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| [PHOTO: Christine Zenino / Flickr / CC BY 2.0] |
New York/Washington: 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 year."
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."