Seminar Abstract

Andrew Fountain

Thursday, March 8, 2007

Glaciers in the American west: Response to climate change during the past century


The glaciers of the American West, exclusive of Alaska, have retreated since the beginning of observations starting at the beginning of the 20th Century. The retreat was initially fast as the climate was warming from the Little Ice Age and then slowed (or reversed) in the 1950's to 1970's.  Retreat accelerated after the 1975-76 shift in winter atmospheric circulation. The circulation shift caused thinner winter snow packs resulting in a more negative net balance. No trend in summer temperatures is evident. The magnitude and rate of retreat for individual glaciers varies greatly. The variability between climate and glacier response, aside from the dynamical time-scale response, results from the interaction between local topography and large scale climate forcing. For example, local topographic factors may enhance or suppress local snow accumulation. As glaciers shrink, they retreat into higher elevations and local climates of favorable energy balance conditions slow the rate of shrinkage.  In these environments the
glaciers can become insensitive to further climatic change, in our case, reduced winter snow accumulation.  We speculate that this unstable state of equilibrium would persist until a climatic threshold is crossed whereby the glacier essentially disappears.


Speaker bio:

Dr. Fountain is a Professor of Geography and Geology at Portland State University in Portland, Oregon.