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This shows the amount of ice gained or lost by Antarctica between 2003 and 2019. Dark reds and purples show large average rates of ice loss near the coasts, while blues show lower rates of ice gain inland. Ice lost near the coasts, especially West Antarctica and the Antarctic Peninsula, far outweighs gains inland. The Thwaites and Crosson ice shelves (seen just below the peninsula) have thinned further. The two ice shelves have lost five meters (16 feet) and three meters (10 feet) of ice per year, respectively, between 2003 and 2019. The circle in the middle is above the South Pole, where the instrument does not collect data. Credit: Smith et al. / Science
Using the most advanced Earth observation laser instrument POT have ever flown in space, a team of scientists led by the University of Washington He has made precise measurements of how the Greenland and Antarctic ice sheets have changed over 16 years.
In a new study published in the journal. Science On April 30, scientists discovered that Antarctica’s net loss of ice, along with the shrinking ice sheet in Greenland, has been responsible for 0.55 inches (14 millimeters) of sea level rise to the global ocean. since 2003. In Antarctica, sea level rise is being driven by the loss of floating ice shelves that melt in a warming ocean. Ice shelves help to retain the flow of land ice into the ocean.
The findings come from the Ice, Cloud and land Elevation Satellite 2 (ICESat-2), which launched into orbit in the fall of 2018 and began taking detailed measurements of global elevation, even over Earth’s frozen regions. By comparing the new data with measurements taken by the original ICESat from 2003 to 2009, the researchers have produced a comprehensive portrait of the complexities of ice sheet change, and insights into the future of Greenland and Antarctica.
Climate change is reshaping the ice sheets in the Arctic and Antarctic, and NASA’s ICESat and ICESat-2 satellites help researchers determine what those disturbances are like.
“If you watch a glacier or ice cap for a month or a year, you won’t learn much about what the weather is doing to it,” said lead author Benjamin Smith, a glaciologist at the University of Washington. “We now have a 16 year period between ICESat and ICESat-2 and we can be much more confident that the changes we are seeing on the ice have to do with long-term changes in the climate. And ICESat-2 is a truly remarkable tool for making these measurements. We are seeing high-quality measurements that cover both ice sheets, allowing us to make a detailed and accurate comparison with the ICESat data. “
This shows the amount of ice gained or lost by Greenland between 2003 and 2019. Dark reds and purples show high rates of ice loss near the coasts. Blues show lower rates of ice gain inside the ice sheet. The ice sheets together have lost enough ice in the ocean to raise the global sea level by approximately 14 millimeters (0.55 inches) between 2003 and 2019. From global sea level rise due to melted ice from the ice sheet and calving icebergs, about two-thirds came from Greenland, and the rest from Antarctica. Credit: Smith et al. / Science
Previous ice loss or gain studies often analyzed data from multiple satellites and airborne missions. The new study takes only one type of measurement: the height measured by an instrument that bounces laser pulses off the ice surface, providing the most detailed and accurate picture of the ice sheet change to date.
The researchers tracked the ICESat measurements and overlayed the densest tracks from the 2019 ICESat-2 measurements. Where the two data sets intersected, tens of millions of sites processed the data through computer programs that They explained the density of the snow and other factors, and then calculated the lost or gained ice mass.
“The new analysis reveals the response of the ice sheets to changes in the climate in unprecedented detail, revealing clues as to why and how the ice sheets are reacting the way they are,” said co-author Alex Gardner, Glaciologist at the NASA Jet Propulsion Laboratory. in Pasadena, California
The study found that the Greenland Ice Sheet lost an average of 200 gigatons of ice per year, and the Antarctic Ice Sheet lost an average of 118 gigatons of ice per year. One drop of ice is enough to fill 400,000 Olympic pools.
About the sea level rise that resulted from the melting of the ice sheet and iceberg calving, about two-thirds of them arrived in Greenland, the other third of Antarctica, Smith and colleagues found.
“It was surprising to see how good the ICESat-2 data looked from the beginning,” said co-author Tom Neumann at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “These early results analyzing land ice confirm the consensus of other research groups, but also allow us to see the details of the change in individual glaciers and ice shelves at the same time.”
In Greenland, there was a significant amount of thinning of the coastal glaciers, Smith said. The Kangerlussuaq and Jakobshavn glaciers, for example, have lost 14 to 20 feet (4 to 6 meters) of elevation per year. Warmer summer temperatures have melted ice from the surface of glaciers and ice sheets, and in some places the warmer ocean water erodes the ice on their foreheads.
In Antarctica, dense footprints from ICESat-2 measurements showed that the ice cap is thickening in parts of the interior of the continent, likely as a result of increased snowfall, Smith said. But the loss of ice from the continent’s margins, especially in West Antarctica and the Antarctic Peninsula, far outweighs any gains inland. In those places, the ocean is also likely to blame.
“In West Antarctica, we are seeing many glaciers thin very quickly,” said Smith. “There are ice shelves at the downstream end of those glaciers, which float in the water. And those ice shelves are thinning out, allowing more ice to flow into the ocean as the warmer water erodes it. “
These ice shelves, which rise and fall with the tides, can be difficult to measure, said co-author Helen Amanda Fricker, a glaciologist at the Scripps Institute of Oceanography at the University of California, San Diego. Some of them have rough surfaces, with cracks and ridges, but the precision and high resolution of ICESat-2 allows researchers to measure overall changes, without worrying about these characteristics that skew the results.
This is one of the first times that researchers have measured the loss of floating ice shelves around Antarctica simultaneously with the loss of the continent’s ice sheet.
Melting ice from ice shelves does not raise sea level as it is already floating, just like an ice cube in a cup filled with water does not overflow the glass. But the ice shelves provide stability for the glaciers and the ice sheets behind them.
“It is like an architectural buttress that supports a cathedral,” Fricker said. “Ice shelves support the ice sheet. By removing the ice packs, or even thinning them out, you’re reducing that reinforcing force, so grounded ice can flow faster. “
The researchers found ice shelves in West Antarctica, where many of the continent’s fastest-moving glaciers are located, are losing mass. Thinning patterns show that the Thwaites and Crosson ice shelves have thinned the most, averaging approximately five meters (16 feet) and three meters (10 feet) of ice per year, respectively.
For more information on this study, see 16 years of ice sheet loss mapped by the most advanced Earth-observation laser NASA has flown in space.
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Reference: “The loss of mass of the generalized ice sheet reflects competitive processes of the ocean and the atmosphere” by Ben Smith, Helen A. Fricker, Alex S. Gardner, Brooke Medley, Johan Nilsson, Fernando S. Paolo, Nicholas Holschuh, Susheel Adusumilli, Kelly Brunt, Bea Csatho, Kaitlin Harbeck, Thorsten Markus, Thomas Neumann, Matthew R. Siegfried and H. Jay Zwally, April 30, 2020, Science.
DOI: 10.1126 / science.aaz5845
The study was funded by NASA. Other co-authors are Johan Nilsson and Fernando Paolo at NASA’s Jet Propulsion Laboratory; Brooke Medley, Thorsten Markus and H. Jay Zwally at NASA’s Goddard Space Flight Center; Nicholas Holschuh at Amherst College; Susheel Adusumilli at the University of California, San Diego; Kelly Brunt at the University of Maryland; Bea Csatho at the University of Buffalo; Kaitlin Harbeck at KBR; and Matthew Siegfried at the Colorado School of Mines.
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