RESPONSE OF U.S. GLACIERS TO POST-LITTLE-ICE-AGE CLIMATE

Glaciers exist in Alaska (AK) and 9 western contiguous states (WCS). A survey was conducted to determine how these U.S. glaciers are responding to post-Little Ice Age (LIA) climate. In AK, glaciers occur on 11 mountain ranges and 3 island areas; cover ~ 5% of the State (~ 75,000 sq. km); and range in elevation from > 6,000 m to below sea level, and latitude from 55 to 69 degrees N. In the WCS, glaciers exist in 19 mountain ranges and on 8 volcanoes, cover < 0.00001 of the WCS (~ 600 sq. km), and range in elevation from ~ 4,300 m to ~1,250 m, and latitude from 39 to 49 degrees N. Many types of data were used to construct baselines and determine glacier change. These include: published and manuscript descriptions of glaciers; historic and modern maps; aerial, ground, and space photography; airborne and satellite radar; multi-spectral satellite imagery; various types of proxy data; and aerial reconnaissance and field observations by the author. Data available varied for each region and glacier.

In the WCS (Washington, Oregon, California, Montana, Wyoming, Colorado, Idaho, Utah, and Nevada), every area investigated is characterized by significant glacier retreat, thinning, and/or stagnation, especially at lower elevations. At some locations, glaciers have completely disappeared during the 20th century. In places, retreat that started pre-mid-19th century has continued into the 21st century.

In AK, every glacier ending below ~ 1,500 m in the Wrangell Mountains, Alaska Range, Talkeetna Mountains, Ahklun-Wood River Mountains, Kigluaik Mountains, Brooks Range, Alexander Archipelago, Aleutian Islands, and on Kodiak Island is retreating, thinning, and/or stagnating. In the Coast Mountains, Saint Elias Mountains, Chugach Mountains, Kenai Mountains, and the Aleutian Range, more than 98% of glaciers ending below ~ 1,500 m are also retreating, thinning, and/or stagnating. However, ~ 15 glaciers are currently advancing. Some advancing glaciers have tidewater termini. Many glaciers have disappeared during the 20th century. In places, retreat is resulting in the number of glaciers increasing, but volume and area decreasing. Glaciers at elevations above ~ 1,500 m show little or no change.

AK's two largest glaciers, Bering and Malaspina, are thinning and retreating, losing several cubic kilometers of ice each year to melting and calving. U.S. glaciers are a major contributor of meltwater to global sea level rise, with > 99% coming from AK.