Glacier Response to Climate ChangeGlaciers respond to climate in an attempt to achieve equilibrium. A glacier advances due to a climate cooling/snowfall increase that causes positive mass balance. A climate warming/snowfall decrease leads to negative mass balances and glacier retreat. To reestablish equilibrium a retreating glacier must lose enough of its highest ablating sections, usually at the lowest elevations, so that accumulating snows near the head of the glacier once again are equivalent to overall ablation, and an equilibrium balance is approached. This is akin to a corporation layoff some workers or selling a poor division to try to return to profitability. If a glacier cannot retreat to a point where equilibrium is established, it is in disequilibrium with the climate system. That is it is bankrupt and will not survive.
The primary focus of attention has been on changes in terminus position of a glacier which tells us how the glacier is currently responding to recent climate. This portion of smaller alpine glaciers responds very quickly to climate. However, a glacier can retreat rapidly and still survive if it has an accumulation zone. Terminus behavior is not a good indicator of glacier survival.
For a glacier to survive it must have a consistent and persistent accumulation zone. Thus, to forecast survival we need to focus on the accumulation zone, not the terminus. If the accumulation zone no longer retains accumulation consistently it will begin to thin. Symptoms of accumulation zone thinning are: 1) The margins of the glacier in the accumulation zone-upper potion of the glacier recede. 2) New outcrops of rock maybe exposed in the accumulation zone due to thinning. 3) The upper portion of the glacier, what should be the accumulation zone, has little or no snowcover. This year was our 28th consecutive year measuring North Cascade glaciers and the forecast method emerged from our mass balance observations. This behavior has been observed both in the North Cascades, Italian Alps and Swiss Alps.
Comparison of image pairs from the North Cascades of Washington will indicate if the top of the glacier is receding. For example Foss Glacier has considerable retreat even in the margin at the the head of the glacier and has little retained snowpack even in early August in many recent summers 2003, 2004, 2005, 2007 and 2009 for example.
Easton Glacier on Mount Baker is not shrinking in the accumulation zone and is forecast to survive current climate.
This method of assessment needs to be done glacier by glacier whether you are in the Italian Alps, Peruvian Andes or Canadian Rockies. In Glacier National Park not all the glaciers lack a consistent accumulation zone, most did and have or are disappearing. Jackson Glacier is not retreating rapidly and still does have an accumulation zone.
Now it your turn to examine those pictures of glaciers you have returned to and that seemed to be shrinking considerably. Let me know what their symptoms are.
External LinksForecasting temperate alpine glacier survival from accumulation
Glacier Mass balance and equilibrium or disequilibrium response
Donne Glacier Retreat
Helm Glacier Melting Away