A new study based on NASA and ESA satellite data shows that Arctic sea ice is thinning at a "frightening rate."
Measuring the ice via satellites each month from 2018 to 2021, polar scientists Sahra Kacimi of the California Institute of Technology's Jet Propulsion Laboratory and Ron Kwok of the University of Washington's Applied Physics Laboratory observed that it thinned 1.5 feet (0.5 meters) during that period.
"We weren't really expecting to see this decline, for the ice to be this much thinner in just three short years," Kacimi said in a statement released by the American Geophysical Union, which published the new research in one of its journals.
Related: 10 devastating signs of climate change satellites can see from space
Each year, seasonal sea ice melts entirely in the summertime, so naturally, the ice does get thinner during this period. But the 0.5-meter loss was recorded in what scientists call multi-year ice — thicker ice that sticks around all year long and typically accumulates year-over-year. The loss represents about 16% of the multiyear ice's volume.
To determine the sea ice's thickness, researchers measure the height of the ice above sea level, taking into account the depth of the snow atop the ice, as that affects how the ice floats. For their study specifically, Kacimi and Kwok used lidar data from NASA's ICESat-2 and radar data from the European Space Agency's CryoSat-2. Both approaches bounce a beam of light off the surface of Earth and time how long the signal takes to return using the speed of light to more precisely measure the depth of snow and the height of ice below it.
"This is the first time anyone has several years' worth of data from the difference between lidar and radar data for snow depth," Robbie Mallett, a polar ice researcher at University College London who did not participate in the study, said in the statement.
Kacimi and Kwok placed the results of their research within the context of 18 years by adding measurements taken by NASA's ICESat, which operated from 2003 to 2010. All told, the scientists determined that the Arctic sea ice has lost one-third of its volume over the past two decades due to the decrease in multiyear ice and the increase in seasonal ice.
"Current models predict that by the mid-century we can expect ice-free summers in the Arctic, when the older ice, thick enough to survive the melt season is gone," said Kacimi.
The study was published in the journal Geophysical Research Letters on March 10.
Editor's note: This story has been updated to correct the thickness of melted ice. Follow Stefanie Waldek on Twitter @StefanieWaldek. Follow us on Twitter @Spacedotcom and on Facebook.