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Professional Paper 1386–A

Chapter A-2 (Figures 1–87)

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Figure 1.—Elements of the Earth’s Cryosphere. Graphics design by James Tomberlin, U.S. Geological Survey.
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Figure 2.—A, Geographic distribution of the principal glacierized regions (red) on Earth. Modified from Canadian Geographic (Shilts and others, 1998, figure on p. 52).
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Figure 2.—B, Schematic diagram of a glacierized area, delineating features of a glacier and its landscape. Modified from Müller and others (1977, p. 4, fig. 1).
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Figure 3.—Diagenetic facies on the Greenland ice sheet. Modified from Benson (1961).
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Figure 4.—Cross-sections of a glacier showing glacier facies at the end of the balance year. A, From glaciological field observations. B, From spectral-reflectance measurements from satellite sensors. Modified from Williams and others (1991). Schematic diagrams of glacier facies.
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Figure 4.—Cross-sections of a glacier showing glacier facies at the end of the balance year. C, Field-identifiable facies. D, Facies identifiable on satellite images. Modified from Williams and Hall (1993).
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Figure 5.—A, Types of glaciers, based on the glacier inventory of the U.S.S.R. Modified from Vinogradov (1966).
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Figure 5.—B, Diagrams showing variation in forms of glaciers in different basins and, C, frontal characteristics of glaciers. Modified from Müller and others (1977, p. 15–17, figs. 3a–3e and figs. 4a–4e).
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Figure 6.—Continental ice sheet. A, NOAA AVHRR image mosaic of the Antarctic ice sheet (http://terraweb.wr.usgs.gov/projects/Antarctica/AVHRR.html) used as the image base for the USGS Satellite Image Map of Antarctica (I-2560) (Ferrigno and others, 1996, 2000).
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Figure 6.—Continental ice sheet. B, NOAA-H AVHRR image of the Greenland ice sheet (for an extended caption, see Chapter C of “Satellite Image Atlas of Glaciers of the World,” p. C92, fig. 66).
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Figure 7.—Ice field. Landsat 7 ETM+ image of the Harding Icefield, Alaska (for an extended caption see Chapter K of “Satellite Image Atlas of Glaciers of the World,” p. K338, fig. 312).
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Figure 8.—Ice cap. Landsat 1 MSS false-color composite image of the Vatnajökull ice cap, Iceland, on 22 September 1973. Image no. 1426-12070 was enhanced digitally by the USGS Earth Resources Observation System (EROS) Digital Image Enhancement System (EDIES). See Sigurðsson and Williams (2008, p. 197, fig. 188).
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Figure 9.—Outlet glacier. Landsat 2 MSS false-color composite image of outlet glaciers flowing from the ice field on Bylot Island, Nunavut, Canada 
(for an extended caption, see Chapter J of “Satellite Image Atlas of Glaciers of the World,” its cover page and p. J173, fig. 3).
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Figure 10.—Valley glacier. Landsat 3 RBV image of valley glaciers, northwestern St. Elias Mountains, Alaska and Canada (for extended captions see Chapter K, and Chapter J of “Satellite Image Atlas of Glaciers of the World,” p. K191, fig. 175; and p. J306, fig. 3, respectively).
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Figure 11.—Mountain glacier. Landsat 5 TM image of cirque glaciers and valley glaciers in the Coast Mountains, Alaska (for an extended caption see Chapter K of “Satellite Image Atlas of Glaciers of the World,” p. K103, fig. 84).
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Figure 12.—Ice shelf. Landsat 1 MSS image of the Filchner Ice Shelf, Antarctica (for an extended caption see Chapter B of “Satellite Image Atlas of Glaciers of the World,” p. B103, fig. 76).
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Figure 13.—Sensitivity of ice caps and valley glaciers to changes in the equilibrium line altitude (ELA) in response to warmer climate as indicated in changes in areas of their respective accumulation and ablation areas.
Modified from Sugden and John (1976, p. 105, fig. 63).
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Figure 14.—Evolution of glacierization of a mountainous area from accumulation of snow and ice during a period of climate cooling. A, The lowering of equilibrium line altitude (ELA) and concomitant increase in the accumulation area results in the formation of mountain glaciers; B, The increase in amount of precipitation from orographic uplift of moist maritime air masses leads to the formation of a highland ice cap; C, An additional expansion of the glacier cover produces an ice sheet. Modified from Flint (1957, p. 317, fig. 18-4; 1971, figure on p. 598).
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Figure 15.—MODerate-resolution Imaging Spectroradiometer (MODIS) image of Île Kerguelen (Îles Kerguelen) on 4 March 2004. Cook Glacier (ice cap) and its outlet glaciers (12 named) are visible, as are glaciers (5 named) on three peninsulas: Presqu’ île de la Société de Géographie (north of Cook Glacier), Presqu’ île Rallier du Baty (southwest of Cook Glacier), and Presqu’ île Gallieni (southeast of Cook Glacier). NASA Aqua MODIS image. [http://visibleearth.nasa.gov; KerguelenIslands; File-Kerguelen. A2004064.0945.250m.jpg]
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Figure 16.—MODerate-resolution Imaging Spectroradiometer (MODIS) image of South Georgia Island on 15 July 2004. The island is completely covered with snow, masking the 43 percent of the island not covered with glaciers (see fig. 17). The A-38B tabular iceberg and associated smaller icebergs can be seen east of the island. The “parent” A-38 iceberg (140 km long, 40 km wide; Ferrigno and others, 2005) calved from the Ronne Ice Shelf, East-Antarctica in early October 1998, before breaking into two tabular icebergs (A-38A and A-38B) on 22 October 1998 (Ferrigno and others, 2005). During the 6-year interval between the initial calving event and the date of this MODIS image, the A-38B iceberg has been reduced from its original dimension to about 60 km long, 15 km wide. MODIS image from the Terra satellite of the National Aeronautics and Space Administration.  NASA Terra MODIS image at http://veimages.gsfc.nasa.gov/6835/SouthGeorgia.A2004197.1635.250m.jpg.
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Figure 17.Maps of the Glaciers of Kerguelen and of the Glaciers of South Georgia showing glaciers on the two subantarctic islands. Map plate from the American Geographical Society Glacier Studies (Mercer (1967, p. 325, Map 18.2©)).Used with permission of the American Geographical Society.
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Figure 18.—Wordie Ice Shelf map inset, part of “Coastal-change and Glaciological Map of the Larsen Ice Shelf area, Antarctica: 1940–2005.” Selected ice-front positions between 1947 and 2004 are shown, as well as named and unnamed glacial features. See Ferrigno and others (2008) for full map, map explanation, and accompanying pamphlet with tables. Named glacial features and numbered unnamed glacial features are listed in pamphlet and in tables 3 and 4, respectively. Average annual change of the ice front, calculated for the time intervals between years when measurements were made, is detailed in table 5A.
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Figure 19.—Maps of the Greenland ice sheet modeled for two warmer steady-state climates. A, +3°C, and B, +5°C. Snow accumulation was allowed to remain within the range of present-day distribution. Modified from Fabre and others (1995, p. 5, fig. 3).
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Figure 20.—Maximum area of summer melt on the surface of the Greenland ice sheet in 1992 and as of 2002. Modified from K. Steffan in Arctic Climate Impact Assessment (ACIA) (2004, p. 40; 2005, p. 205, fig. 618).
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Figure 21.—Percentage of ice-sheet melt derived from MODerate-resolution Imaging Spectroradiometer (MODIS) images and data on MASs CONcentration (mascon) derived from the Gravity Recovery and Climate Experiment (GRACE) for the entire Greenland ice sheet, for the 3-year trend July 2003 through July 2006. Signals from Earth and ocean tide and atmospheric mass have been removed. Modified from Hall and others (2008, p. 10, fig. 11).
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Figure 22.—A, Annual variations of the terminus of Sólheimajökull outlet glacier (blue), southern Iceland, and the mean summer (May–September) temperature (red) at the Stykkishólmur meteorological station, northwestern Iceland, 5-year running mean, 1930–2005. Modified from Sigurðsson (2006, p. 89, fig. 2). The vertical scale is adjusted to facilitate comparison.
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Figure 22.—B, Oblique aerial photograph of Sólheimajökull on 30 October 1985 by Oddur Sigurðsson, Icelandic Meteorological Office. (From the “Geographic Names of Iceland’s Glaciers: Historic and Modern” (Sigurðsson and Williams, 2008, cover page and p. 181, fig. 171)).
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Figure 23.—MODerate-resolution Imaging Spectroradiometer (MODIS) image on 2 October 2005 of the Northern Patagonian Ice Field, the Southern Patagonian Ice Field, the ice field of the Cordillera Darwin, outlet glaciers from each ice field, and other glaciers. Some of the glacially scoured “Finger Lakes” (south to north, Lago Argentino, Lago Viedma, and Lago San Martín) in the center of the image are “robin’s-egg-blue color”, the result of glacial rock-flour sediment entering the lakes. MODIS image from the Aqua satellite; Goddard Space Flight Center, National Aeronautics and Space Administration.
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Figure 24.—The margin of the Quelccaya Ice Cap, Perú, photographed from the same camera position on the ground in 1977 and in 2002 and a sequence of four photographs showing the recession of the Qori Kalis outlet glacier, Quelccaya Ice Cap, Perú, in 1978, 2002, 2005, and 2008.  Photographs by Lonnie G. Thompson, Byrd Polar Research Center, Ohio State University.
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Figure 25.—A, Extent of glaciers in the glacierized regions of the world, from the least glacierized (Irian Jaya, Indonesia, 7.5 km2) to the most glacierized (Canadian Arctic islands; 151,057 km2). The Antarctic and Greenland ice sheets were excluded from the original diagram; both ice sheets are added to this modified figure. At the same scale on which the bar graph for Svalbard reaches about 3 cm, a bar graph for the Antarctic ice sheet would have to be 10.45 m long and for the Greenland ice sheet 1.35 m long (see table 1).  The area of the Antarctic ice sheet contains 85.32 percent of the Earth’s glacierized area, and the area of the Greenland sheet contains 10.90 percent of Earth’s glacierized area; both ice sheets together contain 96.22 percent of the Earth’s glacierized area (see table 2). Only 3.78 percent of the area of the Earth’s glaciers are non-ice-sheet glaciers. Modified from Zemp and others (2007, p. 132–133, fig. 6B.11a).
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Figure 25.—B, Color-coded bar graphs showing decreasing glacierized areas in the main geographic regions. Changes in the area of the Antarctic ice sheet are seen primarily as retreat of ice shelves on the Antarctic Peninsula. Changes in the area of the Greenland ice sheet are seen as increased area of summer melt (water) on the surface of the ice sheet. Modified from Zemp and others (2007, p. 132–133, fig. 6B.11b).
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Figure 26.—Annual discharge rate of glacial meltwater emanating from rapidly melting ice sheets at the end of the Pleistocene Epoch and near the beginning of the Holocene Epoch, plotted against the annual rate of rise in eustatic sea level. The 230Th/234U-dated sea-level curve is shown with a solid line. The 14C-dated sea-level curve is shown by a dashed line; it is not corrected for changes in production of 14C. The meltwater pulse IB coincides with the 1,787 m δ18O anomaly in the ice core from the Dye 3 site in the Greenland ice sheet (10,720±150 years layer-counting calendar age) based on the 230Th/234U calendar chronology. The Younger Dryas chronozone is shown by a shaded pattern (see fig. 35). Modified from Fairbanks (1990, p. 943, fig. 3).
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Figure 27.—A, Climate “forecast” for the next 25,000 years. A CO2-induced “super-interglacial” at the end of the current interglacial may produce a much warmer climate, thereby delaying the natural onset of the next glacial. Modified from Imbrie and Imbrie (1979, p. 186, fig. 48).
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Figure 27.—B, Past, current, and projected global temperature from about 20,000 years before the present to 2100 C.E. Modified from data published by the World Health Organization, the World Meteorological Organization, and the United Nations Environment Programme in 2003 (McMichael and others, 2003) and data published by the International Panel on Climate Change (IPCC) (2007a).
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Figure 28.—Geologic time scale from the beginning of the Hadean Eon (4+ Ga) to the present, showing subdivisions into eons, eras, periods, and epochs. 
Age of start and ending of each interval is modified from Orndorff and others (2007).
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Figure 29.—Proxy temperatures [δ18O (‰)], climatic events, and tectonic events during the Cenozoic Era. A long-term trend of decreasing global temperatures
is apparent, along with a change from global “greenhouse” climate to global “icehouse” climate, resulting in increased glaciation, starting in the late Eocene. Modified from Zachos and others (2001, p. 688, fig. 2).
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Figure 30.—Schematic diagram of continental spreading from the Neoproterozoic Era to the present time (Cenozoic Era). The coalesced Rodinia supercontinent  (Neoproterozoic Era) was followed by the breakup of the Rodinia supercontinent during the middle Paleozoic Era, the recoalescence into the Pangea supercontinent (middle Paleozoic Era), and the subsequent breakup of the Pangea supercontinent into Gondwana in the southern Hemisphere and Laurasia in the Northern Hemisphere during the late Paleozoic Era. Subsequent fragmentation and continental drift produced the current configuration of the continents.
Modified from Servais and others (2009, p. 5, fig. 11B).
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Figure 31.—The great ocean conveyor belt of global ocean currents as described in Broecker (1991). Winds drive warm salty ocean currents in the global pattern of atmospheric circulation. Note that the flow of warm currents is relatively unimpeded in the Pacific Ocean. In the Atlantic Ocean, however, México and Central America block the westward flow, forcing the current northward (Gulf Stream). The cold currents in the polar regions are denser than warm equatorial waters, and therefore they sink, forming cold deep water. Atlantic deep water forms near Greenland, travels to Antarctica, adds cold salty water from Antarctica, and then continues into the Pacific Ocean. Modified from Intergovernmental Panel on Climate Change (IPCC) (1996, p. 271, fig. 2); after Broecker (1991).
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Figure 32.—Variations in the oxygen-isotope ratio of a marine sediment core showing the 100,000-year cycles of glacials and interglacials. The curves record the slow onset of glaciation and six intervals of rapid deglaciation at the end (“termination”) of each cycle. Modified from Imbrie and Imbrie (1979, p. 157, fig. 38).
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Figure 33.—Schematic diagram showing some of the changes in the Earth System during the transition between the end of the Pleistocene Epoch and the beginning of the Holocene Epoch. These changes decreased dust in the Earth’s atmosphere, whereas CO2 concentration and production of deep water in the North Atlantic Ocean increased. Elevation of the snow line (and therefore the glaciation limit) in mountain ranges increased, signifying the retreat of mountain glaciers, of ice caps, and of snowfields and the melting of continental ice sheets in North America, Eurasia, and South America. A sudden short interval of cooling is indicated by the Younger Dryas. Modified from Broecker and Denton (1990).
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Figure 34.—Temperature variations in the Summit ice core (Greenland ice sheet) during the last 35 kyr of the late Pleistocene and Holocene Epochs. The late Pleistocene was characterized by cold temperatures, interrupted by about 7 short Dansgaard-Oescher warm intervals. One Heinrich event (H3) is shown when an ice stream on the eastern margin of the Laurentide ice sheet surged. At the end of the Pleistocene, longer warm intervals occurred, including Bølling and Allerød. A final cold period, the Younger Dryas, occurred at the end of the Pleistocene near the beginning of the Holocene. The Holocene is a warm interval with less extreme variations in temperature after the Younger Dryas (see fig. 35). Modified from Ahn and Brook ( 2008, figure on p. 84). The original source is the Greenland Ice-Core Project (see also Kerr (1993, figure on p. 891)).
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Temperature variations during the late Pleistocene Epoch and near the beginning of the Holocene Epoch, determined as proxy temperatures from ice cores extracted from the central part of the Greenland ice sheet. Note the 1,000-year Younger Dryas cold interval (about 10 ka to 11 ka), the short Medieval Warm Interval (about 1100–1300 C.E.), and the Little Ice Age (about 1400–1880 C.E.). Modified from Alley (2000, p. 9, fig. 12).
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Figure 36.—Schematic diagram of glacier fluctuations worldwide during the last 7,000 years of the Holocene Epoch. Modified from Sugden and John (1976, p. 124, figure 6.17).
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Figure 37.—Geographic locations of sites where ice cores have been obtained by the ice-core paleoclimate research group at the Byrd Polar Research Center, The Ohio State University. PARCA, Program for Arctic Regional Climate Assessment.
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Figure 38.—A, Geographic location of ice cores used in the ice-core composite record. B, Northern Hemisphere temperature records. The ice-core reference period for B is 1961–1990. The blue line is a reconstruction of temperature from Jones and Mann (2004); the short red segment of the line depicts the meteorological observations compiled by Jones and Moberg (2003). C, Composite of decadal averages of the isotope δ18O from ice cores from the Andes Mountains and Tibetan Plateau during the past two millennia. The Z score is the standard deviation from its respective mean (Mosley-Thompson and others, 2006). The ice-core reference period for C is the 2,000 years preceding the 21st century.
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Figure 39.—Outlines of the Kilimanjaro Ice Fields in 1912, 1953, 1976, 1989, and 2000. The inset graph shows a least-squares regression line plot of the 5 discrete years of area calculations and the nearly linear (R2, the coefficient of determination, is 0.98) decrease in ice area from 1912 to 2000. The red dots on the map indicate locations of ice-core sites, three from the Northern Ice Field, one from the Furtwängler Glacier, and two from the Southern Ice Field. See also Young and Hastenrath (1991) and Hastenrath and Greischar (1997).
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Figure 40.—Photographic and cartographic history of the retreat of Qori Kalis, an outlet glacier from the Quelccaya Ice Cap, Perú, 1963–2002. Accompanying graph shows retreat of terminus during that period of time.
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Figure 41.—Late 20th-century status (retreat or advance) of selected high-mountain glaciers of the Earth’s cryosphere, the location of ice-core sites, and the contemporary location of important human activities.
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Figure 42.—Variation in global (eustatic) sea level during the Phanerozoic Eon. Modified from Servais and others (2009, p. 5, fig. 1 (c)).
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Figure 43.—Variation in global sea level during the last 100 Ma (light blue and purple lines), from the Late Cretaceous of the Mesozoic Era through the Cenozoic Era to the present time. The red line is a benthic foraminiferal δ18O synthesis; the purple line is for the interval 0 to 7 Ma. Note the fluctuating decline in sea level (light blue, 7 to 100 Ma) after the peak in the early Eocene. Modified from Miller and others (2005, p. 1,295, fig. 3).
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Figure 44.—Volume of glacier ice on land during the past 800,000 years. Modified from Alley (2000, p. 94, fig. 10.1).
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Figure 45.—Various estimates of changes in global sea level during the last 440,000 years: four glacial cycles of about 100,000 years each. Modified from IGBP Science No. 3 (Alverson and others, 2001, p. 7, fig. 1).
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Figure 46.—Tide-gauge observations from about 1870 to 2005. Note change in rate of rise in sea level, the result of steric increase in volume of a warmer ocean and from runoff of glacial meltwater. Modified from Church and White (2006).
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Figure 47.—Globally averaged rise in sea level from tide-gauge observations (black line) and from satellite altimetry data (from sensors on Topex/Poseidon and Jason-1 satellites) (red line). Modified from Bentley and others (2007, p. 156, fig. 6C.3); original source is Church and White (2006).
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Figure 48.—Estimated sources of global rise in sea level from 1993 through 2003, estimated from ocean thermal expansion
(steric rise) and as meltwater from non-ice-sheet glaciers and from the Greenland and Antarctic ice sheets (2.83±0.7 mm a-1).
Satellite data and tide-gauge observations indicate a higher mean rise (3.1±0.7 mm a-1) during the same period.
Modified from Bentley and others (2007, p. 157, fig. 6C.4).
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Figure 49.—Change in global sea level during three time periods: 1800 to 1870 (estimated), 1870 to 2007 (from the instrumental record), and 2007 to 2100 (projections into the future). Modified from Bindoff and others (2007, p. 409, FAQ 5.1, fig. 1).
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Figure 50.—Locations of glaciers for which glaciologists have produced mass-balance records.
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Figure 51.—Scatterplot showing the significant variability in annual mass balances of 18 selected glaciers with lengthy observational records: White Glacier, Canada; Devon NW (ice cap), Canada; Peyto Glacier, Canada; Blue Glacier, Washington; South Cascade Glacier, Washington; Gulkana Glacier, Alaska; Austre Brøggerbreen, Svalbard (Norway); Storbreen, Norway; Nigardsbreen, Norway; Storglaciären, Sweden; Griesgletscher, Switzerland; Vernagtferner, Austria; Sonnbliekgletscher, Austria; Maliy Aktru Glacier, Russia; Djankuat Glacier, Russia; Abramov Glacier, Kyrgyzstan; Ts. Tuyuksu Glacier, Kazakhstan; and Ürümqi S. No. 1 Glacier, China.
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Figure 52.—Cumulative mass balances of selected glacier systems compiled from individual time series showing differing changes over time until the beginning of the 21st century.
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Figure 53.—Cumulative mass balances calculated for large glacierized regions. For these calculations, we used the time series of mass balance for all glaciers—more than 300 from time to time and from 30 to 100 with multiyear records (see http://www.nsidc.org). We weighted the annual mass-balance data for individual glaciers by their surface area and then by the aggregate surface area of 49 primary glacier systems (20 of them are shown in fig. 52). By the end of the 1980s, and more clearly during the 1990s, these cumulative curves for large glacierized regions show a significant shift toward accelerated loss of mass.
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Figure 54.—A, Annual variability in global mass balance of glaciers and cumulative mass-balance values globally. B, Change in volume and variability computed for the worldwide system of mountain glaciers and subpolar ice caps, which has an aggregate area of 785,000 km2. The results of direct mass-balance observations on 300 glaciers worldwide are averaged by area of individual glaciers—49 primary systems, 13 larger regions, 7 continental-size regions, and globally—to construct the single global curve. Vertical bars on B are estimated standard errors.
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Figure 55.—Glacier contribution to rise in sea level from mountain glaciers and subpolar ice caps, which have an aggregate area of 785,000 km2. Observational data from figure 54 have been used to express change in glacier volume in terms of contribution to rise in sea level by dividing the change in glacier volume (mass balance), in cubic kilometers of water, by 362 x 106 km2, which is the surface area of the world oceans. Air-temperature data from the National Center for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR). At http://www.cdc.noaa.gov/cdc/reanalysis/reanalysis.shtm.
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Figure 56.—Malaspina Glacier, with an area of about 5,000 km2, is one of the two largest glaciers in Alaska. With annual losses averaging about 1 m of water equivalent, it and its neighbors are major contributors to current and future rise in sea level. These glaciers are so massive and so thick that their areas and volumes will not appreciably shrink during the 21st century. Painting by Mark F. Meier, 2004.
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Figure 57.—Time series of the Earth’s oblateness (J2). J2 is decreasing over a long term, due to tidal friction, postglacial rebound, and other effects; as J2 decreases, the speed of the Earth’s rotation is increasing in order to preserve angular momentum. Dickey and others (2002) suggest that the marked increase in J2 around 1998 might have been caused by the recent acceleration of glacier wastage. The offset green line represents the change in J2 due to changes in surface height of the Greenland and Antarctic ice sheets; the blue line represents the changes implied by uniform fluctuations in sea level; and the purple line represents the changes implied by spatially variable changes in sea level. These changes, however, do not account for the 1998 increase in J2. Modified from Cox and Chao (2002, p. 832, fig. 2). Figure courtesy of Science magazine. Used with permission.
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Figure 58.—The differences between reference mass balances (glacier area considered constant) and conventional mass balances (glacier area changing in time, per observations), calculated for the mass-time series of 33 Northern Hemisphere benchmark glaciers. This difference, expressed in percent, shows an increase during 35 years (1965–2000) and may be indirectly related to the increase in positive air-temperature anomalies (temperature anomalies are from Hansen and others, 1999).
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Figure 59.—Winter snow accumulation, <bw>, from benchmark glaciers (averaged for all available observations; see Dyurgerov, 2002), and annual precipitation, <Pa>, averaged for Northern Hemisphere latitude 40° to 60°, at two altitudinal ranges, 0 to 500 m and 2,000 to 2,500 m. From the Global Historical Network Climatology database. The apparent trend from 1960 to 2000 indicates winter snow accumulation sharply increasing from 1998 to 2000.
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Figure 60.—Spatially distributed patterns of autocorrelations computed for annual snow accumulation on glaciers and for annual precipitation at 1,000- to 1,500-m elevation in the Northern Hemisphere. From meteorological stations, National Climate Data Center (NCDC) database. The winter snow accumulation, bw, is the maximum amount of snow accumulation measured at the glacier surface at the end of accumulation season. These bw are usually 20 to 30 percent less than the annual amount of snow accumulation.
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Figure 61.—Changes in mass balance for winter (bw), summer (bs), and in annual/net mass balance (b) for a single glacier, Djankuat Glacier, Central Caucasus, Russia, at increasing elevation. Observational data have been averaged from 1968 to 1997. Meltwater runoff (≈bw) is about zero at elevations near 4,000 m where annual mass balance equals winter balance, which is annual snow accumulation. The equilibrium-line altitude (ELA) is the elevation on a glacier that separates the ablation area from the accumulation area (Paterson, 1994).
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Figure 62.—Change in mass-balance gradient between cold (1972) and warm (1990) years. Data on mass balance were averaged for 21 Northern Hemisphere glaciers and adjusted to the same elevation.
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Figure 63.—Variability of AAR (AARi), and the change with time of the accumulation-area ratio <AAR> in terms of standardized cumulative departure. AARi averages data for all time series longer than 5 years; bars are standard errors. The change with time of <AAR> shifts to a decrease at the end of 1970s; data after 2001 are incomplete. AARi is the mean of the annual values for AAR for all time series; it averages <AAR> during the period from 1961 to 2001.
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Figure 64.—A, Glacier mass-balance turnover dramatically increased after 1987, and annual variability decreased at the same time. B, The mass-balance sensitivity to the globally averaged air temperature also has increased, accompanied by a decrease in annual variability at about the same time. Northern hemisphere glacier mass balances are used to calculate sensitivity to annual air temperature. Long-term annual mass-balance time series averaged for about the same 40 benchmark glaciers have been used to calculate averages (Dyurgerov, 2001). Note that this is a different measure of sensitivity than that used by the Intergovernmental Panel on Climate Change (IPCC) (Church and Gregory, 2001); the IPCC measure involves a change between two steady states. Modified from Bentley and others (2007, p. 157, fig. 6C.4).
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Figure 65.—A, Temperature as a function of time and latitude showing zonal anomalies. Data from National Center for Atmospheric Research (NCAR) reanalysis dataset calculated by McCabe (in Dyurgerov and McCabe, 2006). At http://www.cdc.noaa.gov/cdc/reanalysis/reanalysis.shtml.
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Figure 65.—B, Shifts in timing towards acceleration in wastage of glacier volume are expressed in standardized cumulative departures. These graphs show that different glacier systems have responded to large-scale changes in climate at differing times, from the early 1970s until the end of the 1990s. This process of change in glacier volume in response to climate has taken about three decades; bi is the regional and global mass balances for individual years, i; <b> is average mass balance during the period 1961–2003.
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Figure 66.—The components of meltwater runoff from glaciers. Observational results for winter mass balance were used to calculate the steady-state runoff for 40 glaciers worldwide during the period 1961–2003, steady-state runoff increased by one-third to account for accumulation in four summer months to approximate the annual value. These annual values of mass gain were multiplied by the glacier area of 785,000 km2 to obtain the annual rate of flux of total freshwater volume from glaciers to the world ocean, excluding flux from the Greenland and Antarctic ice sheets (steady-state components in this figure). Runoff from storage is (equal to) glacier mass balance.
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Figure 67.—The pan-Arctic drainage area includes the Arctic archipelagoes as well as continental watersheds. The 10 large pan-Arctic river basins (boundaries are shown) with available annual runoff data were used to calculate river runoff to the Arctic Ocean. Red dots show benchmark glaciers with mass-balance records that we used to calculate fresh water runoff from glaciers to the Arctic Ocean. Two precipitation data zones are also shown. Basins are numbered from 1 to 10. First number in each pair of parentheses indicates basin area in thousands of square kilometers; second number indicates discharge in cubic kilometers per year (Lammers and others, 2000). Note that the Yukon River Basin (as defined by Lammers and others (2000)) includes the entire Brooks Range, including the benchmark McCall Glacier (see Chapter K, p. K471–p. K476, and figs. 440 and 441 on p. K474 and p. K475, respectively) and many other river basins that drain to the Arctic Ocean; however, accurate discharge data are not available for basins 1, 2, 3, and 10. Basin 10 does not include calculations of river discharge and glacier meltwater production to reduce the overlap between gauged and ungauged data.
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Figure 68.—A, Annual net inflow from pan-Arctic rivers and glaciers, not including the Greenland ice sheet. B, Cumulative contribution from rivers (standardized departures) and glaciers during the period from 1961 to 2001.
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Figure 69.—A, Change in volume of glaciers, calculated for large Arctic archipelagoes during the study period from 1960 to 2010. B, Cumulative values of the annual contribution of runoff during the study period from 1960 to 2010 for the same glacier areas.
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Figure 70.—Loss of mass from Arapaho Glacier, Colo., mean loss of mass from glaciers in the Pacific Northwest, and mean loss of mass in glaciers worldwide.
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Figure 71.—Mass balance, meltwater runoff, and runoff derived from storage for Arapaho Glacier, Colo., during the 2003 ablation season (May–October); cumulative values begin with May 2003 data and end with October 2003 data.
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Figure 72.—Some glaciological parameters of a mountain glacier shown in, A, cross-sectional view and, B, plan view. The accumulation area plus ablation area represents the total glacier area. The positive net mass balance (bn) of the accumulation area and the negative net mass balance of the ablation area are separated by the equilibrium line altitude (ELA) where net mass balance is zero (bn=0). The accumulation area ratio (AAR) is determined by dividing the accumulation area by the total area of the glaciers. The length of a glacier is measured from the terminus along its mid-line (dashed line) to its uppermost margin. Modified from Andrews (1975, p. 33, fig. 3-1A).
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Figure 73.—The status in 2003 of the compilation of inventories of glaciers in the 41 nations and other geographic entities (for example, Antarctica) that are currently glacierized (have glaciers). Modified from Jiskoot (2003, figure on p. 97).
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Figure 74.—Schematic diagrams of input (accumulation) and output of mass (ablation), A, mountain glaciers and, B, for ice caps and ice sheets. The accumulation and ablation areas of mountain glaciers, A, tend to be approximately similar, except for metastable tidewater glaciers. In a steady-state or in an increase-in-mass state, ice caps (miniature ice sheets) and ice sheets have much larger accumulation areas than ablation areas, which are toroidal in shape because of their parabolic bilateral symmetry in cross section (see fig. 4B). Under conditions of climate warming, an increase in elevation (altitude) of the equilibrium line (ELA) reverses this relationship of accumulation and ablation areas (for example, the toroidal ablation area is larger and the circular accumulation area is smaller). If the ELA rises above the surface of the ice cap or ice sheet, the accumulation area no longer exists, and the ice cap or ice sheet will rapidly disappear (melt away). Modified from Sugden and John (1976, p. 6, fig. 1.5). See also figure 13, which shows the sensitivity of both types of glacier systems to change in elevation (altitude) of the equilibrium line.
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Figure 75.—A, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) spectral bands, for comparison with Landsat Enhanced Thematic Mapper (ETM+). The rectangular boxes (red: ASTER; black: ETM+) indicate the sensor channels, with their respective spatial resolution indicated above the boxes. The superimposed colored curve represents the atmospheric transmission in percent dependency on wavelength. The vertical dashed line marks the approximate margin of long-wavelength visible light. Abbreviations for bands of the spectrum: VNIR (visible and near infrared), SWIR (short-wave infrared), and TIR (thermal infrared). B, ASTER stereo geometry and timing of the nadir-band 3N and the back-looking sensor 3B. An ASTER nadir scene, approximately 60 km in length, and a correspondent scene looking back by 27.6° off-nadir angle and acquired about 60 seconds later together form a stereo scene. Modified from Kääb and others (2003, p. 44, figs. 1, 2).
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Figure 76.—Fresh (newly fallen) snow, firn (denser than snow but not yet ice), bare glacier ice, and debris-covered glacier ice discriminated on four spectral bands (1–4) recorded by the Landsat Thematic Mapper (TM) sensor. Modified from Hall and others (1989, p. 28, fig. 7); see also Hall and others (1988, p. 317, fig. 4).
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Figure 77.—Spectral bands that selected instruments on Earth-orbiting satellites record. The bandwidths of past, present, and experimental instruments are shown against the spectral-reflectance curves of bare glacier ice, coarse-grained snow, and fine-grained snow. The numbers in the gray boxes are band numbers of the electromaganetic spectrum. The Hyperion sensor records 220 bands between 0.4 μm and 2.5 μm; in the diagram the individual bands are not numbered. Instruments are abbreviated as: ASTER, Advanced Spaceborne Thermal Emission and reflection Radiometer; ALI, Advanced Land Imager; ETM+, Enhanced Thematic Mapper Plus (Landsat 7); MISR, Multiangle Imaging SpectroRadiometer; MODIS, MODerate-resolution Imaging Spectroradiometer (36 bands, of which 19 are relevant to discrimination of snow and ice); MSS, MultiSpectral Scanner (Landsats 1–3); and TM, Thematic Mapper (Landsats 4 and 5). Several of these instruments also have bands in the thermal infrared. Landsat bands 1 through 3 generally saturate over snow (Ferrigno and Williams, 1983), but ASTER bands, with their adjustable gains, were designed to avoid the saturation problem (Raup and others, 2007).
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Figure 78.—A, Advanced Spaceborne Thermal Emission and reflection Radiometer (ASTER) image (false color infrared composite) draped over an ASTER digital elevation model (DEM) showing the terminus of Llewellyn Glacier, northwestern British Columbia, and proglacial lake; perspective view looking to the northeast. B, Part of an ASTER scene showing Llewellyn (top left) and Tulsequah (lower right) Glaciers. C, Map showing water and glacier features and created from partial ASTER scene shown in B using an enhanced maximum likelihood supervised classification of three derived bands (after Sidjak and Wheate, 1999). The ASTER DEM is the shaded relief base image. Areas of no visible relief are null areas. Image and caption courtesy of Rick Wessels, U.S. Geological Survey, Alaska Volcano Observatory, Anchorage, Alaska. ASTER image (ID SC:AST_L1A.003:2003795732, bands 3, 2, 1 (RGB), acquired on 8 August 2001). From U.S. Geological Survey, EROS Data Center, Sioux Falls, S. Dak.
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Figure 79.—Annotated section of Landsat 7 Enhanced Thematic Mapper (ETM+) image (band 8), acquired on 14 October 2001, showing Glaciar Upsala, Southern Patagonian Ice Field, Argentina, with overlay of representative velocity vectors. The vectors were determined automatically using the IMCORR IMage CORRelation software (Scambos and others, 1992) and were simplified for this figure. P1-P1ʹ and P2-P2ʹ indicate position of depth profiles in Brazo Upsala (arm of Lago Argentino) and Lago Guillermo, respectively. Rectangles indicate areas of velocity analysis, and are given in Skvarca and others (2003). Modified from Skvarca and others (2003, p. 185, fig. 1).
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Figure 80.—The rapid retreat of Columbia Glacier, Alaska, during 1978–2001 observed and documented using the Advanced Spaceborne Thermal Emission and reflection Radiometer (ASTER), and other imaging systems, such as Landsats 3, 5, and 7 and the U.S. Department of Energy’s Multispectral Thermal Imager (DOE MTI). Image panels left to right: (1) ASTER L1B bands 3, 2, 1, SC: AST_L1A.003 (2004702997) as red, green, blue, acquired on 24 October 2001 at 21:30:18 UTC; (2) MTI DOE (false-color infrared) acquired on 23 September 2001 at 20:25:40 UTC; (3) MTI DOE (color infrared), acquired on 20 March 2001 at 20:41:29 UTC; (4) ETM+ image ID 7067017000017650, band 8, acquired on 24 June 2000 at 20:53 UTC; (5) TM5 image ID 5067017008620910 (Path 67 , Row 17) band 4, acquired on 28 July 1986 at 20:23 UTC; and (6) Landsat 3 MSS acquired on 26 August 1978 at 19:27 UTC ID: p073-17-3m 19780826. The panel on the right includes sketches of 1982–2001 locations of the terminus. Images and caption courtesy of Rick Wessels, U.S. Geological Survey, Alaska Volcano Observatory, Anchorage, Alaska. See also Krimmel (2008, p. K54–K74, figs. 42–56).
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Figure 81.—Base map of the world’s glaciers (blue), including the Greenland ice sheet and the Antarctic ice sheet, and glaciers assessed by GLIMS (red). The blue patches for glaciers represent the dataset of the Earth’s glaciers, an augmented version of the Digital Chart of the World (DCW) described in Raup and others (2000). At http://glims.org.
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Figure 82.—The components of meltwater runoff from glaciers. Observational results for winter mass balance were used to calculate the steady-state runoff for 40 glaciers worldwide during the period 1961–2003, steady-state runoff increased by one-third to account for accumulation in four summer months to approximate the annual value. These annual values of mass gain were multiplied by the glacier area of 785,000 km2 to obtain the annual rate of flux of total freshwater volume from glaciers to the world ocean, excluding flux from the Greenland and Antarctic ice sheets (steady-state components in this figure). Runoff from storage is (equal to) glacier mass balance.
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Figure 83.—Components of the GLIMS Glacier Database, its public interfaces, and links to GLIMS Regional Centers (RCs). RCs can use the GLIMS MapServer to search for appropriate ASTER scenes, which can be ordered from the Land Processes Distributed Active Archive Center (LP DAAC) at the USGS Center for Earth Resources Observation and Science. RCs produce the results of their analysis using GLIMSView and other tools, and then transfer the results to NSIDC. Using a Web browser, anyone can search GLIMS data graphically or with text-based constraints, and GLIMS data can be downloaded in a variety of formats, including Environmental Systems Research (ESRI) shapefiles, Geography Markup Language (GML), Generic Mapping Tools (GMT), and Keyhole Markup Language (KML) for viewing in virtual globes such as Google Earth.
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Figure 84.—Inundation of low-lying coastal regions and islands in the Gulf of Mexico, Caribbean Sea, Pacific Ocean, and Atlantic Ocean projected as occurring if sea level rises 6 m. Note especially the loss of land in the southeastern United States, Florida, the Louisiana delta, and other areas of the Gulf Coast of the United States and México, especially the inundation of most of the Bahamian islands, which will force its citizens to migrate. Inhabitants of all areas marked in red would be displaced inland. During the last interglacial, most of the Greenland ice sheet melted (Koerner, 1989). The resulting rise in sea level was about 6 m. From Rowley and others (2007, p. 105, fig. 1).
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Figure 85.—A, Oblique aerial photograph looking south across the terminus of the surge-type glacier, Eyjabakkajökull, as it appeared on 25 July 1973 after it had completed a 2.8-km surge. Photograph by Richard S. Williams, Jr., U.S. Geological Survey. B, Part of Landsat image 30157-11565-D, acquired on 9 August 1978, of Eyjabakkajökull, after the melting and retreat of the glacier’s terminus more than 5 years after its surge. The fractured ice in its lower part, including stagnation during that interval, shows the kind of detail that Landsat 3 return-beam vidicon (RBV) images offer (Williams, 1986a, p. 8, fig. 3).
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Figure 86.—Diagram showing the location of impounded water on, within, under, and adjacent to a glacier; the sudden release of water from such impoundments produces a jökulhlaup. A, Ice-margin lake caused by damming of a tributary valley or distributary glacier from the main trunk of a valley or outlet glacier; B, Proglacial lake at the terminus of a valley glacier or outlet glacier from an ice cap or ice field. C, Supraglacial lake (see fig. 87). D, Englacial lake. E, Subglacial lake. Modified from figure in Roberts (2005, p. 3 of 21, fig. 1).
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Figure 87.—Oblique aerial photograph of a supraglacial lake taken on 27 July 1995, one year after the surge of Síõujökull, an outlet glacier of the Vatnajökull ice cap, Iceland. Photograph by Oddur Sigurðsson, Icelandic Meteorological Office.
 


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