Environmental Change

Little Ice Age glacier variations

Gore Receding Glaciers Canada 1980

During the last few centuries glaciers advanced on all continents, indicating that the Little Ice Age was a global phenomenon. In the European Alps, the main advance around ad 1850 was preceded by another of similar magnitude around ad 1300. Thirteenth to fourteenth-century advances in Scandinavia and North America are not well documented however, the evidence for such advances in the Himalayas and New Zealand are better documented (Grove, 1988). In the European Alps, the initiation of the main...

Mass balance

Glacier Mass Balance Monthly

Glaciers and ice sheets are stores of water, exchanging mass with other components involved in the global hydrological system. Glaciers and ice sheets grow by snow and ice accumulation, and lose mass by different ablation processes. The difference between accumulation and ablation over a given time span is the mass balance, which can be either positive or negative. The mass balance reflects the climate of the region, together with glacier morphology and local topographic conditions. Mass...

Temperature distribution in glaciers and ice sheets

Height Ice Sheets

Temperatures in glaciers and ice sheets vary in space and time. Temperate glaciers have temperatures at or close to 0 C, while the upper part of the Antarctic ice sheet may be as cold as -40 to -60 C (Fig. 4.2). The melting temperature of ice decreases with increasing pressure at a rate of 0.072 C per 106 pascals (MPa lPa INm-2). As an example, the pressure at the base of a 2000 m thick glacier or ice sheet is about 17.6 MPa, corresponding to a lowering of the melting point to 1.27 C. Therefore...

Glacier movement

Black Outline Horsetooth Fort Collins

Information about glacier movement has been obtained from mathematical and numerical modelling, laboratory experiments, measurements in boreholes, observations in natural and artificial ice cavities, and interpretation of landforms and sediments in formerly glaciated regions. Snow and ice are transferred from the accumulation area to the ablation area by glacier flow. Flow takes place as sliding, deformation of the ice, and deformation of the bed under the glacier. The deformation and sliding...

Stable isotope variations in ice cores

Environmental Stable Isotope Chart

The atoms of oxygen (O) and hydrogen (H) present in glacier ice occur in different isotopes. Isotopes are different forms of an element that result from variations in atomic mass, or the combined number of protons and neutrons in each atomic nucleus. The number of protons in atoms of each element is constant. Mass variations are therefore a result of variations in the number of neutrons in the atom. Oxygen atoms have eight protons, but may have eight, nine or ten neutrons, giving three...

Variations in solar output

Since ancient times it has been known that the sun is the main source of energy driving the Earth's climate system (e.g. Gilliland, 1989). Changes in the solar constant were predicted by Milankovitch, who calculated the gravitational effect of the planets on the orbital parameters of the Earth. Until recently, it has been generally believed that the energy output from the sun is fairly stable. Since 1978, however, high-precision measurements of solar irradiance by satellite-based radiometers...

Box I I The concept of ice ages historical background

Environmental change is a continuous process where dynamic systems of energy and material operate on a global scale to cause gradual and sometimes catastrophic changes in the atmosphere, hydrosphere, lithosphere and biosphere. During most of the Earth's history the agents in the environmental system have been the natural elements (wind, ice, water, plants and animals). Some 2-3 million years ago, however, a new and perhaps the most powerful generator of environmental change, the hominids,...

Glacialinterglacial cycles during the Quaternary

Quaternary Sea Level Curve

The Quaternary is conventionally subdivided into glacials and inter glacials, with further subdivision into stadials (shorter cold periods within interstadial or interglacial stages) and interstadials (shorter mild episodes within a glacial phase). Glacial stages are normally considered as cold phases of major expansion of glaciers and ice sheets. Interglacials are considered as warm periods when temperatures were at least as high as during the present Holocene interglacial. These terms,...

Relative sealevel changes

Eustatic Sea Level Change Earth

A wide range of sediments and landforms may be used to reconstruct sea-level histories, such as deltas, beaches, shore ridges and erosional platforms marking former shorelines. More accurate sea-level data can be obtained from sediment cores retrieved from small lakes and bogs situated at different elevations in a small area or along the same isobase (e.g. Svendsen and Mangerud, 1987). In northwest Europe, the sea-level rise since deglaciation has been reconstructed at numerous sites along the...

Glacioeustasy and glacioisostasy

Glacial Sea Level

The basic idea of isostasy is that the Earth's crust, with a mean density of approximately 2800 kg m 3, is floating on the underlying plastic mantle with a mean density of about 3300 kg m 3 The amount of crustal depression resulting from ice sheet loading is a function of ice thickness and the ratio between the densities of ice and rock. The density of ice is about a third that of the crust, and therefore the crustal depression beneath an ice sheet is about a third of the ice thickness....

Energybalance models and glacier variations

An energy-balance model has been developed by Oerlemans (1988, 1991, 1992). This model calculates the components of the surface energy balance. It takes meteorological data, the area distribution with altitude of ice mass, and parameters defining the global radiation as input values. This model has also been used to calculate mass balance for glaciers in the Austrian Alps (Oerlemans and Hoogendoorn, 1989), southern Norway (Oerlemans, 1992), the Greenland ice sheet (Oerlemans, 1991) and NW...

Models of Late Quaternary climate and icesheet evolution

At present, glaciers and ice sheets cover about 10 per cent of the Earth's surface, locking up about 33 million km3 of freshwater, which would correspond to a sea-level rise of 70 m. During the Quaternary glacial periods, ice sheets were more extensive, covering about 30 per cent of the Earth's land area. Glaciers and ice sheets are also sensitive to climate change, varying in response to winter precipitation and summer temperature. To answer the questions of why, where and when glaciers form,...

Reconstruction of icesurface profiles and calculation of basal shear stress

From studies of modern glaciers, the basal shear stress is known to be related to the surface profile and thickness of glaciers, expressed by the equation where tb is basal shear stress, r and g the ice density and gravitational constant, respectively, a the surface slope of the glacier, and h the glacier thickness (Paterson, 1994). The value of tb (the basal shear stress) can be calculated from measurements of ice thickness h and surface slope a. Most calculated values of basal shear stress...

Chapter summary

Long ice cores from Greenland and Antarctica and shorter cores from minor ice caps and glaciers have documented annual and decadal climate change during the last interglacial glacial cycle. The recent central Greenland ice cores (GRIP and GISP2) have clearly demonstrated the occurrence of large, rapid, regional to global climate oscillations during most of the last 110,000 years on a scale not recorded in modern times. Most of the glacial-interglacial changes occur over decades, while some...

In 11111 i u 11 I ill nu

Figure 3.7 Multiparameter sequence between 270 and 275 m in the GISP2 ice core. Twenty strati-graphic layers and > 180 peaks were counted in conjunction with 22 electrical conductivity method (ECM) and 23 laser-light scattering from dust (LLS) peaks. Annual layer markers are shown as vertical white lines, corresponding to the spring summer inputs for each parameter. (Modified from Meese et al., 1997) Figure 3.7 Multiparameter sequence between 270 and 275 m in the GISP2 ice core. Twenty...

Future research priorities

Ice cores are extremely valuable palaeoenvir-onmental archives, and it seems unlikely that their potential has been exploited fully, as far as both precision and resolution are concerned. The future challenge will be to measure the full range of proxy environmental information stored in ice cores. New ice cores should therefore be obtained in order to validate existing ice-core data. Hopefully, new ice cores from Greenland will penetrate in situ Eemian ice. Differences in magnitude and timing...

Climate records from ice cores

Bored Schoo Quots

Palaeoclimatic records can be obtained from ice cores drilled from glaciers and ice sheets, containing information on accumulation and atmospheric composition through time. In the upper part of ice cores, annual layers are commonly preserved as alternating bands of clear and bubbly ice. Deeper in the ice cores, however, annual layers are usually not discernible and dating is made indirectly. Short ice cores can be drilled manually, but long cores have to be retrieved by sophisticated mechanical...

Glacier monitoring

International monitoring of glacier variations started in 1894. At present, the World Glacier Monitoring Service (WGMS) collects standardized glacier information. The data basis includes observations on specific balance, cumulative specific balance, accumulation area ratio (AAR), the equilibrium line altitude (ELA), and changes in length. Most of the data and the longest records come from the Alps and Scandinavia. About 90 years of observations reveal a general shrinkage of mountain glaciers on...

Determination of the equilibrium line altitude ELA

Glacier Diagram Decreasing Altitude

The equilibrium line altitude marks the area or zone on the glacier where accumulation is balanced by ablation. The ELA is sensitive to variations in winter precipitation, summer temperature, and wind transport of dry snow. When the annual net mass balance is negative, the ELA rises, and when the annual net balance is positive, the ELA drops. The steady-state ELA is defined as the ELA when the annual net balance is zero, and can be calculated by linear regression analysis of annual net balance...

Greenhouse gasinduced warming

The IPCC (1992, 1995) developed several scenarios of future greenhouse gas and aerosol emissions based on assumptions of population growth, economic development, land use, technological changes, energy availability and Box 7.1 Future climate change and glaciation As the understanding of past global climates and mechanisms of climatic change increases, the need to be able to predict future climate change and the growth and decay of ice sheets becomes increasingly important. Such predictions...

Lacustrine sediments

One of the best archives of terrestrial palaeo-climate information is lake sediment. Annual and decadal climate shifts influence sediment production and deposition in lakes. During the winter, lakes, at least in mountainous regions, are normally frozen and little clastic sediment enters the lakes. Organic production is effectively reduced due to little sunlight and snow-covered lake ice. In spring and early summer, strengthened sunlight, ice-free lake conditions, and nutrients released from...

Glaciers as monitors of environmental change

Glaciers and ice sheets are commonly located in remote areas far from population centres. Despite this physical and mental distance, past and modern glacial environments provide an important key to our knowledge of past, present and future global environmental conditions. Glacial environments may at first look chaotic and complex. However, few other environments exhibit such rapid, dynamic and spatially variable changes of processes. Past and present glaciers and ice sheets have had a...

Volcanism and climate

Large, explosive volcanic eruptions commonly inject huge amounts of silicate microparticles and acid gases into the stratosphere. This normally leads to warming of the stratosphere due to absorption of incoming solar radiation. Sulphate aerosols are formed, causing a cooling of the lower troposphere by back-scattering of solar radiation (e.g. Rampino and Self, 1982). The volcanic particles have a residence time in the stratosphere of at least one to three years and are distributed by...

Laminaevarves

Palaeoenvironmental interpretations and reconstructions based on varved sediments began early in the history of varve-sediment research, and focused on using the interannual variations in the varve laminae thickness as a monitor of past environmental change (Anderson, 1961 Saarnisto, 1979 Renberg and Segerstrom, 1981 Perkins and Sims, 1983 Leonard, 1986 0strem and Olsen, 1987 Cromack, 1991 Lotter, 1991 Deslodges, 1994). Variations in varve laminae thickness have since been related to other...

The astronomical Milankovitch theory of climate variation

Theory Change Climate Policy

During at least the last million years, climate has fluctuated in a distinctive way. In recent years there have been attempts to explain the causes of the long-term climatic fluctuation (e.g. Imbrie and Imbrie, 1979 Bradley, 1985). The astronomical theory or the Milankovitch theory has undoubtedly attracted the greatest attention. This theory was in fact developed by Croll about 100 years ago, but was later elaborated by the Serbian geophysicist Milutin Milankovitch. The theory is based on the...

Pre Quaternary glaciations

Devonian Ice Sheets

A general global temperature curve (Fig. 5.1) suggests that favourable conditions for glaciation occurred during at least five periods of Earth's history. Most probably, however, the Earth has experienced some kind of glaciation during the entire time span, but glaciation may have varied from continental ice sheets to minor ice caps or alpine glaciers. For pre-Quaternary glaciations, it is important to pay attention to continental drift and mountain building in order to explain the timing and...

Orbitallyinduced Milankovitch climate change

Climate is extremely complex to explain in physical terms. The study of the main climate processes responsible for climate variation requires the construction of mathematical models to describe quantitatively the interacting physical elements. Reconstructions of icesheet variations over the last million years indicate that climate, directly or through feedback mechanisms, is sensitive to variations in the orbital parameters. Climate models have been used to reconstruct the relationship between...

Mapping and measuring glacierfront variations

Long-term glacier observations which were coordinated internationally began in 1894 with the establishment of the International Glacier Commission in Zurich, Switzerland. The goal of this worldwide monitoring programme was to provide information on mechanisms of modern climate and glacier variations. At present, glacier variations are recognized as summer temperature and winter precipitation indicators used in the early detection of possible human-induced climate change (IPCC, 1992, 1995)....

Response timetime lag

Advance and retreat of the glacier front normally lag behind the climate forcing because the signal must be transferred from the accumulation area to the snout. This is referred to as the time lag, or preferably the response time, which is longest for long, low-gradient and slowly moving glaciers, and shortest on short, steep and fast-flowing glaciers (e.g. Johannesson et al., 1989 Paterson, 1994). Kinematic wave theory has been applied Figure 4.35 The annual (upper panel) and cumulative (lower...

Glacier hydrology

Equipotential Rises

Meltwater is an important component in glacier systems, and glacial meltwater exerts a strong influence on the hydrology of proglacial areas. Within and underneath glaciers and ice sheets, water affects glacier behaviour, controlling rates of glacier flow and influencing processes and rates of erosion and deposition. Surface and basal melting of glacier ice can produce large volumes of meltwater. In regions with low summer precipitation, but with glaciers in their catchment, glacial meltwater...

Holocene glacier and climate variations

The Little Ice Age was the most extensive Neo-glacial glacier advance in the Canadian Rocky Mountains (Luckman et al, 1993). Evidence of earlier, less extensive Neoglacial advances is based on wood recovered from several glacier forefields. Three radiocarbon dates, ranging between 8230 and 7550 yr bp, obtained from wood flushed out of Athabasca Glacier, and two dates from Dome Glacier ranging between 6380 and 6120yrbp, indicate that forests occurred upvalley of present glacier fronts during the...

Lateglacial glacier and climate variations in NW Europe

High-frequency climatic fluctuations during the last d glaciation (ca. 14,000-9000 14cyrbp) are well documented in terrestrial data, marine records and ice cores from the North Atlantic region (e.g. Lowe and Walker, 1997, and references therein). These climatic changes occurred at a time of maximum solar radiation receipt in the northern hemisphere and cannot therefore be explained by orbital forcing. The cause(s) of these climatic fluctuations must therefore be sought in the ocean atmosphere...

Supraglacial ice morphology

Supraglacial structures reflect glacier formation, deformation and flow. Glacier ice exhibits a wide variety of internal and superficial structures, such as crevasses, icefalls, ogive banding, and layering. Crevasses form where ice is pulled apart by tensile stresses that exceed the strength of the ice, and they are commonly oriented at right angles to the main stress direction (e.g. Paterson, 1994). Crevasses are therefore a reflection of the stress orientation in a glacier. Chevron crevasses...

Seaice ice shelves

Temperate Glaciers

Sea-ice ice shelves are normally formed by a combination of thickening by snow accumulating on the surface, and freezing of seawater. Movement and deformation in such a shelf is entirely determined by the weight of the ice mass. Sea-ice ice shelves exist where annual temperatures are sufficiently low for ice to form and where embayments and islands Figure 4.1 Tentative temperature profiles through polar, subpolar and temperate glaciers. (Adapted from Skinner and Porter, 1987) -25 -20 -15 -10 -S...

The significance of environmental change

The Earth is a dynamic, non-static and constantly changing system, in which all components (the atmosphere, geosphere, cryo-sphere, hydrosphere, and biosphere including mankind) interact. Research on global environmental change tries to understand how these complex systems interact, and to identify the nature of linkages between them. This research may ultimately provide the basis for predicting future global environmental changes and their human consequences. To be able to forecast future...

Reconstruction of the equilibrium line altitude

Cosa Equilibrio Ambientale

Fluctuations in the ELA provide an important indicator of glacier response to climate change which may allow reconstructions of palaeoclimate, but also of future glacier response to given climate change. reconstruction of the equilibrium line altitude 59 Figure 4.6 The principle of calculating the depression of the equilibrium line altitude on a glacier based on the maximum elevation of lateral moraines. The previous extent (a) is compared with the modern extent (b) for an idealized glacier....

Gas content in ice cores

Environmental Impact Ice Cores

Below the surface of a glacier or ice sheet, air bubbles become isolated and trapped during the transformation of snow into ice. If no diffusion occurs, the bubbles contain 'fossil' air from the time of the inclusion. The composition of the bubbles in ice cores therefore provides a way to analyse changes in the atmospheric composition several thousands of years back in time. The reconstruction of atmospheric C02 concentration from ice cores is, however, not straightforward, due to (a) possible...

Physicochemical techniques

Several physicochemical dating techniques based on isotopes or radiological processes, rock surface weathering, tephrochronology, varves (annual laminae in sediments) and palaeomagnetism have been applied to glacier forelands. Radiocarbon dates for wood, peat, soil or lacustrine sediments obtained from glacial forelands can either be of the actual event (contemporary), bracketing or limiting (Porter, 1981b). Most commonly, samples provide either maximum or minimum ages of the actual event....

Glacier monitoring by satellites

The Earth Observing System (EOS) has been developed to build a uniform database covering most glaciers of the world and to monitor changes in glaciers on a periodic basis (Kieffer et al., 1994). This planned survey will build on current and previous projects, including 20 years of space-based observations of glaciers, such as observations by LANDSAT, SPOT, ERS and RADARSAT. The satellite can observe all of the Earth's surface at latitudes less than 85 . The project is presently developed to...

Terminal moraines

Present and former positions of glaciers are marked by different moraine types formed by the deposition of sediment at the margins, or by stresses induced by the glaciers. Such deposits exhibit a number of features, such as glacitectonic landforms, push and squeeze moraines, dump moraines, and later frontal fans and ramps. It is often difficult to classify ice marginal deposits. Moraines of supraglacial and englacial origin are difficult to recognize because the material is lowered on to the...

Variations of local glaciers during the last glaciation

For the Colombian Andes, a radiocarbon-dated framework of pre-Late-glacial maximum was presented by Helmens et al (1997). During each of three pre-LGM advances, glaciers extended beyond the LGM. In other parts of the Andes, in New Zealand, and in some Eurasian mountain ranges, glaciers advanced farther earlier in the last glacial cycle than at the LGM (Gillespie and Molnar, 1995 Bon-darev et al, 1997 Clapperton et al, 1997 Fitzsimons, 1997 Clapperton, 1998). The interval of greatest glacier...

Outlet glaciers and ice streams

The ice movement in an ice sheet can be divided into sheet flow in the central dome areas, and stream flow in outlet glaciers and ice streams, characterized by rapidly moving, channelled ice flow. Outlet glaciers draining plateau glaciers normally have the form of valley glaciers. The accumulation area may be difficult to delimit. The longest glacier in the world, the 700 km Lambert Glacier in Antarctica, and the world's fastest moving glacier, Jacobshavn Glacier in western Greenland, are both...

Morphological classification

Glacier form is a function of climate and topography, and therefore a variety of glacier morphologies exists, from the smallest niche glacier to the largest ice sheet. A first-order classification into ice sheets and ice caps unconstrained by topography can be subdivided into a second-order classification of ice domes, ice streams and outlet glaciers. Glaciers constrained or controlled by topography include icefields, valley glaciers, transection glaciers, cirque glaciers, piedmont lobes, niche...

Surging and tidewater glaciers

A surging glacier commonly shows little sign of unusual activity for several years. Then it starts to move rapidly and the glacier surface, especially in the lower part, is transformed from a fairly smooth surface into deep crevasses and ice pinnacles. The frontal part may move several kilometres in a few months or years before it suddenly stops. Ice velocities during most surges are 10-100 times those in normal glaciers. Observed velocities vary from about 100 m per day over short periods, to...

Frontal variations

Cenozoic Continental Glacier Eustatic

The retreat and advance of glacier fronts has probably been used as a measure of climatic variations as long as humans have lived close to glaciated environments. Climate is constantly changing, with annual fluctuations superimposed on long-term trends. Such climatic changes are reflected in variations in the glacier extent. One example is the growth and decay of the Cenozoic continental ice sheets. Another example is the glacier advances during the 'Little Ice Age' and the subsequent frontal...

Calving glaciers

Several mechanisms of glacier calving have been described however, the fundamental control and relationship with calving rate is poorly known. This makes it difficult to explain the lack of climatic sensitivity of different glaciers, in particular the order-of-magnitude difference in calving rate between tidewater and lake-calving glaciers (Fig. 4.49). The mechanism for 'normal' slab calving includes the development of an overhang before failure occurs as a result of deformation of the glacier...

Global circulation models GCMs

To gain a better understanding of atmospheric conditions, we simulate global-scale climatic processes using global circulation models (GCMs), which are computer simulations of mathematical models of how the atmosphere operates and interacts with the hydrological cycle (Wright et ah, 1993). GCM experiments have provided pertinent information about relationships between atmospheric circulation and mechanisms of climate forcing such as land uplift (Ruddiman and Kutzbach, 1990), vegetation cover...

Natural versus anthropogenic forcing

Since the IPCC (1990, 1992, 1995) scientific assessments, progress has been made towards identifying possible anthropogenic effects on climate. Firstly, model experiments are now incorporating the possible climatic effects of human-induced sulphate aerosols and stratospheric ozone. As a result, the potential climate change signal due to human activities is better defined, although several uncertainties still remain. Secondly, the background climatic variability has been better defined. This is...

Dating techniques in glacier forelands

The resolution and reliability of any moraine chronology is only as good as the precision and accuracy of the dating technique, and the interpretation of the relationship between dated layers and geomorphological processes. The interpretation of dated chronological records obtained from landforms, and moraine sequences in particular, rarely pay attention to the inherited complexity in interpreting landform formation. The uncertainties may include availability of datable material, the...

Volcanic activity and climate variations

Explosive volcanic events inject fine-grained ash and dust into the atmosphere. This commonly leads to short-lived temperature drops due to reduction of incoming radiation. Dust particles may also act as foci for formation of water droplets and thereby cloud formation. Sulphur volatiles are, however, more significant in terms of climate change. In the atmosphere these are converted into sulphuric acid and these aerosols result in cooling of the lower troposphere by back-scattering of long...

Models of future sealevel changes

Future sea-level rise has led to concern because of possible impacts to coastal regions, in the form of loss of land through inundation and erosion, increased frequency of storm floods, and saltwater intrusion. Global mean sea-level is a sensitive indicator of climatic change. Global warming will lead to sea-level rise from the thermal expansion of seawater, the melting of alpine glaciers and polar ice sheets. Several studies have reported rates of annual global sea-level rise during the last...

Biological dating

Two biological dating techniques have proved useful for dating glacier forelands dendrochronology and lichenometry. In regions where glaciers descend into areas with trees, the annual pattern of tree growth may be affected by the proximity to the glacier. In recently deglaciated glacier forelands, it is important to establish the age of living trees by counting annual rings and the age of abnormal (normally reduced) growth rates both in living and dead trees (e.g. Schweingruber, 1988). The age...

Box 31 Extracting the climate signal from varved sediments

Varved sediments have been used to generate palaeoenvironmental reconstructions based on variations in the varve thickness and composition, as well as on variations of fossil or other signals in the sediments. However, it may be difficult to identify the type of environmental signal recorded in the sediments, and to quantify the relationship between sediment variations and a given environmental parameter (temperature, precipitation, runoff). It can be hard to estimate the rate at which a...

Historical documents

Historical documents have been considered to be one of the most accurate sources for reconstructing recent glacier variations. In addition, this information has been used to calibrate data on glacier variations further back in time. The Icelandic Sagas (ad 870-1264) seem to be the oldest documents mentioning glacier variations. Some of the oldest historical data do not, however, fulfil modern scientific standards and must not be looked upon uncritically. In Iceland, Norway and the Alps,...

Preface to the series

The study of environmental change is a major growth area of interdisciplinary science. Indeed, the intensity of current scientific activity in the field of environmental change may be viewed as the emergence of a new area of 'big science' alongside such recognized fields as nuclear physics, astronomy and biotechnology. The science of environmental change is fundamental science on a grand scale rather different from nuclear physics but nevertheless no less important as a field of knowledge, and...

Variation in atmospheric gas content and climate change

Direct measurements of the atmospheric concentration of the greenhouse gas carbon dioxide (C02) began in 1958, and this figure has shown a significant increase from 315 parts per million by volume (ppmv) to 364 ppmv in 1997 (data from Keeling et al, 1995 Keeling and Whorf, 1998 Fig. 2.2). The increase in atmospheric CO2 is caused by burning of fossil fuels and a change in land use. Previous investigations showed that the atmospheric C02 concentration was about 280 ppmv 315310 1 1 1 1 1 1 1 * 1...

Glaciers environmental change and the human race

Glacier chronologies obtained from different parts of the world have demonstrated that glaciers respond in different ways to climatic triggers. Predictions of future climate trends and glacier response must therefore avoid general statements about the linkage between recent glacier variations and climate change. Global warming scenarios invoke higher sea-levels, increased melting of the glaciers, and accelerated calving rates for the West Antarctic ice sheet. A warmer climate does not, however,...

Box 41 Physical properties of ice

When the annual amount of snow and ice exceeds ablation, there is net accumulation successive layers of snow build up and the deeper layers are transformed into ice as the volume of air-filled pores is reduced and density increases (Paterson, 1994). New-fallen snow has a density of 0.02-0.2gem 3, while firn (snow that has survived one melt season) has a density of 0.4-0.83gem-3. Glacier ice has a density of 0.83-0.91 g cm-3, while pure ice has a density of 0.917gem-3. The transformation...

Svein Olaf Dahl

Department of Geography, University of Bergen, Norway A member of the Hodder Headline Group LONDON Co-published in the United States of America by Oxford University Press Inc., New York First published in Great Britain in 2000 by Arnold, a member of the Hodder Headline Group, 338 Euston Road, London NWI 3BH Co-published in the United States of America by 198 Madison Avenue, New York, NY10016 2000 Atle Nesje and Svein Olaf Dahl All rights reserved. No part of this publication may be reproduced...