NASA Satellites Measure and Monitor Sea Level
For the first time, NASA has the tools and expertise to
understand the rate at which sea level is changing, some of
the mechanisms that drive those changes and the effects that
sea level change may have worldwide.
Image right: The observed rate of sea level increase year over year, in millimeters. Image credit: NASA.
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"It's estimated that more than 100 million lives are potentially
impacted by a one-meter (3.3-foot) increase in sea level," said
Dr. Waleed Abdalati, head of the Cryospheric Sciences Branch at
NASA's Goddard Space Flight Center, Greenbelt, Md. "When you
consider this information, the importance of learning how and
why these changes are occurring becomes clear," he added.
Although scientists have directly measured sea level since the
early part of the 20th century, it was not known how many of the
observed changes in sea level were real and how many were related
to upward or downward movement of the land. Now satellites have
changed that by providing a reference by which changes in ocean
height can be determined regardless of what the nearby land is
doing. With new satellite measurements, scientists are able to
better predict the rate at which sea level is rising and the
cause of that rise.
"In the last 50 years sea level has risen at an estimated rate
of .18 centimeters (.07 inches) per year, but in the last 12 years
that rate appears to be .3 centimeters (.12 inches) per year. Roughly
half of that is attributed to the expansion of ocean water as it has
increased in temperature, with the rest coming from other sources,"
said Dr. Steve Nerem, associate professor, Colorado Center for
Astrodynamics Research, University of Colorado, Boulder.
Another source of sea level rise is the increase in ice melting.
Evidence shows that sea levels rise and fall as ice on land grows
and shrinks. With the new measurements now available, it's possible
to determine the rate at which ice is growing and shrinking.
"We've found the largest likely factor for sea level rise is
changes in the amount of ice that covers the Earth. Three-fourths
of the planet's freshwater is stored in glaciers and ice sheets or
the equivalent of about 67 meters (220 feet) of sea level," said Dr.
Eric Rignot, principal scientist for the Radar Science and Engineering
Section at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "Ice
cover is shrinking much faster than we thought, with over half of
recent sea level rise due to the melting of ice from Greenland,
West Antarctica's Amundsen Sea and mountain glaciers," he said.
Additionally, NASA scientists and partner researchers now are able
to measure and monitor the world's waters globally in a sustained
and comprehensive way using a combination of satellite observations
and sensors in the ocean. By integrating the newly available satellite
and surface data, scientists are better able to determine the causes and
significance of current sea level changes.
"Now the challenge is to develop an even deeper understanding of what is
responsible for sea level rise and to monitor for possible future changes.
That's where NASA's satellites come in, with global coverage and ability
to examine the many factors involved," said Dr. Laury Miller, chief of
the National Oceanic and Atmospheric Administration Laboratory for
Satellite Altimetry, Washington, D.C.
NASA works with agency partners such as the National Oceanic and Atmospheric
Administration and the National Science Foundation to explore and understand
sea level change. Critical resources that NASA brings to bear on this
issue include such satellites as:
-- Topex/Poseidon and Jason, the U.S. portions of which are managed by JPL,
which use radar to map the precise features of the oceans' surface,
measuring ocean height and monitoring ocean circulation;
-- Ice, Cloud and Land Elevation Satellite (IceSat), which studies
the mass of polar ice sheets and their contributions to global sea level change;
-- Gravity Recovery And Climate Experiment (Grace), also managed by JPL,
which maps Earth's gravitational field, allowing us to better understand
movement of water throughout the Earth.
For more information about sea level change on the Internet, visit:
For information about Topex/Poseidon and Jason on the Internet, visit:
For information about Grace on the Internet, visit:
For information about NASA and agency programs on the Internet, visit:
JPL is managed for NASA by the California Institute of Technology in Pasadena.
Alan Buis (818) 354-0474
Jet Propulsion Laboratory, Pasadena, Calif.
Dolores Beasley/Marta Metelko (202) 358-1753/1642
NASA Headquarters, Washington, D.C.