[strikingly informative photos on url - glacier in 1898, much smaller in
Change in the air, part 2: Going, going, gone?
Front Range glaciers declining; researchers point to a warming world
By Jim Erickson, Rocky Mountain News
October 26, 2004
ARAPAHO GLACIER - "And Men shall fashion Glaciers into Greenness and
harvest April rivers in the Autumn." - Inscription beneath a mural in
the Colorado Capitol
The state's largest glacier is shrinking fast, and University of
Colorado researchers suspect global warming is playing a role.
The surface of the 62-acre Arapaho Glacier along the Continental Divide
west of Boulder has dropped 100 to 130 feet since 1960, according to
recent CU reports.
A third CU analysis concludes that the surface of the 25-acre Arikaree
Glacier, about five miles north of the Arapaho, has also sunk some 66
feet since 1965.
The three reports are the first to document significant present-day
declines in Colorado's pint-size Front Range glaciers, which are
clustered along the Continental Divide from Rocky Mountain National Park
south to Interstate 70.
"We can argue about the rate of decline, but I think we can say
confidently that both of them are losing ice - and they've been losing
it fairly seriously," said CU hydrologist Nel Caine, author of the
CU researchers say there is no reason to believe that other Front Range
glaciers aren't experiencing similar declines. Some of them could be
gone in a few decades.
Just two years ago, at the height of Colorado's multiyear drought, two
year-round ice patches along the Continental Divide disgorged ancient
bison horns that have been radiocarbon dated between 2,090 and 2,280
The animal remains suggest that, in some cases, ice along the divide has
retreated to levels unseen since before the time of Christ.
"Over the last couple of decades, and especially over the last 10 years,
we have entered a period of warming and retreat that is as great, or
greater, than any we know of since the end of the last ice age" 10,000
years ago, said glaciologist Tad Pfeffer, of CU's Institute of Arctic
and Alpine Research, or INSTAAR.
"The Front Range glaciers and snowfields could be gone in a couple of
decades," Pfeffer said.
"Are we directly responsible for this? Is this the smoking gun that says
this is caused by fossil-fuel emissions? That's a harder question to
answer," he said.
Change in the high country
Water managers say the loss of the state's 14 named mountain glaciers
and the hundreds of unnamed year-round snow patches along the
Continental Divide would have little effect on municipal water supplies,
since their contribution is small.
But the loss of glaciers and the so-called perennial snowfields would
redefine places such as Rocky Mountain National Park. It would reduce
habitat for fish that rely on late-summer runoff from glacial sources.
Some alpine plants and high-altitude forests also could suffer.
And the extinction of the alpine ice would cut deeper, beyond what can
be measured in tourist dollars or acre-feet of water. Those scattered
scraps of flowing mountaintop ice are remnants of the last ice age, the
last links to a vanished time, when mammoths roamed the landscape.
"Compare these mountains to a really dry mountain range in New Mexico or
Arizona or Nevada. They're very different places," Pfeffer said. "And to
the extent that we care about the landscape that we live in, that matters."
"Aesthetically and emotionally, they're worth a lot," he said.
Mountain glaciers have been retreating worldwide for a century, and
there's no end in sight.
The declines are viewed by many scientists as strong evidence that
global warming - caused, in part, by the buildup of carbon dioxide and
other heat-trapping greenhouse gases emitted when fossil fuels are
burned - is reshaping the natural world.
During the past 40 years, the total volume of mountain glaciers around
the globe has declined by about 10 percent, according to INSTAAR
glaciologist Mark Dyurgerov.
The losses have been especially severe in Alaska, the Alps, the
Himalayas and the Andes.
Western U.S. glaciers also have suffered, especially in places such as
Glacier National Park.
U.S. Geological Survey maps show 1,700 glaciers or perennial mountain
ice patches in the West. Most are in Washington, Montana and Wyoming,
but 34 are listed in Colorado.
The only known growing glacier in the contiguous United States was,
until recent weeks, inside Mount St. Helens, said Portland State
University glaciologist Andrew Fountain. Now that one is shrinking, too,
While glaciologists have flocked to remote mountain glaciers to document
their decline, Colorado's glaciers have been largely overlooked. There
have been few systematic, long-term monitoring studies here, in part
because the puny Front Range ice slabs barely qualify as glaciers.
Surprisingly little work has been done on the status of the glaciers in
Rocky Mountain National Park, home to about half the Colorado glaciers
named on U.S. Geological Survey maps. Park officials blame tight
One unfinished U.S. Geological Survey study of the park's Andrews
Glacier, however, suggests it has retreated a bit since 1991.
And Fountain recently embarked - with funding from NASA and the National
Science Foundation - on a multiyear study of Western glaciers, including
some in Rocky Mountain National Park.
He said the park's glaciers appear to be "holding steady," but that
early assessment is based mainly on a review of archival glacier
Warming's effects disputed
INSTAAR researchers Caine, Pfeffer and Dyurgerov are among the few who
have made an effort to study the local glaciers in detail.
Pfeffer compared the Arapaho Glacier's current surface elevation with
measurements made in 1960 and determined that the ice surface has
dropped 100 feet.
Caine has measured May-through-October runoff at Arikaree Glacier weekly
since 1981. Combining his runoff records with data from two nearby
weather stations, he calculated that the Arikaree has lost up to 66 feet
in depth since 1965.
Dyurgerov used 2003 Arapaho Glacier measurements, weather records and
some of Caine's Arikaree data to calculate a loss of about 130 feet at
Arapaho Glacier since 1960.
Though the INSTAAR researchers are convinced the losses are real, they
can't say for sure why the changes are happening.
But given the condition of mountain glaciers worldwide, it seems likely
that global climate change is playing some role, Pfeffer and Dyurgerov
"We know the temperature is rising globally, and we know that glacial
volumes are shrinking globally," Pfeffer said.
"My feeling is that global warming is probably involved.
"But I can't point at Arapaho - by itself, in isolation - and say this
is evidence of global warming. You just can't do that.
"You have to look at these things in aggregate."
Boulder geologist and archaeologist Jim Benedict says it would be "bad
science" to blame global warming for any of the Arapaho decline.
Benedict began photographing Arapaho Glacier annually in 1980. When he
compares his pictures with an 1898 archival photograph taken by CU's
R.S. Brackett, it's clear to him that "this poor thing has taken a
beating, no question."
Archival photos reveal that the Arapaho lost a tremendous amount of ice
between 1898 and 1960. The losses since then are less obvious in the
photos, although the CU reports suggest declines are continuing.
Dyurgerov's "mass balance study" concludes that the Arapaho actually
gained ice and snow from 1969 to 1975, but has been declining since
1976, with sharp drops during the current multiyear drought.
"We're losing this glacier," Benedict said as he mounted his Hasselblad
camera on a tripod at the Arapaho Col overlook during an early September
hike to the glacier. "It used to be big and convex. Now it's little,
shrinking and sad."
Due to local peculiarities of weather and topography, however, the Front
Range glaciers don't behave like typical mountain glaciers. So
assumptions about the effects of global climate change simply don't
apply here, he said.
"It's more difficult to interpret the effects of climate change here
than it is in other places, because things are complex here, not
straightforward," Benedict said.
State's temperature up
So why then are the Arapaho and Arikaree glaciers shrinking?
Are the declines simply a reaction to local and regional conditions, or
is global climate change involved?
In general, mountain glaciers are considered sensitive indicators of
temperature change: They advance when it gets colder and they retreat
when it warms.
During the 20th century, the global average surface temperature
increased by about 1 degree, according to the Intergovernmental Panel on
The IPCC was established by the World Meteorological Organization and
the United Nations in 1988 and includes hundreds of climate researchers
from around the world.
Some of that warming is likely due to natural climate variability.
But most of the observed warming during the past 50 years is probably
the result of human activities, the IPCC concluded in 2001.
And Colorado has not escaped the warming trend.
The state's average annual temperature has increased 1.5 degrees during
the past century, according to research meteorologist Martin Hoerling,
of the U.S. Climate Diagnostics Center in Boulder.
Six of Colorado's 10 warmest years have occurred since 1981, according
to temperature records from the National Climate Data Center.
"It's hard to pooh-pooh it and say that it doesn't look like a trend,"
said Assistant State Climatologist Nolan Doesken. "One can argue why
it's there, but it's hard to deny that it's there."
In some mountainous regions, including the Himalayas, Andes and Alps,
the warming of recent decades is more pronounced at higher altitudes.
But for reasons that remain unclear, that does not appear to be the case
- at least not yet - along Colorado's Front Range, said Henry Diaz,
another Climate Diagnostics Center meteorologist.
"In Colorado, there isn't any clear signal as far as (warming)
differences between the elevations," Diaz said.
Weather data from CU's Mountain Research Station on Niwot Ridge, several
miles northwest of Nederland, demonstrate that the warming picture is a
bit muddled along the Front Range.
In 1951, CU biologist John Marr established weather stations at various
elevations on the ridge to help clarify the Front Range ecology.
Conditions at four of the stations - known as A-1, B-1, C-1 and D-1 -
have been continuously monitored since 1953.
The C-1 station is in subalpine forest at an elevation of 9,973 feet.
Between 1976 and 2000, the average annual air temperature there
increased by about 3 degrees, according to Mark Losleben, manager of the
Mountain Climate Program at Niwot Ridge.
But the weather records from the highest station, D-1, tell a different
D-1 is in alpine tundra at 12,339 feet, roughly the same elevation as
The D-1 station has the longest unbroken high-altitude weather record in
At D-1, which is about five miles north of Arapaho Glacier, near
Arikaree Glacier, there's been no statistically significant temperature
change since 1953, Losleben said.
During that span, annual precipitation has increased by nearly half an
inch a year at D-1.
State Climatologist Roger Pielke Sr. and colleagues at Colorado State
University have suggested that increased cropland irrigation and
irrigated landscaping along the Front Range has boosted the amount of
cool, wet air flowing into the mountains in recent decades.
Moister air and an accompanying increase in mountain cloudiness could be
holding temperatures in check at places such as Niwot Ridge, Pielke and
his colleagues have suggested.
So, if the average annual temperature at D-1 hasn't changed and
precipitation is up, why are the Arapaho and Arikaree glaciers retreating?
Pfeffer suspects it's because the summer melting season is starting
earlier and lasting longer.
Caine wonders if more and more dust is being blown into the high
country, darkening the glacial ice and causing increased melting.
But no one knows for sure why it's happening.
"That's a puzzle," Caine said. "And it will probably remain a puzzle."
The long age of ice
During the Pleistocene Epoch, from 1.8 million to 10,000 years ago, the
Front Range was lined with rivers of ice that flowed down mountain
valleys as far east as present-day Nederland, Georgetown, Allenspark,
Fairplay and nearly to Estes Park.
The Cache la Poudre Glacier, northwest of present-day Fort Collins, was
the region's largest.
It sprawled nearly 30 miles from its source in the southern Medicine Bow
Mountains and was up to 2,000 feet thick, according to Richard Madole,
of the U.S. Geological Survey.
Scattered scraps of glacial ice persist today because west winds blow
snow over the Continental Divide. In many cases, the snow collects in
high, sheltered, bowl-shaped rock basins called cirques.
Over time, the snow is compressed into granules called firn, then
pressure welds the granules into glacial ice.
The Arapaho is Colorado's largest survivor and the southernmost active
glacier in the Rockies, according to INSTAAR researchers.
It is a cirque glacier, a tongue of ice and snow that creeps down the
Silver Lake Valley at 3 to 6 feet a year.
But if the melting continues at its current rate, when will Arapaho
That depends on the thickness of the remaining ice slab, which has never
been precisely measured.
To probe the depths of the Arapaho ice, seven researchers from INSTAAR
and the National Snow and Ice Data Center in Boulder recently backpacked
into the glacier - a six-mile round-trip hike - lugging a 170-pound
portable radar system.
Affectionately known as the Wright Flyer, the radar contraption looks
like a cross between the famous Kitty Hawk biplane and a high-tech dog
Like a giant Lego toy, the Flyer's wobbly 12-foot framework is pieced
together from segments of plastic PVC tubing. The frame rests on two
cross-country skis, so it can be hauled back and forth across the glacier.
A radar transmitter, receiver and batteries are strapped to the frame,
and fiber-optic cables send a digitized signal to a laptop computer.
The transmitter sends radar pulses through the ice to bedrock.
The time it takes for that signal to bounce back to the receiver -
measured in milliseconds - tells researchers the depth of the ice.
Boulder geophysicist Ted Scambos supervised the effort, as several
graduate student "Sherpas" lugged the Flyer across slushy snow, beneath
towering walls and spires of ancient gray gneiss and granite.
The radar reflection appeared to show an ice/rock boundary at a depth of
about 150 feet.
But the result was deemed inconclusive, and Pfeffer suspects the true
depth is less. A previous attempt to probe the glacier with radar,
conducted by the same group in 2002, yielded a depth of 73 feet.
"I'm not happy with either one of those numbers," Pfeffer said after the
The Boulder researchers are planning a return visit, possibly next month.
If 150 feet is in the ballpark, then Arapaho Glacier has lost at least
40 percent of its thickness since 1960. It would last another 60 years
or so if melting continues at its current rate.
But if the slab is just 73 feet thick, the glacier could be gone in half
If the latter measure is accurate, Arapaho Glacier, a final vestige of
the last ice age, could be gone from the face of Colorado within 30 years.