broeke, David G. Vaughan, Isabella Velicogna, John Wahr, Pippa L. Whitehouse, Duncan J. Wingham, Donghui Yi, Duncan Young and H. Jay Zwally, 30 November 2012, Science.