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The acceleration of glacier shrinkage after 1985 indicates a transition toward rapid down- wasting rather than a dynamic glacier response to a changed climate

I am unable to distinguish between downwasting and glacier response to climate change. The above extract is from the paper by Zemp, Michael, et al. "Glacier fluctuations in the European Alps, 1850–2000." Darkening Peaks Glacier Retreat Sci. Soc (2008). Thank you

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Downwasting refers to glacier thinning due to melting ice. The statement seems to try to clarify the ambiguity that occurs when glacier changes are studied using non-stereo satellite images. With such images, people usually link changes in area (which can be observed in the images) to changes in glacier mass (which cannot be observed in such images). However, changes in area do not necessarily mean changes in mass.

For example, a warmer climate means more melt in the ablation area, but warmer air also carries more moisture, leading to an increase in snow accumulation in the upper accumulation area. Therefore, such climate change triggers a dynamic response that can reduce the area of the glacier with or without a change in glacier mass. In this example, the upper accumulation area can get thicker and the ablation area smaller. This could, in some cases, lead to a reduction in area without a reduction in mass.

In that sentence, as I understand it. The author is trying to make clear that the changes observed are due to overall glacier thinning and not to a dynamic response (or mass redistribution with some areas getting thicker and others thinner).

With the context given by the author, I also find the sentence a bit unclear. But is it easier to understand if you look at the original citation they give:

Paul, F. 2004. The new Swiss glacier inventory 2000: Application of remote sensing and GIS. Ph.D. diss., University of Zurich.

There they say:

Although changes in glacier surface elevation cannot be measured with TM, the observed changes in glacier geometry indicate a massive down-wasting since 1985 rather than a dynamic response to a changed climate.

Where TM refers to the "Thematic Mapper" sensor onboard the old Landsat satellites.

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