The visible and measurable retreat of glaciers in Alaska and worldwide over recent decades is only expected to continue, a new study says.
By the year 2100, glaciers could lose 25 percent to 48 percent of their volume and the resulting runoff could contribute 3-6 inches to sea-level rise, according to the first major projection of global glacial melting. Publication of the final version of the study in the journal Frontiers in Earth Sciences is expected Tuesday.
"There is a significant loss of ice mass expected from the world's glaciers with dire implications for sea-level rise, streamflow and tourism," said study co-author Regine Hock, a professor of geophysics at the University of Alaska Fairbanks. Even fisheries could be affected indirectly due to the influx of water with distinct properties, she added.
Alaska's glaciers will fare worse than the global average, with 30 percent to 60 percent of glacial ice expected to melt away. Increased melting in Southeast Alaska, where the climate is more temperate, is driving the higher rate. .
The study combined an analysis of glacial behavior with predicted temperature increases and levels of precipitation, using 14 leading global climate models. The range of possible melting reflects three different scenarios of future greenhouse gas emissions.
"Under the best case scenario -- which is not very likely -- the world is still expected to lose a quarter of its glacier volume," Hock said.
The new projection marks a significant improvement over the handful of prior attempts to quantify likely future melting. "Now we have more data," the researcher said.
Previously, the calving of coastal glaciers was not included in calculations of future glacial retreat. At 10 percent of the overall ice loss, calving is a significant source of future glacial loss, the study says.
"Especially in Alaska," Hock said, "many big glaciers terminate in the ocean discharging icebergs into the water. It's a very different dynamic than land terminating glaciers."
Secondly, the new analysis included a more sophisticated look at how glaciers shrink -- including more thinning at lower elevations and less at high elevations -- compared to other global studies.
Finally, better data about the proportion of ice located under water allowed the researchers to more accurately project how melting would affect sea-level rise.
Alpine glaciers in Europe and North America and the coastal glaciers of western Canada could vanish almost entirely. "We see that many have disappeared already," Hock said. "Glacier National Park does not deserve its name anymore."
But the situation will remain more stable closer to the North Pole, where it's so cold that a few degrees of change will keep temperatures well below freezing.
The expected melting of enormous ice sheets in Greenland and Antarctica were not part of the study.