melting of glaciers

The retreat of glaciers since 1850 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. Deglaciation occurs naturally at the end of ice ages, but glaciologists find the current glacier retreat is accelerated by the measured increase of atmospheric greenhouse gases—an effect of climate change. Mid-latitude mountain ranges such as the Himalayas, Rockies, Alps, Cascades, Southern Alps, and the southern Andes, as well as isolated tropical summits such as Mount Kilimanjaro in Africa, are showing some of the largest proportionate glacial losses. Excluding peripheral glaciers of ice sheets, the total cumulated global glacial losses over the 26 year period from 1993–2018 were likely 5500 gigatons, or 210 gigatons per yr.Fox-Kemper, B., H.T. Hewitt, C. Xiao, G. Aðalgeirsdóttir, S.S. Drijfhout, T.L. Edwards, N.R. Golledge, M. Hemer, R.E. Kopp, G.  Krinner, A. Mix, D. Notz, S. Nowicki, I.S. Nurhati, L. Ruiz, J.-B. Sallée, A.B.A. Slangen, and Y. Yu, 2021
Ocean, Cryosphere and Sea Level Change
I
Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change
[Masson-Delmotte, V., P. Zhai, A. Pirani, S.L.  Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1211–1362, doi:10.1017/9781009157896.011.

The retreat of mountain glaciers, notably in western North America, Asia, the Alps and tropical and subtropical regions of South America, Africa and Indonesia, provide evidence for the rise in global temperatures since the late 19th century. The acceleration of the rate of retreat since 1995 of key outlet glaciers of the Greenland and West Antarctic ice sheets may foreshadow a rise in sea level, which would affect coastal regions.

Glacier mass balance is the key determinant of the health of a glacier. If the amount of frozen precipitation in the accumulation zone exceeds the quantity of glacial ice lost due to melting or in the ablation zone a glacier will advance; if the accumulation is less than the ablation, the glacier will retreat. Glaciers in retreat will have negative mass balances, and if they do not find an equilibrium between accumulation and ablation, will eventually disappear.

The Little Ice Age was a period from about 1550 to 1850 when certain regions experienced relatively cooler temperatures compared to the time before and after. Subsequently, until about 1940, glaciers around the world retreated as the climate warmed substantially. Glacial retreat slowed and even reversed temporarily, in many cases, between 1950 and 1980 as global temperatures cooled slightly. Since 1980, climate change has led to glacier retreat becoming increasingly rapid and ubiquitous, so much so that some glaciers have disappeared altogether, and the existence of many of the remaining glaciers is threatened. In locations such as the Andes and Himalayas, the demise of glaciers has the potential to affect water supplies.

Causes

The mass balance, or difference between accumulation and ablation (melting and sublimation), of a glacier is crucial to its survival. Climate change may cause variations in both temperature and snowfall, resulting in changes in mass balance. A glacier with a sustained negative balance loses equilibrium and retreats. A sustained positive balance is also out of equilibrium and will advance to reestablish equilibrium. Currently, nearly all glaciers have a negative mass balance and are retreating.

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 decreases overall ablation, thereby increasing mass balance and potentially reestablishing equilibrium. 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.

For example, Easton Glacier in Washington state, U.S. 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 in Montana, U.S. 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 range are most likely to fall into disequilibrium with the climate.

Measurements

Methods for measuring retreat include staking terminus location, global positioning mapping, aerial mapping and laser altimetry. The key symptom of disequilibrium is thinning along the entire length of the glacier. This indicates a diminishment of the accumulation zone. The result is marginal recession of the accumulation zone margin, not just of the terminus. In effect, the glacier no longer has a consistent accumulation zone and without an accumulation zone cannot survive.

Estimated glacial losses

Excluding peripheral glaciers of ice sheets, the total cumulated global glacial losses over the 26 year period from 1993–2018 were likely 5500 gigatons, or 210 gigatons per yr.

Effects

Water supply

The continued retreat of glaciers will have a number of different quantitative effects. 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.

Ecosystems

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 oceans, may affect existing fisheries upon which humans depend as well.

Floods

One major concern is the increased risk of Glacial Lake Outburst Floods (GLOF), which have in the past had great effect on lives and property. Glacier meltwater left behind by the retreating glacier is often held back by moraines that can be unstable and have been known to collapse if breached or displaced by earthquakes, landslides or avalanches. If the terminal moraine is not strong enough to hold the rising water behind it, it can burst, leading to a massive localized flood. The likelihood of such events is rising 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 of water from the lake of the Tête Rousse Glacier, resulting in the deaths of 200 people in the French town of Saint-Gervais-les-Bains. 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.

Sea level rise

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. If all the ice on the polar ice caps were to melt away, the oceans of the world would rise an estimated . Although previously it was thought that the polar ice caps were not contributing heavily to sea level rise (IPCC 2007), recent studies have confirmed that both Antarctica and Greenland are contributing a year each to global sea level rise. The Thwaites Glacier alone, in Western Antarctica is "currently responsible for approximately 4 percent of global sea level rise. It holds enough ice to raise the world ocean a little over 2 feet (65 centimeters) and backstops neighboring glaciers that would raise sea levels an additional 8 feet (2.4 meters) if all the ice were lost." The fact that the IPCC estimates did not include rapid ice sheet decay into their sea level predictions makes it difficult to ascertain a plausible estimate for sea level rise but a 2008 study found that the minimum sea level rise will be around by 2100.

Management approaches

To retard melting of the glaciers used by certain Austrian ski resorts, portions of the Stubai and Pitztal Glaciers were partially 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.

Middle latitude

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

Northern hemisphere – Eurasia

Europe

In the French alps, all the glaciers there are retreating. On Mont Blanc, the highest peak in the Alps, the Argentière Glacier has receded since 1870. Other Mont Blanc glaciers have also been in retreat, including the Mer de Glace, which is the largest glacier in France at in length but retreated between 1994 and 2008. The glacier has retreated since the end of the Little Ice Age. The Argentière and Mer de Glace glaciers are expected to disappear completely by end of the 21st century if current climate trends persist. The Bossons Glacier once extended from the summit of Mont Blanc at to an elevation of in 1900. By 2008 Bossons Glacier had retreated to a point that was above sea level.

Other researchers have found that glaciers across the Alps appear to be retreating at a faster rate than a few decades ago. In a paper published in 2009 by the University of Zurich, the Swiss glacier survey of 89 glaciers found 76 retreating, 5 stationary and 8 advancing from where they had been in 1973. The Trift Glacier had the greatest recorded retreat, losing of its length between the years 2003 and 2005. The Grosser Aletsch Glacier is the largest glacier in Switzerland and has been studied since the late 19th century. Aletsch Glacier retreated from 1880 to 2009. This rate of retreat has also increased since 1980, with 30%, or , of the total retreat occurring in the last 20% of the time period.

The Morteratsch Glacier in Switzerland has had one of the longest periods of scientific study with yearly measurements of the glacier's length commencing in 1878. The overall retreat from 1878 to 1998 has been with a mean annual retreat rate of approximately per year. This long-term average was markedly surpassed in recent years with the glacier receding per year during the period between 1999 and 2005. 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. In 2005, the Italian Glacier Commission found that 123 glaciers in Lombardy were retreating. A random study of the Sforzellina Glacier in the Italian Alps indicated that the rate of retreat from 2002 to 2006 was much higher than in the preceding 35 years. To study glaciers located in the alpine regions of Lombardy, researchers compared a series of aerial and ground images taken from the 1950s through the early 21st century and deduced that between the years 1954–2003 the mostly smaller glaciers found there lost more than half of their area. Repeat photography of glaciers in the Alps indicates that there has been significant retreat since studies commenced.

Research, published in 2019 by ETH Zurich, says that two-thirds of the ice in the glaciers of the Alps is doomed to melt by the end of the century due to climate change. In the most pessimistic scenario, the Alps will be almost completely ice-free by 2100, with only isolated ice patches remaining at high elevation.

Though the glaciers of the Alps have received more attention from glaciologists than in other areas of Europe, research indicates that glaciers in northern Europe are also retreating. Since the end of World War II, Storglaciären in Sweden has undergone the longest continuous mass balance study in the world conducted from the Tarfala research station. 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. In Norway, glacier studies have been performed since the early 19th century, with systematic surveys undertaken regularly since the 1990s. Inland glaciers have had a generally negative mass balance, whereby during the 1990s, maritime glaciers showed a positive mass balance and advanced. The maritime advances have been attributed to heavy snowfall in the period 1989–1995. However, reduced snowfall since has caused most Norwegian glaciers to retreat significantly. A survey of 31 Norwegian glaciers in 2010 indicated that 27 were in retreat, one had no change and three advanced. Similarly, in 2013, of 33 Norwegian glaciers surveyed, 26 were retreating, four showed no change and three advanced.

Engabreen Glacier in Norway, an outlet glacier of the Svartisen ice cap, had several advances in the 20th century, though it retreated between 1999 and 2014. Brenndalsbreen glacier retreated between the years 2000 and 2014, while the Rembesdalsskåka glacier, which has retreated since the end of the Little Ice Age, retreated between 1997 and 2007. The Briksdalsbreen glacier retreated between 1996 and 2004 with of that in the last year of that study; the greatest annual retreat recorded on that glacier since studies began there in 1900. This figure was exceeded in 2006 with five glaciers retreating over from the fall of 2005 to the fall of 2006. Four outlets from the Jostedalsbreen ice cap, the largest body of ice in continental Europe, Kjenndalsbreen, Brenndalsbreen, Briksdalsbreen and Bergsetbreen had a frontal retreat of more than . Overall, from 1999 to 2005, Briksdalsbreen retreated . Gråfjellsbrea, an outlet glacier of the Folgefonna ice cap, had a retreat of almost .

In the Spanish Pyrenees, recent studies have shown important losses in extent and volume of the glaciers of the Maladeta massif during the period 1981–2005. These include a reduction in area of 35.7%, from to , a loss in total ice volume of and an increase in the mean altitude of the glacial termini of . For the Pyrenees as a whole 50–60% of the glaciated area has been lost since 1991. The Balaitus, Perdigurero and La Munia glaciers have disappeared in this period. Monte Perdido Glacier has shrunk from 90 hectares to 40 hectares.

As initial cause for glacier retreat in the alps since 1850, a decrease of the glaciers' albedo, caused by industrial black carbon can be identified. According to a report, this may have accelerated the retreat of glaciers in Europe which otherwise might have continued to expand until approximately the year 1910.

West Asia

All the glaciers in Turkey are in retreat and glaciers have been developing proglacial lakes at their terminal ends as the glaciers thin and retreat. Between the 1970s and 2013, the glaciers in Turkey lost half their area, going from in the 1970s to in 2013. Of the 14 glaciers studied, five had disappeared altogether. Mount Ararat has the largest glacier in Turkey, and that is forecast to be completely gone by 2065.

Siberia and the Russian Far East

Siberia is typically classified as a polar region, owing to the dryness of the winter climate and has glaciers only in the high Altai Mountains, Verkhoyansk Range, Cherskiy Range and Suntar-Khayata Range, plus possibly a few very small glaciers in the ranges near Lake Baikal, which have never been monitored and may have completely disappeared since 1989. Between the years 1952 and 2006, the glaciers found in the Aktru Basin region shrank by 7.2 percent. This shrinkage has been primarily in the ablation zone of the glaciers, with recession of several hundred meters being observed for some glaciers. The Altai region has also experienced an overall temperature increase of 1.2 degrees Celsius in the last 120 years according to a report from 2006, with most of that increase occurring since the late 20th century.

In the more maritime and generally wetter Russian Far East, Kamchatka, exposed during winter to moisture from the Aleutian Low, has much more extensive glaciation totaling around with 448 known glaciers as of 2010. Despite generally heavy winter snowfall and cool summer temperatures, the high summer rainfall of the more southerly Kuril Islands and Sakhalin in historic times melt rates have been too high for a positive mass balance even on the highest peaks. In the Chukotskiy Peninsula small alpine glaciers are numerous, but the extent of glaciation, though larger than further west, is much smaller than in Kamchatka, totaling around .

Details on the retreat of Siberian and Russian Far East glaciers have been less adequate than in most other glaciated areas of the world. There are several reasons for this, the principal one being that since the collapse of Communism there has been a large reduction in the number of monitoring stations. Another factor is that in the Verkhoyansk and Cherskiy Ranges it was thought glaciers were absent before they were discovered during the 1940s, whilst in ultra-remote Kamchatka and Chukotka, although the existence of glaciers was known earlier, monitoring of their size dates back no earlier than the end of World War II. Nonetheless, available records do indicate a general retreat of all glaciers in the Altai Mountains with the exception of volcanic glaciers in Kamchatka. Sakha's glaciers, totaling seventy square kilometers, have shrunk by around 28 percent since 1945 reaching several percent annually in some places, whilst in the Altai and Chukotkan mountains and non-volcanic areas of Kamchatka, the shrinkage is considerably larger.

Himalayas and Central Asia

The Himalayas and other mountain chains of central Asia support large glaciated regions. An estimated 15,000 glaciers can be found in the greater Himalayas, with double that number in the Hindu Kush and Karakoram and Tien Shan ranges, and comprise the largest glaciated region outside the poles. These glaciers provide critical water supplies to arid countries such as Mongolia, western China, Pakistan, Afghanistan and India. As with glaciers worldwide, those of the greater Himalayan region are experiencing a decline in mass, and researchers claim that between the early 1970s and early 2000s, there had been a 9 percent reduction in ice mass, while there has been a significant increase in mass loss since the Little Ice Age with a 10-fold increase when compared to rates seen currently. Change in temperature has led to melting and the formation and expansion of glacial lakes which could cause an increase in the number of glacial lake outburst floods (GLOFs). If the present trends persist the ice mass will gradually be reduced, and will affect the availability of water resources, though water loss is not expected to cause problems for many decades.

In the Wakhan Corridor of Afghanistan 28 of 30 glaciers examined retreated significantly between 1976 and 2003, with an average retreat of per year. One of these glaciers, the Zemestan Glacier, retreated during this period, not quite 10% of its length. 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 Rongbuk Glacier, draining the north side of Mount Everest into Tibet, has been retreating per year. In the Khumbu region of Nepal along the front of the main Himalaya of 15 glaciers examined from 1976 to 2007 all retreated significantly and the average retreat was per year. The most famous of these, the Khumbu Glacier, retreated at a rate of per year from 1976 to 2007. In India, the Gangotri Glacier retreated between the years 1936 and 1996 with of that retreat occurring in the last 25 years of the 20th century. However, the glacier is still over long. In Sikkim, 26 glaciers examined between the years 1976 and 2005 were retreating at an average rate of per year.
Overall, glaciers in the Greater Himalayan region that have been studied are retreating an average of between annually. The only region in the Greater Himalaya that has seen glacial advances is in the Karakoram Range and only in the highest elevation glaciers, but this has been attributed possibly increased precipitation as well as to the correlating glacial surges, where the glacier tongue advances due to pressure build up from snow and ice accumulation further up the glacier. Between the years 1997 and 2001, long Biafo Glacier thickened mid-glacier, however it did not advance.

With the retreat of glaciers in the Himalayas, a number of glacial lakes have been created. A growing concern is the potential for GLOFs researchers estimate 21 glacial lakes in Nepal and 24 in Bhutan pose hazards to human populations should their terminal moraines fail. One glacial lake identified as potentially hazardous is Bhutan's Raphstreng Tsho, which measured long, wide and deep in 1986. By 1995 the lake had swollen to a length of , in width and a depth of . 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 areas of that mountain range show that the glaciers that help supply water to this arid region, lost nearly 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.

The Pamirs mountain range located primarily in Tajikistan, has approximately eight thousand glaciers, many of which are in a general state of retreat. During the 20th century, the glaciers of Tajikistan lost of ice. The long Fedchenko Glacier, which is the largest in Tajikistan and the largest non-polar glacier on Earth, retreated between the years 1933 and 2006, and lost of its surface area due to shrinkage between the years 1966 and 2000. 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.

Northern hemisphere – North America

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. Apart from the few tidewater glaciers such as Taku Glacier, in the advance stage of their tidewater glacier cycle prevalent along the coast of Alaska, virtually all of those in North America are in a state of retreat. This rate has increased rapidly since around 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.

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 within the over 700 glaciers of the North Cascades, a portion of those located between the Canada–US border and I-90 in central Washington. These contain as much water as is found 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 .

As recently as 1975 many North Cascade glaciers were advancing due to cooler weather and increased precipitation that occurred from 1944 to 1976. By 1987 the North Cascade glaciers were retreating and the pace had increased each decade since the mid-1970s. Between 1984 and 2005 the North Cascade glaciers lost an average of more than in thickness and 20–40 percent of their volume.

Glaciologists researching the North Cascades found that all 47 monitored glaciers are receding while four glaciers— Spider Glacier, Lewis Glacier, Milk Lake Glacier and David Glacier—are almost completely gone. The White Chuck Glacier (near Glacier Peak) is a particularly dramatic example. The glacier area shrank from in 1958 to by 2002. Between 1850 and 1950, the Boulder Glacier on the southeast flank of Mount Baker retreated . William Long of the United States Forest Service observed the glacier beginning to advance due to cooler/wetter weather in 1953. This was followed by a advance by 1979. The glacier again retreated 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.

U.S. Rocky Mountains

On the sheltered slopes of the highest peaks of Glacier National Park in Montana, the eponymous glaciers are diminishing rapidly. The area of each glacier has been mapped for decades by the National Park Service and the U.S. Geological Survey. Comparing photographs from the mid-19th century with contemporary images provides ample evidence that they have retreated notably since 1850. Repeat photography since clearly show that glaciers 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 area of Glacier National Park covered by glaciers in 1850 remained covered by 1993. Researchers believe that between the year 2030 and 2080, that some 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.

File:Grinnell Glacier 1938.jpg, 1938 ''T.J. Hileman GNP''
File:Grinnell Glacier 1981.jpg, 1981 ''Carl Key (USGS)''
File:Grinnell Glacier 1998.jpg, 1998 ''Dan Fagre (USGS)''
File:Grinnell Glacier 2009.jpg, 2009 ''Lindsey Bengtson (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 is located slightly southwest of Grand Teton is one of the more easily reached glaciers in the park and it 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.

Canadian Rockies and Coast and Columbia Mountains

In the Canadian Rockies, glaciers are generally larger and more widespread than to the south in the Rocky Mountains. One of the more accessible in the Canadian Rockies is the Athabasca Glacier, which is an outlet glacier of the Columbia Icefield. The Athabasca Glacier has retreated since the late 19th century. Its rate of retreat has increased since 1980, following a period of slow retreat from 1950 to 1980. The Peyto Glacier in Alberta covers an area of about , and retreated rapidly during the first half of the 20th century, stabilized by 1966, and resumed shrinking in 1976.
The Illecillewaet Glacier in British Columbia's Glacier National Park (Canada), part of the Selkirk Mountains (west of the Rockies) has retreated since first photographed in 1887.

In Garibaldi Provincial Park in Southwestern British Columbia over , or 26%, of the park, was covered by glacier ice at the beginning of the 18th century. Ice cover decreased to by 1987–1988 and to by 2005, 50% of the 1850 area. The loss in the last 20 years coincides with negative mass balance in the region. During this period all nine glaciers examined have retreated significantly.

Alaska

There are thousands of glaciers in Alaska but only few have been named. The Columbia Glacier near Valdez in Prince William Sound retreated in the 25 years from 1980 to 2005. Its calved icebergs partially caused the Exxon Valdez oil spill, when the tanker changed course to avoid the ice tips. The Valdez Glacier is in the same area, and though it does not calve, 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

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