Climate Change and the Earth's Mountain Glaciers:

Observations and Implications

Greenpeace International - May 1998

"Thinning of glaciers since the mid-19th century has been obvious and pervasive in many parts of the world."

- Intergovernmental Panel on Climate Change, 1996 [1]

"... so far the length reduction of mountain glaciers still remains the most detectable, unequivocal proof from cold regions that fast and worldwide climatic change is taking place."

- Professor Wilfreid Haeberli, Swiss glaciologist, 1990 [2]

Summary

As the climate has changed over the last century, the world's land ice cover has responded. Nowhere is this more noticeable than in mountain glaciers. Global temperatures have increased by 0.3-0.6oC since late last century and the United Nation's Intergovernmental Panel on Climate Change (IPCC) has concluded that "the balance of evidence suggests a discernible human influence on global climate".[3] In response to increasing temperatures over the past 100 years, mountain glaciers have generally thinned, lost mass and retreated. This glacial retreat is consistent with an observed alpine warming of 0.6oC - 1.0oC.[4]

The publication of a major new survey on mountain and subpolar glaciers and their contribution to sea level rise in November 1997, the most comprehensive such survey since 1984, has contributed much new information to this overall picture. [5]

This survey finds that the vast majority of the glacier contribution to sea level rise comes from melting glaciers in central Asia and northwestern North America. On average, glaciers contributed 14-18 percent of the estimated long term annual rate of sea level rise. However, this rate of melting has varied widely from region to region and year to year. The glacier contribution to sea level rise appears to be accelerating. Glaciers lost more ice in 1990 than in any other year in the 1961-90 period, and their meltwater contribution reached 50 percent of the estimated long term annual rate of sea level rise in that year.

Scientists project pronounced reductions in glacial mass in the future. Up to a quarter of global mountain glacier mass could disappear by 2050 and up to a half could be lost by 2100.

Over the last century, global sea level has risen by between 10-25cm and the loss of mountain glaciers has been estimated to have contributed between 2-5cm to this change. Scientists estimate that for the mid-range sea level rise

scenarios mountain glaciers and small ice caps could contribute 16cm of the 50cm projected by 2100.

In addition to affecting global sea level, glacial discharges are an important contributor to some regional water resources. As glaciers melt some areas will experience increases in water supply and flood risk while others would see the opposite. Alpine tourism is also likely to be affected by the retreat of glaciers as ski fields disappear and the visual appeal of mountain regions diminishes.

The worldwide twentieth century retreat of glaciers supports the conclusion that the Earth is warming. The speed at which this is occurring also strengthens findings that the Earth is entering a period of climate change unprecedented in the last 10,000 years.

Region	Observations
Circum-Arctic	Glaciers have generally lost mass over the last 30 years. In East and West Greenland glaciers are retreating rapidly while in North Greenland the situation is unclear. Svalbard glaciers are losing mass
Central Asia	From the 1950s to the 1980s, 73% of glaciers were retreating, 15% were advancing and 12% were stable.
Tropical mountains	The retreat of glaciers has been documented in the Ecuadorian Andes, New Guinea, East Africa (Mount Kenya's glacier has receded markedly since the late 1800s and since the 1960s its mass has decreased by 40%), Venezuela and Peru.
New Zealand	Most glaciers have retreated during the 20th century. The Tasman Glacier has thinned by more than 100m. Since 1983, the recession of western glaciers has reversed and these glaciers are growing (e.g. the Franz Josef glacier).
Southern and central South America	The Upsala glacier has retreating about 60m per year over the last 60 years and this rate appears to be accelerating. In the last 40 years, the area of the South Patagonian Ice Field has diminished by about 500km2. The Soler and Tyndall Glaciers also appear to have lost mass, while the Pio XI glacier in Patagonia is larger now than at any time in the last 6,000 years.
Europe	For the Alps as a whole, the glacial area since about 1850 has been reduced by 30-40 percent, with about a 50 percent reduction in ice volume. However, this has been counterbalanced by the recent growth of some larger glaciers in the Alps such as the Grosse Aletsch in Switzerland and many Scandinavian glaciers, resulting in a small net increase in glacial ice over the last 30 years.
Antarctica and sub-Antarctic Islands	The alpine glaciers of the Dry Valleys in Antarctic have fluctuated with no apparent trends. Numerous glaciers along the Antarctic Peninsula are in retreat. Glaciers in many sub-Antarctic islands are also in retreat, for example, some small glaciers in Heard Island have decreased by up to 65%.

Introduction

During the Earth's history the climate has varied between periods of relative warmth and cold. Within these variations the amount of the planet's surface covered by ice has also changed dramatically. At the height of the last ice age 25,000 years ago, massive sheets of ice covered much of North America, northern Eurasia and Antarctica. One such ice sheet covered most of what is now Canada and Alaska. As the Earth warmed at the end of the ice age the majority of this ice disappeared and now only Antarctica and Greenland are covered by ice sheets. The vast majority of the world's land ice is found in Antarctica and Greenland, with the rest found in permafrost, glaciers and small ice caps.[7] As the climate has changed over the last century, the world's land ice cover has responded and nowhere is this more noticeable than in mountain glaciers.

Global Glacial Loss

Glaciers add to their area and thickness through accumulation of snowfall and freezing of meltwater. Glaciers lose area and thickness due to melting and the calving of icebergs. The net sum of all this is described as changes in the 'mass balance' of the glacier. Because increasing temperatures often mean increased precipitation, there is not always a straight line orrelation between temperature and mass balance.

The world's glaciers have, on average, lost more ice than they have gained over the past century, so they have a "negative mass balance". This meltwater inevitably makes its way into the oceans, where it contributes to sea level rise. Estimates from thousands of gauges throughout the world suggest that sea level has been rising about 2 mm a year for most of the century. Most of this sea level rise is due to thermal expansion of the ocean as the world warms, but glaciers also make a significant contribution.[8]

While it is clear that overall mountain glaciers are losing mass, some of the Earth's glaciers are growing. However, this is not inconsistent with projections of human-induced climate change because precipitation is expected to increase in the high northern and southern latitudes in response to warming temperatures. High latitude precipitation has increased over recent decades9; in some cases this could have counteracted the loss of glacial mass due to warming.[9]

Glacial Loss and Global Climate Change

Measurements taken from glaciers around the world complement the global meteorological record and provide an indirect measure of climate change.[10] In many regions, measurements of glacier length extend back into the 19th century and in Europe some records date back to 1600 AD. Indirect measurements of glacial extent such as sediment deposits left by advancing and retreating glaciers can also be used estimate glacial extent.

Global temperatures have increased by 0.3-0.6oC since late last century and the United Nation's Intergovernmental Panel on Climate Change (IPCC) has concluded that "the balance of evidence suggests a discernible human influence on global climate".[11] In response to increasing temperatures, mountain glaciers have generally thinned, lost mass and retreated over the last 100 years.[12] In addition to this some glaciers are also losing mass at an accelerating pace. The 20th century glacier retreat is consistent with a alpine warming of 0.6oC - 1.0oC.[13]

The publication of a major new survey on mountain and subpolar glaciers and their contribution to sea level rise in November 1997, the most comprehensive such survey since 1984, has contributed much new information to this overall picture.[14]

Mass balances of more than 250 glaciers have been examined since 1946, but only a little over 30 have continuous records since 1960. Estimates based on all available mass balances suggest that the world's mountain and subpolar glaciers lost 6,000-8,000 square kilometres of ice area between 1961 and 1990, or about 1 percent of their total area of about 680,000 square kilometres. This melting ice contributed about 0.25 mm of average annual sea level rise, or about 14-18 percent of estimated annual sea level rise. However, glacial contribution to sea level rise differs considerably from region to region and over time. Subpolar glaciers on the Arctic islands and the coasts of Greenland and Antarctica, make up 56 percent of total glacier area, but contributed only 26 percent of the glacier contribution to sea level rise over the last 30 years. The vast majority of the contribution to sea level rise came from melting mountain glaciers in Asia (48 percent) and North America (29 percent, with almost all of this from Alaska and the surrounding areas of Canada to its east and south). European glaciers, which only make up 3 percent of the world's glacial area, are now believed to be growing on average, helping to reduce sea level rise. While many small glaciers in the Alps are shrinking rapidly, some larger ones, such as the Grosse Aletsch in Switzerland, are growing, and many glaciers in Scandinavia are also expanding.

There are major differences over time as well. From 1960-80, a period with a small cooling trend in North America, Asian and subpolar glaciers contributed almost of the glacier contribution to sea level rise, and North American glaciers were stagnant. However, from 1981 to 1990, the rate of Asian glacier melting was reduced somewhat, and North American glaciers began shrinking much more rapidly. As a result, Asian and North American glaciers made about equal contributions to sea level rise between 1980 to and 1990.

Overall glacial contribution to sea level rise has been accelerating in recent years. 1990 is estimated to have had the most negative mass balance in the entire 1961-90 period, with a sea level rise contribution of about 0.9 mm, or about half the total estimated long term annual sea level rise.

One weakness of the survey is that it only includes data from one long term study program for the Gulf of Alaska, the Wolverine Glacier, and none at all from South America. The survey authors comment that more data is needed. In particular, for the Gulf of Alaska, "we suspect that the actual contribution to sea level change from this area is considerably larger than estimated".[15]

The Bering Glacier: An Example of a Global Phenomenon

The Bering Glacier, North America's largest glacier, is an example of a major glacier in retreat, and an illustration of the complexity of glacier behavior. Originating some 25 kilometres east of the US border in Canada, the Bering Glacier flows 191 kilometres to its terminus near the Gulf of Alaska. The areal extent of the glacier is over 5170 km2 and in some places the glacier is over 800 metres thick. During the last 10,000 years the size of the glacier has varied in response to climate changes, including significant and rapid retreat over the last 100 years.[16]

An important feature of changes in the Bering Glacier's mass has been its "surging" behaviour. Glacial surging is defined as short and periodic rapid displacements and movements of large quantities of ice within the glacier. Surges are frequently accompanied by a significant advance of the glacial front. The Bering Glacier surged around 1900 and 1920 and in 1938-40, 1957-60, 1965-67 and 1993-94. After each surge the glacier generally stagnated, continued thinning and then resumed retreat. As US Geological Survey scientists have noted, "The interplay of retreat and surging has resulted in rapid and very dramatic changes throughout the entire glacier."[17] It is unclear whether climatic factors influence glacial surging.

Since the beginning of this century the glacier's frontal region has declined 130 km2 in area. As the glacier has retreated, several large lakes have formed, the greatest being the 70 km2 Vitus Lake. Over recent decades the rate of glacial retreat has been increasing with maximum rates of surge since 1990. Parts of the glacier retreated by over one kilometer a year before the 1993-94 surge. (Glacial retreat is usually measured in metres to tens of metres annually.)

In addition to the overall retreat of the glacial front the Bering Glacier has thinned dramatically over the past century. Aerial photography shows that parts of the glacier have thinned by as much as 180 metres in the last 50 years and in some places the glacier has lost between 20-25% of its thickness. The Bering Glacier is only one of the many large maritime glaciers in the Gulf of Alaska, which also includes other major iceberg calving glaciers such as the Columbia, Hubbard and Endicott glaciers. It is these glaciers, along with other large glaciers in central Asia, that will be one of the important determining

factors for the future rate of sea level rise.

Future Changes in the World's Mountain Glaciers

Scientists project pronounced reductions in glacial mass in the future with the predicted disappearance of up to a quarter of global mountain glacier mass by 2050 and up to a half of global mass by 2100.[18] Even in areas where precipitation is expected to increase, changes in temperatures are expected to dominate and glaciers are expected to shrink even if some regions become wetter. One recent study concluded that, "It ... appears that even a significant increase in precipitation cannot compensate for melting, and further shrinkage of glaciers and small ice caps must occur in a warmer climate."[19] One study assessed by the IPCC suggests that if current warming trends continue the glacial mass of the European Alps could be reduced to few percent in decades.[20] While many glaciers are likely to disappear altogether, the largest mountain ones such as those found in the Gulf of Alaska, Patagonia and the Himalayas should continue to exist into the 22nd century.

The Impacts of Glacial Mass Loss

Global sea level has risen by between 10-25cm over the last century.[21] A number of factors such as the expansion of the oceans in response to higher temperatures (called thermal expansion) and changes in the mass balance of glaciers and the Antarctic and Greenland ice sheets are thought to have contributed to a greater or lesser extent to this change.[22]

The biggest known contributor to recent sea level rise has been thermal expansion but the loss of mountain glaciers has been estimated to have contributed between 2-5cm to 20th century sea level rise.[23] The IPCC estimate that for mid-range sea level rise scenarios, glaciers and small ice caps would contribute 16cm to 50 cm projected by 2100.[24] Projected changes in sea level are expected to have major impacts on many coastal and small island communities.[25]

In addition to affecting global sea level, glacial discharges are an important contributor to the water resources of some regions. In some semi-arid places near high mountains such as central Asia and Argentina, increases in future glacial runoff may increase the amount of available water and is likely to increase the risk of river flooding and landslides.[26] Summer water resources in other regions are likely to diminish as glaciers disappear, for example, the Quelcccaya glacier in Peru is crucial for water supply of Lima, a city of 10 million people and is retreating rapidly.

Alpine tourism is also likely to be impacted by the retreat of glaciers as skiing fields are lost and the visual appeal of mountain regions diminishes.

Endnotes

[1] RA Warrick, et al. Changes in Sea Level. in JT Houghton et al. (eds), Climate Change 1995. The Science of Climate Change, Cambridge University Press, Cambridge, 1996: 359-405^.

[2] W Haeberli. Glacier and permafrost signals of the 20th-century warming. Annals of Glaciology 1990; 14.

[3] BD Santer, et al. Detection of Climate Change and Attribution of Causes. in JT Houghton et al. (eds), Climate Change 1995. The Science of Climate Change, Cambridge University Press, Cambridge, 1996: 406-443.

[4] J Oerlemans. Quantifying global warming from the retreat of glaciers. Science 1994; 264: 243-245.

[5] Mark B. Dyurgerov and Mark F. Meier, "Mass balance of mountain and subpolar glaciers: A new global assessment for 1961-1990", Arctic and Alpine Research 29(4):379-391, 1997; and Mark B. Dyurgerov and Mark F. Meier, "Year-to-year fluctuations of global mass balance of small glaciers and their contribution to sea-level changes", Arctic and Alpine Research 29(4):292-402, 1997.

[6] B Fitzharris, et al. The Cryosphere: Changes and Their Impacts. in RT Watson, et al. (eds), Climate Change 1995. Impacts, Adaptations and Mitigation of Climate Change: Scientific -Technical Analysis, Cambridge University Press, Cambridge, 1996: 241-265. Global land ice volume (106 km3). Ice sheets and ice shelves: 33.06; Permafrost: 0.16; Glaciers and small ice caps: 0.9

[7] Numerous sources, see Fitzharris, op cit.

[8] Warrick 1996, op.cit.

[9] Projected changes in the Antarctic ice sheet is a relevant example. Many scientists believe that increases in snowfall over the Antarctic continent will cause the Antarctic ice sheet to gain mass and cause a slight slowing of global sea level rise. For example, the IPCC mid-range projection for 2100 sea level rise (50cm) would be 1cm higher if Antarctic were a neural contributor. See Warrick, op cit.

[10] N Nicholls, et al. Observed Climate Change and Variability. in JT Houghton et al. (eds), Climate Change 1995. The Science of Climate Change, Cambridge University Press, Cambridge, 1996: 132-192.

[11] BD Santer, et al. Detection of Climate Change and Attribution of Causes. in JT Houghton et al. (eds), Climate Change 1995. The Science of Climate Change, Cambridge University Press, Cambridge, 1996: 406-443.

[12] Warrick, op cit.

[13] J Oerlemans. Quantifying global warming from the retreat of glaciers. Science 1994; 264: 243-245.

[14] Dyurgerov and Meier 1997, op.cit.

[15] Ibid., p. 398.

[16] Discussion of the Bering Glacier is based on BF Molnia, A Post. Holocene history of Bering Glacier, Alaska: a prelude to the 1993-1994 surge. Physical Geography 1995; 16: 87-117. As temperatures warmed at the end of the last ice age and in the early Holocene the geological term for the last 10,000 of the Earth's history) the Bering Glacier retreated from the Gulf of Alaska continental shelf to a retracted into the Chugach Mountains. After thousands years of relative stability, the glacier began to advance in spurts around 2,900 years ago and reached its late Holocene maximum extent between 1,000 and 500 years ago. The glacier than retained this position until the beginning of the 20th century.

[17] ibid.

[18] Fitzharris, op.cit.

[19] J Oerlemans, JPF Fortuin. Sensitivity of glaciers and small ice caps to greenhouse warming. Science 1993; 258: 115-117.

[20] see Fitzharris, op cit.

[21] Warrick, op cit.

[22] The contribution of the Antarctic and Greenland ice sheets to recent and future climate change is very uncertain. For example, Antarctica's influence on recently observed sea level rise has been estimated to have been -/+ 14cm.

[23] Thermal expansion is estimated to have contributed between 2-7cm to global sea level rise over this century.

[24] Warrick, op cit.

[25] L Bijlsma, et al. Coastal Zones and Small Islands. in RT Watson, et al.(eds), Climate Change 1995. Impacts, Adaptations and Mitigation of Climate Change: Scientific - Technical Analysis, Cambridge University Press, Cambridge, 1996: 289-324.

[26] ibid.