Dr. Edward Chatelain was a teenager when he first climbed the 12,604-foot Castle Mountain and peered down at the glacier below. Even then, in the mid-1970s, he was awed by the size of the glacier and the deep crevasses that sliced into its core.
But when he returned two decades later, flying over the Absaroka and Beartooth mountains from the west, he could barely recognize the glacier of his memory.
"We were absolutely aghast to see what was left," he said.
The experience prompted Chatelain, now a professor of geology at Valdosta State University in Georgia, to spend the intervening years searching for photographic records and weather data to explain what's happening in the Beartooths.
Chatelain's research, along with that of forest service scientists and other academics, was merged in a study titled "Monitoring Climate Change in the Beartooth Mountains of the Custer National Forest."
The one-year pilot study, released at the end of July, tracks trends in glaciation through photographic images, some dating back more than half a century.
Dan Seifert, who initially coordinated the study, is the physical scientist for the Beartooth Ranger District. He was not surprised to learn that glaciers in the Beartooths are on the wane. But he was startled to discover the rate at which they were receding.
"The average amount of ice loss was higher than other areas of the country and higher than a similar study in (Alberta) Canada," he said.
The study yielded other unexpected findings: Glacial melting is not uniform, nor is it universal.
For example, the Castle Rock Glacier lost 60 meters of ice from its surface between 1952 and 2003, which averages out to 1.26 meters of melt per year. That was far from the case for the East Grasshopper Glacier, which melted at only one-quarter that rate - and actually grew an average of 1.07 meters each year from 1987 to 2003.
"That just demonstrates how dynamic these systems are," Seifert said.
Quantifying the change
Casual observation and anecdotal evidence suggest that glaciers are receding toward possible extinction. The study was intended not only to monitor that activity but also to generate a cost-effective and repeatable method for quantifying the change.
Haans Fisk and Don Evans of the Remote Sensing Applications Center in Salt Lake City provided the technical expertise for the study. Pulling together aerial photos from three different sources - the U.S. Forest Service has been collecting aerial photography for all of its land since the 1940s and in some cases the 1930s - they were able to create a pictorial history of four select glaciers.
"It's a fairly good record of land management and climate change," Fisk said. "A longer record would be better, but it wasn't available."
Comparing photos of the same glacier, taken at five- or 10-year intervals, provided evidence of the transformation. But measuring the amount of change proved a more complex task. Initially, Fisk said, they attempted to map the glacier's perimeter as a point of comparison
"But it was not always easy to tell where the glacier starts and stops," he said.
The main glacier surface was fairly easy to identify, but its boundaries were less distinct, oftentimes fading seamlessly into seasonal snowfields and rock glaciers.
So, they switched tacks. They next attempted to monitor melt rates through changes in surface elevation of the ice within each glacier. To do so, they used aerial photos taken in overlapping sequence, which combined to create a "stereo" view of the landscape below. Using current computer software, the sequential photos produce a three-dimensional image that can be used to calculate relative elevation.
"The two-dimensional aspect doesn't tell the story by a long shot," Evans said. "The 3-D part, that was the key to this."
Remote sensing analysts then created a "profile" for each glacier, based on elevation measurements taken along a line running down the surface of each. To measure the ebb and flow of glacial ice, profiles were compared against earlier and later profiles.
"It's a repeatable process for assessing change," Fisk said. "Whether or not it's global warming, this is a technology that allows us to monitor the trends."
Interpreting the science
But is global warming playing out in the Beartooths? And if so, what accounts for the variability among glaciers?
Overall, those involved in the study agree that the glaciers are disappearing faster then they're growing. The study notes that, despite inexact interpretation, "the changing boundaries of these glaciers tell a compelling story about glacial retreat."
As for the difference in melt rates, the authors offer several theories that relate to the glacier's exposure.
"That's the thing that jumps out at us," Fisk said.
The southeastern-facing Castle Rock Glacier, which seems to be leading the meltdown, is subject to more solar radiation than the other glaciers measured in the study.
Evans agrees, suggesting that other, related factors may be involved. The glacier's southeastern aspect also positions it away from the dominant wind and weather patterns, he said.
"Most storms come from the southwest," he explained. "So there would be a tendency for snow to accumulate in the northeast, which the East Grasshopper Glacier has."
Likewise, a glacier's rock component could play a role. When rocks accumulate on a glacier's surface, creating a "rock glacier," they tend to insulate the ice and prevent it from melting. Or it could be, as the study notes, "because the East Grasshopper Glacier has a far larger rock component, the loss of ice may simply be less evident."
Whatever the cause, the result could have far-reaching implications.
Glaciers are vital as reservoirs of water for downstream users. On a more local scale, they are critical in supporting localized ecosystems. Glaciers cool stream runoff that is key to aquatic habitats, and they cool the land in their proximity, creating a specific environment for small terrestrial inhabitants.
"Those are just some of the potential impacts of losing glaciers and glacial ice," Seifert said.
A maverick scientist
Chatelain, whose research extends beyond the scope of the study, offers his own personal take. Describing himself as a "maverick scientist," he talks about possible glacier extinction.
"But, I'm not going to say all are going to die due to global warming," he said.
According to Chatelain, the glaciers in the Beartooths are not remnants of an ancient ice age. Rather, they date back to a cold period that chilled the earth from A.D. 1200 to 1880.
"So, we're not dealing with the extinction of ice age glaciers," he said. "Most ice age glaciers in the Beartooths were probably completely gone 8,000 years ago."
Photos dating back to 1898, gleaned from the Wilse Survey in the archives at the Montana Historical Society in Helena, show Grasshopper Glacier as a valley glacier with three or four smaller glaciers feeding into it, he said.
"Now those glaciers are small glaciers, up in the cirques," and the main glacier is reduced to "a little bit of ice clinging to the northeast face of Iceberg Peak," he said.
He refers to another photo, taken in 1961, of Castle Rock Glacier.
"It was a lot bigger then than I had seen in my experience," he said. "It was just monstrous."
In an attempt to explain glacial activity, Chatelain has not only studied photographs, he also has probed weather reports of the area. He has determined that winter snowfall and summer's maximum temperatures provide the checks and balances for glacial activity.
"Glaciers are like a bank," he said. In the winter, you make all the deposits and in the summer you take all the withdrawals."
Chatelain says the "health" of a glacier can be noted by observing whether its surface remains snow-covered late into the summer. Bare ice indicates melting, he said.
"If you're hard put to see the ice in September, things are going well," he said.
Two warming cycles
After perusing the available information, Chatelain rejects the notion of one gradual warming trend. Instead, he said, the data suggest that glaciers in the Beartooths have been affected by at least two separate cycles of melting and stabilization over the past century.
"There are intervals in which the variables combine to be detrimental to glaciers and there are intervals at which the variables offset each other and therefore the glaciers are stabilized," he said.
Chatelain says the period from 1920 to 1948 was the worst for glaciers in the Beartooths. It was also then, he pointed out, that the majority of high summer temperature records were set.
During the warm, dry spell of the dust bowl era, many of the glaciers melted to half their size. After several decades of cooling, he noted a second period of accelerated melting between 1978 and 2001.
"In 2001, it was about as devoid of snow as I've ever seen it," he said.
Since then, he said, the glaciers seem to have stabilized. Both 2008 and 2009 were good snow years with relatively moderate summer high temperatures, he said.
Yet a handful of the Beartooths' smaller glaciers - such as several unnamed glaciers north toward Mt. Wood - seem to have already melted away.
"Now, when I look at Google Earth, I can't really see them anymore," he said.
Chatelaine is hopeful that glaciers in the Beartooths won't disappear entirely. They make the mountains special, he said.
Meanwhile, he continues to keep his eye on incoming data.
"It's a very interesting story," he said. "I wouldn't write it off yet. I don't think it's over."
To request a copy of the study, contact Gail Shaw at firstname.lastname@example.org.