For decades, glaciers in the United States have been shrinking in response to climate change. In 1957, the U.S. Geological Survey began the Benchmark Glacier Program, tracking three glaciers in three climatic regions in the U.S. The purpose of this program is to collect long-term data on how glaciers in these regions are responding to climate shifts. The results of this study show an alarming trend towards a warming climate and shrinking glaciers.
The USGS Benchmark Glacier Program
The Benchmark Glacier Program focused on three glaciers in three U.S. regions: 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. Data was collected annually starting in 1957 for the South Cascade Glacier and in 1966 for the Wolverine and Gulkana Glaciers. Data was collected based on three techniques to measure glacier change annually and interannually:
- Cumulative net-balance, which is the total loss or gain of glacier mass during the 50-year study and is used to show whether the glacier is growing or shrinking.
- Seasonal mass balance, which can show if seasonal variations in precipitation and temperature are reasons for glacier change.
- Mass turnover, which describes the amount of water moving through the glacier system and the intensity of the local hydrologic cycle, and is estimated by averaging the absolute values of summer and winter glacier masses. For example, glaciers in high-precipitation areas grow a lot in the winter and shrink a lot in the summer. But glaciers in more arid regions change little from winter to summer.
Analyzing the glacier data using these three techniques has provided scientists with cumulative surveys showing overall glacier retreat over the past 50 years.
Mass Balance, Accumulation and Ablation
Three very important key words in glacier studies are accumulation, ablation and mass balance. Accumulation of a glacier occurs when ice is added to a glacier through snowfall and other forms of freezing precipitation. Ablation occurs when the glacier melts as water run-off or evaporating water vapor. Or, in the case of coastal ice shelves, ablation occurs when chunks of ice fall off and become icebergs. Mass balance is the difference between accumulation and ablation and it can be in reference to interannual or annual variations.
In 2009, glaciologists with the USGS created a Fact Sheet titled, "Fifty-Year Record of Glacier Change Reveals Shifting Climate in the Pacific Northwest and Alaska, USA." This Fact Sheet explained the science behind their conclusions that global warming was responsible for shrinking glaciers in the U.S. Glacier data collected over a 50-year period was analzyed using the cumulative net-balance, seasonal mass balance, and mass turnover techniques. The results showed that, any way the data is looked at, glaciers are shrinking at an incredibly fast rate and accumulation during winter months can not offset ablation during the summer months.
Source:
"Fifty-Year Record of Glacier Change Reveals Shifting Climate in the Pacific Northwest and Alaska, USA," usgs.gov
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Alexandra Matiella Novak - With a PhD in Geology and expertise in science education, Alexandra is passionate about increasing the public's Earth science literacy.
