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Abstract
The world’s icy and snowy regions—the cryosphere—are where the most profound changes will occur as the globe continues warming. In many areas, the levels of cryospheric change today are surpassing any seen in the past hundreds to thousands of years. This amplified response has a simple explanation: Most of the cryosphere is, on average, near the freezing point. Small shifts in temperature push large regions to a different physical state. However, while the processes leading to the loss of ice are quickly started, they do not quickly stop. We are on the verge of committing ourselves to sizable increases in sea level. The 2007 Intergovernmental Panel on Climate Change (IPCC) report estimated sea level rise in this century at just 20 to 60 centimeters, but that total did not include contributions from the break-up and flow of ice sheets. The melting of mountain glaciers and ice in Greenland and Antarctica could add an additional meter of sea level rise. An equally important effect may be the feedback that changes in ice—especially the ice-covered ocean—have on climate in both the polar and the temperate regions of the world. The author describes the processes that are rapidly eroding polar ice.
Notes
1 For example, ice has a highly non-linear and strongly temperature-dependent stress-strain relationship. Its mechanical and optical properties are very anisotropic as a result of its crystal structure, and it forms fabrics of oriented crystals easily under typical glacier flow conditions. Fracture properties, the effect of salt on ice, its expansion upon freezing, and the fact that most terrestrial ice is near the melting point make it a very complex material in an earth science context. See CitationPaterson (1994); CitationKamb (1972); CitationLliboutry and Duval (1985); CitationAzuma and Higashi (1985); and CitationGoldsby and Kohlstedt (2001).
2 For a range of estimates from various compilation methods, see CitationRignot and Kanagaratnam (2006); CitationLuthcke et al. (2006); CitationShepherd and Wingham (2007); CitationPfeffer et al. (2008); and CitationRignot et al. (2008).
3 For the Greenland ice sheet as a whole, the rate of ice mass loss appears to be increasing at about 30 Gt per year (CitationKerr, 2009; CitationVelicogna, 2009). For Antarctica, the areas of greatest concern (described later in the text) also appear to be losing mass at an increasing rate, but the pace of change is unsteady (CitationKerr, 2009; CitationJoughin et al., 2003; CitationRignot, 2009).
4 This is inferred from the lack of a gravity change signal, which would indicate viscous mantle movement and therefore long-term rebound; instead, GPS indicates rapid upward movement with no change in gravity, i.e. an elastic crustal response. See CitationKhan et al. (2010).
6 An example of this effect for a glacier in the Rocky Mountains is given in CitationHaugen et al. (2010).
7 See CitationScambos et al. (2004); CitationFahnestock et al. (2002); CitationCathles et al. (2009).
8 Discussed in CitationScambos et al. (2004); for a recent update, see CitationRott et al. (2010) at http://www.the-cryosphere-discuss.net/4/1607/2010/tcd-4-1607-2010.pdf.
10 Smaller by about 3.5 million square kilometers; see the summary of the past several years of Arctic sea ice decline available at the website of the National Snow and Ice Data Center, at http://nsidc.org/arcticseaicenews//2010/100410.html.
11 Data for the submarine traverses was released under the Clinton administration in a region known as the “Gore Box”, after Al Gore; a summary of both remote sensing and submarine evidence is available in CitationKwok and Rothrock (2009); see also http://www.nasa.gov/topics/earth/features/icesat- 20090707.html for a summary of the recent dramatic losses, and http://psc.apl.washington.edu/ArcticSeaiceVolume/IceVolume.php for a combined observation-model estimate of ice volume decline.
12 See the overview provided by CitationBindschadler (1998) and the detailed compendium in CitationMassom and Lubin (2006).
13 The CryoSat-2 satellite, launched by the European Space Agency earlier this year; see http://www.esa.int/SPECIALS/Cryosat/index.html.
14 See the Global Land Ice Measurements from Space (GLIMS) project website at http://www.glims.org.
15 CitationLüthi et al. (2008) report on the earliest part of this range; reports by CitationHansen et al. (2007) and CitationPetit et al. (1999) cover the later period.
17 E.g., references in CitationAlley et al. (2007) and CitationTrudinger et al. (1999: see their Figure 2).
18 See the discussion at http://www.ncdc.noaa.gov/paleo/milankovitch.html; also CitationMartinson et al. (1987) and CitationMilankovitch (1998).
19 Greenhouse gas changes either (a) cause the onsets or ends of the southern hemisphere ice ages or (b) significantly enhance a small initial cooling or warming that is driven by ocean circulation changes. The case for the former is best given in CitationShackleton (2000).
20 A synopsis is available at the website for the “Arctic Report Card”, http://www. arctic.noaa.gov/reportcard/seaice.html, and the NSIDC Sea Ice News and Analysis http://nsidc.org/arcticseaicenews/2010/110210.html. See also CitationOverland et al. (2008).
21 CitationMaslanik et al. (2007) demonstrate this by tracking ice flow continuously using satellite data over the past three decades. A detailed analysis of where multi-year ice has been lost in recent years is given by CitationKwok and Cunningham (2010).
22 See NSIDC Arctic Sea Ice News and Analysis at http://nsidc.org/ arcticseaicenews/2006.html.
23 The extent of several of the sub-glacial fjords was recently revealed in new grids of bedrock elevation data produced by aircraft ice-penetrating radar observations; see https://www.cresis.ku.edu/data/Greenland.
24 Data are available online at http://www.antarctica.ac.uk/met/gjma/sam.html and http://www.cpc.noaa.gov/products/precip/CWlink/daily_ao_index/aao/aao_index.html.
25 CitationArblaster and Meehl (2006); also Chapter 5 of CitationTurner et al. (2009).
26 For the case of the Larsen B Ice Shelf disintegration in 2002, see CitationVan den Broeke (2005).
27 This is a consequence of Ekman Drift, which results from the coriolis effect caused by the rotation of the Earth.
28 For the modeled case, see CitationThoma et al. (2008); observations supporting the model are given in CitationJenkins et al. (2010); a good overview of the Pine Island Bay glacier and ocean system is given by CitationSchoof (2010).
Additional information
Ted Scambos is Senior Research Scientist and Lead Scientist for the National Snow and Ice Data Center, a part of the University of Colorado, Boulder, US. He received a PhD in Geology from the University of Colorado in 1991, followed by three years at NASA’s Goddard Space Flight Center. Scambos is an expert in remote sensing of the cryosphere and in situ glacier measurement, having visited the Antarctic over a dozen times on field expeditions. He has authored or co-authored 74 peer-reviewed articles on a variety of cryosphere and geoscience topics.