Survey Finds Sierra's Glaciers Are Shrinking

Mt. Shasta bucks trend -- ice expands on 'lonely mountain'

by Usha Lee McFarling, Los Angeles Times
San Francisco Chronicle - October 12, 2003

A new survey of glaciers in the Sierra Nevada shows the thick slabs of ice that have frosted many of the state's high peaks for the last thousand years are dramatically shrinking and, in some cases, disappearing altogether.

However, researchers found precisely the opposite phenomena atop Mount Shasta in far Northern California, where glaciers are growing.

Seven Sierra Nevada glaciers that were surveyed and rephotographed over the summer are all smaller than they were a century ago, said Hassan Basagic, a graduate student at Portland State University who initiated the survey. The mountain range is home to most of the state's glaciers.

"There's been lots of melt," said Nathan Stephenson, a research ecologist with the U.S. Geological Survey based at Sequoia National Park. Stephenson led a glacier survey of the Evolution Range in Kings Canyon National Park in August.

Darwin Glacier near Bishop (Inyo County) is an estimated 50 to 100 feet thinner today than it was in historical photos from the early 1900s. The Lyell Glacier off the popular John Muir Trail in Yosemite National Park is retreating to the peaks above Tuolumne Meadows from which it springs.

But the growth of the Shasta glaciers was an unexpected development, given that the majority of the world's glaciers are in retreat. All seven of the moutain's glaciers, including three-mile long Whitney, the state's largest, have grown in recent decades. Three of the mountain's glaciers have doubled in size since 1950, said Slawek Tulaczyk, a glaciologist at UC Santa Cruz who began the Mount Shasta Glacial Survey in 2002.

"We totally expected them to have shrunk, and they've grown dramatically," he said.

The changes in California's ice -- both its growth and retreat -- are a product of vast climatic cycles that have caused ice to ebb and flow across the Earth's surface for millions of years. Most ice worldwide has retreated in the past 100 years as the planet has recovered, through natural processes, from a recent bout of cooling called the "Little Ice Age," which ended around 1850.

But many experts also suspect the transformation of the glaciers may be accelerating as the planet warms in response to the human production of greenhouse gases, such as carbon dioxide.

"I would never point the finger and say this is all human-induced warming," Stephenson said. "But maybe we are speeding it up now."

Glaciers are a product of temperature and precipitation. To grow, they require snowfall and temperatures cold enough that winter snow does not melt during the summer but accumulates each year and eventually compresses itself into a slowly moving slab of ice.

When temperatures warm, the ice naturally melts away. This has resulted in the shrinkage of glaciers in the Sierra Nevada. But higher winter temperatures can also increase snow and fuel glacial growth in some areas, such as Mount Shasta, by allowing the air to hold more moisture.

"The climate of these two places is different," Tulaczyk said. Mount Shasta, which he calls "a lonely mountain," sticks out and captures weather that is passing by. The Sierra Nevada, in contrast "makes its own weather."

As warm, moist air rises up Mount Shasta, it is released as snow in something Tulaczyk calls "the snow-gun effect." Such an effect has been recorded on some of Norway's glaciers, which are growing as well, he said.

The warming trend is expected to continue, Tulaczyk said, to the point where it will overcome the increase in precipitation. When that happens, the Shasta glaciers could start to retreat.

The new data on California's glaciers come after many decades in which the region was ignored by glaciologists, who tend to focus on immense glaciers in the Himalayas, the Arctic and the Antarctic, where ice sheets are large enough to break off chunks as large as small states.

But as climate research has become a high priority, even puny glaciers have become important. Glaciers -- big or small -- are sentinels of climate change. Monitoring them closely can reveal how fast the climate is changing and what role humans may be playing in that change.

The smaller the glacier is, the more valuable it may be in studies of recent climate change, Tulaczyk said. California's glaciers are small and thin enough that they can respond to climate changes within a decade. Some of Alaska's hefty glaciers could take 1,000 years to show the effects of modern warming.

Basagic's glacier survey also aims to refine estimates of how many glaciers exist in California. Those estimates range from several dozen to nearly 500. The survey also could provide a modern baseline against which the erasing of the ice could be measured in the future -- a future that the United Nations Intergovernmental Panel of Climate Change predicts could be 2.5 to 10.4 degrees Fahrenheit warmer in 100 years.

While Basagic and Stephenson expected to see the glaciers of the Sierra in retreat, they were not prepared for how quickly the ice had disappeared. The rapid shrinking is obvious, even when today's glaciers are compared with photos taken in 1976, the last time Stephenson approached and photographed Goddard glacier.

"I thought, 'Oh my gosh, in my lifetime, I'm seeing this change,' " Stephenson said.

Other Sierra Nevada glaciers that the survey found were retreating include Junction Peak, Mendel, Maclure and Dana glaciers.