In 2002, a satellite called GRACE — Gravity Recovery and Climate Experiment — was launched. The result of a collaboration between NASA and the German Aerospace Center, its mission was to “measure changes to Earth’s gravitational pull that result from changes in mass, including water. As water moves around the planet — flowing ocean currents, melting ice, falling rain and so on — it changes the gravitational pull ever so slightly. Scientists use the precise measurements of these variations to monitor Earth’s water reserves, including polar ice, global sea levels and groundwater availability,” NASA says.
The GRACE project ended in 2017. The following year, a second satellite — known as GRACE Follow On — was launched to carry on the original mission. While calibrating the latest satellite, researchers discovered an astonishing change in the ice sheet that covers Greenland. During the exceptionally warm Arctic summer of 2019, Greenland experienced the loss of 600 billion tons of water from melting glaciers.
To put that into perspective, the entire Greater Los Angeles area uses about 1 billion tons of water in a year. Greenland lost enough water in a few months to meet the needs of Los Angeles for 600 years! NASA says adding that much water to the world’s oceans resulted in a rise in average ocean levels of 2.2 millimeters in just two months.
“We knew this past summer had been particularly warm in Greenland, melting every corner of the ice sheet, but the numbers are enormous,” Isabella Velicogna, a professor of Earth system science at University of California Irvine, tells The Guardian. She is the lead author of the new study reporting the findings from the GRACE FO satellite in the journal Geophysical Research Letters.
In the abstract of the study, she and her co-authors write, “In Greenland, the GRACE‐FO data reveal an exceptional summer loss of 600 gigatons in 2019 following two cold summers. In Antarctica, ongoing high mass losses in the Amundsen Sea Embayment of West Antarctica, the Antarctic Peninsula, and Wilkes Land in East Antarctica cumulate to 2130, 560, and 370 gigatons, respectively, since 2002. A cumulative mass gain of 980 gigatons in Queen Maud Land since 2009, however, led to a pause in the acceleration in mass loss from Antarctica after 2016.”
“In Antarctica, the mass loss in the west proceeds unabated, which is very bad news for sea level rise,” Velicogna says. “But we also observe a mass gain in the Atlantic sector of east Antarctica caused by an increase in snowfall, which helps mitigate the enormous increase in mass loss that we’ve seen in the last two decades in other parts of the continent.” Climate deniers often point to a thickening in part of the Antarctic ice sheet as proof that global warming in a hoax. In fact, there are parts of Antarctica that have more ice now than 20 years ago, but overall, the continent has experienced a massive loss of ice.
“The technical brilliance involved in weighing the ice sheets using satellites in space is just amazing,” says Richard Alley, a glaciologist at Penn State University who was not involved in the study. “It is easy for us to be distracted by fluctuations, so the highly reliable long data sets from Grace and other sensors are important in clarifying what is really going on, showing us both the big signal and the wiggles that help us understand the processes that contribute to the big signal.”
A warming planet means higher sea levels, which means up to 400 million people will be displaced from their coastal homes and many cities will be inundated by the end of this century. It’s hard to contemplate such issues today in the midst of the coronavirus pandemic, which threatens to cause the cancellation of the next international climate conference in Glasgow. But every day we ignore the problem, the worse it will get.
Scientific experiments like GRACE can document changes but cannot do anything to alter the trajectory of the global heating. Only people can do that — if they choose to.
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