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article imageNASA's ICESat-2 mission tracks the decline of ice sheets

By Karen Graham     May 1, 2020 in Science
Using the most advanced Earth-observing laser instrument NASA has ever flown in space, scientists have made precise, detailed measurements of how the elevation of the Greenland and Antarctic ice sheets have changed over 16 years.
From the frozen crags of the Andes and the Rockie mountains to the ice sheets covering Greenland and Antarctica, the world's ice has been melting at an accelerated rate in the last five years. This is why observations and data on ice sheet mass changes are essential to our understanding of present and future sea-level changes.
People may not realize this, but humans evolved on a planet where ice was a climate regulator. Not only did it reflect some of the sun's heat back into space, but the ice stored vast amounts of moisture.
The amount of water locked up in ice and snow is only about 1.7 percent of all water on Earth, but the majority of total freshwater on Earth, about 68.7 percent, is held in ice caps and glaciers.
At the end of October 2018  the European Space Agency’s Sentinel-1 satellite observed the glacier ...
At the end of October 2018, the European Space Agency’s Sentinel-1 satellite observed the glacier letting go of a huge chunk of ice. The largest piece, named Iceberg B-46, spanned 226 square kilometers. It is visible here on November 7, 2018, as observed by Landsat 8.
NASA Earth Observatory
Accurately measuring the amount of ice loss is essential to keeping track of sea-level rise. As the ice melts in Greenland and Antarctica, the water surges toward the Equator where sea-level rise is already two to three times as fast as the global average.
In a new study published April 30, 2020, in the journal Science by a team of researchers from around the country, led by Ben Smith of the University of Washington, data from NASA's ICESat ( Ice, Cloud, and Land Elevation Satellite) missions was used to determine that ice sheets are losing billions of tons of mass into the ocean each year, contributing significantly to global sea-level rise.
Launched in September 2018, the mission was a much-anticipated follow-up to a previous ICESat mission, which concluded in 2009, reports Scientific American. ICESat-2 is very precise, too.
Artist s impression of ICESat in orbit
This is the first ICESat mission satellite.
Artist's impression of ICESat in orbit This is the first ICESat mission satellite.
NASA/Ball Aerospace
ICESat-2’s instrument is a laser altimeter, which sends 10,000 pulses of light a second down to Earth’s surface, and times how long it takes to return to the satellite – to within a billionth of a second. The instrument’s pulse rate allows for a dense map of measurement over the ice sheet; its high precision allows scientists to determine how much an ice sheet changes over a year to within an inch.
The findings are disturbing and definitely something to worry about. The study calculated that Greenland lost about 200 gigatons per year during the study period that covered 16 years of satellite data, and Antarctica about 118 gigatons annually, together raising sea level by 0.55 inches.
(Top) Mass change (m ice equivalent per year). (Bottom) Mass changes around the margin. Map and ice ...
(Top) Mass change (m ice equivalent per year). (Bottom) Mass changes around the margin. Map and ice margin mass change have been smoothed with a 35 km median filter for improved visualization.
Ben Smith et al.
The study helped to differentiate between the processes that cause the melting—in some cases shifts in winds that push warmer water toward the ice, or, in other cases, changes within the ice sheets and glaciers themselves. The researchers were able to show how some polar melting is caused by shifting winds and ocean currents, or by rising air temperature alone. And that helps determine if the ice is near a tipping point that could lead to faster melting.
(Top) Mass change for Antarctica. (Bottom) Mass changes at the grounding line. Highest mass loss rat...
(Top) Mass change for Antarctica. (Bottom) Mass changes at the grounding line. Highest mass loss rates are in West Antarctica and Wilkes Land, East Antarctica. Map and grounding line mass change have been smoothed with a 35 km median filter for improved visualization.
Ben Smith et al.
More about NASA, ICESat2, ice sheet loss, laser altimeter, Sea level rise
 
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