Satellites Measure the Melt (Plus Lemmings)


Malaspina Glacier in the Gulf of Alaska (created from a Landsat satellite image and NASA’s Shuttle Radar Topography Mission)

—Image courtesy NASA

I was stunned to hear that ice loss from glaciers in the Gulf of Alaska adds up to 84 gigatons a year, or about five times the average yearly flow of the Colorado River through the Grand Canyon, according to NASA satellite measurements.

“The Gulf of Alaska region is 20 times smaller than the ice-covered area of Greenland, yet it contributes nearly half as much freshwater melt as Greenland and accounts for about 15 percent of present-day global sea level rise stemming from melting ice,” the NASA press release quoted geophysicist Scott Luthcke as saying. “Considering that the Gulf of Alaska makes such a disproportionate contribution, it is vital that we know more about the nature of glacial change there.”

The NASA team’s work is published in the Journal of Glaciology.

The team used NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites to measure changes in Alaska’s coastal glaciers. These twin satellites orbit the Earth 137 miles apart and “weigh” the changes in glaciers’ mass by detecting miniscule changes in the distance between the two satellites. The distance between the satellites changes in response to Earth’s gravity field, which changes with the mass of the land area or body of ice being measured.

Got that? If not, this NASA article probably explains it better than I can.


Columbia Glacier near Valdez, Alaska

—Image courtesy Extreme Ice Survey

Related content: On the National Geographic environment website, we’ve got some amazing time-lapse video of a series of massive calving events at Columbia Glacier near Valdez, Alaska. The video was created by Extreme Ice Survey.

Finally, on a somewhat related note, be glad you’re not a lemming. The mythically suicidal critters are not fairing well by global warming, National Geographic News reported this week. I’m sorry to hear that lemmings (or any animal, for that matter) are suffering due to climate change, but the most shocking piece of news I took away from Kate Ravilious’s report was: “When lemmings boom, they’re hard to miss. Norwegians have had to use snowplows to clear the squashed rodents off the roads.”


–Stephen E. Mather

filling in for Victoria Jaggard