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Retreat of glaciers since 1850

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   Grinnell Glacier in Glacier National Park (US) showing recession since
   1850 of 1.1 km (0.7 miles) USGS
   Enlarge
   Grinnell Glacier in Glacier National Park (US) showing recession since
   1850 of 1.1 km (0.7 miles) USGS

   The retreat of glaciers since 1850, worldwide and rapid, affects the
   availability of fresh water for irrigation and domestic use, mountain
   recreation, animals and plants that depend on glacier-melt, and in the
   longer term, the level of the oceans. Studied by glaciologists, the
   temporal coincidence of glacier retreat with the measured increase of
   atmospheric greenhouse gases is often cited as an evidentiary
   underpinning of anthropogenic global warming. Mid-latitude mountain
   ranges such as the Himalayas, Alps, Rocky Mountains, Cascade Range, and
   the southern Andes, as well as isolated tropical summits such as Mount
   Kilimanjaro in Africa, are showing some of the largest proportionate
   glacial loss.^^

   The Little Ice Age was a period from about 1550 to 1850 when the world
   experienced relatively cool temperatures compared to the present.
   Subsequently, until about 1940 glaciers around the world retreated as
   the climate warmed. Glacial retreat slowed and even reversed, in many
   cases, between 1950 and 1980 as a slight global cooling occurred.
   However, since 1980 a significant global warming has led to glacier
   retreat becoming increasingly rapid and ubiquitous, so much so that
   many glaciers have disappeared and the existence of a great number of
   the remaining glaciers of the world is threatened. In locations such as
   the Andes of South America and Himalayas in Asia, the demise of
   glaciers in these regions will have potential impact on water supplies.
   The retreat of mountain glaciers, notably in western North America,
   Asia, the Alps, Indonesia and Africa, and tropical and subtropical
   regions of South America, has been used to provide qualitative evidence
   for the rise in global temperatures since the late 19th century.^ ^The
   recent substantial retreat and an acceleration of the rate of retreat
   since 1995 of a number of key outlet glaciers of the Greenland and West
   Antarctic ice sheets, may foreshadow a rise in sea level, having a
   potentially dramatic effect on coastal regions worldwide.

Glacier mass balance

   This map of mountain glacier mass balance changes since 1970 shows
   thinning in yellow and red, and thickening in blue.
   Enlarge
   This map of mountain glacier mass balance changes since 1970 shows
   thinning in yellow and red, and thickening in blue.
   Global glacial mass balance in the last fifty years, reported to the
   WGMS and NSIDC. The increasing downward trend in the late 1980s is
   symptomatic of the increased rate and number of retreating glaciers.
   Enlarge
   Global glacial mass balance in the last fifty years, reported to the
   WGMS and NSIDC. The increasing downward trend in the late 1980s is
   symptomatic of the increased rate and number of retreating glaciers.

   Crucial to the survival of a glacier is its mass balance, the
   difference between accumulation 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 is also out of equilibrium, and will advance
   to reestablish equilibrium. Currently, there are a few advancing
   glaciers, although their modest growth rates suggest that 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, 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 and will melt away without a colder climate and or an
   increase in frozen precipitation.

   The key symptom of a glacier in disequilibrium is thinning along the
   entire length of the glacier.^^ 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,
   is melting and has thinned. Small glaciers with minimal altitude gain
   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.

Tropical glaciers

   Tropical glaciers are located between the Tropic of Cancer and the
   Tropic of Capricorn, in the region that lies 23° 26′ 22″ north or south
   of the equator. Tropical glaciers are the most uncommon of all glaciers
   for a variety of reasons. Firstly, the tropics are the warmest part of
   the planet. Secondly, the seasonal change is minimal with temperatures
   warm year round, resulting in a lack of a colder winter season in which
   snow and ice can accumulate. Thirdly, few taller mountains can be found
   in these regions upon which enough cold air exists for the
   establishment of glaciers. All of the glaciers located in the tropics
   are on isolated high mountain peaks. Overall, tropical glaciers are
   smaller than those found elsewhere and are the most likely glaciers to
   show rapid response to changing climate patterns. A small temperature
   increase of only a few degrees can have almost immediate and adverse
   impact on tropical glaciers.^

   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. 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 the volume
   of glacial ice is now 80% less than it was a century ago due to both
   retreat and thinning.^ In the 14-year period from 1984 to 1998, one
   section of the glacier atop the mountain receded 300 m (984 ft).^ A
   2002 study determined that if current conditions continue, the glaciers
   atop Kilimanjaro will disappear sometime between 2015 and 2020.^^ A
   March 2005 report indicated that there is almost no remaining glacial
   ice on the mountain, and it is the first time in 11,000 years that
   barren ground has been exposed on portions of the summit.^^

   The Furtwängler Glacier is located near the summit of Kilimanjaro.
   Between 1976 and 2000, the area of Furtwängler Glacier was cut almost
   in half, from 113,000 m² to 60,000 m².^ During fieldwork conducted
   early in 2006, scientists discovered a large hole near the centre of
   the glacier. This hole, extending through the 6 meter (20 ft) remaining
   thickness of the glacier to the underlying rock, is expected to grow
   and split the glacier in two by 2007.^
   Furtwängler Glacier atop Kilimanjaro in the foreground and snowfields
   and the Northern Icefields beyond.
   Enlarge
   Furtwängler Glacier atop Kilimanjaro in the foreground and snowfields
   and the Northern Icefields beyond.

   To the north of Kilimanjaro lies Mount Kenya, which at 5,199 m
   (17,057 feet) is the second tallest mountain on the African continent.
   Mount Kenya has a number of small glaciers that have lost at least 45%
   of their mass since the middle of the 20th century. According to
   research compiled by the U.S. Geological Survey (USGS), there were
   eighteen glaciers atop Mount Kenya in 1900, and by 1986 only eleven
   remained. The total area covered by glaciers was 1.6 km² (0.62 miles²)
   in 1900; however. by the year 2000 only about 25%, or 0.4 km²
   (0.15 miles²), remained.^ To the west of Mounts Kilimanjaro and Kenya,
   the Ruwenzori Range rises to 5,109 m (16,761 ft). Photographic evidence
   of this mountain range indicates a marked reduction in glacially
   covered areas over the past century. In the 45-year period between 1955
   and 1990, glaciers on the Ruwenzori Range receded about 40%. It is
   expected that due to their proximity to the heavy moisture of the Congo
   region, the glaciers in the Ruwenzori Range may recede at a slower rate
   than those on Kilimanjaro or in Kenya.^

   A study by glaciologists of two small glaciers in South America reveals
   another alarming retreat. More than 80% of all glacial ice in the
   northern Andes is concentrated on the highest peaks in small glaciers
   of approximately one km² (0.38 mile²) in size. A 1992 to 1998
   observation of the Chacaltaya Glacier in Bolivia and Antizana Glacier
   in Ecuador indicated that between 0.6 m (1.9 ft) and 1.4 m (4.6 ft) of
   ice was lost per year on each glacier. Figures for Chacaltaya Glacier
   show a loss of 67% of its volume and 40% of its thickness over the same
   period. Chacaltaya Glacier has lost 90% of its mass since 1940 and is
   expected to disappear altogether sometime between 2010 and 2015.
   Research also indicates that since the mid-1980s, the rate of retreat
   for both of these glaciers has been increasing.^
   Puncak Jaya icecap 1936 USGS
   Enlarge
   Puncak Jaya icecap 1936 USGS
   Puncak Jaya glaciers 1972. Left to right: Northwall Firn, Meren
   Glacier, and Carstensz Glacier. USGS. Also mid 2005 image and
   animation.
   Enlarge
   Puncak Jaya glaciers 1972. Left to right: Northwall Firn, Meren
   Glacier, and Carstensz Glacier. USGS. Also mid 2005 image and
   animation.

   Further south in Peru, the Andes are at a higher altitude overall, and
   there are approximately 722 glaciers covering an area of 723 km²
   (279 miles²). Research in this region of the Andes is less extensive
   but indicates an overall glacial retreat of 7% between 1977 and 1983.^
   The Quelccaya Ice Cap is the largest tropical icecap in the world, and
   all of the outlet glaciers from the icecap are retreating. In the case
   of Qori Kalis Glacier, which is Quelccayas' main outlet glacier, the
   rate of retreat had reached 155 m (508 feet) 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 since 1983, and bare ground has been exposed
   for the first time in thousands of years.^

   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 amount of moisture which has fallen
   during the 20th century. The 7 km² (2.7 mile²) glacial cap on Puncak
   Jaya is the largest on the island, and has retreated from one larger
   mass into several smaller glacial bodies since 1936. Of these smaller
   glaciers, research between 1973 and 1976 showed glacier retreat for the
   Meren Glacier of 200 m (656 ft) and 50 m (164 ft) for the Carstenez
   Glacier. The Northwall Firn, another large remnant of the icecap that
   once was atop Puncak Jaya, has itself split into several separate
   glaciers since 1936. Research presented in 2004 of IKONOS satellite
   imagery of the New Guinean glaciers provided a dramatic update. The
   imagery indicated that in the two years from 2000 to 2002, the East
   Northwall Firn had lost 4.5%, the West Northwall Firn 19.4% and the
   Carstensz 6.8% of their glacial mass. Researchers also discovered that,
   sometime between 1994 and 2000, the Meren Glacier disappeared
   altogether.^ Separate from the glaciers of Puncak Jaya, another small
   icecap known to have existed on the summit of Puncak Trikora completely
   disappeared sometime between 1939 and 1962.^

Mid-latitude glaciers

   Mid-latitude glaciers are located either between the Tropic of Cancer
   and the Arctic Circle, or between the Tropic of Capricorn and the
   Antarctic Circle. These two regions support glacier ice from mountain
   glaciers, valley glaciers and even smaller icecaps, which are usually
   located in higher mountainous regions. All of these glaciers are
   located in mountain ranges, notably the Himalayas; the Alps; Rocky
   Mountains and Pacific Coast Ranges of North America; the Patagonian
   Andes in South America; and mountain ranges in the island nation of New
   Zealand. Glaciers in these latitudes are more widespread and tend to be
   more massive the closer they are located to the polar regions. These
   glaciers are the most widely studied over the past 150 years. As is
   true with the glaciers located in the tropical zone, virtually all the
   glaciers in the mid-latitudes are in a state of negative mass balance
   and are retreating.

Eastern hemisphere

   This map from the annual Glacier Commission surveys in Italy and
   Switzerland shows the percentage of advancing glaciers in the Alps.
   Mid-20th century saw strong retreating trends, but not as extreme as
   the present; current retreats represent additional reductions of
   already smaller glaciers.
   Enlarge
   This map from the annual Glacier Commission surveys in Italy and
   Switzerland shows the percentage of advancing glaciers in the Alps.
   Mid-20th century saw strong retreating trends, but not as extreme as
   the present; current retreats represent additional reductions of
   already smaller glaciers.

   The World Glacier Monitoring Service reports on changes in the
   terminus, or lower-elevation end, of glaciers from around the world
   every five years.^ In their 1995–2000 edition, they noted the terminal
   point variations of glaciers across the Alps. Over the five-year period
   from 1995 to 2000, 103 of 110 glaciers examined in Switzerland, 95 of
   99 glaciers in Austria, all 69 glaciers in Italy, and all 6 glaciers in
   France were in retreat. French glaciers experienced a sharp retreat in
   the years 1942–53 followed by advances up to 1980, and then further
   retreat beginning in 1982. As an example, since 1870 the Argentière
   Glacier and Mont Blanc Glacier have receded by 1,150 (3,800 ft) and
   1,400 m (4,600 ft), respectively. The largest glacier in France, the
   Mer de Glace, which is 11 km (7 miles) long and 400 m (1,300 ft) thick,
   has lost 8.3% of its length, or 1 km (0.6 miles), in 130 years, and
   thinned by 27%, or 150 m (500 ft), in the midsection of the glacier
   since 1907. The Bossons Glacier in Chamonix, France, has retreated
   1,200 m (3,900 ft) from extents observed in the early 20th century. In
   2005, of 91 Swiss glaciers studied, 84 retreated from where their
   terminal points had been in 2004 and the remaining 7 showed no change.^

   Other researchers have found that glaciers across the Alps appear to be
   retreating at a faster rate than a few decades ago. In 2005, of the 91
   glaciers observed, 84 were retreating and none were advancing. The
   Trift Glacier had retreated over 500 m (1,600 ft) just in the three
   years of 2003 to 2005, which is 10% of its total length. The Grosser
   Aletsch Glacier, the largest glacier in Switzerland, has retreated
   2,600 m (8,500 ft) since 1880. This rate of retreat has also increased
   since 1980, with 30%, or 800 m (2,600 ft), of the total retreat
   occurring in the last 20% of the time period.^ Similarly, of the
   glaciers in the Italian Alps, only about a third were in retreat in
   1980, while by 1999, 89% of these glaciers were retreating. Researchers
   found that from 2004 to 2005, every glacier in the Italian Alps was
   retreating.^ Repeat photography of glaciers in the alps provides clear
   evidence that glaciers in this region have retreated significantly in
   the past several decades. ^Morteratsch Glacier, Switzerland is one key
   example. The yearly measurements of the length changes started in 1878.
   The overall retreat from 1878 to 1998 accounts for a total of 2 km with
   a mean annual retreat rate of approximately 17 m/y. This long-term
   average was markedly surpassed in recent years receding 30 m/y from
   1999-2005.^ One major concern which has in the past had great impact on
   lives and property is the death and destruction from a Glacial Lake
   Outburst Flood (GLOF). Glaciers stockpile rock and soil that has been
   carved from mountainsides at their terminal end. These debris piles
   often form dams that impound water behind them and form glacial lakes
   as the glaciers melt and retreat from their maximum extents. These
   terminal moraines are frequently unstable and have been known to burst
   if overfilled or displaced by earthquakes, landslides or avalanches. If
   a glacier has a rapid melting cycle during warmer months, the terminal
   moraine may not be strong enough to continue to impound the rising
   water behind it, leading to a massive localized flood. This is an
   increasing risk due to the creation and expansion of glacial lakes
   resulting from glacier retreat. Past floods have been deadly and have
   resulted in enormous property damage. Towns and villages in steep,
   narrow valleys that are downstream from glacial lakes are at the
   greatest risk. In 1892 a GLOF released some 200,000 m³ (260,000 yd³) of
   water from the lake of the Glacier de Tête Rousse, resulting in the
   deaths of 200 people in the French town of Saint Gervais.^ GLOFs have
   been known to occur in every region of the world where glaciers are
   located. Continued glacier retreat is expected to create and expand
   glacial lakes, increasing the danger of future GLOFs.

   Though the glaciers of the Alps have received more attention from
   glaciologists than in other areas of Europe, research indicates that
   throughout most of Europe, glaciers are rapidly retreating. In the
   Kebnekaise Mountains of northern Sweden, a study of 16 glaciers between
   1990 and 2001 found that 14 glaciers were retreating, one was advancing
   and one was stable.^ During the 20th century, glaciers in Norway
   retreated overall with brief periods of advance around 1910, 1925 and
   in the 1990s. In the 1990s, 11 of 25 Norwegian glaciers observed had
   advanced due to several consecutive winters with above normal
   precipitation. However, following several consecutive years of little
   winter precipitation since 2000, and record warmth during the summers
   of 2002 and 2003, Norwegian glaciers have decreased significantly since
   the 1990s. By 2005 only 1 of the 25 glaciers monitored in Norway was
   advancing, two were stationary and 22 were retreating. The Norweigan
   Engabreen Glacier has retreated 179 m (587 ft) since 1999, while the
   Brenndalsbreen and Rembesdalsskåka glaciers have retreated 116 m
   (380 ft) and 206 m (675 ft), respectively, since 2000. The
   Briksdalsbreen glacier retreated 96 m (314 ft) in 2004 alone—the
   largest annual retreat recorded for this glacier since monitoring began
   in 1900. Overall, from 1999 to 2005, Briksdalsbreen retreated 176 m
   (577 ft).^
   This NASA image shows the formation of numerous glacial lakes at the
   termini of receding glaciers in Bhutan-Himalaya.
   Enlarge
   This NASA image shows the formation of numerous glacial lakes at the
   termini of receding glaciers in Bhutan-Himalaya.

   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 mass. The loss of these
   glaciers would have a tremendous impact on the ecosystem of the region.

   A WWF report concluded that 67% of all Himalayan glaciers are
   retreating. In examining 612 glaciers in China between 1950 and 1970,
   53% of the glaciers studied were retreating. After 1990, 95% of these
   glaciers were measured to be retreating, indicating that retreat of
   these glaciers was becoming more widespread.^ Glaciers in the Mount
   Everest region of the Himalayas are all in a state of retreat. The
   Khumbu Glacier, which is one of the main routes to the base of 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) per year. In India the Gangotri Glacier, which
   is a significant source of water for the Ganges River, retreated 34 m
   (111 ft) per year between 1970 and 1996, and has averaged a loss of
   30 m (100 ft) per year since 2000. With the retreat of glaciers in the
   Himalayas, a number of glacial lakes have been created. A growing
   concern is the potential for Glacial Lake Outburst Floods—researchers
   estimate 20 glacial lakes in Nepal and 24 in Bhutan pose hazards to
   human populations should their terminal moraine dams fail. One glacial
   lake identified as potentially hazardous is Bhutan's Raphstreng Tsho,
   which 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). In 1994 a GLOF from Luggye Tsho, a glacial lake adjacent to
   Raphstreng Tsho, killed 23 people downstream.^

   Glaciers in the Ak-shirak Range in Kyrgyzstan experienced a slight loss
   between 1943 and 1977 and an accelerated loss of 20% of their remaining
   mass between 1977 and 2001.^ 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 per year between 1955 and 2000. The University of
   Oxford study also reported that an average of 1.28% of the volume of
   these glaciers had been lost per year between 1974 and 1990.^

   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 (4.8 mile³) of ice. The 70 km
   (43 mile) long Fedchenko Glacier, which is the largest in Tajikistan
   and the largest non-polar glacier on Earth, lost 1.4% of its length, or
   1 km (0.6 mile), 2 km³ (0.5 mile³) of its mass, and the glaciated area
   was reduced by 11 km² (4.2 mile²) during the 20th century. Similarly,
   the neighboring 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 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 glacial melt water flowing into
   rivers and streams.^
   These glaciers in New Zealand have continued to retreat rapidly in
   recent years. Notice the larger terminal lakes, the retreat of the
   white ice (ice free of moraine cover), and the higher moraine walls due
   to ice thinning. Photo. Enlarge
   These glaciers in New Zealand have continued to retreat rapidly in
   recent years. Notice the larger terminal lakes, the retreat of the
   white ice (ice free of moraine cover), and the higher moraine walls due
   to ice thinning. Photo.

   In New Zealand the mountain glaciers have been in general retreat since
   1890, with an acceleration of this retreat since 1920. Most of the
   glaciers have thinned measurably and have reduced in size, and the snow
   accumulation zones have risen in elevation as the 20th century
   progressed. During the period 1971–75, Ivory Glacier receded 30 m
   (98 ft) at the glacial terminus, and 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. 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 continuing to expand.

   Several glaciers, notably the much visited Fox and Franz Josef Glaciers
   in New Zealand, have periodically advanced, especially during the
   1990s, but the scale of these advances is small when compared to
   20th-century retreat. These large, rapidly flowing glaciers situated on
   steep slopes have been very reactive to small mass-balance changes. A
   few years of conditions favorable to glacier advance, such as increased
   snowfall and cooler temperatures, are rapidly echoed in a corresponding
   advance, followed by equally rapid retreat when those favorable
   conditions end.^ The glaciers that have been advancing in a few
   locations in New Zealand have been doing so due to a temporary weather
   change associated with El Niño, which has brought more precipitation
   and cloudier, cooler summers since 2002.^

Western hemisphere

   The Lewis Glacier, North Cascades National Park after melting away in
   1990
   Enlarge
   The Lewis Glacier, North Cascades National Park after melting away in
   1990

   North American glaciers are primarily located along the spine of the
   Rocky Mountains in the United States and Canada, and the 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 such as Taku
   Glacier, 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. The observed retreat rate has
   increased rapidly since approximately 1980, and overall each decade
   since has seen greater rates of retreat than the preceding one. There
   are also small remnant glaciers scattered throughout the Sierra Nevada
   mountains of California and Nevada.

   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, approximating some 870,000 m³
   (1,140,000 yd³).
   The Boulder Glacier retreated 450 m from 1987 to 2005.
   Enlarge
   The Boulder Glacier retreated 450 m from 1987 to 2005.
   The Easton Glacier retreated 255 m from 1990 to 2005.
   Enlarge
   The Easton Glacier retreated 255 m from 1990 to 2005.

   As recently as 1975, many North Cascade glaciers were advancing due to
   cooler weather and increased precipitation that 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-1970s. Between 1984 and 2005, the North Cascade glaciers lost an
   average of more than 12.5 m in thickness and between 20% and 40% of
   their volume.^

   Glaciologists researching the North Cascades glaciers have found that
   all 47 monitored glaciers are receding and that four glaciers—Spider
   Glacier, Lewis Glacier (pictured), Milk Lake Glacier, and David
   Glacier—have disappeared completely since 1985. 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 barren
   terrain behind. This retreat has occurred during a period of reduced
   winter snowfall and higher summer temperatures. In this region of the
   Cascades, winter snowpack has declined 25% since 1946, and summer
   temperatures have risen 0.7  °C (1.2  °F) during the same period. The
   reduced snowpack has occurred despite a small increase in winter
   precipitation; thus, it reflects warmer winter temperatures leading to
   rainfall and melting on glaciers even during the winter. As of 2005,
   67% of the North Cascade glaciers observed are in disequilibrium and
   will not survive the continuation of the present climate. These
   glaciers will eventually disappear unless temperatures fall and frozen
   precipitation increases. The remaining glaciers are expected to
   stabilize, unless the climate continues to warm, but will be much
   reduced in size.^^

   On the sheltered slopes of the highest peaks of Glacier National Park
   in Montana, 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 for decades. Comparing photographs taken in the
   mid-19th century with contemporary images provides ample evidence that
   the glaciers in the park have retreated notably since 1850. Repeat
   photography over the decades since clearly show that glaciers
   throughout the park such as Grinnell Glacier are all retreating. The
   larger glaciers are now approximately a third of their former 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 covered by 1993. ^Researchers
   believe that by the year 2030, the vast majority of glacial ice in
   Glacier National Park will be gone unless current climate patterns
   reverse their course.^ Grinnell Glacier is just one of many glaciers in
   Glacier National Park that have been well documented by photographs for
   many decades. The photographs below clearly demonstrate the retreat of
   this glacier since 1938.


   1938 T.J. Hileman GNP 1981 Carl Key (USGS) 1998 Dan Fagre (USGS) 2005
   Blase Reardon (USGS)

   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, located
   slightly southwest of Grand Teton, one of the more easily reached
   glaciers in the park, is expected to disappear by 2025.^ 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 during that period. Photographs
   indicate that the glaciers today are only half the size as when first
   photographed in the late 1890s. Research also indicates that the
   glacial retreat was proportionately greater in the 1990s than in any
   other decade over 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 climate patterns
   continue.^
   Fast-melting toe of the Athabasca Glacier, 2005
   Enlarge
   Fast-melting toe of the Athabasca Glacier, 2005
   The Athabasca Glacier in the Columbia Icefield of the Canadian Rockies,
   has retreated 1,500 m in the last century. Also recent animation.
   Enlarge
   The Athabasca Glacier in the Columbia Icefield of the Canadian Rockies,
   has retreated 1,500 m in the last century. Also recent animation.
   Valdez Glacier has thinned 90 m (300 ft) over the last century and the
   barren ground near the glacial margins have been exposed due to the
   glacier thinning and retreating over the last two decades of the 20th
   century.
   Enlarge
   Valdez Glacier has thinned 90 m (300 ft) over the last century and the
   barren ground near the glacial margins have been exposed due to the
   glacier thinning and retreating over the last two decades of the 20th
   century.

   In the Canadian Rockies, the glaciers are generally larger and more
   widespread than they are to the south in Montana. One of the more
   accessible glaciers in the Canadian Rockies is the Athabasca Glacier,
   which is an outlet glacier of the 325 km² (125 miles²) Columbia
   Icefield. The Athabasca Glacier has retreated 1500 m (4,921 ft) since
   the late 19th century. The rate of retreat for this glacier has
   increased since 1980, following a period of slow retreat from 1950 to
   1980. The Peyto Glacier in Alberta covers an area of about 12 km²
   (4.63 miles²), and retreated rapidly during the first half of the 20th
   century, stabilized by 1966, and resumed shrinking in 1976.^
   Illecillewaet Glacier in British Columbia's Glacier National Park
   (Canada) has retreated 2 km (1.25 miles) since first photographed in
   1887.

   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 (9.3 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 the
   icebergs. The Valdez Glacier 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 2,000
   glaciers observed, 99% are retreating." ^Icy Bay in Alaska is fed by
   three large glaciers—Guyot, Yahtse, and Tyndall Glaciers—all of which
   have experienced a loss in length and thickness and, consequently, a
   loss in area. Tyndall Glacier became separated from the retreating
   Guyot Glacier in the 1960s and has retreated 24 km (14.9 miles) since,
   averaging more than 500 m (1,640 ft) per year.^

   The Juneau Icefield Research Program has monitored the outlet glaciers
   of the Juneau Icefield since 1946. On the west side of the ice field,
   the terminus of the Mendenhall Glacier, which flows into suburban
   Juneau, Alaska, has retreated 580 m (1,902 ft). Numerous other glaciers
   in the immediate vicinity are also mostly in a state of general
   retreat. Herbert, Eagle, Norris, East Twin and West Twin glaciers have
   all retreated from 570 m (1,879 ft) to 1,740 m (1.08 miles) since 1946.
   Of the glaciers in this region, only the Taku Glacier has advanced.
   Taku Glacier has been advancing since at least 1890, when naturalist
   John Muir observed a large iceberg calving front. By 1948 the adjacent
   fjord had filled in, and the glacier no longer calved 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 averaged 17 m (55 ft) per year between 1988 and 2005. The mass
   balance was very positive for the 1946–88 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.^

   Long-term mass balance records from Lemon Creek Glacier in Alaska show
   slightly declining mass balance with time.^ The mean annual balance for
   this glacier was −0.23 m (−0.75 ft) each year during the period of 1957
   to 1976. Mean annual balance has been increasingly negatively averaging
   −1.04 m (−3.4 ft) per year from 1990 to 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] per year) and 1995 to 2001 (1.8 m
   [5.9 ft] per year).^ This is a systemic trend with loss in mass
   equating to 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
   has been retreating 24 m (78 ft) per year and the Cantwell Glacier 10 m
   (32 ft) per year.^ Well documented in Alaska are surging glaciers that
   have been known to rapidly advance, even as much as 100 m (333 ft) per
   day, though the reasons they do this is not fully understood.
   ^Varigated, Black Rapids, Muldrow, Susitna and Yanert are examples of
   surging glaciers in Alaska that have made rapid advances in the past.
   These glaciers are all retreating overall, punctuated by short periods
   of advance.

   A large region of population surrounding the central and southern Andes
   of Argentina and Chile reside in arid areas that are dependent on water
   supplies from melting glaciers. The water from the glaciers also
   supplies rivers that have in some cases been dammed for hydroelectric
   power. Some researchers believe that by 2030, many of the large ice
   caps on the highest Andes will be gone if current climate trends
   continue. In Patagonia on the southern tip of the continent, the large
   ice caps have retreated a full kilometer (0.6 miles) 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 in
   any other region in the world.^ The Northern Patagonian Ice Field lost
   93 km² (35 miles²) of glacier area during the years between 1945 and
   1975, and 174 km² (67 miles²) from 1975 to 1996, which indicates that
   the rate of retreat is increasing. The Southern Patagonia Ice Sheet has
   exhibited a general trend of retreat on 42 glaciers, while four
   glaciers were in equilibrium and two advanced during the years between
   1944 and 1986. The largest retreat was on Glacier O’Higgins, which
   during the period 1896–1995 retreated 14.6 km (9 miles). The Perito
   Moreno Glacier is 30 km (18 mile) long and is a major outflow glacier
   of the Patagonian ice sheet, as well as the most visited glacier in
   Patagonia. Perito Moreno Glacier is presently in equilibrium, but has
   undergone frequent oscillations in the period 1947–96, with a net gain
   of 4.1 km (2.5 miles). This glacier has advanced since 1947, and has
   been essentially stable since 1992. Perito Moreno Glacier is one of
   three glaciers in Patagonia known to have advanced, compared to several
   hundred others in retreat.^^

Polar regions

   Despite their proximity and importance to human populations, the
   mountain and valley glaciers of tropical and mid-latitude glaciers
   amount to only a small fraction of glacial ice on the Earth. About 99%
   of all freshwater ice 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 much of 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.

   The northern Atlantic island nation of Iceland is home to the
   Vatnajökull, which is the largest ice cap in Europe. The
   Breiðamerkurjökull Glacier is one of the Vatnajökull outlet glaciers,
   and had 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, but by 2004 Breiðamerkurjökull's terminus had
   retreated three kilometers (1.86 miles) further inland. This glacier
   retreat exposed a rapidly expanding lagoon that is filled with icebergs
   calved from its front. The lagoon is 110 m (360 ft) deep and nearly
   doubled its size between 1994 and 2004. All but one of the Vatnajökull
   outlet glaciers, roughly 40 named glaciers in all, were receding as of
   2000.^ In Iceland, of 34 glaciers studied between 1995 and 2000, 28
   were found to be retreating, four were stable and two were advancing.^
   Bylot Ice Cap on Bylot Island, one of the Canadian Arctic islands, 14
   August 1975 (USGS)
   Enlarge
   Bylot Ice Cap on Bylot Island, one of the Canadian Arctic islands, 14
   August 1975 (USGS)

   The Canadian Arctic islands have a number of substantial ice caps,
   including 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) per year in
   the lower elevations from 1995 to 2000. Overall, between 1995 and 2000,
   ice caps in the Canadian Arctic lost 25 km³ (6 miles³) of ice per
   year.^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 (0.6–1.8 miles)
   since 1960.^ On the Hazen Plateau of Ellesmere Island, the Simmon Ice
   Cap has lost 47% of its area since 1959.^ If the current climatic
   conditions continue, the remaining glacial ice on the Hazen Plateau
   will be gone around 2050.

   Arctic islands north of Norway, Finland and Russia have all shown
   evidence of glacier retreat. In the Svalbard archipelago, the island of
   Spitsbergen has numerous glaciers. Research indicates that Hansbreen
   Glacier on Spitsbergen retreated 1.4 km (0.87 miles) from 1936 to 1982
   and another 400 m (1,312 ft) during the 16-year period from 1982 to
   1998.^ Blomstrandbreen, a glacier in the King's Bay area of
   Spitsbergen, has retreated approximately 2 km (1.24 miles) in the past
   80 years. Since 1960 the average retreat of Blomstrandbreen has been
   about 35 m (114 ft) a year, and this average was enhanced due to an
   accelerated rate of retreat since 1995.^ Similarly, the Midre
   Lovenbreen Glacier retreated 200 m (656 ft) between 1977 and 1995.^ In
   the Novaya Zemlya archipelago north of Russia, research indicates that
   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.^

   In Greenland, glacier retreat has been observed in 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. The period
   since 2000 has brought retreat to several very large glaciers that had
   long been stable. Three glaciers that have been researched—Helheim
   Glacier, Kangerdlugssuaq Glacier, and Jakobshavn Isbræs—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 had
   remained in the same place for decades. In 2001 the glacier began
   retreating rapidly, and by 2005 the glacier had retreated a total of
   7.2 km (4.5 miles), accelerating from 21.33 m (70 ft) per day to 33.5 m
   (110 ft) per day during that period.^

   Jakobshavn Isbræ in west Greenland, a major outlet glacier of the
   Greenland Ice Sheet, is the fastest moving glacier in the world over
   the past half century. It had been moving continuously at speeds of
   over 24 m (78 ft) per day with a stable terminus since at least 1950.
   In 2002, the 12 km (7.5 mile) long floating terminus of the glacier
   entered a phase of rapid retreat, with the ice front breaking up and
   the floating terminus disintegrating and accelerating to a retreat rate
   of over 30 m (98 ft) per day. On a shorter timescale, portions of the
   main trunk of Kangerdlugssuaq Glacier that were flowing at 15 m (49 ft)
   per day from 1988 to 2001 were measured to be flowing at 40 m (131 ft)
   per day in the summer of 2005. Not only has Kangerdlugssuaq retreated,
   it has also thinned by more than 100 m (328 ft).^

   The rapid thinning, acceleration and retreat of Helheim, Jakobshavns
   and Kangerdlugssuaq glaciers in Greenland, all 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.^
   The collapsing Larsen B Ice Shelf in Antarctica is similar in area to
   the U.S. state of Rhode Island.
   Enlarge
   The collapsing Larsen B Ice Shelf in Antarctica is similar in area to
   the U.S. state of Rhode Island.

   The climate of Antarctica is one of intense cold and great aridity.
   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
   glacier retreat on the continent is the loss of large sections of the
   Larsen Ice Shelf on the Antarctic Peninsula. Ice shelves are not stable
   when surface melting occurs, and the collapse of Larsen Ice Shelf has
   been caused by warmer melt season temperatures that have led to surface
   melting and the formation of shallow ponds of water on the ice shelf.
   The Larsen Ice Shelf lost 2,500 km² (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.^ Recent studies
   by the British Antarctic Survey have anticipated a potential breakup of
   the George VI Ice Shelf due to warming ocean currents resulting from
   global warming.^

   Pine Island Glacier, an Antarctic outflow glacier that flows into the
   Amundsen Sea, thinned 3.5 ± 0.9 m (11.5 ± 3 ft) per year and retreated
   a total of 5 km (3.1 miles) in 3.8 years. The terminus of the Pine
   Island Glacier is a floating ice shelf, and the point at which it is
   afloat is retreating 1.2 km (0.74 miles) per 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.^ This same
   pattern of thinning and accelerated retreat is evident on the
   neighboring Thwaites Glacier. Additionally, the Dakshin Gangotri
   Glacier, a small outlet glacier of the Antarctic ice sheet, receded at
   an average rate of 0.7 m (2.2 ft) per year from 1983 to 2002. On the
   Antarctic Peninsula, which is the only section of Antarctica that
   extends well north of the Antarctic Circle, there are hundreds of
   retreating glaciers. In one study of 244 glaciers on the peninsula, 212
   have retreated an average of 600 m (1,968 ft) from where they were when
   first measured in 1953.^ The greatest retreat was seen in Sjogren
   Glacier, which is now 13 km (8 miles) further inland than where it was
   in 1953. There are 32 glaciers that were measured to have advanced;
   however, these glaciers showed only a modest advance averaging 300
   meters (984 ft) per glacier, which is significantly smaller than the
   massive retreat observed.^

Impacts of glacier retreat

   The continued retreat of glaciers will have a number of different
   quantitative impacts. 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 eventually deplete the glacial
   ice and substantially reduce or eliminate runoff. A reduction in runoff
   will affect the ability to irrigate crops and will reduce summer stream
   flows necessary to 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.^
   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 important for hydropower.

   Some of this retreat has resulted in efforts to slow down the loss of
   glaciers in the Alps. To retard melting of the glaciers used by certain
   Austrian ski resorts, portions of the Stubai and Pitztal Glaciers were
   covered with plastic. In Switzerland plastic sheeting is also used to
   reduce the melt of glacial ice used as ski slopes.^ While covering
   glaciers with plastic sheeting may prove advantageous to ski resorts on
   a small scale, this practice is not expected to be economically
   practical on a much larger scale.

   Many species of freshwater and saltwater plants and animals are
   dependent on glacier-fed waters to ensure the cold water habitat to
   which they have adapted. Some species of freshwater fish need cold
   water to survive and to reproduce, and this is especially true with
   salmon and cutthroat trout. Reduced glacial runoff can lead to
   insufficient stream flow to allow these species to thrive. Alterations
   to the ocean currents, due to increased freshwater inputs from glacier
   melt, and the potential alterations to thermohaline circulation of the
   worlds oceans, may impact existing fisheries upon which humans depend
   as well.

   The potential for major sea level rise depends mostly on a significant
   melting of the polar ice caps of Greenland and Antarctica, as this is
   where the vast majority of glacial ice is located. The British
   Antarctic Survey has determined from climate modeling that for at least
   the next 50 years, snowfall on the continent of Antarctica should
   continue to exceed glacial losses from global warming. The amount of
   glacial loss on the continent of Antarctica is not increasing
   significantly, and it is not known if the continent will experience a
   warming or a cooling trend, although the Antarctic Peninsula has warmed
   in recent years, causing glacier retreat in that region.^ If all the
   ice on the polar ice caps were to melt away, the oceans of the world
   would rise an estimated 70 m (229 ft). However, with little major melt
   expected in Antarctica, sea level rise of not more than 0.5 m (1.6 ft)
   is expected through the 21st century, with an average annual rise of
   0.004 m (0.013 ft) per year. Thermal expansion of the world's oceans
   will contribute, independent of glacial melt, enough to double those
   figures.^

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.: Fluctuations of Glaciers 1995–2000,
       Vol. VIII. Paris: World Glacier Monitoring Service.
     * 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.
     * Pelto, M.S. and Hedlund, C. (2001). "The terminus behaviour and
       response time of North Cascade glaciers". Journal of Glaciology 47:
       497–506.


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