Glaciers and the Environment Nairobi, UNEP, 1992 (UNEP/GEMS Environment Library No 9)

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United Nations Environment Programme Glaciers and The Environment Nairobi, UNEP, 1992 (UNEP/GEMS Environment Library No 9)

This publication is produced within the framework of the Earthwotch process of The United Nations system.

Text: Wiltried Haeberli and C. C. Wallhn Layout and artwork: Words and Publications Oxford, England

Printed on Savanna Natural Art, a paper that contains at least áO percent bagosse (sugar cane waste)

The views expressed in this publication arp not necessarily Those of The United al1ohs &wironmenf Programme

Als eries: The Greenhouse Gases The Ozone Layer The African Elephant Urban Air Pollution Food Contamination Freshwater Contamination The Impact of Ozone Depletion The El Nina Phenomenon The Impact of Climate Change Global Biodiversity UNEP/GEMS Environment Library No 9

GLACIERS AND THE ENVIRONMENT

The UNEP/GEMS Environment Library

Earthwatch was the name given in 1972 UNEP/GEMS Environment Library. by the UN Conference on the Human This is the ninth volume in the series, Environment to the assessment activities and is a somewhat unusual one. It deals included in its action plan. Under the with glaciers which, unlike the African plan, each UN agency monitors and elephant or urban air pollution, for assesses those aspects of the environment example, have not recently been the that fall within its mandate. This Global subject of concerned public debate. Environment Monitoring System (GEMS) Why glaciers? Firstly, because glacier was formally created two years later, in monitoring is, rightly, an important part Al Ic/uk'/ D. &; /, i 1974, and the system is coordinated by of GEMS activities. Glaciers are important the United Nations Environment to the environmental health of the planet, Programme (UNEP) and its partner playing subtle roles in the regulation of agencies through a Programme Activity the Earth's heat balance. They also act as Centre at UNEP's Nairobi headquarters. some of the most sensitive instruments GEMS now has more than 15 years of we have for measuring climatic change solid achievement behind it. In that time, and for recording a frozen history of the it has helped make major environmental composition of the atmosphere and of assessments of such things as the impact precipitation back through the ages. of global warming, the pollution of urban Finally, and again unusually for this air, the rate of degradation of tropical series, I also commend this publication to ' Altv .h4 forests and the numbers of threatened you purely for the fascination of the species—including the African science that it contains. elephant—in the world. As is proper, the results of these assessments have been regularly Michael D. Gwynne published as technical documents. Many Director, Earthwatch and GEMS, and are now also published, in a form that can Assistant Executive Director Environment be easily understood by those without Programme, United Nations technical qualifications, in the Environment Programme Contents

Foreword 3

Overview 4

The background ó The history of ice 6 The nature of glaciers 8

The behaviour of glaciers 10 The making of a glacier 10 Taking a glacier's temperature 13 The glacier audit 14 How glaciers move 15

Taking stock 19 Monitoring the world's glaciers 19 Uses of the data 21

Sources 24

Cold polar glaciers on Axe! Heiberg Island near the Arctic Circle in Canada's Northwest Territories.

(Cover photo: J. Alean) Foreword

It is difficult to believe—in these times of global warming and recurrent drought—that the Earth is essentially a glacial planet. Over millennia there have been numerous Ice Ages, the latest of which started to end a mere 20 000 years ago. It takes a global temperature decrease of only 6 °C to revert large expanses of central Europe and Asia to permafrost. Ten percent of the Earth's surface—some 15 million km2—is currently covered by glaciers. There are glacierized regions or mountainous icecaps in every continent of the world, even on the equator. What use glaciers? These great, implacable frozen masses of ice and snow remind us of our place in time and space, and have valuable uses, vital to the daily lives of millions of people. The information they have trapped in their frozen interiors may Mostafa K. To/ba also be critical to human development and survival. Seventy-five percent of the world's freshwater is stored in glaciers, and the water they release is used to produce hydropower and for irrigation. Glaciology—the scientific study of snow and ice—is catalysing the development of early-warning systems for some glacier-related natural disasters such as ice avalanches. Furthermore, glaciers provide a frozen record of atmospheric conditions over long periods of time. Ice cores from glaciers have been used to establish, for example, the levels of carbon dioxide and other chemicals in the atmosphere in pre- industrial times. Finally, glaciers can provide indications of climatic change in the past and of changes occurring at present. The retreat of glaciers worldwide during the past century is evidence of global climate change that can be easily understood by everyone, and it is important that we recognize, document and study this important signal of climate change. Systematic worldwide observation of glaciers started in 1894. In 1976 a worldwide inventory of glaciers and ice sheets was begun, the first report of which—World Glacier Inventory: status 1988—was published in 1989. Glacier monitoring is now coordinated by the World Glacier Monitoring Service, established in 1986 with help from UNEP and other national and international bodies. The aim of this publication is to make the knowledge we have gained about glaciers more widely known, and to emphasize the need to develop this knowledge. Glaciology holds one of the keys to our past. It may also hold many to our future.

Mostafa K. Tolba Executive Director United Nations Environment Programme Overview

There have been two Ice Ages over the past 150 000 years, and a long interglacial period which lasted from about 125 000 to 75 000 years ago. We are currently enjoying another interglacial period—one that this time may be intensified far beyond natural ranges as a result of global warming caused by the accumulation of greenhouse gases in the atmosphere. Indeed, it is possible that this global warming could be greater than any of the temperature fluctuations undergone during the transition from an Ice Age to an interglacial period. Yet much of the Earth— which can justly be referred to as a glacial planet—is blanketed in ice and snow, even during interglacial periods. During winter in the northern hemisphere, ice and snow cover half the world's land area and some 30 percent of the oceans. About 10 percent of the land area is covered with glaciers, which contain 75 percent of the world's freshwater resources. Most of this is stored in the huge ice sheets of Greenland and Antarctica. The remaining glaciers and mountainous ice caps cover an area of some 550 000 km2, nearly all of it in North America and Eurasia. Glaciers can be regarded as the residual remains of the large ice bodies of the past Ice Age—or as the precursors of the ice sheets of the next Ice Age. And just as the sizes of the massive ice sheets that characterize Ice Ages are a crude During winter in indicator of climatic and environmental change, so are the the northern planet's glaciers a sensitive instrument for measuring more hemisphere, ice subtle changes over shorter timeframes. and snow cover Because the ice in glaciers is near melting point, glaciers half the world's act as sensitive indicators of climate change. The spectcular land area and and worldwide retreat of mountain glaciers this century is some 30 percent the strongest evidence so far of the fact that the Earth's of the oceans. average surface temperature has changed significantly and rapidly since the Little Ice Age ended in the last century. Glaciers are of great scientific interest in their own right but their study also has practical importance in many fields. As ice accumulates over thousands of years it provides a record, in cold storage, of the atmospheric conditions prevailing when the ice was formed. It was a study of ice cores that enabled scientists to establish background levels of carbon dioxide and other chemicals in the atmosphere before industrialization began. The study of glaciers is also important in the design of hydroelectric schemes, since it is often the water released 1 Al9thcenturyprint showing an advancing glacier—the Upper Grindelwald Glacier in Switzerland—pressing against the timber line and agriculture, during is the Little Ice Age. The painting was made by Thomas Fairnley in August 1835.

by glaciers that provides their power. Additionally, glaciers are implicated in the onset of flooding, avalanches The spectacular and debris flows, and their advance and retreat can cause and worldwide the formation and abrupt release of the contents of large retreat of lakes blocked by ice. Finally, the melting of glaciers is mountain glaciers thought to have been responsible for roughly one-third of this century is the the 10- to 20-cm rise in sea level that has been observed strongest over the past 100 years. evidence so far The systematic worldwide observation of glaciers began of the fact that in earnest in 1894, with the creation of an International the Earth's Glacier Commission. In 1976, with help from UNESCO's average surface International Hydrological Programme (IHP), a project to temperature has inventory the world's glaciers and ice sheets was begun. A changed first report was issued in 1988; glacier monitoring is now significantly and coordinated by the World Glacier Monitoring Service, rapidly since the supported by the Global Environment Monitoring System Little Ice Age (GEMS, UNEP), IHP and the International Association of ended in the last Scientific Hydrology. century. The background

The history of ice

A few million years ago, as the Antarctic century but the whole process takes a long continent migrated towards the South Pole time—at least 20000 years. Although the and began to build up a large ice sheet, last Ice Age started to end some 20 000 conditions became ripe for the onset of the years ago, land at the head of the Gulf of modern Ice Ages. The seas cooled as ice Bothnia is still rising by 90 cm a century, flowed into the sea from the Antarctic ice and the Stockholm archipelago is rising by sheet, air temperatures fell and the climate 50 cm a century. eventually became sensitive to periodic The Earth's climatic history is better variations in solar radiation caused by understood from about 75 000 years ago fluctuations in the Earth's orbit round the when the first of two Ice Ages—Wisconsin I Sun. Continental ice sheets began to form and Wisconsin Il—set in. Wisconsin II and their whiteness reduced the amount of reached its coldest about 20000 years ago solar radiation absorbed by the Earth, (see Figure 1). At that time, the largest ice accentuating the cooling still further. sheet, the Laurentide, was still covering the During an Ice Age, the land becomes northern part of North America, and other depressed by the weight of ice that covers ice sheets lay over Scmdinavia, the British it. Land levels fall, generally by about one- Isles and Eastern Siberia in the northern third of the thickness of ice that covers the hemisphere (see Figure 2) and over land. At the same time, ice sheets trap Patagonia and Tierra del Fuego in the much of the available moisture in frozen southern hemisphere. Although the average form, and sea levels fall. The evidence temperature of the Earth's surface was only suggests that sea levels fall by 100 to 140 some 6°C cooler than now, the ground was metres during an Ice Age. permanently frozen in central Europe and There is no agreed view on how many Ice much of Asia. The sea level fell more than Ages occurred during the past two million 100 metres, the Bering Strait dried up, and years. It is clear, however, that they were early man was able to hunt mammoths not separated by a number of much warmer, only in Eurasia but in what later became interglacial periods. As the ice melts at the known as the New World. end of an Ice Age, the land begins to rise The build-up of large ice sheets caused again, quickly to begin with and more complex meteorological changes, notably slowly later on. During the initial ice melt, the deflection of winds from the Pacific land levels can rise as much as 9 metres a around the northern edge of the Figure 1 shows the sequence of ice ages average 20°C enhanced global warming over the past 150 000 annual air from greenhouse gases super-interglacial years, and a projection temperature 18 C for the next 25 000 çerIaciaI

years. The current years interglacial period is likely to become a superinterglacial period intensified by an enhanced 25 000 greenhouse effect. -15d 000 -25 000 -J0 000 -75 000 50 000 -25 000 today the background

Figure 2 Extent of ice northern hemisphere Ice sheets 150 sheets in the northern r 1 1 20 hemisphere during the past Ice Age. Sea levels were lowered by 700

- metres or so as b moisture became 150 -. 90 cf' Oc O ) locked up in ice sheets.

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120

- INVOrth Ati ntiC Oceofl -

- --- 90 60 30 -- 0 30

Laurentide. These cold winds cooled the far away from the remaining ice sheets Atlantic, and ice cover spread further were as small as now, though cold south, as far as the Pyrenees. The Eurasian periods—such as the Little Ice Age that ice sheets were then denied the Atlantic as gripped the land from about the early 17th a source of their moisture, and the Alpine to the mid-19th century—occurred glaciers thinned and froze to their beds. repeatedly, lengthening and swelling the This was the time of the cold desert. As glaciers once again. Since the mid-19th precipitation dropped, glaciers and ice century both the length and mass of sheets began to lose mass, snow and ice glaciers worldwide have been shrinking- cover began to retreat, and the frozen probably at a faster rate than at the end of ground began to absorb more solar the past Ice Age. While this is presumably a radiation. Within a few thousand years, the natural phenomenon, it is also possible that ice cover had gone and global warming an enhanced greenhouse effect could be had set in, accompanied by a sharp partly responsible. If we fail to prevent an increase in the levels of greenhouse gases enhanced greenhouse effect a super- in the atmosphere. This was a catastrophic interglacial period with a warmer climate period of climate change, which resulted in may occur during the coming centuries, the extinction of many large mammals. with temperatures perhaps warmer than By about 10 000 years ago, average global any experienced for millions of years. Some temperature and precipitation were similar 10 000 or 20 000 years after that, the climate to those of today. Many mountain glaciers may shift again towards another Ice Age. Glaciers and the environment

The nature of glaciers

Glacier ice currently covers 10 percent of is true. It follows that somewhere in the Glacierized the Earth's surface, or some 15 million km2 . middle of the glacier there is an areas (km2 ) Although this resource contains 75 percent equilibrium line, where snowfall equals South America of the world's freshwater, most of it is snow loss. The area above the equilibrium 25 908 stored far away from human habitat and lme is called the accumulation area, and North America action, in the massive ice sheets of that below it the ablation area. The surface 276100 Greenland and Antarctica. of the accumulation area is composed Greenland The remaining 3-4 percent of ice is found mainly of snow, while that of the ablation 1726400 spread over an area of 550 000 km 2 as area is mainly of ice (see Figure 3). Europe glaciers and on mountainous ice caps. Of There are two main types of glacier: 53 967 this total, 50 percent is found in North maritime and continental. Maritime Asia and CIS America, 44 percent in Eurasia, 5 percent in glaciers are characterized by heavy 185211 South America and 1 percent in New precipitation (more than 2000 mm a year), New Zealand/ sub-Antarctic Zealand. In most of these areas, glaciers are mean annual air temperatures close to islands of considerable economic importance as a freezing point, and low-altitude 7860 result of the water they provide for equilibrium lines near or below the timber Antarctica hydroelectric schemes and irrigation. line. Because of the heavy snowfall they 13 586 310 Glaciers are basically moving bodies of experience, these glaciers flow rapidly. snow and of ice that has been formed as a They include temperate ice caps in TOTAL result of the recrystallization of snow. The Patagonia, Iceland and Norway, networks 15861 766 snow falls high up on the glacier, becomes of large temperate glaciers, particularly in compressed under subsequent layers of the coastal mountains bordering the Gulf of snow, turns first to a heavier but still Alaska, and temperate mountain glaciers in porous intermediate material called firn, the Caucasus, the outer Alps and on Kenai and finally turns to ice. All the while, the Peninsula in Alaska. snow, fim and ice of which the glacier is Continental glaciers are found where composed move downhill, from colder precipitation is less than about 500 mm a areas to warmer ones. year. Their equilibrium line retreats far At the top of a glacier more snow falls above alpine meadows and into regions of than disappears through melting, run-off permafrost where the mean annual air and evaporation. At the bottom, the reverse temperature is less than about —8 °C. These

glaciers: - ablation area: ice surface accumulation area: snow surfoce the key elements

firn

Figure 3 Main elements of a typical ice glacier in a steady- state situation the background

air temperature Figure 4 The cold flrn cold ice and precipitation relationship between for three types of Continuous glacier permafrost precipitation and average annual air discontinuous we temperature permafrost determines the nature e firn -1-c sporadic or of a glacier: maritime, temperate ice no permafrost transitional or maritime glacier transitional glacier continental glacier continental. 2500 precipitation (mm/a) 500

glaciers flow slowly, and are found mainly freezing point. They are common in Three types of glacier: in the polar regions and in the driest parts Svalbard, the Argentinian Andes, the maritime mountain of the Asian mountains. inner Alps and most mountain ranges in (Portage, in southern There is also a third type of glacier with Asia. The relationship between these three Alaska, below left); characteristics midway between these types of glacier, average air temperature transitional (Svalhnrd, extremes. These transitional glaciers are and precipitation is shown in Figure 4. in the Arctic north of found where precipitation is between 500 The photographs below show typical Scandinavia, below); and 2000 mm a year, and average examples of maritime, transitional and and continental temperatures are a few degrees below continental glaciers. (Liruniqi in China, bottom). 1

4-1

Pell The behaviour of glaciers

The making of a glacier

Glaciers are formed in areas where more becomes trapped as bubbles. This material snow falls in the winter than melts or is impermeable, is milky or even brilliantly evaporates in the summer. Glacier white because of the air trapped in it, and movement transfers this excess snow (and is called glacier ice. ice formed from it) from the accumulation In Greenland and Antarctica, this area on the upper part of the glacier to the process occurs at temperatures of —20 OC ablation area, where melting or less, takes a century or more, and predominates, on the glacier's lower part. happens 50 or 100 metres below the snow Fresh snow has a density of 100 kg/rn3 or surface. The ice and air bubbles that have less. When it becomes compressed by been trapped in glaciers provide a frozen substantial accumulations of snow above archive of the composition of the Figure 5 Analysis of it, fragile snow crystals are transformed atmosphere and the nature of ice cores s/tows that into spherical particles. As these pack precipitation many years ago. Ice cores CO2 concentration in closer and closer together, density reaches from glaciers have also revolutionized our the atmosphere and air some 500 kg/rn3 after a year or more, knowledge of earlier climates. temperature (as creating a porous material known as firn. The longest ice core thoroughly analysed revealed by oxi/gen or If such conditions prevail year after year, so far is from Vostok in Antarctica, with a hydrogen isotopes) increasing pressure gives rise to larger length of 2521 metres and spanning 160 000 moved closely in step crystals and higher densities. When the years. It provided a fascinating picture of with one another over density reaches 830 kg/rn3, the crystals the fluctuations of carbon dioxide (CO2) in the past two Ice Ages. join together and the air between them the atmosphere before and during the last Ice Age, as well as during the past 10 000, more temperate years. Drilling by American concentration 320

of CO2 and European scientists in Greenland has (ppmv) 280 been going on since 1989, and researchers there hope to reach even older ice. 240 The Vostok research showed that the concentration of CO2 in the atmosphere 200 and atmospheric temperature (as recorded by the ratio of hydrogen and oxygen

160 isotopes) changed almost perfectly in step 150 100 50 10 with one another during the past two Ice time before present (1000 years) Ages and during the interglacial period temperature, warm Inferred from that separated them (see Figure 5). oxygen or Ice core analysis also helped establish hydrogen Isotopes baseline levels for CO2 . which became badly needed as concern over greenhouse warming mounted during the 1970s and 1980s. A baseline pre-industrial value of 270-290 parts per million (ppm) was cold established by several methods, and this 150 100 50 10 C was later refined to 260 ppm as a result of time before present (1000 years) the analysis of ice cores.

10 I 0 (D 0

In glacierized areas where there is some it is governed mainly by the amount of Gaissbergfcrner in the melting during the summer, small amounts snow that falls on the head of the glacier. Oetztal Alps, Austria: of meitwater can infiltrate the snow layer Ablation is more complicated. The the exposed lateral that fell earlier in the year. This meitwater intensity of melting caused by solar inoraines clearly then refreezes, leaving a distinctive trace of radiation depends on the reflectivity of the indicate 20th-century warmer summers which will remain material exposed on the glacier surface, mass loss. hidden deep below the surface after since only absorbed—not reflected- centuries of snowfall have covered it up. radiation contributes to heating. Fresh The amount of refrozen melt layers in a snow reflects 80-95 percent of solar Sketch below shows the core taken from such a glacier is a reliable radiation, old snow 50-80 percent, firn Rhône glacier in 1856. guide to summer temperatures. As Figure 6 30-60 percent and ice 15-40 percent. These shows, analysis of an ice core taken from figures illustrate the importance of Devon Island in the Arctic shows that the summer snowfall in protecting glaciers 20th century must have been by far the from ablation. warmest century since the Middle Ages. Radiation contributes about two-thirds of Similarly, analysis of ice cores on Colle the energy available for melting. The Gnifetti in the Swiss Alps has revealed the remaining third comes mainly from rise of acid precipitation since the middle heating by the atmosphere as warm air is of the last century (see Figure 7). convected onto the glacier surface. The rate The way in which a glacier builds up of melting depends largely on the air through accumulation is relatively simple: temperature above the glacier and hence Glaciers and the environment

convection causes less melting on glaciers percentage of retrozen nitrate concentrations, 1880-1980 (ppb) melt layers in ice core at high altitudes and latitudes than at low 0 from Devon Island ones. Some reduction in glacier mass is also 400 average I trend 0 10 20 caused by the evaporation of snow, firn 00 300 0 and ice when humidity is low. 9 1963 An understanding of the factors 10 200 0 responsible for accumulation and ablation

20 1925 in glaciers enabled scientists to make a 100 0

number of useful deductions about glacier 0 30 1894 0 behaviour in the first half of this century. 1860 1880 1900 1920 1940 1960 1980 Although solar radiation is the most 40 1859 important process quantitatively, the sulphate concentrations. 1880-1980 (ppb) 1000 ______0 50 1820 intensity of solar radiation varies little from average 0 year to year compared to the variations 800 trend 60 1778 that occur in precipitation and air 00 temperature. It was therefore concluded 600 70 1732 that precipitation rates alone could be used 400 > I e0 1684 to estimate accumulation rates, and air 000 200 temperature alone could be used to 0 o 90 1632 estimate ablation rates. 0 I 1860 1880 1900 1920 1940 1960 1980 One practical result of this work is that 100 1577 hydrologists can use records of air 110 1519 temperature to estimate the rate at which Figure 7 Concentrations of nitrate and I glaciers are melting and so supplying water sulphate ions in ice core samples taken from 120 1458 to, for example, a hydroelectric plant. Colle Gnifetti in the Swiss Alps chart the rise of Another concerns the position of the acid precipitation. 130 1393 equilibrium line on a glacier, the point at 140 1325 which the accumulation rate equals the ablation rate. Meteorologists argued that 150 1254 since accumulation must equal ablation mechanism involved is simply that if a depth year along the equilibrium line, the air small rise in temperature occurs, the area of (m) (AD) temperature there can be used to predict snow cover will decrease. More dark precipitation rates. The glacier itself can thus ground will be exposed, the reflectivity of Figure 6 Percentage of be used as a kind of giant precipitation the area will fall, and more solar radiation refrozen melt layers gauge, providing meteorologists with will be absorbed in areas adjacent to the above or below average information that it would be hard to obtain glacier. This will increase the rate of ice in an ice core from in any other way—precipitation rates are melt, establishing a feedback mechanism in Devon Island in the difficult to measure high up on remote and which a small change in temperature Arctic shows that the cold glaciers. results in a large change in ice and snow 20th century must A reduction in snow cover can amplify cover. Glaciers in polar regions are less have been by far the temperature changes, turning the areas of sensitive to warming because meltwater warmest century since glaciers above the equilibrium line into tends to refreeze, but feedbacks will the Middle Ages. sensitive climatic indicators. The enhance the effect of global warming. It the behaviour of glaciers

Taking a glacier's temperature

Most people regard freezing point as cold. represents the limiting penetration depth of Not so glaciologists, who describe glaciers seasonal temperature variations. in which the main body of snow, firn and Such polar measurements suggest that ice is at 0 °C as temperate, and reserve the there has been a rise in average annual air word cold for cooler glaciers. Glaciers that temperature this century of 1-2 °C- contain some material at 0 °C and some considerably more than the world average colder are called polythermal. of 0.5 °C. This confirms the results, found in Glacier temperatures are measured by climate models used to simulate greenhouse lowering probes down boreholes. Such warming, that warming trends are strongly measurements reveal that glacier amplified in the sensitive polar areas. temperatures below about 10 metres are remarkably stable, and that seasonal Figure 8 Temperature evidence for global warming as variations of air temperature have little revealed by borehole temperatures profiles from cold polar impact. The body of the glacier is insulated in the Greenland ice sheet accumulation areas by snow in the accumulation area; in the such as Greenland difference of 2-4°C ablation area, the surface is ice which reveal both a 2-4 °C cannot become warmer than 0 °C. r warming during this a century, and a cooling Temperatures in the firn of the 0 since 1950 which accumulation area are higher in many offsets about half the glaciers than might be expected. This is warming. The effects of because meltwater can run down through the warm 1980s are the firn and freeze; in doing so, it gives up not yet apparent. its latent heat of condensation, warming the firn. This is why temperate firn is found even in glaciers where the average annual air temperature is as low as -10 °C. In cold accumulation areas, where there is little meltwater, firn temperatures echo air 100-200 m depth temperatures—although they also increase gradually from 10 metres down to bedrock as a result of geothermal heat, the energy released by ice deformation and the friction generated by ice sliding over rock. Temperatures in the upper 200 metres of cold accumulation areas in polar glaciers show strong deviations, suggesting a rise in recorded profile air temperature of 2-4 °C during 1900-50. expected profile The uppermost layers, however, show a deviation produced by 20th-century warming cooling since 1950 which offsets about half the earlier warming (see Figure 8). The cooling since 1950 effects of the remarkably warm 1980s are In now starting to affect the temperature proffle below the critical 10 metre level which temperature of ice and tim

13 Glaciers and the environment

The glacier audit

Measuring whether glaciers are getting glaciers retain more water in frozen form; bigger or smaller, and by how much, is a and when the summer is hot and dry, complex and often exhausting business. glaciers release more water to the parched Direct methods include digging pits regions below. Unfortunately, if global through the snow and sinking boreholes warming becomes pronounced, glaciers into the ice, measuring the annual change will contract, their stabilizing effect will be in glacier depth at different altitudes, reduced, and summer water shortages in multiplying the average by the ablation or dry, lowland areas will be amplified. So accumulation area, and arriving at an may winter floods. estimate of annual accumulation and Glaciers are involved in many feedback ablation. The difference, known as the mass mechanisms of this type. For example, balance, is a measure of the mass of water global warming would lead inevitably to the glacier as a whole is gaining or losing. increased mass loss in glaciers, with the Figure 9 shows a 38-year history of the result that glaciers would become thinner Storbreen glacier in Norway derived using and their surfaces less elevated. With the these techniques. Another technique glacier surface at lower altitude, melting involves creating a 'farm' of stakes over the would increase, thus amplifying the glacier from which annual changes in glacier's response to global warming. depth can be measured from year to year. There is always a net loss of material at the Mapping or photographing the glacier snout, where the mass balance is at glacierized area, or even trying to calculate its lowest. Mass balance rises to zero at the the difference between precipitation and equilibrium line and reaches its maximum run-off plus evaporation, are methods of at the top of the glacier. The gradient of this Figure 9 Mass balance obtaining a regional overview of changes change in mass balance at the equilibrium nieasuremen ts for in glacier size, but reveal less about the line is called the glacier's activity index. Storbreen, a glacier in processes that bring these changes about. A glacier's activity depends greatly on Norway, 1949-87. The estimation of mass balance is an levels of precipitation—activity is high in Mass loss has averaged important part of any hydroelectric or areas of high precipitation, lower in dry afew tenths of a metre irrigation scheme fed by glacier run-off. areas. For example, the activity index of the of water equivalent a Glaciers have an interesting stabilizing South Cascade Glacier in western year since the middle effect on run-off: when the summer is Washington is about 1-2 m per 100 m of the 20th centun/. moist and cool, and valley rivers are full, altitude increase. This high value results

mass balance c 3 data for Storbreen, 2

mcn 1949-50 1954-55 1959-60 1964-65 1969-70 1974-75 1979-80 1984-85 1949-87 the behaviour of glaciers

from a snow accumulation of about three metres a year. By contrast, glaciers situated Mass balance measurements for Alpine glaciers high up in inland regions, where snowfall glacier period area elevation mass balance (rn/year) is much less, may have activity indices as (km2 ) (metres) low as 10 cm or less per metre. Rhóne 1882-1987 17.38 2940 -0.25 The higher the index, the more will mass Vernagt 1889-1979 9.55 3228 -0.19 balance change in response to global Guslar 1889-1979 3.01 3143 -0.26 1894-1979 9.70 3050 -0.41 warming. Glaciers in areas of high snowfall Hinterels North Schnee 1892-1979 0.39 2690 -0.35 may therefore give us one of the first clues to the onset of warming, and today's glaciers will react more sensitively to warming than did glaciers in the drier of water equivalent. Thus total glacier atmosphere of the past Ice Age. thinning over the past century has reached Mass balance measurements based on tens of metres. Much of this loss appears to mapping carried out over the past century have been in the first half century; from 1950 have already revealed the extent of loss in to 1970 there was a global cooling, when Alpine glaciers (see table). The annual mean many glaciers maintained their mass. The niass balance for these glaciers is –40 cm, 1980s were warmer—and their effects have with a possible error of plus or minus 20 cm been detected in recent studies of mass loss.

How glaciers move

If glaciers did not move the accumulation Photo,raph left sliozvs area would mount ever higher and the scientists drilling ablation area would disappear altogether. throng/i a glacier using a hot water jet. That this does not happen is proof that, in a steady state, what is lost from the ablation area is compensated for by the movement of material downhill from the accumulation area. This also equals the amount of material that falls on the accumulation area. Although glaciers usually move only slowly—typically a few tens of metres a tending to bury the firn deeper within the year—the amount of material transported glacier. In the ablation area, however, the is massive. The movement consists of ice begins to slow down and the force of layers of snow, firn and ice moving over deceleration attempts to compress the ice- one another with increasing speed as they with little success because ice is virtually approach the equilibrium line. This incompressible. The ice is therefore forced acceleration serves to stretch and extend to spread sideways towards the margins of the glacier in the downhill direction, the glacier, giving rise to the typical claw- producing not only crevasses but also shaped glacier tongue (see photo page 16).

15 TL/pical animal claw Material in the ablation area is also forced parts of the glacier. The journey up-glacier glacier tongue (above) up towards the surface. The claw shape is reveals more and more recent surface ice caused by compression reinforced by the fact that glaciers moving until the equilibrium point is reached forces generated by down steep slopes tend to be thin, and where recently formed ice stays on the deceleration of the ice. those moving down gentle slopes tend to surface. It follows that pre-industrial levels Since ice is resistant to be fat. As the glacier reaches flatter ground, of the pollutants found in today's compression, it spreads it thus both thickens and spreads. atmosphere are best defined from ice sidewais. An unfortunate mountaineer falling into a samples taken from glacier tongues in high crevasse in the accumulation area would mountain areas. therefore undergo some unexpected If the bottom of the glacier is at melting transformations. He would first be point, the glacier slides its way downhill stretched and buried deeper until, in time, against the bedrock. Its path is lubricated he crossed the equilibrium line. Decades.or by meltwater running through the glacier's centuries later he would break surface own internal drainage system. This again, doubtless somewhat distorted, near drainage system serves important the glacier tongue. The 5000-year old body functions in the glacier but its channels can of a man was recently recovered from an become blocked as a result of movement Italian glacier on the Austrian border. The within the glacier. Drainage water may man had been buried under a ridge-top then become stored up in or behind the section of the glacier, and therefore had not glacier. Eventually, such water will find a travelled through it. However, the fact that narrow path along which to escape. Should he appeared at all confirms that Alpine the escaping water be warm enough, it will glaciers are smaller today than at any other then melt a larger conduit, allowing more time during the past 5000 years. water to flow which, in its turn, melts more The complexities of glacier flow have ice and enlarges the conduit still further. more useful characteristics than this. One is This is a recipe for potential catastrophe, that the glaciologist can collect frozen since these events can happen quite swiftly, precipitation from the past by walking up releasing extremely large volumes of water the ablation zone from the lowest point of in a very short space of time. These glacier the glacier, where the oldest ice of all floods can be very destructive, sweeping appears at the surface having travelled large quantities of water and eroded from the uppermost point via the deepest moraine material rapidly downhill.

Wel the behaviour of glaciers

Glacier floods are often called by their A glacier surge happens after decades in Icelandic name, jøkulhlaup, since some of the which glacier material has built up; it most dramatic have occurred in that usually lasts a few months to a year or country. The 1922 Grimsvötn flood, for more, during which time the glacier may example, released an estimated 7.1 km3 of move as much as 50 metres a day or even water in a flood that delivered some 57000 more for a period of a year or so. Some m3 of water a second. The photograph below surging glaciers have advanced several shows the results of a similar catastrophe in kilometres in as many months. Münster in Switzerland in 1987. The basic cause of a glacier surge is a build- Glacier flow involves two basic processes: up of stress and meltwater within the glacier the sliding of layers of ice over one another with which the glacier's natural drainage within the glacier, and the sliding of the system cannot cope. Water is blocked glacier floor over rock. Where one can keep underneath the upper part of the glacier, pace with the other, the glacier's behaviour and a bulging, heavily-fissured surge front is that of a steadily flowing river of ice. begins to migrate down the glacier. If this This peaceful image is shattered, however, front reaches the edge of the glacier, it may when baserock sliding becomes the advance several kilometres very rapidly, A sudden glacier flood dominant force. Two forms of instability sometimes blocking up valley rivers. The that carried mud and can then set in: the surge and calving rumblings and vibrations of a surging debris through the instability, both intensively investigated in glacier can often be heard several kilometres Swiss village of Alaska where they occur frequently. away. The surge normally ends when a MQnster in 1987.

0 0 Cr 0 014,

Ss-

17 Glaciers and the environment

a) sudden flood releases the pressurized water a) 0 blocked under the upper part of the glacier. I , The characteristics of calving instability I are the exact opposite: the slow advance and catastrophic retreat of glaciers that end in the deep water of lakes and fjords. What triggers the onset of calving instability is not clear but the effects can be dramatic. Parts of the glacier snout, which normally rest on a moraine—the accumulation of debris brought down by the glacier—in shallow water, break off as a result of melting by warm water. As the glacier retreats, it encounters deeper water and calving accelerates rapidly as more and a) 2 more of the glacier comes into contact with 'a) 0 I water warm enough to melt it. This continues until the glacier has retreated so far that its snout rests once again in shallow water. The largest glacier retreat ever observed was probably the 100-km recession of ice in Alaska's Glacier Bay. Fortunately, glaciology is now sufficiently advanced to be able to predict, in some cases, the onset of calving instability. Such was the case with the retreat of the Columbia glacier, which spewed icebergs into Prince William Sound and across the paths of tankers travelling to and from the pipeline terminal at Valdez. 'a) n 'a) 0 I I Photographs illustrate the main characteristics of glacier movement: A steady-state glacier, a river of ice flowing like a giant freeway. The surge of the Plomo glacier in Argentina in 1985, which caused the temporarif damming of a river. The Columbia glacier in 1978 before the onset of the calving instability that triggered the expected 40-km retreat. IN Taking stock

Monitoring the world's glaciers

The coordinated collection of information considered during the International about glaciers was begun in 1894, in the Hydrological Decade operated by hope of clarifying the relationship between UNESCO during 1965-74. The glaciers and climate, and improving International Commission on Snow and Ice understanding of the Ice Ages. Until about (ICSI, of the International Association of 1950, most of the information collected Scientific Hydrology) was asked to prepare related to glacier lengths, particularly in the guidelines on compiling glacier inventory Alps, Scandinavia and Iceland, and many of data, and these were produced in 1970. the observations were made in connection Several countries then started to compile with hazards such as ice avalanches and glacier data and in 1976 a Temporary outbursts from ice-dammed lakes. Technical Secretariat was established in the Direct mass balance measurements began Swiss Federal Institute of Technology to be taken after World War II, first in (ETH) in Zurich, Switzerland. It soon Many of the first mass Scandinavia and then elsewhere, many in became clear that the data compiled would balance measurements conjunction with hydroelectric schemes. It not only provide an instantaneous were made as part of was this work that really established the snapshot of the planet's frozen water the design and link between climate change and glacier resources but that they could also serve as operation of fluctuations. the basis for the long-term monitoring of hydropower schemes The need for a worldwide inventory of glaciers and would be useful in the study (left, in photo below) perennial snow and ice masses was first of long-term climatic change. Accordingly, fed by glaciers. Glaciers and the environment

when the Global Environment Monitoring covered by some kind of inventory, most of System (GEMS) was established, it was them detailed but a few still preliminary. It agreed that the World Glacier Inventory is planned to fill the remaining gaps in the could be included in GEMS. In 1986 a new near future. service, the World Glacier Monitoring The work of the World Glacier Figure 10 Status of Service, was set up in Zurich as part of Monitoring Service continues. Its aims are the World Glacier GEMS, with financial help from several to collect and publish data on glacier Inventory in 1988. bodies, mainly UNEP, ETH and the fluctuations every five years, and to Monitoring is being International Council of Scientific Unions. complete and upgrade the original continued by the The original inventory was published in inventory. In addition, mass balance data World Glacier 1989, and reflected the state of glaciological are being published every two years Monitoring Service in data in the previous year (World Glacier because of glaciers' role as key indicators Zurich. Antarctica is Inventonj: status 1988, IAHS (ICSI), IJNEP, within climate monitoring. not included since, UNESCO, 1989). Its aim was firstly to although it contains provide a snapshot of ice conditions on some 30 million kin3 of Earth during the second half of the 20th ice, no formal attempt century. Glacier inventories were made has yet been made to worldwide, and then compiled to provide compile a glacier a statistical basis for the study of glaciers. inventory for As Figure 10 shows, all the relevant mainland Antartica. glacierized areas of the world are now

taking stock

Uses of the data

The inventory data are already proving today's area and a few percent of today's useful in a number of ways. For example, volume is to be expected if the next century the data showed that most of the ice in is markedly warmer than this one. regions of North America where there are Glacier monitoring now attempts to long valley glaciers is contained in the provide several types of information. largest and thickest glaciers; in the Alps, by Observations on glacier length are the key contrast, most of the ice is to be found in to comparing today's glaciers with those of small, thin mountain glaciers. This has the past. The technical difficulties of glacier implications related to global warming. monitoring mean that remote glaciers must The North American glaciers are likely to be monitored by aerial photography and Figure 11 Long time- provide glacier meltwater to the sea—one high-resolution satellite imagery. At the series data on glacier of several causes of sea level rise— for a same time, meaningful comparisons of length are invaluable considerable time before the flow is glacier data can be made only where the material for the world- reduced because the glaciers have become data span relatively long periods of times wide analysis of glacier smaller. In the Alps, however, most and exist for carefully designed groups of response to climatic glaciers will be reduced in size fairly glaciers. A good example is shown in changes over long time rapidly and many could disappear. About Figure 11. These groups will provide the scales. Note how much half the ice that existed in the Alps at the baseline data from which glaciologists will more valley glaciers end of the Little Ice Age has already melted have to work as they try to interpret what respond to climate as a result of 20th-century warming; a future changes in mass balance tell us of change than do small further reduction to perhaps one-quarter of climate change and global warming. mountain glaciers.

cumulative 0 length change in four types of -012 glacier, 1900-80 (km)

-04

1 3

-10 1

- ' 1. small cirque and mountain glacier, 1..- -1.2 -' less than 2 km long cirque and mountain glacier, 2-5 km long small valley glacier, 5-10 km long -1 4 4. valley glacier, 10-25 km long

1900 1910 1920 1930 1940 1950 1960 1970 1980

21 Glaciers and the environment

> 0 a

The Belvedere glacier in Italy, covered with debris and including a moraine-trapped lake. The risk of glacier floods from such lakes is increasing as 20th- century warming causes glaciers to retreat.

22 taking stock

More detailed information will be useful disasters and may be of future use in on glaciers where physical measurements elaborating early warning systems to can be made. Mass balance observations mitigate the effects of glacier-related can be correlated with climate change and hazards. The relevance of these data is this has enabled experts to assess the likely to increase, if only because the sensitivity of glaciers to climate change in formation of lakes on the margins of relation to the altitude of their equilibrium retreating glaciers as a result of 20th- lines. Observed changes in glacier mass can century warming is continually increasing also be expressed as energy changes, thus the hazards from glacier floods. allowing experts to make direct A century ago, when glacier monitoring comparisons between changes in glacier began, it was clear that decades of patient mass and anthropogenic enhancement of work would be needed before the scientific the greenhouse effect. The overall shrinking study of glaciers could bear useful fruit. tendency of glaciers in the Alps—for which This it has now done—just in time, the best documentation exists—is broadly probably, to help in the battle against the consistent with the estimated effects of the enhanced greenhouse effect anthropogenic greenhouse warming and and the global warming that seems likely now seems to be leading, increasingly to follow it. Glacier fluctuations already quickly, to climatic conditions outside the provide the most important evidence we range of the climatic variations that have have of 20th-century warming. The occurred since the end of the past Ice Age. importance of monitoring glaciers will One of the original aims of the inventory certainly increase if enhanced greenhouse was to evaluate the freshwater resources gas warming turns from a prediction to a stored in perennial snow and ice on a reality. Glaciology has always been global scale. This aim proved somewhat interesting; more recently it also became ambitious but the inventory data so far important. Now its development has compiled have already been of great use in become urgent. estimating high-altitude precipitation and Much more remains to be done. There is a potential run-off from mountain areas need for more and better data, for where it is difficult to establish improved communication between precipitation gauges. observers, modellers and theorists, and for Finally, monitoring is providing a the more widespread introduction of systematic collection of data on special advanced techniques, particularly high- events such as glacier surges, the instability resolution remote sensing. The World of tidal glaciers, glacier floods, ice Glacier Inventory is a beginning on a long avalanches and eruptions of ice-clad road—a road that may turn out to be very volcanoes. The compilation of this material long indeed. is an important addition to data on natural

23 Sources

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