Climate Change is Forcing Glaciers to Retreat
USGS Fact Sheet 2009–3046
Fifty-Year Record of Glacier Change Reveals Shifting Climate in the Pacific Northwest and Alaska, USA
U.S. Geological Survey (USGS) 50-year research on glacier change shows recent dramatic shrinkage of glaciers in three climatic regions of the United States. These long periods of record provide clues to the climate shifts that may be driving glacier change.
The USGS Benchmark Glacier Program which began began in 1957 , collected data annually at three glaciers that represent three climatic regions in the United States:
- South Cascade Glacier in the Cascade Mountains of Washington State
- Wolverine Glacier on the Kenai Peninsula near Anchorage, Alaska
- and Gulkana Glacier in the interior of Alaska
“These are the three glaciers in North America that have the longest record of mass change,” said Shad O’Neel, a USGS glaciologist and one of the report authors. “All three of them have a different climate from the other two, yet all three are showing a similar pattern of behavior, and that behavior is mass loss.”
Fig 1. USGS Benchmark Glaciers
Glaciers respond to climate changes by thickening and advancing down-valley towards warmer lower altitudes or by thinning and retreating up-valley to higher altitudes. Glaciers average changes in climate over space and time and provide a picture of climate trends in remote mountainous regions. A qualitative method for observing these changes is through repeat photography—taking photographs from the same position through time (fig. 2).
The most direct way to quantitatively observe changes in a glacier is to measure its mass balance: the difference between the amount of snowfall, or accumulation, on the glacier, and the amount of snow and ice that melts and runs off or is lost as icebergs or water vapor, collectively termed ablation (fig. 3).
Positive mass balance occurs when accumulation is greater than ablation and if maintained over long periods results in glacier growth. Conversely, sustained periods of negative mass balance, where accumulation is less than ablation, results in glacier shrinkage. A shrinking glacier thins faster near the terminus (the lowest part of the glacier) than near the head (the highest part of the glacier), which is why the terminus retreats up-valley while the glacier head remains in place (fig. 2). The net balance is the average mass balance over the entire glacier for one glaciological year, the time between the end of the summer ablation season from one year to the next.
Figure 2. Retreat of South Cascade Glacier, Washington, during the 20th Century and the beginning of the 21st Century.
“[The study] certainly says that the place where these glaciers are, the climate is not supportive of healthy glaciers anymore,” O’Neel said.
Figure 3. Diagram of a glacier showing components of mass balance.
Ed Josberger, a USGS hydrologist, and the report coordinator, said the results from the Gulkana, South Cascade and Wolverine glaciers represent global trends.
“There is no doubt that most mountain glaciers are shrinking worldwide in response to a warming climate,” He said.
Full report is available at USGS.
Map showing Gulkana Glacier and other major glaciers of the central and eastern Alaska Range . Click on Gulkana Glacier to go to map of Gulkana Glacier basin. USGS
Gulkana Glacier, Oct. 5, 2003. Photo by Rod March. USGS
Regional Map of South Central Alaska showing location Gulkana and Wolverine Glaciers. USGS
Wolverine Glacier, Sept. 10, 2003. Photo by Rod March. USGS.
South Cascade Glacier, Oct. 5, 2000. Photo by Bob Krimmel. USGS
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