Glacier Length Research Articles

The response of glaciers to intrinsic climate variability: observations and models of late-Holocene variations in the Pacific Northwest

AbstractDiscriminating between glacier variations due to natural climate variability and those due to true climate change is crucial for the interpretation and attribution of past glacier changes, and for the expectations of future changes. We explore this issue for the well-documented glaciers of Mount Baker in the Cascades Mountains of Washington State, USA, using glacier histories, glacier modeling, weather data and numerical weather model output. We find that natural variability alone is capable of producing kilometer-scale excursions in glacier length on multi-decadal and centennial timescales. Such changes are similar in magnitude to those attributed to a global Little Ice Age. The null hypothesis, that no climate change is required to explain the glacier fluctuations in this setting, cannot be rejected. These results for Mount Baker glaciers are also consistent with an earlier study analyzing individual glaciers in Scandinavia and the Alps. The principle that long-timescale fluctuations of glacier length can be driven by short-timescale fluctuations in climate reflects a robust and fundamental property of stochastically forced physical systems with memory. It is very likely that this principle also applies to other Alpine glaciers and that it therefore complicates interpretations of the relationship between glacier and climate history. However, the amplitude and timescale of the length fluctuations depends on the details of the particular glacier geometry and climatic setting, and this remains largely unevaluated for most glaciers.

Subglacial modulation of the hydrograph from glacierized basins

AbstractThe extent of basin glacierization has important implications for the hydrograph in part, because snow, firn and ice impart different delays in water transport through the system. Here, the significance of subglacial drainage morphology in modulating the hydrograph is examined with a one‐dimensional physically based model. The conceptual model of subglacial drainage comprises both ‘fast’ and ‘slow’ elements, respectively associated with summer and winter drainage regimes. The additional possibility of a permeable glacier substrate is taken into account by allowing water transport in a subglacial aquifer. Forced by prescribed rates of melt‐water delivery to the glacier bed, the model predicts glacier discharge by drainage system provenance. The effects of (1) ‘hard’ versus ‘soft’ glacier beds, (2) subsurface permeability and groundwater flow, and (3) glacier geometry are then investigated. Hydrograph character, in the form of peak timing and amplitude, symmetry with respect to the forcing, and the amplitude of diurnal fluctuations, is affected by the partitioning of water through the various flow elements. Hard beds and impermeable substrates maximize the discharge routed through the fast‐drainage system in the simulations, generally resulting in higher seasonal discharge maxima and stronger diurnal variations in discharge. High hydraulic transmissivities, either at the glacier bed or in underlying strata, hinder the development of the fast‐drainage system in the simulations, producing hydrographs of lower amplitude. Glacier geometry has a modest effect, with adverse bed slopes, very thick or very thin ice and short glacier lengths favouring prolonged drainage through the slow system. These results suggest that the morphology and evolution of the subglacial drainage system may play a significant role in determining the character of the hydrograph from glacierized basins. Copyright © 2008 John Wiley & Sons, Ltd.

Sensitivity of European glaciers to precipitation and temperature – two case studies

A nonlinear backpropagation network (BPN) has been trained with high-resolution multiproxy reconstructions of temperature and precipitation (input data) and glacier length variations of the Alpine Lower Grindelwald Glacier, Switzerland (output data). The model was then forced with two regional climate scenarios of temperature and precipitation derived from a probabilisticapproach:Thefirstscenario(nochange)assumesnochangesintemperatureand precipitation for the 2000-2050 period compared to the 1970-2000 mean. In the second scenario (combined forcing) linear warming rates of 0.036-0.054°C per year and changing precipitation rates between −17% and +8% compared to the 1970-2000 mean have been used for the 2000-2050 period. In the first case the Lower Grindelwald Glacier shows a continuous retreat until the 2020s when it reaches an equilibrium followed by a minor advance. For the second scenario a strong and continuous retreat of approximately −30 m/year since the 1990s has been modelled. By processing the used climate parameters with a sensitivity analysis based on neural networks we investigate the relative importance of different climate configurations for the Lower Grindelwald Glacier during four well-documented historical advance (1590- 1610, 1690-1720, 1760-1780, 1810-1820) and retreat periods (1640-1665, 1780-1810, 1860-1880, 1945-1970). It is shown that different combinations of seasonal temperature and

Predicting the response of seven Asian glaciers to future climate scenarios using a simple linear glacier model

Observations from seven Central Asian glaciers (35–55°N; 70–95°E) are used, together with regional temperature data, to infer uncertain parameters for a simple linear model of the glacier length variations. The glacier model is based on first order glacier dynamics and requires the knowledge of reference states of forcing and glacier perturbation magnitude. An adjoint‐based variational method is used to optimally determine the glacier reference states in 1900 and the uncertain glacier model parameters. The simple glacier model is then used to estimate the glacier length variations until 2060 using regional temperature projections from an ensemble of climate model simulations for a future climate change scenario (SRES A2). For the period 2000–2060, all glaciers are projected to experience substantial further shrinkage, especially those with gentle slopes (e.g., Glacier Chogo Lungma retreats ∼4 km). Although nearly one‐third of the year 2000 length will be reduced for some small glaciers, the existence of the glaciers studied here is not threatened by year 2060. The differences between the individual glacier responses are large. No straightforward relationship is found between glacier size and the projected fractional change of its length.

An inventory and morphometric analysis of British Columbia glaciers, Canada

AbstractWe describe an automated method to generate an inventory of glaciers and glacier morphometry from a digital topographic database containing glacier boundaries and a digital elevation model for British Columbia, Canada. The inventory contains over 12 000 glaciers with a total cumulative area that exceeds 25 000 km2, based on mapping from aerial photographs circa the mid-1980s. We use the inventory to examine dimensional characteristics among glaciers, namely the scaling relations between glacier length, width and area. Glacier length is a good predictor of glacier area, and its predictive ability improves when glaciers are stratified by the number of up-valley accumulation basins. The spatial pattern of glacier mid-range altitude parallels glaciation limits previously mapped for British Columbia and similarly reflects large-scale controls of orographic precipitation and continentality. The inventory is also used to refine models that relate glacier mid-range and terminus altitudes to regional position, aspect and, in the case of terminus altitudes, an index of glacier shape. Relations between glacier altitude limits and controlling spatial and topographic factors are used to make further climatic and mass-balance inferences from the glacier inventory.

Reconstructing the glacier contribution to sea-level rise back to 1850

Abstract. We present a method to estimate the glacier contribution to sea-level rise from glacier length records. These records form the only direct evidence of glacier changes prior to 1946, when the first continuous mass-balance observations began. A globally representative length signal is calculated from 197 length records from all continents by normalisation and averaging of 14 different regions. Next, the resulting signal is calibrated with mass-balance observations for the period 1961–2000. We find that the glacier contribution to sea level rise was 5.5±1.0 cm during the period 1850–2000 and 4.5±0.7 cm during the period 1900–2000.

Un service d’observation des glaciers des alpes françaises « glacioclim-alpes », pour quoi faire ?

Glaciers act as very good climate indicators, and the relationship they develop with climate can be exploited at 2 levels. First of all, changes in meteorological conditions are directly recorded in glacier mass balance changes (in the form of either winter precipitation or summer ablation). Therefore, from separately measuring these two terms, climatic trends can be inferred and corresponding results are all the better as mass balance series are spanning longer periods. These mass balance changes then later express under the form of fluctuations in glacier length and thickness and/or ice surface velocities. Measuring these changes is another means of inferring climate change, although the relationship is much more complex because of a time-lagging non-linear response due to complicated processes such as ice rheology or basal gliding which only a deterministic ice-flow model can capture. Due to this specificity and complexity of the dynamical response of glaciers, using these glacier changes for climate reconstructions will also require as long as possible measurement series. It is therefore in this context of a better understanding of climate through glacier change that the glacier survey network was initiated. Three main types of measurements are undertaken ; (i) mass balance measurements with both winter accumulation and summer ablation, (ii) glacier dynamical response to mass balance change in the form of thickness and length changes as well as surface velocity measurements and last (iii) measurements of local meteorology with the help of Automatic Weather Stations. This paper describes the structure and the context in which the survey network was initiated as well as all the ensuing measurements. Some scientific applications are then presented as the results of these observations like the significant changes in surface mass balance connected to the strong changes in radiative and turbulent heat fluxes at the surface of glaciers over the last decades, or the better understanding of ice dynamics from direct inspection of glacier dynamical changes or from using these latter changes for tuning, validating and exploiting the results of an ice flow model.

Recalibration of the yellow Rhizocarpon growth curve in the Cordillera Blanca (Peru) and implications for LIA chronology

A new lichen dating method and new moraine observations enabled us to improve the chronology of glacier advances in the Cordillera Blanca (Peru) during the Little Ice Age (LIA). Our results reveal that an early LIA glacial advance occurred around AD 1330 ± 29. However, a second major glacial advance at the beginning of the 17th century overlapped the earlier stage for most glaciers. Hence, this second glacial stage, dated from AD 1630 ± 27, is considered as the LIA maximum glacial advance in the Cordillera Blanca. During the 17th–18th centuries, at least three glacial advances were recorded synchronously for the different glaciers (AD 1670 ± 24, 1730 ± 21, and 1760 ± 19). The moraines corresponding to the two first stages are close to the one in 1630 suggesting a slow recession of about 18% in the total length of the glacier. From the LIA maximum extent to the beginning of the 20th century, the 24 glaciers have retreated a distance of about 1000 m, corresponding to a reduction of 30% in their length. This rate is comparable to that observed during the 20th century. Estimates of palaeo-Equilibrium Line Altitudes show an increase in altitude of about 100 m from the LIA maximum glacial extension at the beginning of the 17th century to the beginning of the 20th century. Because long time series are not available for precipitation and temperature, this glacial retreat is difficult to explain by past climate changes. However, there is a fair correspondence between changes in glacier length and the δ 18O recorded in the Quelccaya ice core at a century timescale. Our current knowledge of tropical glaciers and isotope variations leads us to suggest that this common tropical signal reflects a change from a wet LIA to the drier conditions of today. Finally, a remarkable synchronicity is observed with glacial variations in Bolivia, suggesting a common regional climatic pattern during the LIA.

Holocene rockwall retreat and the estimation of rock glacier age, prins karls forland, svalbard

.This paper presents a simple analytical model for estimating rock glacier age by coupling the ratio of frontal advance to total rock glacier length and the ratio of debris volume in the rock glacier to present debris flux in the talus cone–rock glacier transition zone. The model was applied to two rock glaciers at Prins Karls Forland, Svalbard. By assuming volumetric debris contents in the deforming layer of the rock glacier of between 0.3 and 0.4, we obtained age estimates for the rock glaciers of between 12 ka and 24 ka. The corresponding average rockwall retreat rates are between 0.30 and 0.62 mm a‐1. Considering the limitations of the model, we suggest a minimum age of 13 ka for the initiation of rock glacier development. Using this age, rockwall retreat rates for the seven rock glaciers investigated at Prins Karls Forland are between 0.13 and 0.64 m ka‐1 (assuming the volumetric debris content for the whole rock glacier/talus cone is 0.35). The model requires further testing on other datasets, better field estimates of the debris content and depth of the deforming layer, and could also benefit from the inclusion of an unsteady debris supply function in order to refine age estimates.

19th century glacier representations and fluctuations in the central and western European Alps: An interdisciplinary approach

European Alpine glaciers are sensitive indicators of past climate and are thus valuable sources of climate history. Unfortunately, direct determinations of glacier changes (length variations and mass changes) did not start with increasing accuracy until just before the end of the 19th century. Therefore, historical and physical methods have to be used to reconstruct glacier variability for preceeding time periods. The Lower Grindelwald Glacier, Switzerland, and the Mer de Glace, France, are examples of well-documented Alpine glaciers with a wealth of different historical sources (e.g. drawings, paintings, prints, photographs, maps) that allow reconstruction of glacier length variations for the last 400–500 years. In this paper, we compare the length fluctuations of both glaciers for the 19th century until the present. During the 19th century a majority of Alpine glaciers – including the Lower Grindelwald Glacier and the Mer de Glace – have been affected by impressive glacier advances. The first maximum extent around 1820 has been documented by drawings from the artist Samuel Birmann, and the second maximum extent around 1855 is shown by photographs of the Bisson Brothers. These pictorial sources are among the best documents of the two glaciers for the 19th century. In addition to an analysis of historical sources of the 19th century, we also study the sensitivity of the Lower Grindelwald Glacier to climate parameters (multiproxy reconstructions of seasonal temperature and precipitation) for an advance and a retreat period in the 19th century using a new neural network approach. The advance towards 1820 was presumably driven by low summer temperatures and high autumn precipitation. The 1860–1880 retreat period was mainly forced by high temperatures. Finally, this nonlinear statistical approach is a new contribution to the various investigations of the complex climate–glacier system.

Norwegian mountain glaciers in the past, present and future

Documentation of glacier changes is a key element for reconstruction of past climate variability and early detection of global climate change. In this paper, records of Holocene glacier variations in different regions in Norway have been synthesised. During the period from approximately 8000 to 4000 cal. yr BP, most glaciers in Norway were completely melted away at least once due to high summer temperatures and/or reduced winter precipitation. Lichenometrically and historically dated moraines at Jostedalsbreen, in Jotunheimen, at Hardangerjøkulen, and at Folgefonna were used to extend records of glacier length variations back to their maximum position during the ‘Little Ice Age’. The timing of the maximum ‘Little Ice Age’ glacial advance in different parts of southern Norway varied considerably, ranging from the early 18th century to the late 19th century. Cumulative glacier length variations of glaciers in southern Norway show an overall retreat from ∼ AD 1750 to the 1930s–40s. Thereafter, most Norwegian glaciers retreated significantly. Short maritime outlet glaciers with a short response time (< 10–15 yr) started to advance in the mid-1950s, whereas long outlet glaciers with longer frontal time lag (> 15–20 yr) continued their retreat to the 1980s. In the 1990s, however, several of the maritime glaciers started to advance as a response to higher winter accumulation during the first part of the 1990s. Since 2000 most of the observed glaciers have retreated remarkably fast (annual frontal retreat > 100 m) mainly due to high summer temperatures. The last glacier inventory in Norway published in 1988 shows that there were 1627 glaciers covering a total area of 2609 km 2 with an estimated volume of 164 km 3. Modern climate–glacier relationships from mass balance data in Scandinavia have been used to present possible effects on the Norwegian glaciers of climate scenarios between 1961–1990 and 2070–2100 presented by the ‘RegClim’ project. This long-term weather ‘forecast’ for western Norway indicates a rise in the summer temperature of 2.3 °C and an increase in the winter precipitation of 16% by the end of the 21st century. This climate scenario may, if it occurs, cause the equilibrium-line altitude (ELA) to rise 260 ± 50 m. As a result, about 98% of the Norwegian glaciers are likely to disappear and the glacier area may be reduced ∼ 34% by AD 2100.

20th-century glacier fluctuations on Disko Island (Qeqertarsuaq), Greenland

AbstractThis study assesses glacier fluctuations on Disko Island (Qeqertarsuaq), central West Greenland, during the 20th century. A total of 247 glaciers, of which 75 are classified as surge-type glaciers, are included, representing about 95% of the glacierized area. Based on expedition accounts and early maps, it is concluded that recession rates were highest during the first half of the century. Between 1953 and 2005, 70% of the glaciers showed recession, 28% remained stationary and 2% experienced overall advance due to glacier surging. The mean recession rate of quiescent surge-type glaciers was 20 ma–1 compared to 8ma–1 for normal glaciers. Identification of changes in glacier length controlled by climate changes is achieved by excluding surge-type glaciers from the dataset. The result indicates that glaciers with ablation areas facing in the arc south to northwest, covering an area above 5 km2 and having a terminus elevation below 800 m are the most climate-sensitive.

Glacier inventory of the Gran Campo Nevado Ice Cap in the Southern Andes and glacier changes observed during recent decades

The Gran Campo Nevado (GCN) forms an isolated ice cap on the Península Muñoz Gamero (PMG) located 200 km to the south of the Southern Patagonia Icefield (SPI). We present a glacier inventory of the GCN made up by 27 drainage basins (in total 199.5 km 2) and other small cirque and valley glaciers of the southern part of PMG (in total 53 km 2). The glacier inventory is based on a digital elevation model (DEM) and ortho-photos. Contour lines from maps, relief information derived from Landsat TM satellite imagery from 1986 and 2002 and stereoscopic data from aerial photos were combined in a knowledge-based scheme to obtain a DEM of the area. A digital ortho-photo map based on aerial photos from 1998 and several ortho-photos based on aerial photos from 1942 and 1984 could be produced from the initial DEM. A geographical information system (GIS) served to outline the extent of the present glaciation. All major glaciers of the GCN show a significant glacier retreat during the last 60 yr. Some of the outlet glaciers lost more than 20% of their total area during this period. Overall glacier retreat amounts to 2.8% of glacier length per decade and the glacier area loss is 2.4% per decade in the period from 1942 to 2002. We hypothesise that GCN glaciers may have reacted faster and more synchronously with the observed warming trend during recent decades when compared with the SPI.

A geochronological approach to understanding the role of solar activity on holocene glacier length variability in the swiss alps

.We present a radiocarbon data set of 71 samples of wood and peat material that melted out or sheared out from underneath eight presentday mid‐latitude glaciers in the Central Swiss Alps. Results indicated that in the past several glaciers have been repeatedly less extensive than they were in the 1990s. The periods when glaciers had a smaller volume and shorter length persisted between 320 and 2500 years. This data set provides greater insight into glacier variability than previously possible, especially for the early and middle Holocene. The radiocarbon‐dated periods defined with less extensive glaciers coincide with periods of reduced radio‐production, pointing to a connection between solar activity and glacier melting processes. Measured long‐term series of glacier length variations show significant correlation with the total solar irradiance. Incoming solar irradiance and changing albedo can account for a direct forcing of the glacier mass balances. Long‐term investigations of atmospheric processes that are in interaction with changing solar activity are needed in order to understand the feedback mechanisms with glacier mass balances.

Comparison of glacier‐inferred temperatures with observations and climate model simulations

A reconstructed temperature history for different regions of the globe was prepared by Oerlemans (2005) from length changes of 169 glaciers. In this study, we compare the glacier‐inferred temperature variations over 1900–1990 with observed and climate model simulated temperatures for the global average and for five regions: Southern Hemisphere, northwest America, Atlantic, Asia, and the Alps. There is reasonable agreement between the glacier‐inferred temperature trends and the observed temperature trends for the globe and in four of the five regions (except northwest America, NWAme). The trends for the globe and in these regions are significantly different from zero, cannot be explained by natural variability (again except for NWAme), and are consistent with the model‐simulated response to anthropogenic forcing in all regions. Hence, it is likely that the glacier length reductions are outside the range of natural variations and due in part to regional warming associated with increasing concentrations of greenhouse gases in the atmosphere.

Multivariate Controls on the Incidence of Glacier Surging in the Karakoram Himalaya

ABSTRACTSurge-type glaciers experience cyclic flow instabilities characterized by alternating periods of slow and fast flow. The geographical distribution of surge-type glaciers has been shown to be distinctly non-random in that they are clustered in some regions yet are completely absent from others. In order to identify factors that influence glacier surging, a number of environmental and glacial attributes were examined for an area in the Karakoram Himalaya, Central Asia. A new GIS-based glacier inventory was produced using a combination of ASTER and Landsat remotely sensed images and paper maps. A total of 150 glaciers were digitized, with 19 of these (12.6%) being classified as of surge-type. Attribute data for 10 glacial and environmental attributes were recorded either during the digitization phase or extracted automatically from the GIS. Simple data visualization techniques revealed a positive correlation between glacier surging and glacier length, area, perimeter size, average width, debris cover, and orientation. The use of univariate logit regression analysis showed that length, area, perimeter, average width, and the heaviest debris cover class showed significant correlation with surging. Multivariate logit regression techniques were employed to show that length, area, average width, and debris cover were all multicollinear, with the strongest statistically modeled relationship using the variable perimeter size. The significance of glacier perimeter on surging may be explained by an increased availability of avalanche-fed snow and debris material which may act as a mass balance proxy. The findings that glacier size (in particular length and perimeter) is most strongly related to surging are consistent with the findings of studies in a number of different regions.

Late nineteenth to early twenty-first century behavior of Alaskan glaciers as indicators of changing regional climate

Alaska's climate is changing and one of the most significant indications of this change has been the late 19th to early 21st century behavior of Alaskan glaciers. Weather station temperature data document that air temperatures throughout Alaska have been increasing for many decades. Since the mid-20th century, the average change is an increase of ∼ 2.0 °C. In order to determine the magnitude and pattern of response of glaciers to this regional climate change, a comprehensive analysis was made of the recent behavior of hundreds of glaciers located in the eleven Alaskan mountain ranges and three island areas that currently support glaciers. Data analyzed included maps, historical observations, thousands of ground-and-aerial photographs and satellite images, and vegetation proxy data. Results were synthesized to determine changes in length and area of individual glaciers. Alaskan ground photography dates from 1883, aerial photography dates from 1926, and satellite photography and imagery dates from the early 1960s. Unfortunately, very few Alaskan glaciers have any mass balance observations. In most areas analyzed, every glacier that descends below an elevation of ∼ 1500 m is currently thinning and/or retreating. Many glaciers have an uninterrupted history of continuous post-Little-Ice-Age retreat that spans more than 250 years. Others are characterized by multiple late 19th to early 21st century fluctuations. Today, retreating and/or thinning glaciers represent more than 98% of the glaciers examined. However, in the Coast Mountains, St. Elias Mountains, Chugach Mountains, and the Aleutian Range more than a dozen glaciers are currently advancing and thickening. Many currently advancing glaciers are or were formerly tidewater glaciers. Some of these glaciers have been expanding for more than two centuries. This presentation documents the post-Little-Ice-Age behavior and variability of the response of many Alaskan glaciers to changing regional climate.

Modeling topographic and climatic control of east‐west asymmetry in Sierra Nevada glacier length during the Last Glacial Maximum

Glaciers draining westward from the Sierra Nevada divide, California, during the Last Glacial Maximum (LGM) were ∼7 times longer than east‐draining glaciers. We address the degree to which this difference may be attributed to the topographic asymmetry of the west‐tilted Sierran block and the climate asymmetry resulting from orographic modification of Pacific Ocean storms. We simulate kilometer‐scale glaciers within the 50 × 50 km Kings Canyon region of the southern Sierra by employing a two‐dimensional numerical model that is driven by simple, spatially variable climates and treats ice transport by deformation, sliding, and avalanching. In numerical experiments, we match simulated termini to LGM moraine positions to constrain the parameters of different climate scenarios. The 38‐km‐long LGM glacier in Kings Canyon was reproduced by a climate specified by an equilibrium line altitude (ELA) of 3170 m, a mass balance gradient of 0.01 m/yr/m, and a maximum positive balance of 2 m/yr. This climate generates much shorter (average ∼6 km long) east‐draining glaciers that, however, overshoot the LGM moraines by ∼1 km. Roughly 97% of the E‐W difference in glacier lengths can therefore be attributed to topographic asymmetry alone. A second experiment suggesting a 120‐m‐higher ELA of 3290 m east of the divide can explain the shorter east‐draining glaciers. An experiment in which orographic precipitation is explicitly simulated and melt is prescribed using a positive degree‐day algorithm matches both Kings Canyon and the average east‐draining glacier length with an LGM climate that was 5.6°C cooler and ∼2 times wetter than the modern Sierra Nevada.

How extreme was northern hemisphere seasonality during the Younger Dryas?

In explaining the rapid transitions associated with the Younger Dryas cooling, a reduced meridional overturning circulation has traditionally been invoked, but such a scenario has been difficult to reproduce in model studies without adding excessive amounts of freshwater to the North Atlantic. More recent studies challenge this view and indicate that the role of an extensive sea ice cover may have been as important in promoting abrupt climate change as reorganisations of the North Atlantic Ocean [Gildor, H., Tziperman, E., 2003. Sea-ice switches and abrupt climate change. Philosophical Transactions Of The Royal Society Of London Series A—Mathematical Physical And Engineering Sciences 361, 1935–1942]. Based on glacier evidence from eastern Greenland [Denton, G.H., Alley, R.B., Comer, G.C., Broecker, W.S., 2005. The role of seasonality in abrupt climate change. Quaternary Science Reviews 24, 1159–1182] suggest that the seasonal temperature amplitude increased by about 20 °C during the Younger Dryas. Such a ‘switching of seasonality’ lends support to the idea of a fast-expanding sea ice cover, because it allows for extremely cold winters that are balanced by relatively mild summers. However, climatic interpretations based on the geometry and length of glaciers under such conditions as in Scoresby Sund is not well understood, and equilibrium-line-altitude (ELA) estimates should, therefore, be regarded as tentative. Here, we discuss the absolute seasonal amplitude during the Younger Dryas by taking winter precipitation into account and show that the changes in seasonality may have been limited to 10 °C. We propose that by reducing the seasonal response in Greenland compared with western Europe we better understand the hinged-door modus operandi [COHMAP, 1988. Climatic changes of the last 18,000 years: observations and model simulations. Science 241, 1043–1052] of the polar front and sea-ice cover, where the absolute southward migration of sea-ice is highest in the East Atlantic region.

Effect of climate change on runoff of a glacierized Himalayan basin

The continuous increase in the emission of greenhouse gases has resulted in global warming, and substantial changes in the global climate are expected by the end of the current century. The reductions in mass, volume, area and length of glaciers on the global scale are considered as clear signals of a warmer climate. The increased rate of melting under a warmer climate has resulted in the retreating of glaciers. On the long-term scale, greater melting of glaciers during the coming years could lead to the depletion of available water resources and influence water flows in rivers. It is also very likely that such changes have occurred in Himalayan glaciers, but might have gone unnoticed or not studied in detail. The water resources of the Himalayan region may also be highly vulnerable to such climate changes, because more than 50% of the water resources of India are located in the various tributaries of the Ganges, Indus and the Brahmaputra river system, which are highly dependent on snow and glacier runoff. In the present study, the snowmelt model SNOWMOD has been used to simulate the melt runoff from a highly glacierized small basin for the summer season. The model simulated the distribution and volume of runoff with reasonably good accuracy. Based on a 2-year simulation, it is found that, on average, the contributions of glacier melt and rainfall in the total runoff are 87% and 13% respectively. The impact of climate change on the monthly distribution of runoff and total summer runoff has been studied with respect to plausible scenarios of temperature and rainfall, both individually and in combined scenarios. The analysis included six temperature scenarios ranging between 0·5 and 3 °C, and four rainfall scenarios (−10%, −5%, 5%, 10%). The combined scenarios were generated using temperature and rainfall scenarios. The combined scenarios represented a combination of warmer and drier and a combination of warmer and wetter conditions in the study area. The results indicate that, for the study basin, runoff increased linearly with increase in temperature and rainfall. For a temperature rise of 2 °C, the increase in summer streamflow is computed to be about 28%. Changes in rainfall by ±10% resulted in corresponding changes in streamflow by ±3·5%. For the range of climatic scenarios considered, the changes in runoff are more sensitive to changes in temperature, compared with rainfall, which is likely due to the major contribution of melt water in runoff. Such studies are needed for proper assessment of available water resources under a changing climate in the Himalayan region. Copyright © 2005 John Wiley & Sons, Ltd.