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Glacier retreat is the reduction in size of glaciers, due to losses in mass, generally in response to climate change. It is one of the most important topics in the field of glaciology because of the extent of the worldwide general reduction in size of glaciers. This is especially the case in mid-latitude mountain ranges such as the Himalayas, Alps, Rocky Mountains, Cascade Range, and the Andes as well as isolated tropical summits such as Mount Kilimanjaro in Africa.Template:Ref harv Since accurate measurement techniques and the ability to record changes photographically became widespread in the mid-19th century, glaciers have been in a state of recession in almost every region of the Earth. The demise of glaciers in arid regions has potential widespred impacts on water supplies during droughts and dryer seasonal periods in locations such as the Andes of South America and Himalayas in Asia. Since the end of the Little Ice Age around the year 1850, there has been a period of general retreat of glaciers worldwide. This glacier retreat has become much more significantly pronounced since 1980.Template:Ref harvTemplate:Ref harv
In historic times, glaciers grew during the Little Ice Age, a cool period from about 1550 to 1850. Subsequently, until about 1940, glaciers around the world retreated as the climate warmed. Glacial retreat declined and reversed, in many cases, from 1950 to 1980 as a slight global cooling occurred. However since 1980, glacial retreat has become increasingly rapid and ubiquitous, so much so that it has threatened the existence of many of the glaciers of the world. The retreat of mountain glaciers, notably in western North America, Asia, the Alps, Indonesia and Africa, and tropical and sub-tropical regions of South America, has been used to provide qualitative support to the rise in global temperatures since the late 19th century.Template:Ref harv Template:Ref harv Also of great importance is the substantial retreat and acceleration since 1995 of a number of key outlet glaciers of the Greenland and West Antarctic Ice Sheet that may foreshadow a rise in sea level.
Glacier mass balance impact on terminus behavior
Crucial to the survival of a glacier is its mass balance, the difference between accumulation (snow and ice precipitation, and net wind-driven and avalanche deposition) and ablation (melting and sublimation). Climate change may cause variations in both temperature and snowfall, causing changes in mass balance. A glacier with a sustained negative balance is out of equilibrium and will retreat. A glacier with sustained positive balance would also be out of equilibrium, and will advance to reestablish equilibrium. There are current advancing glaciers, but all are advancing at modest rates, suggesting they are not far from equilibrium.
Glacier retreat results in the loss of the low elevation region of the glacier. Since higher elevations are cooler than lower ones, the disappearance of the lowest portion of the glacier reduces overall ablation, thereby increasing mass balance and potentially reestablishing equilibrium. However, if the mass balance of a significant portion of the accumulation zone of the glacier is negative, it is in disequilibrium with the climate. Such a glacier will melt away with a continuation of this climate.
The key symptom of a glacier in disequilibrium is thinning along the entire length of the glacier.Template:Ref harvTemplate:Ref harv For example, Easton Glacier (see below) will likely shrink to half its size, but at a slowing rate of reduction, and stabilize at that size, despite the warmer temperature, over a few decades. However, the Grinnell Glacier (pictured above) will shrink at an increasing rate until it disappears. The difference is that the upper section of Easton Glacier remains healthy and snow-covered, while even the upper section of the Grinnell Glacier is bare, melting and has thinned. Small glaciers with shallow slopes are most likely to fall into disequilibrium with the climate.
Methods for measuring glacier retreat include staking terminus location, Global Positioning Mapping, aerial mapping, and laser altimetry.
Europe
The glaciers of Europe and in particular the Alps, have have been among some of the most photographed and studied on Earth. Since the dawn of photography we have visible conclusive evidence that since the mid-19th century, all of the glaciers of Europe have been in a general state of retreat. This retreat appears to have accelerated since the 1980's.
Alps
The World Glacier Monitoring Service reports on changes in the terminus, or lower-elevation end, of glaciers from around the world every five years.Template:Ref harv In their 1995–2000 edition they noted the terminal point variations of glaciers across the Alps.
Over the five year period the measurements taken from glaciers in Switzerland indicated that 103 of 110 glaciers examined were retreating. Similarly, in Austria 95 of 99 glaciers were retreating while in Italy all 69 observed glaciers were in retreat and in France all 6 measured glaciers were retreating. French glaciers experienced a sharp retreat in the years 1942–53 followed by advances up to 1980, then further retreat a couple years later in 1982. As an example, the Argentière Glacier and Blanc Glacier have receded by 1,150 (3,772 ft) and 1,400 m (4,593 ft) respectively since 1870. The largest glacier in France, the Mer de Glace, which is 11 km (6.85 miles) long and 400 m (1,312 ft) thick, has lost 1,000 m (3,280 ft) in 130 years and thinned 150 m (492 ft) in the mid-section of the glacier since 1907.
Glaciers across the Alps appear to be retreating at a faster rate than a few decades ago. The Grosser Aletsch Glacier is the largest glacier in Switzerland and has retreated 2,600 m (8,530 ft) since 1880. The rate of retreat has also increased since 1980, with 800 m (2,625 ft) or 30% of the total retreat occurring in the last 25 years.Template:Ref harv Similarly, of the glaciers in the Italian Alps only 34% were in retreat in 1980. By 1999, a full 89% of these glaciers were found to be retreating.Template:Ref harv Early 20th Century visitors to Chamonix, France remember the Bossons Glacier coming almost as far as the nearest roadway. It has since lost 1,200 m (3,900 ft) of its length.
Some of this retreat has had immediate human impacts. To retard melting of the glaciers used by certain Austrian ski resorts, portions of the Stubai and Pitztal Glaciers were covered with plastic. New glacial lakes, at the foot of the Mer de Glace, are held behind moraine dams. If these dams were to fail, the result could be widespread flooding in the valley below. In 1892, a similar dam burst thereby releasing some 200,000 m³ (260,000 yd³) of water from the lake of the Glacier de Tête Rousse, and killing 200 people in Saint Gervais.Template:Ref harv
Scandinavia
Though the glaciers of the Alps have received more attention from glaciologists, research from other areas of Europe where glaciers exist show that in most areas, glaciers are rapidly retreating. In the Kebnekaise Mountains of northern Sweden a study of 16 glaciers between the years 1990 and 2001 found that 14 glaciers are retreating, one is advancing and one is stable.Template:Ref harv During the 20th century, glaciers in Norway retreated overall with brief periods of advance around 1910, 1925 and in the 1990's. In the 1990s 11 of 25 Norwegian glaciers observed had advanced due to several winters in a row with precipitation above normal. However, since 2000, Norwegian glaciers have decreased significantly. This is attributed to several consecutive years of little winter precipitation, and record warmth during the summers of 2002 and 2003. By 2005 only 1 of the 25 glaciers monitored in Norway was advancing, two were stationary and 22 were retreating. In Norway, the Engabreen Glacier has retreated 179 m (587 ft) since 1999, while Brenndalsbreen and Rembesdalsskåka glaciers have retreated 116 m (380 ft) and 206 m (675 ft) respectively since 2000. At Briksdalsbreen, the glacier there retreated 96 m (314 ft) just in 2004 alone, and this is the largest annual retreat recorded for this glacier since monitoring began in 1900. Overall, since 1999, Briksdalsbreen had retreated 176 m (577 ft) by the time measurements were taken in 2005.Template:Ref harv
Iceland
The northern Atlantic island nation of Iceland is home to the Vatnajökull, which is the largest ice cap in Europe. The Breiðamerkurjökull Glacier, one of the Vatnajökull outlet glaciers, receded by as much as 2 km (1.2 miles) between 1973 and 2004. In the early 20th century, Breiðamerkurjökull extended to within 250 m (820 ft) of the ocean. By 2004, Breiðamerkurjökull's terminus had retreated three kilometers (1.86 miles) further inland. This glacier retreat exposed a rapidly expanding lagoon, which is filled with icebergs calved from its front. The lagoon is 110 m (360 ft) deep and nearly doubled its size during the decade ending in 2004. All but one of the Vatnajökull outlet glaciers, roughly 40 named glaciers in all, were receding as of 2000.Template:Ref harv In Iceland, of the 34 glaciers with termini observations from 1995–2000, 28 are retreating, four are stable and two are advancing.Template:Ref harv
North America
North American glaciers are found along the spine of the Rocky Mountains and Pacific Coast Ranges extending from northern California to Alaska. While Greenland is geologically associated with North America, it is also a part of the Arctic region. Aside from the few tidewater glaciers, that are in the advance stage of their tidewater glacier cycle prevalent along the coast of Alaska, virtually all the glaciers of North America are in a state of retreat. Even the surging tidewater glaciers are retreating. This retreat rate has increased rapidly since approximately 1980 and overall each decade since has been more severe than the preceding one.
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Cascade Range
The Cascade Range of western North America extends from southern British Columbia in Canada to northern California. Excepting Alaska, about half of the glacial area in the U.S. is contained in the more than 700 glaciers of the North Cascades, a portion of the range between the Canadian border and I-90 in central Washington. These glaciers store as much water as that contained in all the lakes and reservoirs in the rest of the state and provide much of the stream and river flow in the dry summer months, some 870,000 m³ (1,137,917 yd³).
As recently as 1975, many North Cascade glaciers were advancing due to cooler weather and increased precipitation which occurred from 1944 to 1976. However by 1987, all the North Cascade glaciers were retreating and the pace of the glacier retreat has increased each decade since the mid 1970's. Between 1984 and 2005, the North Cascade glaciers lost an average more than 9.5 m in thickness and 20 to 40% of their volume.Template:Ref harv
Glaciologists researching the North Cascades glaciers have found that 47 monitored glaciers are receding and four have disappeared completely. The White Chuck Glacier (near Glacier Peak) is a particularly dramatic example. The glacier shrank from 3.1 km² (1.19 miles²) in 1958 to 0.9 km² (0.34 miles²) in 2002. Similarly, the Boulder Glacier on the southeast flank of Mount Baker retreated 450 m (1,476 ft) from 1987 to 2005, leaving unvegetated terrain behind. This retreat has occurred during a period of less winter snowfall and higher summer temperatures. Winter snowpack has declined 25% since 1946 and summer temperatures have risen 0.7 °C (1.2 °F) during the same period. Four glaciers have been observed to have disappeared since 1985—Spider Glacier, Lewis Glacier, Milk Lake Glacier and David Glacier. As of 2005, most North Cascade glaciers are in disequilibrium and will not survive the continuation of the present climate.Template:Ref harvTemplate:Ref harv
Rocky Mountains
In the Canadian Rockies, the Athabasca Glacier, which is one of the outlet glaciers of the 325 km² (125 miles²) Columbia Icefield, has retreated 1500 m (4,921 ft) since the late 19th century. The rate of retreat has increased since 1980, following a period of slow retreat from 1950–1980. The Peyto Glacier, covering an area of about 12 km² (4.63 miles²), retreated rapidly during the first half of the 20th century, stabilized by 1966 and resumed shrinking in 1976.Template:Ref harv Illecillewaet Glacier in British Columbia's Glacier National Park (Canada) has retreated 2,000 m (1.25 miles) since first photographed in 1887.
On the sheltered slopes of the highest peaks of Glacier National Park, its eponymous glaciers are diminishing rapidly. The area of each glacier has been mapped by the National Park Service and the U.S. Geological Survey.Template:Ref harv Every glacier has retreated notably in the last 140 years. The larger glaciers are now approximately a third of their size when first studied in 1850, and numerous smaller glaciers have disappeared completely. Only 27% of the 99 km² (38 miles²) area of Glacier National Park covered by glaciers in 1850 remained by 1993. The average glacier area in the accumulation zone for September 1993 was 35%. With 65% needed for equilibrium, the mass balances for most glaciers are negative and they continuing to shrink.
An increase of approximately 1 °C (2 °F) in average summer temperatures is reflected in reduced glacier sizes. A computer model indicates that present rates of increased warming will eliminate all glaciers in Glacier National Park by the year 2030. Even with no additional warming over that which has already occurred, the glaciers are likely to be gone by 2100. Without a general cooling trend in conjunction with an increase in snowfall, the glaciers cannot return to a positive mass balance.
The semiarid climate of Wyoming still manages to support about a dozen small glaciers within Grand Teton National Park which all show evidence of retreat over the past 50 years. Schoolroom Glacier is one of the more easily reached in the Park and is expected to be gone in 25 years.Template:Ref harv Research between 1950 and 1999 demonstrated that the glaciers in Bridger-Teton National Forest and Shoshone National Forest in the Wind River Range shrank by over a third of their size over that period. Photographs indicate that the glaciers today are only half the size as when first photographed in the late 1890's. Research also indicates that the glacial retreat was proportionately greater in the 1990s than in any other decade of the last 100 years. Gannett Glacier, on the northeast slope of Gannett Peak, is the largest single glacier in the Rocky Mountains south of Canada. It has reportedly lost over 50% of its volume since 1920 with almost half of that loss occurring since 1980. Glaciologists believe the remaining glaciers in Wyoming will disappear by the middle of the 21st Century, if the current trends continue.Template:Ref harv
Alaska
There are thousands of glaciers in Alaska though only a relative few of them have been named. The Columbia Glacier, near Valdez in Prince William Sound has retreated 15 km (9.32 miles) in the last 25 years. Icebergs calved off this glacier were a partial cause of the Exxon Valdez oil spill, as the oil tanker had changed course to avoid ramming into some of the calved icebergs. The Valdez Glacier pictured is in the same area and though it does not calve it has also retreated significantly.
"A 2005 aerial survey of Alaskan coastal glaciers identified more than a dozen glaciers, many former tidewater and calving glaciers, including Grand Plateau, Alsek, Bear, and Excelsior Glaciers that are rapidly retreating. Of 2000 glaciers observed, 99% are retreating." Template:Ref harv Icy Bay is fed by three large glaciers—Guyot, Yahtse, and Tyndall Glaciers—and they all have undergone excessive downwasting and terminus retreat, much of it due to calving. Tyndall Glacier became separated from the retreating Guyot Glacier in the 1960s and has retreated 24 km (14.9 miles) since then averaging more than 500 m (1,640 ) per year.Template:Ref harv
The Juneau Icefield Research Program has monitored the outlet glaciers of the Juneau Icefield since 1946. On the west side of the icefield from 1946–2005 the terminus of the Mendenhall Glacier, which flows into suburban Juneau, Alaska, has retreated 580 m (1,902 ft), Herbert Glacier has retreated 910 m (2,985 ft) and Eagle Glacier has retreated 1,090 m (3,576 ft). On the south side of the icefield, Norris Glacier retreated 1,740 m (1.08 miles), the East Twin Glacier 720 m (2,362 ft) and the West Twin Glacier 570 m (1,870 ft). Of the glaciers in this region, only the Taku Glacier has advanced. This glacier was advancing in 1890 when viewed by naturalist John Muir and had a large calving front. In 1948 the adjacent fjord had filled in and the glacier no longer calved. The glacier no longer lost icebergs and was able to continue its advance. By 2005 the glacier was only 1.5 km (0.93 miles) from reaching Taku Point and blocking Taku Inlet. The advance of Taku Glacier has averaged a rate of 17 m (55 ft)/year. The mass balance was very positive for the 1946–1988 period fueling the advance, however, since 1988 the mass balance has been slightly negative which should in the future slow the advance of this mighty glacier.Template:Ref harv
Long term mass balance records from Lemon Creek Glacier show declining mass balance with time.Template:Ref harv The mean annual balance for this glacier was −0.23 m (−0.75 ft)/yr 1957–1976. Mean annual balance has been increasingly negatively averaging −1.04 m (−3.4 ft)/yr from 1990–2005. Repeat glacier altimetry, or altitude measuring, for 67 Alaska glaciers find rates of thinning have increased by more than a factor of two when comparing the periods from 1950 to 1995 (−0.7 m (2.3 ft)/yr) and 1995 to 2001 (−1.8 m (5.9 ft)/yr).Template:Ref harv This is a systemic trend with loss in mass equaling loss in thickness, which leads to increasing retreat. The glaciers are not only retreating, but they are also becoming much thinner.
In Denali National Park the terminus of the Toklat Glacier is retreating 24 m (78 ft)/year and the Cantwell Glacier 10 m (32 ft)/year.Template:Ref harv There are many surging glaciers throughout Alaska whose terminal locations are part due to climate and part due to surging behavior, these glaciers are all retreating overall punctuated by a short period of advance.
Africa
With almost the entire continent of Africa located in the tropical and subtropical climate zones, glaciers are restricted to two isolated peaks and the Ruwenzori Range. The Snows of Kilimanjaro may be gone in less than 30 years. Mount Kilimanjaro, at 5,895 m (19,340 feet), is the highest peak on the continent. Since 1912, the glacier cover on the summit of Kilimanjaro has apparently retreated 75% and just from the period of 1984 to 1998, one section of glacier receded 300 m (984 ft).Template:Ref harv A report from March 2005 indicated that there is almost no remaining glacial ice on the mountain and it is the first time much of the surface of the summit has been observable in 11,000 years.Template:Ref harv Over the past century, the ice cap volume on Kilimanjaro has dropped by more than 80%. A 2002 study found that if current conditions continue, the glaciers atop Kilimanjaro will disappear between 2015 and 2020.Template:Ref harvTemplate:Ref harv
Mount Kenya which at 5,199 m (17,057 feet) is the second tallest mountain on the continent, has up to a dozen small glaciers that have shown a loss of glaciated area of at least 45% since the middle of the 20th century. According to research compiled by the USGS, there were 18 glaciers atop Mount Kenya in 1900, and by 1986, only 11 remained. The total glacier area was 1.6 km² (0.62 miles²) in 1900 and 0.4 km² (0.15 miles²) in 2000.Template:Ref harv
The Ruwenzori Range which rise to 5,109 m (16,761 ft), are to the west of the isolated peaks of Kilimanjaro and Kenya. These mountains are oftentimes cloud capped, making satellite imagery difficult and the political dynamics of the surrounding region have made access complicated at best over the past few decades. However, photographic evidence demonstrates a marked reduction in glacially covered regions over the past century. By 1990, glaciers on the Rwenzori mountains had receded to about 40% of their extent recorded in 1955. It is expected that due to their closer distance to the heavy moisture of the Congo region, the glaciers in the Ruwenzori Range may recede at a slower rate than either on Kilimanjaro or in Kenya.Template:Ref harv
Asia
The Himalayas and other mountain chains of central Asia support large regions that are glaciated. These glaciers provide critical water supplies to arid countries such as Mongolia, western China, Pakistan and Afghanistan. As is true with other glaciers worldwide, the glaciers of Asia are experiencing a rapid decline in their mass and the loss of these glaciers would have a tremendous impact on the ecosystem of the region.
Himalayas
A WWF report concluded that 67% of all Himalayan glaciers are retreating rapidly. In examining 612 glaciers in China, 53.44% were found to be retreating in the period between 1950 and 1970 and after 1990 95% of the glaciers were in retreat, indicating that glacier retreat has become more rapid.Template:Ref harv Some of the more famous glaciers in the area indicate that all the glaciers are retreating. The Khumbu Glacier, which is the main route up Mount Everest, has retreated 5 km (3.1 miles) since 1953. The Rongbuk Glacier, draining the north side of Mount Everest into Tibet, has been retreating 20 m (65 ft)/yr. In India, the Gangotri Glacier, which is one of the primary sources of water for the Ganges River, retreated 34 m (111 ft)/yr between 1970 and 1996 and has averaged 30 m (100 ft)/yr since the year 2000. The recent increase in retreat rates and melt rates has led to a recent expansion and creation of glacier lakes in the Himalayas. The growing concern is potential for Glacial Lake Outburst Floods (GLOF) and researchers estimate 20 glacial lakes in Nepal and 24 in Bhutan are potentially dangerous should their moraines fail. Bhutan's Raphstreng Tsho glacial lake measured 1.6 km (0.99 mile) long, 0.96 km (0.59 mile) wide and was 80 m (262 ft) deep in 1986. By 1995 the lake had swollen to be 1.94 km (1.20 mile) long, 1.13 km (0.70 mile) wide and a depth of 107 m (351 ft). Its neighboring glacier could generate a GLOF up to two-and-a-half-times that which caused major devastation in October 1994. The 43 other glacial lakes, pin pointed in the survey and deemed to be in a dangerous state, show similar patterns.Template:Ref harv
Central Asia
Glaciers in the Ak-shirak Range in Kyrgyzstan experienced a slight loss between 1943 and 1977 and then lost over 20% of their mass from 1977 to 2001.Template:Ref harv In the Tien Shan mountains which Kyrgyzstan shares with China and Kazakhstan, studies in the northern potions of that mountain range show that the glaciers that help supply water to this arid region have been losing nearly two cubic km (0.47 mile³) of ice a year between 1955 and 2000. The study, which was led by Stephan Harrison of the University of Oxford, also reported that 1.28% of the volume of the glaciers has been lost every year between 1974 and 1990.Template:Ref harv
To the south of the Tien Shan the Pamirs mountain range located primarily in Tajikistan, has many thousands of glaciers, all of which are in a general state of retreat. During the 20th Century, the glaciers of Tajikistan lost 20 km³ (4.79 mile³) of ice. The 70 km (43 mile) long Fedchenko Glacier, which is the largest in Tajikistan, lost 1 km (0.62 mile) of it's length, 2 km³ (2.61 yds³) of its mass and the glaciated area was reduced by 11 km² (4.24 mile²) during the 1900's. Similarly, the Skogatch Glacier lost 8% of its total mass between 1969 and 1986. The country of Tajikistan and neighboring countries of the Pamir Range are highly dependent upon glacial runoff to ensure river flow during droughts and and the dry seasons experienced every year. The continued demise of glacier ice will result in a short term increase, followed by a long term decrease in water flow into rivers and streams.Template:Ref harv
Oceania
In New Zealand the mountain glaciers have been in a general retreat since 1890, with an acceleration of this retreat after 1920. Most of the glaciers have been reduced in size and the accumulation zone had a corresponding rise to higher elevations as the 20th century progressed. During the period 1971 to 1975, Ivory Glacier was reduced 30 m at the glacial terminus and the loss of ice during the period was 13.9 x 10 m³ (18,180,513 yd³). About 26% of the surface area of the glacier was lost over the same period. Since 1980, numerous small glacial lakes were created behind the new terminal moraines of several of these glaciers. It has also been observed that these glaciers have also shown a measurable loss in thickness. Glaciers such as Classen, Godley and Douglas now all have new glacial lakes below their terminal locations due to the glacial retreat over the past 20 years. Satellite imagery indicates that these lakes are expanding in area as well.
Several glaciers, notably the much visited Fox and Franz Josef Glaciers, have periodically advanced (especially during the 1990s) but the scale of these advances is small compared to 20th century retreat. These rapidly flowing large glaciers which are situated on steep slopes, have been very reactive to small mass-balance changes. A few years of favorable conditions are rapidly echoed in a corresponding advance, followed equally rapidly by renewed retreat when those favorable conditions end.Template:Ref harv This advance by glaciers in certain sections in New Zealand has been primarily attributed to a temporary weather change associated with El nino, which has brought more precipitation and cloudier, cooler summers since 2002.Template:Ref harv
On the large island of New Guinea, there is photographic evidence of massive glacial retreat since the region was first extensively explored by airplane in the early 1930s. Due to the location of the island within the tropical zone, there is little to no seasonal variation in temperature. The tropical location has a predictably steady level of rain and snowfall, as well as cloud cover year round and there has been no noticeable change in the level of moisture which has fallen during the 20th century. Therefore, the glacial retreat evidenced can only be attributed to a general warming trend. The 7 km² glacial cap on the mountain known as Puncak Jaya is the largest on the island, and has retreated from one larger mass into several smaller glacial bodies since 1936. Of these glaciers, between 1973 and 1976, the Meren Glacier retreated 200 m (656 ft) and the Carstensz Glacier retreated 50 m (164 ft) over the three year period. The third larger area that was once part of the icecap and is now known as the Northwall Firn, had split into several smaller glaciers by 1972. One small icecap known to exist on the summit of Puncak Trikora completely disappeared sometime between 1939 and 1962.Template:Ref harv All the glaciers on the island are located within Indonesia, in a region of political instability, which has made ground surveys less common in recent years. However, research presented in 2004 of imagery from the IKONOS satellite of the New Guinean glaciers provided a dramatic update. The imagery indicated that between the years 2000 and 2002, the East Northwall Firn had lost 4.5%, the West Northwall Firn 19.4% and the Carstensz 6.8% of their glacial mass in only those two years. The presentation went on to state that "Sometime between 1994 and 2000 the Meren Glacier appears to have disappeared".Template:Ref harv
Andes
A study by glaciologists on two smaller glaciers in South America show an alarming retreat has occurred. More than 80% of all glacial ice in the northern Andes is concentrated on the highest peaks in smaller glaciers of one km² in size. Chacaltaya Glacier in Bolivia and Antizana Glacier in Ecuador were examined between 1992 and 1998 and there was between 0.6 (1.9 ft) and 1.4 m (4.6 ft) of ice was lost per year on each glacier. Chacaltaya Glacier lost two-thirds of its volume and 40% of its thickness over the same period and it is expected that by 2010 to 2015, Chacaltaya Glacier will no longer exist and the glacier is only 10% of its size since first examined in 1940. The evidence also supported findings that since the mid 1980's, the rate of retreat for both glaciers has also been increasing.Template:Ref harv
Further south in Peru, the Andes are much taller overall and there are approximately 722 glaciers covering an area of 723.4 km² (279 miles²). Research in this region of the Andes is less extensive but indicates that in the years between 1977 and 1983, a glacial retreat of 7% occurred.Template:Ref harv The Quelccaya Icecap, the world's largest tropical icecap, is showing extraordinary signs of retreat. In the case of Qori Kalis, Quelccaya's main outlet glacier, the rate of retreat had reached 155 m per year during the three year period of 1995 to 1998. The melting ice has formed a large lake at the front of the glacier which did not exist in 1983, but now covers more than 10 acres. Bare ground has been exposed for the first time in thousands of years.Template:Ref harv
A large region of population surrounding the central Andes of Argentina and Chile reside in arid areas that are dependant on water supplies from melting glaciers. The water from the glaciers also supply rivers that have in some cases been dammed for hydroelectric power. Some researchers think that by 2030, many of the large ice caps on the highest Andes will be gone, if current trends continue. In Patagonia on the southern tip of the continent, the large ice caps have been shown to have retreated a full kilometer since the early 1990s and 10 km (6.2 miles) since the late 1800s. It has also been observed that Patagonian glaciers are receding at a faster rate than any other region in the world.Template:Ref harv The northern Patagonian Icefield lost 93 km² (35 miles²) of glacier area from 1945–1975 and 174 km² (67 miles²) from 1975–1996.
Arctic
The Canadian Arctic islands have a number of substantial ice caps—Penny and Barnes Ice Cap on Baffin Island, Bylot Ice Cap on Bylot Island, and Devon Ice Cap on Devon Island. All of these ice caps have been thinning and receding slowly. The Barnes and Penny ice caps on Baffin Island have been thinning at over 1 m (3.1 ft)/yr in the lower elevations from 1995–2000. Overall ice caps in the Canadian Arctic lost 25 km³ (6 miles³) of ice per year from 1995–2000.Template:Ref harv Between 1960 and 1999, the Devon Ice Cap lost 67 km³ (16 miles³) of ice, mainly through thinning. All major outlet glaciers along the eastern Devon Ice Cap margin have retreated 1–3 km (0.62–1.8 miles) since 1960.Template:Ref harv On the Hazen Plateau of Ellesmere Island, the Simmon Ice Cap has lost 47% of its area since 1959.Template:Ref harv If the current climatic conditions continue, the remaining glacial ice on the Hazen Plateau will be gone around 2050.
On Svalbard archipelago (Spitsbergen) Hansbreen Glacier retreated 1.4 km (0.87 miles) from 1936 to 1982 and 400 m (1,312 ft) during the six year period of 1982 to 1998.Template:Ref harv Blomstrandbreen, a glacier in the King's Bay area has retreated approximately 2 km (1.24 miles) in the past 80 years. Since 1960, the average retreat of that glacier has been about 35 m (114 ft) a year, accelerating in the last ten years.Template:Ref harv The Midre Lovenbreen Glacier has retreated 200 m (656 ft) from 1977 to 1995.Template:Ref harv On Novaya Zemlya archipelago, in 1952 there was 208 km (129 miles) of glacier ice along the coast. By 1993 this had been reduced by 8% to 198 km (123 miles) of glacier coastline.Template:Ref harv
Greenland
Despite their proximity and importance to human populations, the mountain and valley glaciers of temperate latitudes amount to a small fraction of glacial ice on the earth. About 99% is in the great ice sheets of polar and subpolar Antarctica and Greenland. These continuous continental-scale ice sheets, 3 km (1.8 miles) or more in thickness, cap the polar and subpolar land masses. Like rivers flowing from an enormous lake, numerous outlet glaciers transport ice from the margins of the ice sheet to the ocean.
Glacier retreat has been observed in these outlet glaciers, resulting in an increase of the ice flow rate and destabilization of the mass balance of the ice sheet that is their source. In Greenland the period since the year 2000 has brought retreat to several very large glaciers that had long been stable. Three glaciers that have been researched—Helheim, Jakobshavn Isbræ Kangerdlugssuaq glaciers, jointly drain more than 16% of the Greenland Ice Sheet. In the case of Helheim glacier, researchers used satellite images to determine the movement and retreat of the glacier. Satellite images and aerial photographs from the 1950s and 1970s show that the front of the glacier has remained in the same place for decades. But in 2001 it began retreating rapidly, retreating 7.2 km (4.5 miles) between 2001 and 2005. It has also accelerated from 20 m (65 ft)/day to 32 m (104 ft)/day.Template:Ref harv
Jakobshavn Isbræ in west Greenland, a major outlet glacier of the Greenland Ice Sheet, is generally considered the fastest moving glacier in the world. It had been moving continuously at speeds of over 24 m (78 ft)/day with a stable terminus since at least 1950. In 2002, the 12 km (7.5 mile) long floating terminus entered a phase of rapid retreat. The ice front started to break up and the floating terminus disintegrated accelerating to a retreat rate of over 30 m (98 ft)/day.
The acceleration rate of retreat of Kangerdlugssuaq Glacier is even larger. Portions of the main trunk that were flowing at 15 m (49 ft)/day in 1988–2001 were flowing at 40 m (131 ft)/day in summer 2005. The front of the glacier has also retreated and has rapidly thinned by more than 100 m (328 ft).Template:Ref harv
The rapid thinning, acceleration and retreat of these three large glaciers in close association with one another suggests a common triggering mechanism, such as enhanced surface melting due to regional climate warming. The current flow speeds at the terminus are too fast to be caused solely by internal deformation of the ice, implying that an increase in basal sliding forced by additional meltwater production is the probable cause of the velocity increases. This was termed the Jakobshavns Effect by Terence Hughes at the University of Maine in 1986.Template:Ref harv
Antarctica
Most of the world's freshwater ice is contained in the great ice sheets that cover the continent of Antarctica. The most dramatic example of glacial retreat on the continent is the loss of large sections of the Larsen Ice Shelf on the Antarctic Peninsula. The collapse has been due to warmer melt season temperatures leading to surface melting and the formation of shallow ponds of water on the ice shelf. The Larsen Ice Shelf lost 2,500 square kilometers (965 miles²) of its area from 1995 to 2001. In a 35 day period beginning on 31 January 2002, about 3,250 km² (1,254 miles²) of shelf area disintegrated. The ice sheet is now 40% the size of its previous minimum stable extent.Template:Ref harv
Pine Island Glacier, which flows into the Amundsen Sea thinned 3.5 ± 0.9 m (11.5 ± 3 ft) per year and retreated five kilometers (3.1 miles) in 3.8 years. The terminus of the glacier is a floating ice shelf and the point at which it is afloat is retreating 1.2 km/year. This glacier drains a substantial portion of the West Antarctic Ice Sheet and has been referred to as the weak underbelly of this ice sheet.Template:Ref harv This same pattern of thinning is evident on the neighboring Thwaites Glacier. Additionally, the Dakshin Gangotri Glacier, a small outlet glacier of the continental ice sheet, receded at a rate of 7 m (22 ft)/decade from 1983 to 2002.
Impacts of glacier retreat
The retreat of glaciers will have a quantitative impact in a number of different ways. In areas that are heavily dependent on water runoff from glaciers that melt during the warmer summer months a continuation of the current retreat will affect the ability to irrigate crops, maintain summer streamflows, and keep dams and reservoirs replenished. This situation is particularly acute for irrigation in South America, where numerous artificial lakes are filled almost exclusively by glacial melt.Template:Ref harv Central Asian countries have also been historically dependent on the seasonal glacier melt water for irrigation and drinking supplies. In Norway, the Alps and the Pacific Northwest of North America glacier runoff is key for hydropower.
Many species of freshwater and salt water plants and animals are dependent on glacier fed waters to ensure a cold water habitat that they have adapted to. Some species of fresh water fish need cold water to survive and to reproduce and this is especially true with Salmon and Cutthroat trout as well as the krill that prefer cold water and who themselves are the primary food source for aquatic mammals such as the Sperm whale.Template:Ref harv Alterations to the ocean currents and the thermohaline circulation of the worlds oceans may seriously impact the fisheries of the world, which may mean less fish and shellfish for human consumption. The unbalancing effect of rapid glacier retreat may spell extinction for plants and animals unable to adapt to the changing climate quickly enough. Should glacier retreat continue at the annually increasing rate currently observed, the entire food chain may be affected.
Since at least the end of World War II, glaciologists and those in related professions have been informing the scientific community and the public that glacier retreat is a situation of potential concern. The vast majority of glaciologists attribute global warming as the primary reason for the retreating glaciers. In most cases, they have long supported a worldwide reduction in the levels of fossil fuels consumed, citing, along with climatologists, the surge in carbon dioxide gas in the atmosphere over the past century which has been attributed primarily to increased fossil fuel use. Carbon dioxide helps trap heat within the atmosphere, thereby raising temperatures worldwide. It is this rise in what is referred to as Greenhouse gases that are raising the temperature of the planet and melting the glaciers away.
Projected future trends
The examples from around the globe noted above demonstrate that since at least the year 1850, glaciers around the world have been in a general state of retreat. The general retreat was particularly rapid from 1925–1945, and slower from 1950–1980 with many small alpine glaciers advancing again, though not generally to their originally first-observed positions when research began in the late 19th century. The rate of retreat has increased since 1980; some glaciers have already disappeared since then, and many glaciers will disappear within decades if current climate patterns continue. Even the major icecaps of Greenland and Antarctica show glacier retreat due to global warming. Glaciologists agree that the current trend of rapid retreat is likely to continue and may become more pronounced over the next several decades. The resultant sea level rise, alterations to ecosystems, thermohaline circulation, and to fresh water supplies represent great potential challenges in the near future.
References
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General references
- Michael Pidwirny. "Glacial Processes" (html). PhysicalGeography.net. Retrieved February 2.
{{cite web}}: Check date values in:|accessdate=(help); Unknown parameter|accessyear=ignored (|access-date=suggested) (help) - University College London. "Climate change and the aquatic ecosystems of the Rwenzori Mountains, Uganda" (html). Glaciology—assessing the magnitude of current glacial recession. Retrieved September 3.
{{cite web}}: Check date values in:|accessdate=(help); Unknown parameter|accessyear=ignored (|access-date=suggested) (help) - Andrew Wielochowski. "Glacial recession on Kilimanjaro" (html). Retrieved October 6.
{{cite web}}: Check date values in:|accessdate=(help); Unknown parameter|accessyear=ignored (|access-date=suggested) (help) - National Park Service, U.S. Department of the Interior. "Icefields and Glaciers" (html). Tongass National Forest, Forest Facts. Retrieved July 10.
{{cite web}}: Check date values in:|accessdate=(help); Unknown parameter|accessyear=ignored (|access-date=suggested) (help) - NOAA,. "Arctic Change" (html). Study of Environmental Arctic Change. Retrieved February 15.
{{cite web}}: Check date values in:|accessdate=(help); Unknown parameter|accessyear=ignored (|access-date=suggested) (help)CS1 maint: extra punctuation (link)
Additional reading
- Aniya, M. and Y.Wakao (1997). "Glacier variations of Heilo Patagonico Norte, Chile between 1945–46 and 1995–96". Bulletin of Glacier Research. 15: 11–18.
- Hall M.H. and Fagre, D.B (2003). "Modeled Climate-Induced Glacier Change in Glacier National Park, 1850–2100". BioScience. 53: 131–140.
- IUGG(CCS)/UNEP/UNESCO (2005). Haeberli, W., Zemp, M., Frauenfelder, R., Hoelzle, M. and Kääb, A. (ed.). Fluctuations of Glaciers 1995–2000, Vol. VIII. Paris: World Glacier Monitoring Service.
{{cite book}}: CS1 maint: multiple names: editors list (link) - Pelto, M.S. and Hartzell, P.L. (2004). "Change in longitudinal profile on three North Cascades glaciers during the last 100 years". Hydrologic Processes. 18: 1139–1146.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - Pelto, M.S. and Hedlund, C. (2001). "The terminus behavior and response time of North Cascade glaciers". Journal of Glaciology. 47: 497–506.
{{cite journal}}: CS1 maint: multiple names: authors list (link)