Past Climate Variability and Change in the Arctic and at High Latitudes

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38 The U.S. Climate Science Program Chapter 3 As permafrost thaws under a warmer summer climate, it is likely to release more greenhouse gases. Figure 3.5. Changes in vegetation cover throughout the Arctic can influence albedo, as can altering the onset of snow melt in spring. A) Progression of the melt season in northern Alaska, May 2001 (top) and May 2002 (bottom), demonstrates how areas with exposed shrubs show earlier snow melt. B) Dark branches against reflective snow alter albedo (Sturm et al., 2005; photograph courtesy of Matt Sturm). [Copyright 2005 American Geophysical Union, reproduced by permission of American Geophysical Union.] albedo of the boreal forest, especially in spring when snow cover may bury tundra, results in earlier warming and hence exerts a positive feedback on warming. This warming feedback would tend to be partially balanced for a period of time by the removal of atmospheric CO 2 as stored carbon in forest ecosystems, which have more above-ground carbon than shrub ecosystems (Denman et al., 2007). 3.2.4 Permafrost Feedback Additional but poorly understood feedbacks in the Arctic involve changes in the extent of permafrost and how changes in cloud cover interact both with permafrost and with the release of carbon dioxide and methane from the land surface. Feedbacks between permafrost and climate became widely recognized only in recent decades (building on the works of Kvenvolden, 1988, 1993; MacDonald, 1990; and Haeberli et al., 1993). As permafrost thaws under a warmer summer climate (Figure 3.6), it is likely to release more greenhouse gases such as carbon dioxide and methane from the decomposition of organic matter previously sequestered in permafrost and in widespread Arctic yedoma deposits (e.g., Vörösmarty, 2001; Thomas et al., 2002; Smith et al., 2004; Archer, 2007; Walter et al., 2007). Because carbon dioxide and methane are greenhouse gases, atmospheric temperature is likely to increase in turn, a positive feedback. Walter et al. (2007) suggest that methane bubbling from the thawing of newly formed thermokarst lakes across parts of the Arctic during deglaciation could account for as much as 33–87% of the increase in atmospheric methane measured in ice cores. Such a release would have contributed a strong and rapid positive feedback to warming during the last deglaciation, and it likely continues today (Walter et al., 2006).
TEMPERATURE, °C TEMPERATURE, °C TEMPERATURE, °C Past Climate Variability and Change in the Arctic and at High Latitudes ALASKA NORTHWEST CANADA 1970 1980 1990 2000 2010 1970 1980 1990 2000 1970 0 –1 –2 –3 –4 –5 –6 –7 –8 WD DH FB HV LG GK BL OM 0.0 –0.2 –0.4 –0.6 –0.8 –1.0 –1.2 –1.4 –9 –1.6 –10 –1.8 –11 –2.0 EUROPEAN RUSSIA 1970 0.5 0.0 1980 1990 2000 2010 –0.5 –1.0 –1.5 –2.0 –2.5 –3.0 –3.5 1970 –2.0 1980 YAKUTIA 1990 2000 2010 –2.2 –2.4 –10.6 –10.8 –11.0 A C E VT RG KT MB MB1 TK YK TEMPERATURE, °C TEMPERATURE, °C TEMPERATURE, °C NORTHWEST SIBERIA 1970 0.0 1980 1990 2000 1970 –1.0 –2.0 –4.0 –5.0 –6.0 CENTRAL ASIA 1970 0.0 1980 1990 2000 1970 –0.5 –1.0 –1.5 –2.0 B D F WG NW NA FS UR1503 UR1506 ND12 ND23 ND11 KZ MG1 MG2 Figure 3.6. Warming trend in Arctic permafrost (permanently frozen ground), 1970–present. Local effects can modify this trend. A) Sites in Alaska: WD = West Dock; DH = Deadhorse; FB = Franklin Bluffs; HV = Happy Valley; LG = Livengood; GK = Gulkana; BL = Birch Lake; OM = Old Man. B) Sites in northwest Canada: WG = Wrigley; NW = Norman Wells; NA = Northern Alberta; FS = Fort Simpson. C) Sites in European Russia: VT = Vorkuta; RG = Rogovoi; KT = Karataikha; MB = Mys Bolvansky. D) Sites in northwest Siberia: UR = Urengoi; ND = Nadym. E) Sites in Yakutia: TK = Tiksi; YK = Yakutsk. F) Sites in central Asia: KZ = Kazakhstan; MG = Mongolia (Brown and Romanovsky, 2008). [Copyright 2008 Wiley Interscience. Reproduced by permission of Wiley Interscience.] 39
Page 1 and 2: Past Climate Variability and Change
Page 3 and 4: Past Climate Variability and Change
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88 The U.S. Climate Science Program
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CHAPTER 6 ABSTRACT Past Climate Var
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second, and the Transpolar Drift, t
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EXTENT, IN MILLION SQUARE KILOMETER
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Until recently, and for logistical
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1990; Fyles et al., 1994), the nort
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FREQUENCY 50 45 40 35 30 25 20 15 1
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Seas around icelAnd provide a rare
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at least 14 Ma (Darby, 2008). Sever
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T. quinqueloba, IN SPECIMENS PER GR
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7 6 5 4 3 2 1 Past Climate Variabil
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SEA-ICE COVERAGE, IN NUMBER OF MONT
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QUARTZ WEIGHT, IN PERCENT 6 5 4 3 2
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6.5 SUMMARY Geological data indicat
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GLOSSARY GLOSSARY 8 ka cold event A
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CAPE Project Circum-Arctic PaleoEnv
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Eccentricity Out of roundness (elli
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Innuitian sector The ice sheet that
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Moraine Landforms (typically ridges
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Positive feedback In climate studie
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Trough-mouth fans Undersea deposits
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The U.S. Climate Change Science Pro
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