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- Dyurgerov, Mark, et al.
(författare)
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A new index of glacier area change: a tool for glacier monitoring
- 2009
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Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 55:192, s. 710-716
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Tidskriftsartikel (refereegranskat)abstract
- Since the mid-19th century, most glaciers have been losing area and volume. This loss of area has not been homogeneous in time and space, and direct observations are sparse, making regional and global estimates of glacier change difficult. This paper focuses on developing a single index for monitoring glacier change, one that would be particularly useful for remote-sensing applications. We combine the results of direct glacier mass-balance observations B, total glacier area S and accumulation area S-c derived from maps or remotely sensed images. Using the accumulation-area ratio (AAR = S-c/S), we note the differences between observed AAR, time-averaged < AAR > and the equilibrium state AAR(0), as determined by its value at B = 0 from a regression of B(AAR). We suggest that alpha(d) = (< AAR > - AAR(0))/ AAR(0) quantifies the difference between the currently observed state of glaciers and their equilibrium state and measures the delay in the dynamic response of S relative to the climatic response of S-c. Using all available observations for the period 1961-2004, alpha(d) approximate to -65% for tropical glaciers, which implies their rapid shrinkage as S continues to decrease and 'catch up' with S-c. During the same period, mid-latitude and polar glaciers show less negative values Of alpha(d). Of 86 glaciers from all latitudes and regions, only 11 show positive alpha(d) at any time between 1961 and 2004. Averaged over 1961-2004, alpha(d) is -15.1 +/- 2.2%, and < B > is -360 +/- 42 mm a(-1) w.e. Values for AAR(0) range between about 40% and 80%, but the bulk of the equilibrium values are between 50% and 60%. The average AAR(0) is 57.9 +/- 0.9% and has remained stable over time (the equilibrium AAR has not changed with climate). Overall, the observed negative alpha(d) suggests a committed retreat of glaciers and their continuing contribution to sea level even if global temperature is held constant.
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| 2. |
- Beedle, M., et al.
(författare)
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Improving estimation of glacier volume change: a GLIMS case study of Bering Glacier System, Alaska.
- 2008
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Ingår i: The Cryosphere. - 1994-0416. ; 2:1, s. 33-51
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Tidskriftsartikel (refereegranskat)abstract
- The Global Land Ice Measurements from Space (GLIMS) project has developed tools and methods that can be employed by analysts to create accurate glacier outlines. To illustrate the importance of accurate glacier outlines and the effectiveness of GLIMS standards we conducted a case study on Bering Glacier System (BGS), Alaska. BGS is a complex glacier system aggregated from multiple drainage basins, numerous tributaries, and many accumulation areas. Published measurements of BGS surface area vary from 1740 to 6200 km2, depending on how the boundaries of this system have been defined. Utilizing GLIMS tools and standards we have completed a new outline (3630 km2) and analysis of the area-altitude distribution (hypsometry) of BGS using Landsat images from 2000 and 2001 and a US Geological Survey 15-min digital elevation model. We compared this new hypsometry with three different hypsometries to illustrate the errors that result from the widely varying estimates of BGS extent. The use of different BGS hypsometries results in highly variable measures of volume change and net balance (bn). Applying a simple hypsometry-dependent mass-balance model to different hypsometries results in a bn rate range of −1.0 to −3.1 m a−1 water equivalent (W.E.), a volume change range of −3.8 to −6.7 km3 a−1 W.E., and a near doubling in contributions to sea level equivalent, 0.011 mm a−1 to 0.019 mm a−1. Current inaccuracies in glacier outlines hinder our ability to correctly quantify glacier change. Understanding of glacier extents can become comprehensive and accurate. Such accuracy is possible with the increasing volume of satellite imagery of glacierized regions, recent advances in tools and standards, and dedication to this important task.
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| 7. |
- Hock, Regine, et al.
(författare)
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Mountain glaciers and ice caps around Antarctica make a large sea-level rise contribution
- 2009
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 36:L07501
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Tidskriftsartikel (refereegranskat)abstract
- The Intergovernmental Panel on Climate Change (IPCC) estimates that the sum of all contributions to sea‐level rise for the period 1961–2004 was 1.1 ± 0.5 mm a−1, leaving 0.7 ± 0.7 of the 1.8 ± 0.5 mm a−1 observed sea‐level rise unexplained. Here, we compute the global surface mass balance of all mountain glaciers and ice caps (MG&IC), and find that part of this much‐discussed gap can be attributed to a larger contribution than previously assumed from mass loss of MG&IC, especially those around the Antarctic Peninsula. We estimate global surface mass loss of all MG&IC as 0.79 ± 0.34 mm a−1 sea‐level equivalent (SLE) compared to IPCC's 0.50 ± 0.18 mm a−1. The Antarctic MG&IC contributed 28% of the global estimate due to exceptional warming around the Antarctic Peninsula and high sensitivities to temperature similar to those we find in Iceland, Patagonia and Alaska.
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