Clearest evidence yet of polar ice losses

An international team of satellite and climate experts including physicists  of Utrecht University, has produced the most accurate assessment of ice losses from Antarctica and Greenland to date, ending 20-years of uncertainty. In a landmark study, published on 30 November in the journal Science, the researchers show that melting of the Antarctic and Greenland ice sheets has contributed 11 millimetres to global sea levels since 1992. This amounts to one fifth of all sea level rise over the survey period.

The study also found differences in the pace of change at each pole. About two thirds of the ice loss was from Greenland, and the remainder was from Antarctica. Although the ice sheet losses fall within the range reported by the IPCC in 2007, the spread of the IPCC estimate was so broad that it was not clear whether Antarctica was growing or shrinking. The new estimates are a vast improvement (more than twice as accurate) thanks to the inclusion of more satellite data, and confirm that both Antarctica and Greenland are losing ice.

Ice sheet melting has increased

Importantly, the study also shows that the combined rate of ice sheet melting has increased over time and, altogether, Greenland and Antarctica are now losing more than three times as much ice (equivalent to 0.95 mm of sea level rise per year) as they were in the 1990s (equivalent to 0.27 mm of sea level rise per year).

The Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) is a collaboration between 47 researchers from 26 laboratories, and was supported by the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA).

Led by Professor Andrew Shepherd at the University of Leeds and Dr Erik Ivins at NASA’s Jet Propulsion Laboratory, the study combines observations from 10 different satellite missions to develop the first consistent measurement of polar ice sheet changes.

The researchers were able to reconcile the differences between dozens of earlier ice sheet studies through careful use of matching time periods and survey areas, and by combining measurements collected by different types of satellites.

Significant and accelerating

Professor Michiel van den Broeke, leader of the Utrecht University research group that contributed to the study, says: "This result unambiguously shows that the contribution of both large ice sheets to current sea level rise is significant and accelerating."

Commenting on the findings, Professor Richard Alley, a climate scientist at Penn State University who was not involved in the study, said: "This project is a spectacular achievement. The data will support essential testing of predictive models, and will lead to a better understanding of how sea-level change may depend on the human decisions that influence global temperatures."

‘A reconciled estimate of ice sheet mass balance’ by Prof Shepherd et al is published in Science on 30 November 2012, DOI: 10.1126/science.1228102.

Co-authors of Utrecht Univerity: prof.dr. Michiel van den Broeke (leader of the research group) and dr. Willem Jan van de Berg with their PhD students Jan van Angelen, Jan Lenaerts en Stefan Ligtenberg, Institute for Marine and Atmospheric Research Utrecht, Faculty of Science.