This is not the only means to an end for a glacier, nor is it a robust means for identifying glacier disequilibrium. The equilibrium line is the elevation on a glacier at which annual accumulation equals ablation. It was noted in the Tropical Glacier Retreat post that if the annual equilibrium line rises above the mountain top this will lead to glacier loss. Therefore, it is important to note whether glaciers are undergoing an equilibrium or disequilibrium response to climate change. A glacier that is in disequilibrium will melt away with a continuation of the current climate. If a glacier cannot retreat to a point where equilibrium is established, it is in disequilibrium with the current climate. This is a glacier equivalent to jettisoning bad debt. An equilibrium response occurs when a new equilibrium is reached by a retreating glacier losing enough of its high ablating sections, usually at its lowest elevations, so that accumulation once again balances ablation. A climate warming/snowfall decrease leads to negative mass balances and glacier retreat. The advance increases the glaciers area at low elevation where ablation is highest, returning the glacier to equilibrium. A glacier advances due to a climate cooling/snowfall increase that causes positive mass balance. Glaciers respond to climate change in an attempt to achieve a new equilibrium. For an alpine glacier to have an equilibrium balance it typically must have upwards of 60% of its area in the accumulation zone at the end of the summer melt season. The alpine glaciers discussed here are not calving, nor do they have superimposed ice, two factors that complicate measurement. ![]() A glacier is divided into an ablation zone where all accumulated snow is lost from the winter and an accumulation zone where snowpack is retained to the end of the summer. The World Glacier Monitoring Service (WGMS) collects from alpine glaciers around the world annual mass balance data, which is the difference between annual accumulation and annual ablation (from melting and sublimation). This together with their wide distribution has made them a key marker of current climate change. Glaciers have long been recognised as sensitive and reliable indicators of climate. The question is determining which glaciers are merely out of equilibrium and can retreat to a position of equilibrium, and which are in complete disequilibrium and will melt away? Let me explain. The trend suggests that all of the glaciers are out of balance and that some will disappear. I will focus here on North American glaciers whose mass balance measurements in the West from 1984-2005 indicate a declining trend. I get asked at least once a day about the future prognosis for alpine glaciers and whether they have a future.
0 Comments
Leave a Reply. |