Future fluctuations of Mer de Glace, French Alps, assessed using a parameterized model calibrated with past thickness changes

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Abstract

Simulations of glacier evolution are needed to assess future changes in the runoff regime of mountain catchments. A simplified parameterized model is applied here to simulate future thickness changes and glacier retreat of Mer de Glace, French Alps. A normalized thickness change function describing the spatial distribution of surface-elevation changes as a function of elevation has been determined. The model reveals that under present climatic conditions Mer de Glace will continue to shrink dramatically in the coming decades, retreating by 1200 m between now and 2040. The method has certain limitations related to the uncertainties of the normalized function based on thickness change data. An error of 10% in the normalized function leads to uncertainties of 46%, 30% and 18% in Mer de Glace front, surface area and glacier-wide mass-balance changes respectively in 2040. Because the difference of the normalized function largely exceeds 10% from one glacier to another, even within a given glacier size class and elevation range, it would be very risky to extrapolate the normalized function to unmeasured glaciers. Consequently, the method is applicable only on glaciers where past surface elevation changes are well constrained.

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Rapid wastage of Alaska glaciers and their contribution to rising sea level.

Anthony A Arendt, Keith Echelmeyer, William D. Harrison … (2002)

We have used airborne laser altimetry to estimate volume changes of 67 glaciers in Alaska from the mid-1950s to the mid-1990s. The average rate of thickness change of these glaciers was -0.52 m/year. Extrapolation to all glaciers in Alaska yields an estimated total annual volume change of -52 +/- 15 km3/year (water equivalent), equivalent to a rise in sea level (SLE) of 0.14 +/- 0.04 mm/year. Repeat measurements of 28 glaciers from the mid-1990s to 2000-2001 suggest an increased average rate of thinning, -1.8 m/year. This leads to an extrapolated annual volume loss from Alaska glaciers equal to -96 +/- 35 km3/year, or 0.27 +/- 0.10 mm/year SLE, during the past decade. These recent losses are nearly double the estimated annual loss from the entire Greenland Ice Sheet during the same time period and are much higher than previously published loss estimates for Alaska glaciers. They form the largest glaciological contribution to rising sea level yet measured.

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Time–Scale for Adjustment of Glaciers to Changes in Mass Balance

Ed Waddington, Tómas Jóhannesson, Charles Raymond (1989)

The length of time TM over which a glacier responds to a prior change in climate is investigated with reference to the linearized theory of kinematic waves and to results from numerical models. We show the following: TM may in general be estimated by a volume time-scale describing the time required for a step change in mass balance to supply the volume difference between the initial and final steady states. The factor f in the classical estimate of τM = ƒl/u, where I is glacier length and u is terminus velocity, has a simple geometrical interpretation. Ft is the ratio of thickness change averaged over the full length I to the change at the terminus. Although both u and f relate to dynamic processes local to the terminus zone, the ratio f/u and, therefore, Tm are insensitive to details of the terminus dynamics, in contrast to conclusions derived from some simplified kinematic wave models. A more robust estimate of Tm independent of terminus dynamics is given by TM= h/(–b) where h is a thickness scale for the glacier and –b is the mass-balance rate (negative) at the terminus. We suggest that Tm for mountain glaciers can be substantially less than the 1O2–103 years commonly considered to be theoretically expected.