The massive ice field that caps the mountains towering over southeastern Alaska and neighboring British Columbia will be more than half gone by the end of the century and vanish entirely by the end of next century, according to calculations by experts at the University of Alaska Fairbanks and other institutions.
The 1,500-square-mile Juneau Ice Field, the fifth-largest ice field in the Western Hemisphere, "will lose substantial amounts of mass during the 21st century" and then lose the rest of it in the 22nd century, according to the calculations, which are detailed in a study published this week in the Journal of Glaciology.
The calculations assume that global greenhouse gas emissions will continue rising until 2060, then declining as new energy sources replace fossil fuels. That emission scenario is called Representative Concentration Pathway 6.0, or RCP 6.0, and is a realistic assumption for the future, said glaciologist Regine Hock of UAF's Geophysical Institute, one of the study co-authors. It might even be considered optimistic, she said.
A more pessimistic scenario, called RCP 8.5, is considered the business-as-usual outcome, with carbon emissions continuing at their current rate with no policy changes to reduce them.
If the RCP 6.0 scenario plays out over the coming decades, the ice field by 2099 will have lost 58 percent to 68 percent of its 2010 ice volume and 57 percent to 63 percent of its 2010 area, according to the calculations. If the climate holds steady after that, "the ice field is eliminated by 2200," the study says.
That would mean some big changes in scenery, Hock said.
"The mountains would be there, but no ice," she said.
If that happens, it would be the end of an ice field once considered so impenetrable an iconic Alaska politician and four-time gubernatorial candidate floated the idea of obliterating its glaciers with nuclear weapons to make way for a road and other economic development. "There's gold beneath them," Joe Vogler, founder of the separatist Alaskan Independence Party, said of the glaciers in a debate during the 1982 gubernatorial campaign.
Despite the gloomy outcome predicted by the scientists' new calculations, the Juneau Ice Field is not in as bad shape as other ice fields located at lower elevations, Hock said. "The Juneau Ice Field is actually at the higher end," she said. It will still get snow in the winter, producing snowmelt in the spring, she said.
In contrast, research shows that the smaller and lower Yakutat Ice Field is likely to disappear much sooner, Hock noted. "By the end of the century, it will be gone," she said.
However, a climate turnaround could save the Juneau Ice Field, albeit in smaller form, according to the study. If future warming were averted enough to keep the climate as it was from 1971 to 2010, the ice field would stabilize at 86 percent of its present-day volume, according to the study's calculations.
Among the approximately 140 glaciers that make up the ice field is the Mendenhall Glacier, a major tourist attraction in Juneau and site of a U.S Forest Service visitor center and trail system.
Today's tourists can see the toe of Mendenhall Glacier from visitor facilities at the edge of Mendenhall Lake, but tourists in the future are not likely to have the same opportunity, Hock said. "Soon they'll get to the lake and the glacier won't be visible anymore," she said.
Year-to-year changes there and at other sites are already obvious to frequent visitors, she said.
The new study is the first detailed analysis of the entire ice field, according to UAF officials. This project is one of the first to evaluate a large Alaska glacial region in detail, Hock said.
The Juneau Ice Field is the subject of a long-term research program. However, Hock said, past measurements have been taken at specific glaciers, making data incomplete or very approximate.
Individual glaciers have their unique characteristics, and getting up to different parts of the Juneau Ice Field is "extremely difficult and costly," Hock said. Another challenge to quantifying trends at the ice field is the large amount of snow that is piled up at the end of winter, hindering on-site spring measurements, she said. Some past studies have turned to measurements of elevation differences to estimate past years' mass changes, but elevation data from old maps is also spotty, resulting in only rough estimates of the recent mass loss, she said.
Recent research includes a study published in 2013 in the journal Earth System Science Data, which used decades of measurements from two glaciers as an approximate stand-in for changes at the entire ice field over the past half-century. At Taku Glacier, mass actually grew and the ice thickened from 1946 to 1985, but that trend reversed from 1986 to 2011, when mass loss started at a rate twice that of the previous decades' growth, according to the measurements detailed in the study. At Lemon Creek Glacier, measurements since 1953 show mass loss and a thinning of about 95 feet over 55 years, the study said.