A satellite mission that bounces laser light off the ice sheets of Antarctica and Greenland has found that hundreds of billions of tons’ worth of ice are being lost every year due to Earth’s changing climate.
Scientists involved in NASA’s ICESat-2 project report in the journal Science that the net loss of ice from those regions has been responsible for 0.55 inches of sea level rise since 2003. That’s slightly less than a third of the total amount of sea level rise observed in the world’s oceans over that time.
To track how the ice sheets are changing, the ICESat-2 team compared the satellite’s laser scans with similar measurements that were taken by the original ICESat spacecraft from 2003 to 2009. (ICESat stands for “Ice, Cloud and Elevation Satellite.”)
“If you watch a glacier or ice sheet for a month, or a year, you’re not going to learn much about what the climate is doing to it,” Ben Smith, a glaciologist at the University of Washington and lead author of the Science paper, said in a NASA news release. “We now have a 16-year span between ICESat and ICESat-2 and can be much more confident that the changes we’re seeing in the ice have to do with the long-term changes in the climate.”
ICESat-2 was launched in 2018 to begin what’s expected to be a three-year science mission. The satellite’s laser altimeter sends 10,000 pulses of light down to Earth’s surface every second, and times how long it takes for the reflected pulses to come back. The pulse rate, measured with an accuracy that’s within a billionth of a second, is interpreted to produce high-precision measurements of an ice sheet’s elevation.
Scientists can track how those measurements change over the course of a year to within an inch. For the Science study, they fed the readings from ICESat and ICESat-2 into a computer model that converted changes in volume into changes in mass.
Smith and his colleagues found that the ice sheets are getting thicker in the interior of Antarctica and Greenland, probably due to increased snowfall. But in both cases, the rising ice in the interior is far outweighed by ice loss around the edges.
Greenland’s ice sheet lost an average of 200 billion tons of ice per year, while Antarctica’s ice sheet had an annual loss of 118 billion tons of ice, the research team reported. One billion tons of ice represents enough water to fill 400,000 Olympic-sized swimming pools.
“These first results looking at land ice confirm the consensus from other research groups, but they also let us look at the details of change in individual glaciers and ice shelves at the same time,” said Tom Neumann, ICESat-2 project scientist at NASA’s Goddard Space Flight Center.
In Antarctica, the prime areas for ice loss are West Antarctica and the Antarctic Peninsula, where warmer seas are melting the ice. In Greenland, the Kangerlussuaq and Jakobshavn glaciers have lost 14 to 20 feet of elevation per year due to warmer summer temperatures.
The researchers also studied the floating ice shelves around Antarctica, which are harder to track because they rise and fall with the tides. Close analysis of the ICESat-2 data found that West Antarctica’s Thwaites and Crosson ice shelves have thinned the most, losing an average of 16 feet and 10 feet per year, respectively.
“What we expect by the end of the century is on the order of 2, 3, maybe 4 feet of sea level rise,” Alex Gardner, a glaciologist at NASA’s Jet Propulsion Laboratory, said in a video about the study. “Because we have all of our infrastructure that is built around the coasts, we have a lot of vulnerability to a meter change in sea level rise.”
The study in Science, “Pervasive Ice Sheet Mass Loss Reflects Competing Ocean and Atmosphere Processes,” was funded by NASA. In addition to Smith and Neumann, co-authors include are Helen Fricker, Alex Gardner, Brooke Medley, Johan Nilsson, Fernando Paolo, Nicholas Holschuh, Susheel Adusumilli, Kelly Brunt, Bea Csatho, Kaitlin Harbeck, Thorsten Markus, Matthew Siegfried and H. Jay Zwally.
