Minnesotans For Sustainability©
Sustainable: A society that balances the environment, other life forms, and human interactions over an indefinite time period.
Visit the world’s high mountain ranges and you’ll probably see less ice and snow today than you would have a few decades ago. More than 110 glaciers have disappeared from Montana’s Glacier National Park over the past 150 years, and researchers estimate that the park’s remaining 37 glaciers may be gone in another 25 years. Half a world away on the African equator, Hemingway’s snows of Kilimanjaro are steadily melting and could completely disappear in the next 20 years. And in the Alps, glaciers are retreating and disappearing every year, much to the dismay of mountain climbers, tourist agencies, and environmental researchers.
“Receding and wasting glaciers are a telltale sign of global climate change,” said Jeff Kargel, head of the Global Land Ice Measurements from Space (GLIMS) Coordination Center at the United States Geological Survey (USGS) in Flagstaff, Arizona. Kargel is part of a research team that’s developing an inventory of the world’s glaciers, combining current information on size and movement with historical data, maps, and photos.
In response to climate fluctuations, glaciers grow and shrink in length, width, and depth. Because glaciers are sensitive to the temperature and precipitation changes that accompany climate change, the rate of their growth or decline can serve as an indicator of regional and global climate change. Tracking and comparing recent and historical changes in the world’s glaciers can help researchers understand global warming and its causes (such as natural fluctuations and human activities). Glacial changes can also have a more immediate impact on communities that rely on glaciers for their water supply, or on regions susceptible to floods, avalanches, or landslides triggered by abrupt glacial melt.
This ASTER image shows the lakes left behind by retreating glaciers in the Bhutan-Himalaya. (Image courtesy of Jeffrey Kargel, USGS/NASA JPL/AGU).
Scientists track glacial change by measuring individual glaciers and comparing their size over time with records of the local and regional climate. But measuring every major glacier on Earth would be a monumental task. Approximately 160,000 glaciers occupy the Earth’s polar regions and high mountain environments, and sending a team to each one every year would be costly and difficult to coordinate. In addition, although a few research teams travel to a few glaciers each year to measure ice depth, size, movement, and water content, the data from individual glaciers don’t necessarily reveal how other glaciers in the same region—much less in other parts of the world—are changing. Even glaciers within the same region can react differently to environmental changes. For example, while most glaciers in Glacier National Park are retreating, some are advancing.
The GLIMS team uses high-resolution satellite images from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument and the Landsat Enhanced Thematic Mapper Plus (ETM+), archived at the Land Processes Distributed Active Archive Center (LP DAAC), to track the size and movement of glaciers. For the first time, scientists will be able to assess and track glacial change on a global scale through a worldwide database of glacier information.
This ASTER image, acquired on July 23, 2001, shows Aletsch Glacier, the largest glacier of Europe. (Image by Earth Observatory Team, based on data provided by the ASTER Science Team)
About three-quarters of the Earth’s fresh water is held in ice sheets and mountain glaciers, so recognizing and understanding changes in the world’s glaciers is crucial. “Glaciers serve as a natural regulator of regional water supplies,” said Kargel. During periods of warm weather and intense sunlight, such as during dry seasons and droughts, glaciers melt vigorously and provide a water source for the surrounding ecosystems and communities. Conversely, during cold, rainy seasons, glaciers produce less meltwater. “Glacier changes, especially recent melting, can affect agriculture, drinking water supplies, hydroelectric power, transportation, tourism, coastlines, and ecological habitats,” he added.
This composite ASTER image shows how the Gangotri Glacier terminus has retracted since 1780. Contour lines are approximate. (Image by Jesse Allen, Earth Observatory; based on data provided by the ASTER Science Team; glacier retreat boundaries courtesy the Land Processes Distributed Active Archive Center)
Excessive glacial melt can also result in increased hazards or disasters for communities living near glaciers. “Glaciers don’t always behave nicely. They’re a type of natural reservoir with a temper, in some cases. Some glaciers have a nasty habit of storing up large amounts of water and then releasing it suddenly in a massive melt or calving episode, which may involve floods, landslides, or avalanches,” said Kargel.
As settlements, farming, and tourism extend toward the edges of glaciated regions, melting glaciers and the avalanches and floods that often accompany rapid melt increasingly threaten lives and infrastructure in mountain regions. The ASTER images acquired for the GLIMS project allow researchers to recognize and track changes in glacial hazard indicators such as crevasses, avalanche and debris-flow traces, and glacial lakes.
While current melting trends can’t be slowed or reversed, the information collected through the GLIMS project will enable researchers to better understand the relationship between climate and glaciers, and to better predict areas of future glacier changes.
The ASTER images of each glacier, along with the data collected and
analyzed by the GLIMS team, are stored in a large database jointly developed
by the USGS in Flagstaff and the National Snow and Ice Data Center (NSIDC)
in Boulder, Colorado.
Left: This 1929 photograph
shows Taku Glacier as it winds through the mountains of southeastern Alaska,
calving small icebergs into Taku Inlet. (Image courtesy of U.S. Navy)
Although the GLIMS project is still in a formative stage, the yearly satellite data being compiled and stored with historical data from the last three to five decades will enable scientists to track worldwide glacier changes and the effects of such change on surrounding communities and habitats. “I think we’ll have some interesting data that will be publicly accessible within the coming year,” said Raup. “It won’t be global coverage yet, but there should be some good snapshots of glacier health within a few regions. This is a fascinating time to study and inventory the world’s glaciers because of the recent dramatic changes.”
“I think a hundred years from now, the GLIMS effort to study the world’s glaciers will still be going strong,” said Kargel. “There will still be glaciers to study, although far fewer than there are today. But GLIMS will eventually consist of well over a century’s worth of glacial data.”
This article contributed from Distributed Active Archive Center (DAAC) Alliance: Supporting Earth Observing Science 2004 (to be released in the fall of 2004)
NASA Earth Science Enterprise Data Centers provide data and user
services in support of the Earth observing sciences. See at < http://nasadaacs.eos.nasa.gov/
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