After two decades of satellite observations, an international team of experts brought together by ESA and NASA has produced the most accurate assessment of ice losses from Antarctica and Greenland to date. This study finds that the combined rate of ice sheet melting is increasing.
The new research shows that melting of the Antarctic and Greenland ice sheets has added 11.1 mm to global sea levels since 1992.
This amounts to about 20% of all sea-level
rise over the survey period.
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
Intergovernmental Panel on Climate Change in 2007, the spread of the estimate
at that time 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.
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.
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The 47 experts
combined observations from 10 different satellite missions to reconcile the differences between dozens of earlier ice sheet
studies and produce the first consistent measurement of polar ice sheet
changes. Earth observation satellites are key to monitoring the polar ice
because they carry instruments that measure changes in the thickness of the ice
sheets, fluctuations in the speed of the outlet glaciers and even small changes
in Earth’s gravity field caused by melting ice.
As outlined in the
paper ‘A
Reconciled Estimate of Ice Sheet Mass Balance’ published today in Science, the
researchers carefully matched time periods and survey areas, and combined
measurements from European, Canadian, American and Japanese satellites. The
measurement were acquired by instruments such as the radar altimeters and
synthetic aperture radars flown on ESA’s ERS-1, ERS-2 and Envisat missions from
1991.
“The success of
this venture is due to the cooperation of the international scientific
community, and to the provision of precise satellite sensors by our space
agencies,” said Professor Andrew Shepherd from the University of Leeds and one
of the leaders of the study.“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.”
The study also found variations in the pace of Ice sheet in Antarctica and
Greenland.
“The rate of ice
loss from Greenland has increased almost five-fold since the mid-1990s.
“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,” said co-leader of
the study Dr Erik Ivins from NASA’s Jet Propulsion Laboratory.
The Ice Sheet Mass
Balance Inter-comparison Exercise is a collaboration between 47 researchers
from 26 laboratories, supported by ESA and NASA.
Europe’s Global Monitoring for
Environment and Security programme will continue to monitor changes in the
polar ice sheets during the coming decades, with the SAR and radar altimeter
sensors on the Sentinel-1 and Sentinel-3 satellite series, scheduled to be
launched from 2013 onwards.(ESA news, nov. 30,2012)
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