At both poles, ice melt is speeding up

U. LEEDS (UK) / CALTECH (US) — Ice sheet melting has increased over time and, altogether, Greenland and Antarctica are now losing more than three times as much ice as they were in the 1990s.

“The rate of ice loss from Greenland has increased almost five-fold since the mid-1990s,” says Erik Ivans of NASA’s Jet Propulsion Lab at the California Institute of Technology (Caltech).

“In contrast, while the regional changes in Antarctic ice over time are sometimes quite striking, the overall balance has remained fairly constant—at least within the certainty of the satellite measurements we have to hand,” says Ivans, who led the project with Professor Andrew Shepherd of the University of Leeds.



Today in Science, the researchers show that melting of the Antarctic and Greenland ice sheets has contributed 11.1 millimeters 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.

Altogether, Greenland and Antarctica are now losing the equivalent to 0.95 mm of sea level rise per year, versus the equivalent to 0.27 mm of sea level rise per year in the 1990s.

Although the ice sheet losses fall within the range reported by the Intergovernmental Panel on Climate Change (IPCC) in 2007, the spread of the IPCC estimate was so broad that it was not clear whether Antarctica was growing or shrinking.

The study combines observations from 10 different satellite missions to develop the first consistent measurement of polar ice sheet changes.

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.

The researchers were able to reconcile the differences among 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.

“The success of this venture is due to the cooperation of the international scientific community, and due to the provision of precise satellite sensors by our space agencies,” says Shepherd.

“Without these efforts, we would not be in a position to tell people with confidence how the Earth’s ice sheets have changed, and to end the uncertainty that has existed for many years.”

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

Sources: University of Leeds, JPL/Caltech