Elevation readings captured by satellites confirm that glaciers in the western United States are fading away at a worrisome rate.
The fade-out isn’t a surprise, considering the rise in global mean temperatures that’s ascribed to climate change. The new twist has to do with how the measurements were made.
University of Washington researcher David Shean looked back at satellite readings that have been amassed in databases, plus fresh readings that are being taken by DigitalGlobe’s constellation of GeoEye and WorldView satellites.
An analysis of the data, facilitated with NASA’s Ames Stereo Pipeline software, produces a 3-D elevation model of mountainous terrain. The method supplements other techniques to estimate glacier size, including area measurements based on aerial imagery and depth measurements made using stakes in the snow.
The result is a year-by-year record tracing the ups and downs of a glacier.
“I’m interested in the broad picture: What is the state of all of the glaciers, and how has that changed over the last 50 years?” Shean, who is now a research associate with the UW’s Applied Physics Laboratory, said today in a news release.
Shean is due to present his findings at Seattle’s Washington State Convention Center on Sunday during the Geological Society of America’s annual meeting.
Thanks to the fresh data, the satellite elevation readings can provide a twice-yearly assessment of roughly 1,200 mountain glaciers in the Lower 48 states, down to a resolution of about a foot. Most of the glaciers are in Washington state, and Shean is paying special attention to Mount Rainier.
He estimates that Mount Rainier has lost about a cumulative total of 900 million cubic yards of ice since 1970. If that volume could be distributed evenly across all of Rainier’s glaciers, it would amount to the disappearance of a 25-foot-deep layer of ice.
Of course, the ice loss isn’t distributed evenly. Lower-elevation glaciers have been especially hard hit.
“There are some big changes that have happened, as anyone who’s been hiking on Mount Rainier in the last 45 years can attest to,” Shean said. “For the first time we’re able to very precisely quantify exactly how much snow and ice has been lost.”
Mount Rainier’s level of loss is consistent with what readings from the other glaciers are showing, Shean said.
The comprehensive snapshots of glacial elevation should help resources planners anticipate what’s coming in the decades ahead, and how to plan accordingly.
“We want to know what the glaciers are doing and how their mass is changing, but it’s important to remember that the meltwater is going somewhere. It ends up in rivers, it ends up in reservoirs, it ends up downstream in the ocean. So there are very real applications for water resource management,” Shean said. “If we know how much snow falls on Mount Rainier every winter, and when and how much ice melts every summer, that can inform water resource managers’ decisions.”
Co-authors of the research that Shean will present at the GSA meeting include Anthony Arendt, Erin Whorton, Jon Riedel and Andrew Fountain. The work was funded by the National Park Service, the U.S. Geological Survey and NASA.