Ice loss thrice more than estimated

The combined rate of melting for the ice sheets covering Greenland and Antarctica has increased during the last 20 years, an international team of experts has found in a landmark study.

The team includes 47 researchers from 26 laboratories and was supported by Nasa and the European Space Agency (ESA). They have combined data from multiple satellites and aircraft to produce the most comprehensive and accurate assessment to date of ice sheet losses in Greenland and Antarctica and their contributions to sea level rise.

Together, these ice sheets are losing more than three times as much ice each year (equivalent to sea level rise of 0.04 inches or 0.95 millimeters) as they were in the 1990s (equivalent to 0.01 inches or 0.27 millimeters). About two-thirds of the loss is coming from Greenland, with the rest from Antarctica.

This rate of ice sheet losses falls within the range reported in 2007 by the Intergovernmental Panel on Climate Change (IPCC). The spread of estimates in the 2007 IPCC report was so broad, however, it was not clear whether Antarctica was growing or shrinking.

The new estimates, which are more than twice as accurate because of the inclusion of more satellite data, confirm both Antarctica and Greenland are losing ice. Combined, melting of these ice sheets contributed 0.44 inches (11.1 millimeters) to global sea levels since 1992. This accounts for one-fifth of all sea level rise over the 20-year survey period. The remainder is caused by the thermal expansion of the warming ocean, melting of mountain glaciers and small Arctic ice caps, and groundwater mining.

The study was produced by an international collaboration — the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) — that combined observations from 10 satellite missions to develop the first consistent measurement of polar ice sheet changes.

The researchers reconciled differences among dozens of earlier ice sheet studies by carefully matching observation periods and survey areas. They also combined measurements collected by different types of satellite sensors, such as ESA's radar missions, Nasa's Ice and Cloud and land Elevation Satellite (ICESat).

“Both ice sheets appear to be losing more ice now than 20 years ago, but the pace of ice loss from Greenland is extraordinary, with nearly a five-fold increase since the mid-1990s. In contrast, the overall loss of ice in Antarctica has remained fairly constant with the data suggesting a 50-percent increase in Antarctic ice loss during the last decade,” a researcher said.