Nasa,CJE – An international team of experts supported by NASA and

the European Space Agency (ESA) has 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.

In a landmark study published Thursday in the journal Science, 47
researchers from 26 laboratories report the combined rate of melting
for the ice sheets covering Greenland and Antarctica has increased
during the last 20 years. 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, Cloud and land
Elevation Satellite (ICESat) and the NASA/German Aerospace Center’s
Gravity Recovery and Climate Experiment (GRACE).

“What is unique about this effort is that it brought together the key
scientists and all of the different methods to estimate ice loss,”
said Tom Wagner, NASA’s cryosphere program manager in Washington.
“It’s a major challenge they undertook, involving cutting-edge,
difficult research to produce the most rigorous and detailed
estimates of ice loss from Greenland and Antarctica to date. The
results of this study will be invaluable in informing the IPCC as it
completes the writing of its Fifth Assessment Report over the next

Professor Andrew Shepherd of the University of Leeds in the United
Kingdom coordinated the study, along with research scientist Erik
Ivins of NASA’s Jet Propulsion Laboratory in Pasadena, Calif.
Shepherd said the venture’s success is because of the cooperation of
the international scientific community and the precision of various
satellite sensors from multiple space agencies.

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

The study found variations in the pace of ice sheet change in
Antarctica and Greenland.

“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,” Ivins said. “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.”

Screen shot of animation of Arctic sea ice from January 1 through September 12Animation of Arctic sea ice from January 1 through September 12
Credit: NASA’s Goddard Space Flight Center Scientific Visualization Studio
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Screen shot of animation showing how polar ice reflects light from the sunAnimation showing how polar ice reflects light from the sun. As this ice begins to melt, less sunlight gets reflected into space. It is instead absorbed into the oceans and land, raising the overall temperature, and fueling further melting.
Credit: NASA’s Conceptual Image Lab
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