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| 2. |
- Hock, Regine, et al.
(författare)
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Climate sensitivity of Storglaciären, Sweden : an intercomparison of mass-balance models using ERA-40 re-analysis and regional climate model data
- 2007
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Ingår i: Annals of glaciology, Vol 46, 2007. - : International Glaciological Society. - 9780946417414 ; 46:1, s. 342-348
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Konferensbidrag (refereegranskat)abstract
- Estimates of glacier contributions to future sea-level rise are often computed from mass-balance sensitivities derived for a set of representative glaciers. Our purpose is to investigate how mass-balance projections and sensitivities vary when using different approaches to compute the glacier mass balance. We choose Storglaciären, Sweden, as a test site and apply five different models including temperature-index and energy-balance approaches further varying in spatial discretization. The models are calibrated using daily European Centre for Medium-Range Weather Forecasts re-analysis (ERA-40) data. We compute static mass-balance sensitivities and cumulative mass balances until 2100 based on daily temperatures predicted by a regional climate model. Net mass-balance sensitivities to a +1 K perturbation and a 10% increase in precipitation spanned from −0.41 to −0.61 and from 0.19 to 0.22 m a−1, respectively. The cumulative mass balance for the period 2002-2100 in response to the climate-model predicted temperature changes varied between −81 and −92 m for four models, but was −121 m for the fully distributed detailed energy-balance model. This indicates that mass losses may be underestimated if temperature-index methods are used instead of detailed energy-balance approaches that account for the effects of temperature changes on all energy-balance components individually. Our results suggest that future glacier predictions are sensitive to the choice of the mass-balance model broadening the spectrum in uncertainties.
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| 3. |
- 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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| 4. |
- Radic, Valentina, et al.
(författare)
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Analysis of scaling methods in deriving future volume evolutions of valley glaciers
- 2008
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Ingår i: Journal of Glaciology. - : International Glaciological Society. - 0022-1430 .- 1727-5652. ; 54:187, s. 601-612
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Tidskriftsartikel (refereegranskat)abstract
- Volume-area scaling is a common tool for deriving future volume evolutions of valley glaciers and their contribution to sea-level rise. We analyze the performance of scaling relationships for deriving volume projections in comparison to projections from a one-dimensional ice-flow model. The model is calibrated for six glaciers (Nigardsbreen, Rhonegletscher, South Cascade Glacier, Sofiyskiy glacier, midre Lovenbreen and Abramov glacier). Volume evolutions forced by different hypothetical mass-balance perturbations are compared with those obtained from volume-area (V-A), volume-length (V-L) and volume-area-length (V-A-L) scaling. Results show that the scaling methods mostly underestimate the volume losses predicted by the ice-flow model, up to 47% for V-A scaling and up to 18% for V-L scaling by the end of the 100 year simulation period. In general, V-L scaling produces closer simulations of volume evolutions derived from the ice-flow model, suggesting that V-L scaling may be a better approach for deriving volume projections than V-A scaling. Sensitivity experiments show that the initial volumes and volume evolutions are highly sensitive to the choice of the scaling constants, yielding both over- and underestimates. However, when normalized by initial volume, volume evolutions are relatively insensitive to the choice of scaling constants, especially in the V-L scaling. The 100 year volume projections differ within 10% of initial volume when the V-A scaling exponent commonly assumed, gamma = 1.375, is varied by -30% to +45% (gamma = [0.95, 2.00]) and the V-L scaling exponent, q = 2.2, is varied by -30% to +45% (q = [1.52, 3.20]). This is encouraging for the use of scaling methods in glacier volume projections, particularly since scaling exponents may vary between glaciers and the scaling constants are generally unknown.
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| 5. |
- Radic, Valentina, et al.
(författare)
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Modeling future glacier mass balance and volume changes using ERA-40 reanalysis and climate models: A sensitivity study at Storglaciären, Sweden
- 2006
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 111:F03003
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Tidskriftsartikel (refereegranskat)abstract
- Modeling the response of glaciers to future climate change is important for predicting changes in global sea level rise and local water resources. We compute until the year 2100 the mass balance and volume evolution of Storglacia¨ren, a small valley glacier in Sweden, using a temperature index mass balance model. We focus on the sensitivity of results to the choice of climate model and variants of adjusting ERA-40 temperatures to local conditions. ERA-40 temperature and precipitation series from 1961 to 2001 are validated and used both as input to the mass balance model and for statistical downscaling of one regional and six global climate models (GCMs). Future volume projections are computed using area-volume scaling and constant glacier area. ERA-40 data correlate well with observations and capture observed interannual variability of temperature and precipitation. The mass balance model driven by several variants of ERA-40 input performs similarly well regardless of temporal resolution of the input series (daily or monthly). The model explains _70% of variance of measured mass balance when the input temperatures are reduced by the lapse rate that maximizes model performance. Fitting ERA-40 temperatures to observations close to the glacier does not improve the performance of the model, leading us to conclude that ERA-40 can be used for mass balance modeling independent of meteorological observations. Projected future volume series show a loss of 50–90% of the initial volume by 2100. The differences in volume projections vary by 40% of the initial volume for six different GCMs input to mass balance model, while each volume projection varies by 20% depending on whether volume-area scaling or constant area is used and by 10% depending on details in the mass balance model used. The correction of biases in the seasonal temperature cycle of the GCMs with respect to the ERA-40 data is crucial for deriving realistic volume evolution. Static mass balance sensitivities to temperature and precipitation change in the 21st century are -0.48 m yr_1 K_1 and 0.025 m yr_1 per % increase, respectively.
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| 6. |
- Radic, Valentina, et al.
(författare)
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Volume-area scaling vs flowline modelling in glacier volume projections
- 2007
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Ingår i: Annals of Glaciology. - : International Glaciological Society. - 0260-3055 .- 1727-5644. ; 46:1, s. 234-240
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Tidskriftsartikel (refereegranskat)abstract
- Volume-area scaling provides a practical alternative to ice-flow modelling to account for glacier size changes when modelling future glacier evolutions, however, uncertainties remain as to the validity of the approach under non-steady conditions. We address these uncertainties by deriving scaling exponents in volume-area relationship from one-dimensional ice-flow modelling. We generate a set of 37 synthetic steady-state glaciers of different sizes, and then model volume evolutions due to climate warming and cooling as prescribed by negative and positive mass balance perturbations, respectively, on a century time scale. The scaling exponent derived for the steady-state glaciers (=1.56) differs from the exponents derived from the glaciers in transient (non-steady) state by up to 86%. Nevertheless, volume projections employing volume-area scaling are relatively insensitive to these differences in scaling exponents. Volume-area scaling agrees well with the results from ice-flow modelling and is able to simulate the approach of a glacier to a new steady state, if mass-balance elevation feedback is considered by adding or removing elevation bands at the lowest part of the glacier in response to mass balance variations. Provided area-changes are considered in the mass balance computations in this way, our results indicate that volume-area scaling is a powerful tool for glacier volume projections on multi-century time scales.
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