Sea-Level Rise for the Coasts of California, Oregon, and Washington Past, Present, and Future (2012) / Chapter Skim
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5 Projections of Sea-Level Change
5 Projections of Sea-Level Change
Pages 83-108
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From page 83... ...
The IPCC (2007) projected the individual contributions Projections of future global sea-level change are of steric changes and melting of glaciers and ice caps, commonly made using models of the primary processes the Greenland Ice Sheet, and the Antarctic Ice Sheet that contribute to global sea-level change -- the trans- to future sea-level change for each emission scenario, fer of fresh water from the melting cryosphere to the then summed the contributions.
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From page 84... ...
Term B1 B2 A1B A1T A2 A1FI Thermal expansion 1024 1228 1332 1230 1435 1741 Glaciers and ice caps 714 715 815 815 816 817 Greenland Ice Sheet SMB 15 16 18 17 18 212 Antarctica Ice Sheet SMB -10 -2 -11 -2 -12 -2 -12 -2 -12 -3 -14 -3 Sea-level rise 1838 2043 2148 2045 2351 2659 Scaled-up ice sheet discharge 09 011 -113 -113 -113 -117 SOURCE: Adapted from Table 10.7 in Meehl et al.
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From page 85... ...
(2007) extrapolated loss rates for the Greenland modeled results, shown in Table 5.1 under "Scaled-up and Antarctic ice sheets and for aggregate glaciers and ice sheet discharge." However, the estimates were not ice caps, and estimated that land ice would contribute based on physical models of ice sheet processes, and ca.
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From page 86... ...
. authors also hypothesized a range of accelerated but reasonable glacier dynamic behavior for the Greenland Semi-Empirical Models and Antarctic ice sheets and for glaciers and ice caps, and they projected land ice contributions ranging from Projections of 21st century sea-level rise are subject 0.8 m to 1.7 m by 2100, with roughly equal contribu- to uncertainties arising from the nonlinear responses tions from Greenland, Antarctica, and glaciers and of the Greenland and Western Antarctic ice sheets ice caps.
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From page 87... ...
(2000) emission scenarios, Vermeer and Rahmstorf All of the semi-empirical model projections are (2009)
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From page 88... ...
Although outputs from a new tion found for the past may not hold in the future. In generation of GCMs are beginning to be available, perparticular, the ice sheets appear to have been negligible forming computations of derived quantities like global sea-level contributors during the observational periods sea-level changes from these new outputs is beyond the used by Gornitz and Lebedeff (1987)
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From page 89... ...
(B1A1FI) Glaciers and ice capsb 2.9 ± 0.1 2.73.6 5.5 ± 0.2 5.17.3 14.3 ± 0.7 12.919.4 Greenlandb 2.3 ± 0.2 1.84.0 5.6 ± 0.7 4.310.2 20.1 ± 2.7 14.833.8 Antarcticab 2.9 ± 0.7 1.55.1 7.0 ± 2.1 3.013.3 24.0 ± 8.3 7.746.2 Total Cryosphereb 8.1 ± 0.8 6.612.2 18.0 ± 2.2 13.729.4 58.4 ± 8.8 40.994.1 Sumc 13.5 ± 1.8 8.323.2 28.0 ± 3.2 17.648.2 82.7 ± 10.6 50.4140.2 Semi-empiricald 18 1422 37 2847 121 78175 (B1A1FI)
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From page 90... ...
(2011a) compilation, which fluence on upstream ice dynamics, and time variations combines modeled surface mass balance and measured in outlet glacier dynamics on future losses from the and modeled ice discharge to produce net balances Greenland Ice Sheet.
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From page 91... ...
Prior to 2004, published 20 years and held constant thereafter. The exact choice mass balances for the ice sheets were near zero or even of values for the individual components is less impor- negative, but subsequent work indicates that loss rates tant than the net added flux after the 20-year increase, are rapidly accelerating (see Chapter 3)
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From page 92... ...
Even if dynamics Discussion of Global Projections constitutes only 13 percent of the Greenland's recent ice loss rate, as estimated by Price et al.
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From page 93... ...
The black line at the bottom is the added ice dynamics component. FIGURE 5.5 Range of committee projections for the sum of all individual components of global sea-level rise.
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From page 94... ...
Antarctic ice sheets, which dominate the cryospheric All three curves in Figure 5.5 have a positive curva- term, have response times of centuries to millennia. ture, as do the semi-empirical projections.
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From page 95... ...
Although some studies have pointed out were then adjusted for vertical land motions and for that the number of new reservoirs has been declining model-predicted seasonal and interannual wind-driven over the past three decades (e.g., Chao et al., 2008) , the increases in sea level.
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From page 96... ...
Ranges reflect uncertainty in ice loss rates. d Assumes constant rates of vertical land motion of 1.0 ± 1.5 mm yr-1 for Cascadia and -1.5 ± 1.3 mm yr-1 for the San Andreas region.
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From page 97... ...
. To account 2100 for these effects in the projections, the committee sub- 40 divided ice loss rates into four categories: Greenland Ice Sheet, Antarctic Ice Sheet, Alaska glaciers, and all 30 other glaciers and ice caps.
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From page 98... ...
When uncertainties in The tectonic component of vertical land motion in the ice loss rate are factored in, the fingerprint-adjusted this area can be projected using earthquake cycle decontribution of Alaska, Greenland, and Antarctica to formation models. The CAS3D-2 model (He et al., relative sea-level rise ranges from 3375 cm along the 2003; Wang et al., 2003; Wang, 2007)
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From page 99... ...
. Mean GIA model predicted vertical land motions can vary at length scales that are rates of vertical land motion range from +0.2 mm yr-1 considerably smaller than the CGPS station spacing, so in northernmost Washington to -1.0 mm yr-1 in interpolation using the CGPS data carries substantial southern Washington and northern Oregon.
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From page 100... ...
The vertical land motion components and their uncertainties for the northern and southern part Discussion of Regional Projections of the coast are shown in the shaded areas; the bars on the right margin indicate the range for 2100. North of The projections of sea-level rise off California, Cape Mendocino, the coast is experiencing mean uplift, Oregon, and Washington were made by summing so vertical land motion contributes negatively to relathe cryosphere component, adjusted for the effects tive sea-level rise (although uncertainties are large and of the sea-level fingerprints of Alaska, Greenland, include positive contributions)
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From page 101... ...
The sea-level fingerprint ties are associated with assumptions about the growth effect reduces the projected sea levels along the entire of concentrations of greenhouse gases and sulfate coast and is most pronounced in Washington. The aerosol, which affect the steric contribution, and future fingerprint effect has not been included in previous ice loss rates and the effect of rapid dynamic response, studies and projections of sea level for the west coast which affect the land ice contribution.
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From page 102... ...
. MTJ = Mendocino Triple Junction, where the San Andreas Fault meets the Cascadia Subduction Zone.
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From page 103... ...
Washington and Oregon = coastal areas north of Cape Mendocino; California = coastal areas south of Cape Mendocino. RARE EXTREME EVENTS high astronomical tides, and large waves producing record sea levels along virtually the entire coast (see Extreme events can raise sea level much faster "Changes in Ocean Circulation" in Chapter 4)
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From page 104... ...
sea-level projection (78 cm by that as mean sea level rises, the incidence of extreme 2100) , extreme water heights (exceeding the 99.99th high-sea-level events becomes increasingly common percentile)
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From page 105... ...
A great earthquake also Washington in the past 3,500 years (Atwater and would produce large postseismic vertical land motions Hemphill-Haley, 1997)
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From page 106... ...
106 SEA-LEVEL RISE FOR THE COASTS OF CALIFORNIA, OREGON, AND WASHINGTON FIGURE 5.13 Ghost forests, such as this grove of weather-beaten cedar trunks near Copalis River, Washington, are evidence of sudden subsidence. SOURCE: Courtesy of Brian Atwater, U.S.
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From page 107... ...
The committee's projections to the expected global warming-related sea-level rise. account for factors that affect sea level in the area, in cluding local steric variations; wind-driven differences CONCLUSIONS in ocean heights; the gravitational and deformational effects associated with melting of Alaska, Greenland, Global projections are commonly made using and Antarctic glaciers; and vertical land motions along ocean-atmosphere GCMs, which provide a reasonable the coast.
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From page 108... ...
In addition, the duration of these tions are related to assumptions about the rate of future extremes would lengthen from 1 or 2 hours in the hisice losses and the constant rate of vertical land motion torical period to about 6 hours by 2100. over the projection period.
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