A Few Western Glaciers Exceptions to the Rule: They're Growing

09/15/2009

Shrinking glaciers have turned out to be one of the clearest harbingers of global warming. But while most of the world's glaciers recede, a few in the American West are bucking the trend. Climate change skeptics would have you believe these examples undermine the evidence for global warming. Glacier researchers on the other hand can explain the aberrations. Correspondent Tom Banse takes a closer look.

You're no doubt familiar with the rule: glaciers are shrinking. So we're going to focus on the snowy exceptions. We'll work from of an inventory of western glaciers assembled by Portland State University professor Andrew Fountain. The National Science Foundation commissioned this inventory. Fountain says the general rule is definitely in force.

Fountain: "Up here in the Northwest, we are more fortunate that we only have an area loss between 34 to 40 percent."

That is the loss since the turn of the last century. Fountain counts about eight exceptions among the several hundred glaciers he's tracking in the American West. The first one he mentions is Crater Glacier on Mount St. Helens. This would be hydrologist Joe Walder's baby.

Walder: "If you're thinking of something that is going to be nice and white, you're not seeing that. It's really this very dark mass because of all of the rock debris that's accumulated on top."

It's a warm and sunny day, but powerful gusting winds foil Walder's plan to fly into the crater. The U.S. Geological Survey researcher can get no closer than the volcano observatory about five miles away.

Walder: "We're getting pelted."

Banse: "I got a little ash in my eyes."

At other times, avalanches or falling rocks make the crater a dangerous place to work. Walder says Mount St. Helens' massive 1980 eruption created the perfect setting to form a new glacier. The north facing crater has steep walls that shade the bowl nearly year round. It looks and acts like a catcher's mitt.

Walder: "Snow avalanches off the crater walls constantly during the winter."

The icefield got pushed around by the volcano's most recent lava extrusion. But the mass survived. Now, the glacier has grown so fast, it has overrun instruments placed to track it.

Walder: "It is advancing something like a hundred meters — 300 feet — in a year, roughly speaking."

So, is this an exception that proves the rule or one that creates doubt? For his part, Walder simply classifies Crater Glacier as an anomaly.

Walder: "It is certainly the exception, but it doesn't bear on the general phenomenon of glacier retreat throughout western North America."

At the southern end of the Cascade Range rises a different snow–capped puzzle. It's Mount Shasta. Measurements of Shasta's glaciers show 50 years of nearly continuous expansion. Fountain explains the leading theory for why.

Fountain: "That area has been subject to enhanced precipitation. When you're above the freezing level, that precipitation is snow and those glaciers have responded."

The increased moisture comes thanks to a warming ocean. Fountain says the same mechanism is helping some glaciers on the Northwest's tallest peaks, such as Mount Rainier, Mount Baker and Mount Adams, to hold their own. But Fountain figures these glaciers can't buck the global trend much longer.

Fountain: "We do expect it to be a temporary phenomenon. The modeling done down on Mount Shasta expects the glaciers to retreat within the next decade or so, if they're not already. And we fully expect the glaciers to begin to retreat more rapidly on these volcanoes in Washington and Oregon."

Fountain says climate models call for the freezing level to rise. If that happens, less glacier surface will be nourished by snow and more will be eroded by rain. I'm Tom Banse reporting.

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