The United States Geological Survey has released a Fact Sheet reporting that three "benchmark" glaciers, two in Alaska and one in Washington state, are shrinking. The report is based on data that has accumulated over a fifty-year period.
The United States Geological Survey has released a Fact Sheet reporting that three "benchmark" glaciers, two in Alaska and one in Washington state, are shrinking. The report is based on data that has accumulated over a fifty-year period.
The USGS has been studying glaciers under the aegis of its Benchmark Glacier Program, which began in 1957. The period July 1, 1957 through December 31, 1958 was known as the International Geophysical Year. The successful Soviet attempt to launch an artificial satellite, Sputnik I, and the subsequent successful U.S. launches of Explorer and Vanguard satellites, were part of IGY activities.
Data have been collected on an annual basis at three glaciers, each representing a different climatic region in the United States:
-- the South Cascade Glacier in the Cascade Mountains of Washington State;
-- the Wolverine Glacier on the Kenai Peninsula, near Anchorage, Alaska; and
-- the Gulkana Glacier in the Alaskan interior.
The Fact Sheet contains photos of the the South Cascade Glacier taken in the years 1928, 1959, 1979, and 2003. The pictures show a marked retreat of the South Cascade Glacier....
The USGS measures accumulation and loss of glacial mass using a number of stakes pounded into the glacier. Scientists visit each site at least twice a year, once in the Spring, and then again in the Autumn, to take measurements. The stake measurements are combined with local temperature and precipitation data to estimate the glacier net balance, as well as the seasonal winter (total accumulation) and summer (total ablation or mass loss).
The Fact Sheet includes a graph, as a function of time, of the spatially averaged thickness change for each glacier. The graphs are headed downward at an accelerating slope.
The USGS reports the following Conclusions:
-- All three glaciers have lost mass since USGS monitoring began more than four decades ago.
-- Mass loss has accelerated during the last 15 years, coincident with the highest melt years on record.
-- Mass balance of the coastal South Cascade and Wolverine Glaciers correlate well with the Pacific Decadal Oscillation (PDO), an ocean-climate oscillation similar to the El Niño Southern Oscillation, during the first few decades of the period of record. This shows the effects of ocean-condition periodicity on glacier health.
-- This correlation has weakened during the last two decades, as global average temperature has increased.
-- Mass turnover has increased throughout monitoring and the trend of increase has become stronger during the last two decades.
The accelerating loss of mass, the weakening correlation with the PDO, and increasing mass turnover, are likely the result of changes to warmer or drier (or both) climate conditions that are affecting all three regions.
The climate changes could be overwhelming the previously observed responses of the maritime glaciers to periodic shifts in ocean conditions, such as are represented by the PDO.