As glaciers melt, 'hard end dates are hard to come by'

As glaciers melt, 'hard end dates are hard to come by'

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With the new year, a few signs at Glacier National Park became obsolete.

Recently, Glacier removed a few interpretive displays that told guests the mountain’s glaciers would be gone by 2020 — a prediction that didn’t come to pass. The move was first reported by CNN and other news outlets.

In an emailed statement, National Parks Service spokesperson Michael Litterst wrote that “Glacier National Park regularly updates its interpretive material, including exhibits, based on the latest research available for multiple park resource topics. In 2019, the park was able to fund an update to exhibits regarding glacial retreat to reflect the latest modeling.”

The display at St. Mary Visitor Center now states that the glaciers' final disappearance "depends on how and when we act." While the park’s glaciers have been melting for decades due to climate change, they're not gone entirely. As of the most recent count in 2015, 26 named glaciers remained in the park. However, all have been shrinking, and photos comparing the glaciers in the park's early years and today are widely cited evidence of climate change. 

Some of the scientists who keep tabs on these glaciers told the Missoulian that since the gone-by-2020 prediction was made, the techniques used to predict the future of Glacier National Park’s namesake glaciers have evolved.

“Hard end dates are hard to come by, because the system is so complicated and understanding what’s going to happen in the future is complicated,” said Joel Harper, a glaciologist at the University of Montana.

Scientists have been studying Glacier National Park’s namesake glaciers for decades, mapping their maximum extents and charting their retreat using photographs, tree rings and other clues, and building complex mathematical models to predict how they would change in the future. In 2003, researchers Dan Fagre and Myrna Hall used this work to model how glaciers would retreat in the Blackfoot-Jackson Basin.

Their work predicted that, if atmospheric carbon dioxide emissions increased as expected by the year 2030, all of the basin’s glaciers would disappear. Field measurements of glacier melt collected in 2005 and 2006 led to the 2010 prediction that the end could come even earlier. “Without a significant reversal in the upward trend in temperatures, the glaciers will continue to disappear, perhaps as early as 2020,” wrote Fagre and another Geological Survey scientist, Lisa McKeon.

That date made its way into park signs, but “we don’t just take that (early work) as gospel and move on,” said UM’s Harper. “We as scientists critique it and try to improve it ourselves.”

There was still more to learn about the park’s glaciers — for one thing, how thick they were. “As far as I know, when the 2003 study (predicting a 2030 end date) was done, there were not robust measurements or estimates of how thick Glacier National Park glaciers were,” explained Caitlyn Florentine, a research physical scientist with the U.S. Geological Survey’s Northern Rocky Mountain Science Center. That knowledge wasn’t essential for the 2003 model, she said, because it was based on the extent of past ice coverage to predict how the glacier would change in the future.

But the thickness of ice is critical for understanding glacier behavior, she continued. “A glacier that’s, say, 100 meters thick is going to take longer to melt and go away … than a glacier that’s only 10 meters thick.”

Joel Brown and Joel Harper with UM and Neil Humphrey at the University of Wyoming collected thickness data on a different glacier, Sperry, from 2005 through 2008. That enabled them to build a model that was based more on physics and less on past behavior of the glacier. It predicted that depending on future emissions, it could remain largely in place or shrink to almost nothing by 2100.

Scientists are also learning that, while climate is the main driver of glaciers’ health, it’s not the only factor. As Sperry Glacier melts back into its “cirque” — a steep, bowl-shaped valley —  the remaining bit is more shaded, and the overhead mountains shed snow that will eventually get compacted into ice.

Those factors won’t necessarily save the remaining glaciers from a warming climate — but they should be taken into account when predicting their future behavior, Florentine and her colleagues wrote in a 2018 paper. “If indeed these cirque glaciers are more affected by these local processes, if these processes are local, you might expect them to vary from place to place,” she said. “Even though there is certainty in future glacier loss, predicting the same exact fate for some population of glaciers at some exact snapshot in the next few decades can be problematic.”         

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