Most of the world's mountain glaciers and small ice caps will disappear or shrivel dramatically by the end of the century, with Alaska glaciers and ice fields shrinking by 25 to 60 percent over the next nine decades, according to new findings published last week in the journal Nature Geoscience. The study -- the most comprehensive ever done on the role of glacier wastage in sea level rise -- has already received extensive news coverage for its global perspective.
But Alaska's portion of the projected meltdown raises questions about the future of regional hydroelectric projects like the proposed multi-billion-dollar Susitna Dam, as well as Anchorage's drinking water source in Eklutna Lake and any other Alaska stream that relies on glacial melt for its summer flow.
If Alaska's climate continues to warm over the next 89 years as projected, summer runoff in glacier-fed basins like Susitna and Eklutna could initially soar by as much as 60 percent above the present during periods when the melt accelerates, said Regina Hock, a University of Alaska Fairbanks geophysicist who produced the study with lead author Valentina Radi?, now a post-doctoral fellow at the University of British Columbia.
But after 2100, look out. As the source glaciers and ice fields recede, this annual summer surge could fall away. And eventually, perhaps, stop.
Alaskans hoping to build dams, secure drinking water or ensure future stream-flow for salmon and navigation should be asking: What then?
"Concerning both the Susitna dam and Eklutna Lake or any other hydropower scheme, it is essential to know how much total annual runoff will change," Hock said in an e-mail to Alaska Dispatch. "However, it seems that this has not really 'trickled in' yet in Alaska."
The research triggered similar concerns elsewhere in North America, according to a story posted last week by the Vancouver Sun.
"In Western Canada and the United States, 50 percent of glacier ice could disappear by 2100, which could have substantial impacts on regional power dams and water supplies," the Sun reported. "'For the long term, it's not good for the economy because there will be a drop in river run-off and less water in reservoirs,'" Radic told the Sun.
The state has endorsed the concept of building a 700-foot-tall dam and hydropower plant on the Susitna River as a major step toward generating half of the state's electric power with renewable sources by 2025. The project, under discussion for many decades, would cost an estimated $4.5 billion in 2008 dollars and create a 39-mile-long reservoir. Extensive studies still need to be done, with a round of public workshops expected in February.
Closer to Anchorage is Eklutna Glacier in Chugach State Park. Its summertime melt fills the stunning Eklutna Lake to the brim with pristine, azure water to sate the thirst of Alaska's largest city and power a historic hydro plant on the Knik River.
Most Anchorage residents take Eklutna Lake for granted. But will the time come when Chugach glaciers won't fill Anchorage's mountain lake for drinking and power? Will snowmelt alone cover local water needs?
Stay tuned, Hock said.
"This is actually the Ph.D. thesis topic of one of my graduate students, but no results yet. He will do exactly these calculations."
Alaskan glaciers to feed the sea big time
The research - conducted largely by Radi? as part of her doctoral studies under Hock, first in Sweden and later at Fairbanks - examined the fate of 2,638 ice caps and 120,229 mountain glaciers under 10 different "state-of-the-art climate models" and then applied the results to 19 different regions around the globe.
It found that half of the world's smallest glaciers - 1,200 acres or less - will melt away entirely over the next nine decades. How much overall volume might be lost varied from region to region as well as from climate model to model, Hock explained.
For instance, glaciers of New Zealand and the European Alps are projected to lose more than 75 percent of their present volume, she said. In contrast, Himalayan glaciers and the mountain glaciers of Greenland won't lose as much, maybe only a few percent. Some Himalayan glaciers might even grow due to additional snowfall.
"These glaciers are very sensitive to changes in snow precipitation," Radi? told Nature News.
To get at Alaska's proportion of the loss, they used all of the local glaciers listed in the World Glacier Inventory database: about 450 glaciers in the Alaska Range, about 400 glaciers in the Kenai and Chugach mountains, and about 1,500 glaciers in the Wrangell-St. Elias region.
Still, that inventory includes only about 40 percent of the 31,000 square miles covered by ice in Alaska, Radi? said, so they had to extrapolate to the rest of the state's glaciers.
In a sense, Alaska still remains the "last frontier" in glaciology, with 60 percent of the state's ice locked up in glaciers that haven't been measured or inventoried, Radi? said. "So, still lots of work to be done in this field."
The data doesn't zero in on single glaciers or even individual basins. But it gives a broad picture of extensive melting across the state. Depending on the model, Alaska's loss ranged from 25 percent to more than 60 percent, with an average of about 40 percent.
"Alaska is in-between," Hock said. Still, "there will be substantial mass loss of glaciers by the end of the century."
Most of that cold, silty water rushes to the ocean, and the study found that Alaska glaciers will contribute as much as 1.5 inches to the global ocean rise - up to one-third of the total increase caused by all of the glacial melt across the planet, Radi? said.
To put it another way, Alaska's melting glaciers have directly been responsible for about .11 millimeters per year of sea level rise during the past 40 years. The new calculations suggest that Alaska's share of the annual rate will double to .26 millimeters per year, or about one-tenth of an inch per year.
"This makes Alaskan glaciers an important contributor to global sea level rise," Radi? said.
How can an area as small as Alaska contribute so much?
Fairbanks science writer Ned Rozell tackled the explanation in a recent column about the pair's study.
"Radi? and Hock wanted to sum up how much water the world's smaller bodies of ice were contributing to sea level rise because other scientists had overlooked mountain glaciers like those in Alaska and Canada. Even though Antarctica and Greenland account for 99 percent of all the ice-bound water on the planet, the meltwater from smaller glaciers has caused about 40 percent of recent sea-level rise," Rozell wrote.
"'(It's) because they are in warmer climates,' Hock said. 'The Greenland and especially the Antarctic ice sheets are so much colder. It doesn't matter if the climate there warms from minus 40 to minus 35; the ice still won't melt. But it makes a lot of difference for glaciers where temperatures are around the freezing point (which includes most of those in Alaska).'"
It gets worse. These calculations don't include calving by Alaska's tidewater glaciers, like those found in Prince William Sound and Kenai Fjords National Park. So Radi? cautioned that their figures should probably be considered minimum estimates.
"Alaska will keep its dominating role as one of the largest regional contributors of mountain glaciers to sea-level rise," Hock said. "However, it is not only sea-level rise that is important, but locally there will be significant changes in stream flow."
Without glaciers, streams live or die on precipitation
Hence the concerns over the future for hydropower projects like Susitna, as well as flood management and water resources planning. Some key questions for planners: When will runoff peak? How fast will it decline?
"These aspects are often overlooked and explain why glaciers are not really on the screen when hydrologists, engineers, etc... discuss hydropower schemes, especially in Alaska," Hock said in an e-mail.
Think of glaciers as "water savings accounts," storing the precipitation deposited over decades by snowfall. Summer melt can be likened to the annual withdrawal.
If more water gets withdrawn than was deposited as snow - something predicted by the climate models - then glaciers will begin to lose mass and shrink. This process has two opposing effects, Hock explained.
As the loss of glacier ice accelerates, the total runoff to streams soars and remains high for decades, producing peak flows that may be as much as 60 percent higher than what is currently seen. But later, perhaps after many decades of meltdown, the glacier shrivels or even disappears, and the stream flows plummet.
"Total glacier runoff and peak flow will initially increase, because water is released from the glacier storage," Hock said. "However, eventually this will be followed by a reduction in runoff totals as the glaciers retreat to higher altitudes and either stabilize or melt away."
Radi? accompanied Hock, a leading geophysicist and climate scientist in Sweden, when she moved to UAF a few years ago. By then, Radi? was already deep into her investigation of the world's small glaciers.
Born in the Adriatic Coast country of Croatia, Radi? originally studied meteorology and physical oceanography at the University of Zagreb. Glaciers weren't on her radar back then. (She still prefers to take her vacations at the beach.)
"Surprisingly, I grew up not knowing what glacier was because Croatia does not have any," she said. "Neither was I particularly interested in the mountains."
But Radi? was drawn toward applied physics and climate studies. When Hock, then at Stockholm University, advertised for a student to work on a Ph.D project estimating sea level rise from glacial melt, Radi? applied, got the job, and then followed Hock "for a year and a half of incredibly interesting life" at the University of Alaska Fairbanks.
"Years back in Croatia, I would never guess that my paths would take me that far North into the wild," Radi? added in an e-mail.
The geophysics study meant crunching numbers and sitting in front of a computer week after week -- and no field work. But Radi? did get to view a few of her glaciers on road trips to Valdez and Seward.
"I do admire Alaskan glaciers," she said. "They are like the main actors on the stage featuring the play 'Icy, beautiful and eternal wilderness.'"