Steve Cole
Headquarters, Washington
202-358-0918
stephen.e.cole@nasa.gov
Maria-Jose Vinas
Goddard Space Flight Center, Greenbelt, Md.
301-614-5883
mj.vinas@nasa.gov
RELEASE: 13-141
NASA SATELLITE DATA HELP PINPOINT GLACIERS' ROLE IN SEA LEVEL RISE
WASHINGTON -- A new study of glaciers worldwide using observations
from two NASA satellites has helped resolve differences in estimates
of how fast glaciers are disappearing and contributing to sea level
rise.
The new research found glaciers outside of the Greenland and Antarctic
ice sheets, repositories of 1 percent of all land ice, lost an
average of 571 trillion pounds (259 trillion kilograms) of mass every
year during the six-year study period, making the oceans rise 0.03
inches (0.7 mm) per year. This is equal to about 30 percent of the
total observed global sea level rise during the same period and
matches the combined contribution to sea level from the Greenland and
Antarctica ice sheets.
The study compares traditional ground measurements to satellite data
from NASA's Ice, Cloud, and Land Elevation Satellite (ICESat) and
Gravity Recovery and Climate Experiment (GRACE) missions to estimate
ice loss for glaciers in all regions of the planet. The study period
spans 2003 to 2009, the years when the two missions overlapped.
"For the first time, we have been able to very precisely constrain how
much these glaciers as a whole are contributing to sea level rise,"
said Alex Gardner, Earth scientist at Clark University in Worcester,
Mass., and lead author of the study. "These smaller ice bodies are
currently losing about as much mass as the ice sheets."
The study was published Thursday in the journal Science.
ICESat, which stopped operating in 2009, measured glacier change
through laser altimetry, which bounces lasers pulses off the ice
surface to inform the satellite of changes in the height of the ice
cover. ICESat's successor, ICESat-2, is scheduled to launch in 2016.
GRACE, still operational, detects variations in Earth's gravity field
resulting from changes in the planet's mass distribution, including
ice displacements.
The new research found all glacial regions lost mass from 2003 to
2009, with the biggest ice losses occurring in Arctic Canada, Alaska,
coastal Greenland, the southern Andes and the Himalayas. In contrast,
Antarctica's peripheral glaciers -- small ice bodies not connected to
the main ice sheet -- contributed little to sea level rise during
that period. The study builds on a 2012 study using only GRACE data
that also found glacier ice loss was less than estimates derived from
ground-based measurements.
Current estimates predict all the glaciers in the world contain enough
water to raise sea level by as much as 24 inches (about 60
centimeters). In comparison, the entire Greenland ice sheet has the
potential to contribute about 20 feet (about 6 meters) to sea level
rise and the Antarctic ice sheet just less than 200 feet (about 60
meters).
"Because the global glacier ice mass is relatively small in comparison
with the huge ice sheets covering Greenland and Antarctica, people
tend to not worry about it," said study co-author Tad Pfeffer, a
glaciologist at the University of Colorado in Boulder. "But it's like
a little bucket with a huge hole in the bottom: it may not last for
very long, just a century or two, but while there's ice in those
glaciers, it's a major contributor to sea level rise."
To make ground-based estimates of glacier mass changes, glaciologists
perform on-site measurements along a line from a glacier's summit to
its edge. Scientists extrapolate these measurements to the entire
glacier area and carry them out for several years to estimate the
glacier's overall mass change over time. While this type of
measurement does well for small, individual glaciers, it tends to
overestimate ice loss when the findings are extrapolated to larger
regions, such as entire mountain ranges.
"Ground observations often can only be collected for the more
accessible glaciers, where it turns out thinning is occurring more
rapidly than the regional averages," Gardner said. "That means when
those measurements are used to estimate the mass change of the entire
region, you end up with regional losses that are too great."
GRACE does not have fine enough resolution and ICESat does not have
sufficient sampling density to study small glaciers, but the two
satellites' estimates of mass change for large glaciered regions
agree well, the study concluded.
"We now have a lot more data for the glacier-covered regions because
of GRACE and ICESat," said Gardner. "Without having these independent
observations, there was no way to tell that the ground observations
were biased."
The research involved 16 researchers from 10 countries, with major
contributions from Clark University, the University of Michigan,
Scripps Institution of Oceanography in San Diego, Trent University in
Ontario, the University of Colorado at Boulder and the University of
Alaska Fairbanks.
For images of glaciers studied for this paper, visit:
http://go.nasa.gov/15JSmzl For information about NASA and agency programs, visit:
http://www.nasa.gov
