Sensitivity Of Glaciers Research Articles

Modelled mass balance of Xibu glacier, Tibetan Plateau: sensitivity to climate change

AbstractDue to a lack of in situ measurements, model-based studies of glacier mass balance in the Tibetan Plateau are very limited. An energy-balance model is applied to analyse the mass-balance sensitivity of Xibu glacier, in the Nyainqêntanglha mountain range, to climatic change. A sensitivity calculation shows that a temperature change of ±1°C or a precipitation change of ±35% changes the equilibrium-line altitude (ELA) by 140 ± 125 m. We use a clustering method to link local weather parameters, including wet-season temperatures, to weather types observed over the period 1955–2006. Modelled variability of the Xibu glacier mass balance seems to be controlled by air-temperature variations during the wet season (May–September) and by a long-term warming trend that is unrelated to weather type. The observed wet-season temperature trend of 0.23°C (10 a)−1 leads to an estimated lengthening of the ablation season by 8 days at the glacier terminus (5000 m a.s.l.) and by 23 days at the ELA (5590 m a.s.l.) over the period 1966–2005. The calculated rise in the ELA was 49 m (10 a)−1.

Glaciation in the Andes during the Lateglacial and Holocene

This review updates the chronology of Andean glaciation during the Lateglacial and the Holocene from the numerous articles and reviews published over the past three decades. The Andes, which include some of the world's wettest and driest mountainous regions, offer an unparalleled opportunity to elucidate spatial and temporal patterns of glaciation along a continuous 68-degree meridional transect. The geographic and altitudinal extent of modern glaciers and the sensitivity of both modern and former glaciers to respond to changes in specific climatic variables reflect broad-scale atmospheric circulation and consequent regional moisture patterns. Glaciers in the tropical Andes and in the mid-latitude Andes are likely to have been far more sensitive to changes in temperature than glaciers in the dry subtropical Andes. Broad-scale temporal and spatial patterns of glaciation during the Lateglacial are apparent. In the southernmost Andes, the Lateglacial chronology appears to have a strong Antarctic signature with the best-dated moraines correlating closely with the Antarctic Cold Reversal. The southernmost Andes do not appear to have experienced a significant ice advance coeval with the Younger Dryas (YD) climatic reversal. At the other end of the Andes, from ∼0 to 9°N, a stronger YD connection may exist, but critical stratigraphic and geochronologic work is required before a YD ice advance can be fully demonstrated. In the central Andes of Peru, well-dated moraines record a significant ice readvance at the onset of the YD, but ice was retreating during much of the remaining YD interval. The spatial–temporal pattern of Holocene glaciation exhibits tantalizing but incomplete evidence for an Early to Mid-Holocene ice advance(s) in many regions, but not in the arid subtropical Andes, where moraines deposited during or slightly prior to the Little Ice Age (LIA) record the most extensive advance of the Holocene. In many regions, there is strong evidence for Neoglacial advances in the interval between 1.0 and 2.5 ka. Moraines that correlate with the LIA of the Northern Hemisphere are seen in all presently glacierized mountain ranges; most of these date to within the past 450 years. Outboard of these moraines in many regions are moraines of a slightly more extensive advance that occurred several hundred years prior to the onset of the LIA. Priorities for future work include filling in several prominent spatial gaps in the distribution of chronologic studies. For the Lateglacial these gaps include the arid regions of northern Chile and Argentina, the southern Peruvian Andes between 11.5°and 13.5°S, and the Andes of northern Peru and southern Ecuador between 3° and 9°S. Areas in need of better representation in regional datasets of Holocene glaciation include all of the Andes north of the Equator. Specific chronologic priorities include the need for close bracketing radiocarbon ages for purported Early and Mid-Holocene moraines, and the increased application of cosmogenic radionuclide dating to Lateglacial and Early Holocene moraines that are already constrained by maximum-limiting radiocarbon ages.

Glacier fluctuations of Jostedalsbreen, western Norway, during the past 20 years: the sensitive response of maritime mountain glaciers

The steep outlet glaciers of Jostedalsbreen, western Norway, are good examples of sensitively reacting maritime mountain glaciers. Their changes in length, frontal position and lower tongue's morphology during the past 20 years have been well documented. At first they experienced a strong frontal advance. After AD 2000 glacier behaviour was dominated by a strong frontal retreat, in some cases causing a separation of the lowermost glacier tongue. In this paper, the glacier length changes are presented both visually and numerically, supplemented by mass balance and meteorological data. The glacier behaviour is interpreted and its causes are discussed. Whereas the factors controlling the advance during the 1990s seem clear, the interpretation of the most recent retreat still leaves some uncertainties. The actual glacier front behaviour cannot fully be related to the mass balance data. Terminus response times and relations between individual mass balance and meteorological parameters have changed. Some hypotheses are given, including disturbance of the `normal' mass transfer and dynamical response of the glacier front because of excessive ablation on the lowermost glacier tongues and summer back melting. These findings underline the sensitivity of maritime glaciers to climate changes. The empirical findings need to be taken into account in the interpretation of recent glacier length changes and their future modelling.

Satellite-Derived Equilibrium Lines in Northern Patagonia Icefield, Chile, and Their Implications to Glacier Variations

The Northern Patagonia Icefield (NPI), covering 3953 km2, is the second largest temperate ice body in South America. Despite its importance as a climate change indicator because of its location and size, data on ground-based mass balance and meteorological records for the analysis of glacier (snout) variations are still lacking. The use of multitemporal satellite images to estimate equilibrium line altitude variations could be a surrogate for such analyses. Since late-summer snowlines of temperate glaciers coincide with the equilibrium line, we analyzed five Landsat images spanning 1979–2003 and an ASTER-derived digital elevation model to reveal oscillations in the equilibrium line altitude (ΔZ ELA ). The average ELAs range between 870 m and 1529 (± 29 m), with lower altitudes on the west side. Winter snow cover accumulation indicates higher elevations (relative to the glacier snout) of the transient snowlines in the west. Thus, one of the reasons for the higher retreating rates observed on the west side is that the lower part of the ablation area is likely exposed to year-round ablation. Glacier sensitivity to ΔZ ELA oscillations would depend upon the topographic condition of the accumulation area (gentle or steep). In outlet glaciers with gentle accumulation areas such as San Rafael and San Quintin, ΔZ ELA of up to 65 and 70 m at the central flow part and bare ice area variations > 5 km2 and > 13 (± 0.6 km2) were observed, respectively.

Quaternary glaciation of Mount Everest

The Quaternary glacial history of the Rongbuk valley on the northern slopes of Mount Everest is examined using field mapping, geomorphic and sedimentological methods, and optically stimulated luminescence (OSL) and 10Be terrestrial cosmogenic nuclide (TCN) dating. Six major sets of moraines are present representing significant glacier advances or still-stands. These date to >330 ka (Tingri moraine), >41 ka (Dzakar moraine), 24–27 ka (Jilong moraine), 14–17 ka (Rongbuk moraine), 8–2 ka (Samdupo moraines) and ∼1.6 ka (Xarlungnama moraine), and each is assigned to a distinct glacial stage named after the moraine. The Samdupo glacial stage is subdivided into Samdupo I (6.8–7.7 ka) and Samdupo II (∼2.4 ka). Comparison with OSL and TCN defined ages on moraines on the southern slopes of Mount Everest in the Khumbu Himal show that glaciations across the Everest massif were broadly synchronous. However, unlike the Khumbu Himal, no early Holocene glacier advance is recognized in the Rongbuk valley. This suggests that the Khumbu Himal may have received increased monsoon precipitation in the early Holocene to help increase positive glacier mass balances, while the Rongbuk valley was too sheltered to receive monsoon moisture during this time and glaciers could not advance. Comparison of equilibrium-line altitude depressions for glacial stages across Mount Everest reveals asymmetric patterns of glacier retreat that likely reflects greater glacier sensitivity to climate change on the northern slopes, possibly due to precipitation starvation.

Deglaciation and landscape history around Annapurna, Nepal, based on 10Be surface exposure dating

The High Himalaya is a key area for tectonic, geomorphological and climate studies, because of its extreme relief and location at the transition zone between areas with abundant monsoonal precipitation and the arid/semiarid Tibetan Plateau. We present 10Be surface exposure ages on 22 boulders from the Annapurna area in Nepal. The ages improve understanding of the Late Quaternary landscape history and the geomorphological processes operating in this part of the Himalaya. Although our study is reconnaissance in nature, it highlights the importance of catastrophic events, such as landslides and debris flows, for denudation of high mountains. Holocene exposure ages for the Dhampu–Chooya landslide (∼4.1 ± 0.6 ka) and for 600 m of alluviation in Kali Gandaki Valley (∼2.1 ± 0.6 ka), for example, indicate the frequent occurrence and extent of catastrophic events and their implications for natural hazards. We also offer an explanation for the differences in Late Quaternary glacial chronologies at closely spaced study sites in the Nepal Himalaya. Topographically controlled and spatially variable precipitation in the Himalaya determines the sensitivity of glaciers to changes in temperature and precipitation. Accordingly, some glaciers advanced in-phase with Northern Hemisphere ice sheets, whereas others reached their maximum extent at times of increased monsoonal precipitation during Marine Isotope Stage 3 and the early Holocene.

Latest Pleistocene and Holocene glaciation of Baffin Island, Arctic Canada: key patterns and chronologies

Melting glaciers and ice caps on Baffin Island contribute roughly half of the sea-level rise from all ice in Arctic Canada, although they comprise only one-fourth of the total ice in the region. The uncertain future response of arctic glaciers and ice caps to climate change motivates the use of paleodata to evaluate the sensitivity of glaciers to past warm intervals and to constrain mechanisms that drive glacier change. We review the key patterns and chronologies of latest Pleistocene and Holocene glaciation on Baffin Island. The deglaciation by the Laurentide Ice Sheet occurred generally slowly and steadily throughout the Holocene to its present margin (Barnes Ice Cap) except for two periods of rapid retreat: An early interval ∼12 to 10 ka when outlet glaciers retreated rapidly through deep fiords and sounds, and a later interval ∼7 ka when ice over Foxe Basin collapsed. In coastal settings, alpine glaciers were smaller during the Younger Dryas period than during the Little Ice Age. At least some alpine glaciers apparently survived the early Holocene thermal maximum, which was several degrees warmer than today, although data on glacier extent during the early Holocene is extremely sparse. Following the early Holocene thermal maximum, glaciers advanced during Neoglaciation, beginning in some places as early as ∼6 ka, although most sites do not record near-Little Ice Age positions until ∼3.5 to 2.5 ka. Alpine glaciers reached their largest Holocene extents during the Little Ice Age, when temperatures were ∼1–1.5 °C cooler than during the late 20th century. Synchronous advances across Baffin Island throughout Neoglaciation indicate sub-Milankovitch controls on glaciation that could involve major volcanic eruptions and solar variability. Future work should further elucidate the state of glaciers and ice caps during the early Holocene thermal maximum and glacier response to climate forcing mechanisms.

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

Influence of the Pacific Decadal Oscillation and El Niño Southern Oscillation on Operation of the Capilano Water Supply Reservoir, Vancouver, British Columbia

The magnitude and duration of low reservoir inflows in the summer and early fall are critical for water supply planning and operations for the Greater Vancouver Regional District (now Metro Vancouver). The influence of climate fluctuations on summer and fall reservoir inflows was investigated and a reservoir operation model developed to simulate Capilano Reservoir operations. Flow records for the gauge on the Capilano River above Intake were adjusted to account for releases from the upstream Palisade Lake. It was found that reservoir inflows for the June to September period are affected by the El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). The 15 lowest June to September inflows over the period of gauge records have all been associated with warm or neutral ENSO conditions typically combined with warm or neutral PDO conditions. Annual reservoir drawdown, defined as the annual extended period of no spill, was used as an indicator of stress on reservoir operations. Simulation of reservoir inflows and outflows from 1914 to 2005 showed that the longest reservoir drawdown durations were almost always associated with warm ENSO and warm PDO conditions. The shortest periods of drawdown were normally associated with both cool ENSO and cool PDO conditions. Due to the storage effects, reservoir drawdown is a good indicator of periodic climate variations because of amplification, similar to the sensitivity of glaciers to climate episodes.

An improved technique for the reconstruction of former glacier mass-balance and dynamics

The recognition of past glacier extent and dynamics is a fundamental aspect of investigations of the climatic sensitivity of glaciers, especially when examining short-lived climate events such as the Younger Dryas or Little Ice Age. Existing approaches to the reconstruction of glacier form and dynamics depend on speculative reasoning of key glacier dynamic parameters, including the role of basal slip and subglacial deformation in glacier mass-transfer. This study reviews approaches to glacier reconstruction, derivation of former glacier equilibrium line altitudes (ELA's) and estimation of mass-balance and dynamics, concluding that most reconstructions of glacier mass-balance are compromised by a lack of glaciological considerations. An alternative approach to glacier reconstruction is presented, demonstrated and discussed, by which an empirical relationship between ablation gradient and mass loss at the ELA is used to derive mass-balance, mass-flux through the ELA and average balance velocity at the ELA. This ‘glaciological’ approach is applied to four reconstructed glaciers to test previous interpretations that each reflects Younger Dryas glaciation in the UK. The study concludes that this approach provides a more robust technique for reconstructing former glacier dynamics, and may be applied to test geomorphological interpretations of former mountain glaciation.

Latest Pleistocene advance of alpine glaciers in the southwestern Uinta Mountains, Utah, USA: Evidence for the influence of local moisture sources

Cosmogenic surface-exposure 10 Be dating of Last Glacial Maximum (LGM) moraines indicates that glaciers in the southwestern Uinta Mountains remained at their maximum positions until ca. 16.8 ± 0.7 ka, ∼2 k.y. after glaciers in the neighboring Wind River Range and Colorado Rockies began to retreat. The timing of the local LGM in the southwestern Uintas overlaps with both the hydrologic maximum of Lake Bonneville and preliminary estimates of the local LGM in the western Wasatch Mountains. This broad synchroneity indicates that Lake Bonneville and glaciers in northern Utah were responding to similar climate forcing. Furthermore, equilibrium line altitudes (ELAs) for reconstructed LGM alpine glaciers increase with distance from the Lake Bonneville shoreline, rising from ∼2600 m to ∼3200 m over the 120 km length of the glaciated Uintas. This pronounced ELA gradient suggests that the magnitude of the latest Pleistocene glacial advance in the western Uintas was due, at least in part, to enhanced precipitation derived from Lake Bonneville; thus, the lake acted as a local amplifier of regional climate forcing. This relationship underscores the sensitivity of alpine glaciers to moisture availability during the latest Pleistocene, and further demonstrates the importance of local moisture sources on glacier mass balance.

Fast shrinkage of tropical glaciers in Colombia

AbstractAs a consequence of ongoing atmospheric temperature rise, tropical glaciers belong to the unique and threatened ecosystems on Earth, as defined by the Intergovernmental Panel on Climate Change (Houghton and others, 2001). Worldwide glacier monitoring, especially as part of the Global Climate Observing System (GCOS), includes the systematic collection of data on such perennial surface ice masses. Several peaks in the sierras of Colombia have lost their glacier cover during recent decades. Today, high-altitude glaciers still exist in Sierra Nevada de Santa Marta, in Sierra Nevada del Cocuy and on the volcanoes of Nevados del Ruiz, de Santa Isabel, del Tolima and del Huila. Comparison of reconstructions of maximum glacier area extent during the Little Ice Age with more recent information from aerial photographs and satellite images clearly documents a fast-shrinking tendency and potential disappearance of the remaining glaciers within the next few decades. In the past 50 years, Colombian glaciers have lost 5 0% or more of their area. Glacier shrinkage has continued to be strong in the last 15 years, with a loss of 10−50% of the glacier area. The relationship between fast glacier retreat and local, regional and global climate change is now being investigated. Preliminary analyses indicate that the temperature rise of roughly 1°C in the last 30 years recorded at high-altitude meteorological stations exerts a primary control on glacier retreat. The investigations on the Colombian glaciers thus corroborate earlier findings concerning the high sensitivity of glaciers in the wet inner tropics to temperature rise. To improve understanding of fast glacier retreat in Colombia, a modern monitoring network has been established according to the multilevel strategy of the Global Terrestrial Network for Glaciers (GTN-G) within GCOS. The observations are also contributions to continued assessments of hazards from the glacier-covered volcanoes and to integrated global change research in mountain biosphere reserves.

Investigating the Sensitivity of Glacier Mass-Balance/Elevation Profiles to Changing Meteorological Conditions: Model Experiments for Haut Glacier D'Arolla, Valais, Switzerland

This paper presents the results of a distributed surface energy balance model which is used to calculate season-long patterns of melt on a small valley glacier, Haut Glacier d’Arolla, Valais, Switzerland, under different summer meteorological conditions and winter snow depth distributions. The model uses a Digital Elevation Model of the glacier and the surrounding topography, together with meteorological data collected at a site in front of the glacier to determine hourly totals of the surface energy balance components, and hence melt, over the entire glacier surface throughout a melt season, with a spatial resolution of 20 m. From these results, the spatially averaged mass-balance/elevation profile for the glacier can be calculated. A cubic relationship with elevation gives the best fit to the calculated mass-balance curve. The shape of this profile varies with the imposed change in meteorological conditions, however, becoming increasingly “S” shaped for warmer or less snowy conditions. These mass-balance profile changes are due to the complex interplay between albedo variations due to different snow depths over the glacier surface (and eventual removal of the snow cover), the variations in solar energy receipts caused by slope and aspect variation over the glacier and the changing patterns of shading by the surrounding topography. The changes in mass-balance profile lead to maximum calculated mass-balance sensitivity to imposed change occurring at intermediate elevations on the glacier; the calculated equilibrium-line altitude (ELA) occurs at the upper end of this zone, resulting in very large calculated changes in the ELA for different climatic conditions.

GIS-based modelling of glacial sediment balance

In view of ongoing atmospheric warming, there is concern as to whether retreating glaciers uncover a rocky or sedimentary bed. Sedimentary beds are abundant in high-mountain areas and represent, if exposed, a severe hazard potential for outbursts of periglacial lakes or debris flows. Furthermore, knowledge about glacier sediment balance is needed when dealing with climate sensitivity of recent and historical glaciers. The main factors influencing sediment balance of a glacierised mountain catchment have been organised into an index (Ies) of glacier erosion and sedimentation, which distinguishes between glaciers eroding into bedrock and those building up thick sedimentary beds. GIS-based methods were developed to extract the needed Ies-parameters from Digital Elevation Models (DEM), digitised glacier outlines and central flowlines. These methods were automated and tested on 84 Swiss Alpine glaciers. The results were validated through comparisons with forefield classifications and manually derived index results. The comparison with classified forefields confirms that the index allows for a rough assessment of the glacial sediment balance. In order to improve the predictability of glacier-bed characteristics, a better understanding of the periglacial debris production is necessary. However, the high overall accuracy of the comparison with the manual glacier-by-glacier investigation shows the potential of using GIS-based modelling with DEM in geomorphodynamics.

Static mass-balance sensitivity of Arctic glaciers and ice caps using a degree-day approach

AbstractFuture climate warming is predicted to be more pronounced in the Arctic where approximately two-thirds of all small glaciers on Earth are located. A simple mass-balance model was applied to 42 glaciers and ice caps north of 60° N to estimate mass-balance sensitivities to a hypothetical climate perturbation. The model is based on daily temperature and precipitation data from climate stations in the vicinity of each glacier and ice cap. A regression analysis was made using a degree-day approach where the annual sum of positive daily air temperatures was correlated to measured summer mass balance, and the total annual snow precipitation was correlated to measured winter mass balance. The net mass-balance sensitivity to a hypothetical temperature increase of +1 K ranged from -0.2 to -2.0 m a-1, and an assumed increase in precipitation of +10% changed the mass balance by <+0.1 to +0.4 m a-1, thus on average offsetting the effect of a temperature increase by approximately 20%. Maritime glaciers showed considerably higher mass-balance sensitivities than continental glaciers, in agreement with similar previous studies. The highest sensitivities were found in Iceland, exceeding those reported in previous studies. Extrapolating our results, glaciers and ice caps north of 60° N are estimated to contribute ∼0.6 mm a–1 K–1 to global sea-level rise. Our results highlight the value of long-term mass-balance records and meteorological records in remote areas.

Surface mass balance of glaciers in the French Alps: distributed modeling and sensitivity to climate change

AbstractA new physically based distributed surface mass-balance model is presented for Alpine glaciers. Based on the Crocus prognostic snow model, it resolves both the temporal (1 hour time-step) and spatial (200 m grid-step) variability of the energy and mass balance of glaciers. Mass-balance reconstructions for the period 1981–2004 are produced using meteorological reconstruction from the SAFRAN meteorological model for Glacier de Saint-Sorlin and Glacier d’Argentière, French Alps. Both glaciers lost mass at an accelerated rate in the last 23 years. The spatial distribution of precipitation within the model grid is adjusted using field mass-balance measurements. This is the only correction made to the SAFRAN meteorological input to the glacier model, which also includes surface atmospheric temperature, moisture, wind and all components of downward radiation. Independent data from satellite imagery and geodetic measurements are used for model validation. With this model, glacier sensitivity to climate change can be separately evaluated with respect to a full range of meteorological parameters, whereas simpler models, such as degree-day models, only account for temperature and precipitation. We provide results for both mass balance and equilibrium-line altitude (ELA) using a generic Alpine glacier. The sensitivity of the ELA to air temperature alone is found to be 125 m °C–1, or 160 m °C¯1 if concurrent (Stefan–Boltzmann) longwave radiation change is taken into account.

Calving speed and climatic sensitivity of New Zealand lake-calving glaciers

AbstractCalving speeds and calving mechanisms in fresh water contrast with those in tidewater. We obtained calving speeds for six lake-calving glaciers in New Zealand’s Southern Alps, and surveyed the depths and temperatures of their ice-contact lakes. The glaciers are temperate, grounded in shallow (≤20 m) water, and exhibit compressive flow at their termini. These data increase the global dataset of fresh-water calving statistics by 40%, bringing the total to 21 glaciers. For this dataset, calving rates (uc) correlate positively with water depths (hw) (r2 = 0.83), the relationship being expressed by: uc = 17.4 + 2.3 hw. This is an order of magnitude lower than values of uc at temperate tidewater glaciers. For a subset of 10 glaciers for which ice-proximal water temperature (tw) data are available, uc also correlates positively with tw, supporting a physical relation between calving and melting at and below the water-line. Fluctuations of New Zealand lake-calving glaciers in the period 1958–97 show that although the transition from non-calving to calving dramatically increases frontal retreat rates, the onset of calving does not isolate terminus change from climatic forcing. In terms of climatic sensitivity, lake-calving glaciers occupy an intermediate position between tidewater glaciers (least sensitive) and non-calving glaciers (most sensitive).

Responses of various-sized alpine glaciers and runoff to climatic change

AbstractThis paper presents a glacier ice-flow model that simulates changes to alpine glaciers of various sizes and their runoff response to climate change in the Yili river basin in the Tien Shan mountains, northwestern China. It is suggested that the sensitivity of glaciers to climatic change is determined by glacier size. The change in glacial runoff does not keep pace with climatic change. As climate warms and glaciers retreat, the glacier runoff tends to increase and then decrease. The runoff peak and its timing depend not only on glacier size but also on the rate of air-temperature rise.

On rates and acceleration trends of global glacier mass changes

Worldwide glacier mass changes are considered to represent natural key variables within global climate‐related monitoring programmes, especially with respect to strategies concerning early detection of enhanced greenhouse effects on climate. This is due to the fact that glacier mass changes provide important quantitative information on rates of change, acceleration tendencies and pre‐industrial variability relating to energy exchange at the earth/athmosphere interface. During the coming decades, excess radiation income and sensible heat (a few watts per square metre) as calculated with numerical climate models are both estimated to increase by a factor of about two to four as compared to the mean of the 20th century. The rate of average annual mass loss (a few decimetres per year) measured today on mountain glaciers in various parts of the world now appears to accelerate accordingly, even though detailed interpretation of the complex processes involved remains difficult. Within the framework of secular glacier retreat and Holocene glacier fluctuations, similar rates of change and acceleration must have taken place before, i.e. during times of weak anthropogenic forcing. However, the anthropogenic influences on the atmosphere could now and for the first time represent a major contributing factor to the observed glacier shrinkage at a global scale. Problems with such assessments mainly concern aspects of statistical averaging, regional climate variability, strong differences in glacier sensitivity and relations between mass balance and cumulative glacier length change over decadal to secular time scales. Considerable progress has recently been achieved in these fields of research.

Spatial climatic variation and its control on glacier equilibrium line altitude in Taylor Valley, Antarctica

The altitude of the equilibrium line (ELA) is an important variable describing a glacier because it helps to define the relation between the local climate and distribution of glacier mass. For the glaciers in the McMurdo Dry Valleys of Antarctica, the ELA rises rapidly with distance from the coast at a rate of about 30 m km −1, which is almost an order of magnitude greater than rates found in temperate glacier regimes. In one of the dry valleys, Taylor Valley, the ELA trend is not smooth but exhibits an abrupt shift of about 700 m yielding a local gradient of about 70 m km −1. The geographic location of the shift coincides with the Nussbaum Riegel, a ridge in the middle of the valley, which apparently exerts a strong control on the climatic pattern in Taylor Valley. To reveal the specific climatic factors responsible for the abrupt shift in ELA, we applied a theoretical analysis of ELA response to step changes in climate. Model results predicted an ELA rise of 729 m, which compares favorably to the observed 700 m change. The two most important climatic factors are differences in precipitation and wind speed. Whereas precipitation is expected to be a major factor determining ELA position for glaciers worldwide, because it determines the rate of mass accumulation, wind speed has not been previously recognized. In polar regions, where melting is typically absent, sublimation is the only significant process by which glaciers lose mass and its rate largely depends on wind speed rather than temperature. These findings highlight the sensitivity of polar glaciers to climatic differences over short distances, which have profound effects on the ELA and, in turn, glacier geometry. This study also points to the importance of understanding spatial differences in climates before piecing together a temporal climatic history based on data derived from different glaciers.