Glaciers are dynamic.  Over time, they advance or retreat depending on climatic conditions.  They form, and spread, when more snow accumulates in the winter than melts in the summer. Since the end of the Little Ice Age in the mid-1800s, most glaciers have been either stable or in slow retreat.  In the last half century, however, that rate of retreat has increased.

This summer, I had the opportunity to travel around Alaska. While there, I visited a few of its nearly one hundred thousand glaciers and learned more about how they are responding to climate change.

According to the U.S. Fish and Wildlife Service,  Alaska’s  statewide  glacial  mass  balance – the net gain or loss of ice – has been negative since the middle of the 20^th century.  While conditions at individual glaciers vary, the majority are melting. Recognizing that natural variables like the Pacific Decadal Oscillation (PDO) and El Nino Southern Oscillation (ENSO) have always affected Alaska’s glaciers, most scientists agree that human-caused global warming has accelerated glacial retreat across the state.   Earth’s average temperature increased 1.4°F in the last century, but Alaska is warming even faster.  The E.P.A. reports that Alaska’s average temperature has increased 3.4°F in the past fifty years with winters warming by an average of 6.3°F.  These warmer temperatures coupled with shifting precipitation patterns are causing glaciers to both shrink in length and thin in volume.

A striking visual example to this process is Exit Glacier in Kenai Fjords National Park. It is one of forty glaciers in the park that flow out of the Harding Ice Field, but is the only one easily accessible by foot. As such, the trail leading up to it is marked with signs that point out the glacier’s previous extent and progressive retreat over nearly two hundred years. The first sign, 1815, is now over one and a half miles from the current terminus.  According to the National Park Service, this glacier has been receding at a rate of forty three feet per year, on average.  Between September 2011 and October 2012, however, it retreated one hundred thirty three feet.

While shrinking glaciers in Alaska may seem like a remote environmental issue, they have far reaching impacts. A recent study by NASA and the University of Alaska – Fairbanks found that the state’s melting glaciers are one of the largest contributors to rising global sea levels.

Exit Glacier with melt water running off into the outwash plain.                                                  Image Credit: The Weather Gamut

Sign along the Exit Glacier trail that marks the location of the terminus in 1926. The glacier’s current position is visible in the background behind the trees.                                                       Image Credit: The Weather Gamut

Mapping the progressive retreat of Exit Glacier in Kenai Fjords National Park, Alaska.                     Image Credit: NPS