Four degrees and beyond: the potential for a global ... - Amper

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number of people displaced by 2100 (millions) 60 50 40 30 20 10 0 Sea-level rise and possible impacts 173 Africa Atlantic Ocean Africa Indian Ocean Asia Indian Ocean Atlantic Ocean small islands Baltic Sea Central America Atlantic Central America Pacific Caribbean islands coasts of the C.I.S. east Asia coast Gulf states Indian Ocean small islands North America Atlantic North America Pacific northern Mediterranean north and west Europe Pacific Ocean large islands Pacific Ocean large islands South America Atlantic South America Pacific southeast Asia southern Mediterranean southern Atlantic small islands Figure 3. The distribution of net population displacement over the twenty-first century by region assuming no protection for a 0.5 m (grey bars) and a 2.0 m (black bars) rise in sea level. C.I.S., Commonwealth of Independent States. If we assume protection with dikes and nourishment, the number of displaced people falls dramatically to comparatively minor levels of 41 000–305 000 people displaced over the twenty-first century. Hence, in contrast to the no-protection scenario, the problem of environmental refugees almost disappears. The costs of protection are zero if we assume no protection. In contrast, the dike and nourishment responses have substantial costs. The incremental adaptation costs 7 are estimated at roughly between US $25 and $270 billion (1995 values) per annum for 0.5 and 2.0 m in 2100, respectively. Dike costs dominate these response costs, and dike maintenance becomes an increasing component of the costs over time. This illustrates an important long-term consequence of a widespread protection response to sea-level rise that will continue to grow beyond 2100. In 2100, the relative mix of nourishment, dike construction/upgrade and dike maintenance costs is 36, 39 and 25 per cent; and 13, 51 and 37 per cent for the 0.5 and 2.0 m rise in sea level, respectively. The regional spread of these costs is quite variable with east Asia, North America Atlantic, North America Pacific, north and west Europe and South America Atlantic being the five regions with the highest costs (figure 4). In terms of avoided human displacement as a function of protection investment, not surprisingly, the benefits are highest in the regions with most threatened people: east Asia, south Asia and southeast Asia. It directly affects those on the coast, but also has knock-on effects further inland. 7 Hence, these results assume an existing adaptation infrastructure that can be upgraded. If this is not the case, this is termed an ‘adaptation deficit’, which will require further investment to address [76,77]. Phil. Trans. R. Soc. A (2011) Downloaded from rsta.royalsocietypublishing.org on November 30, 2010
174 R. J. Nicholls et al. global adaptation cost in 2100 (%) 14 12 10 8 6 4 2 0 Africa Atlantic Ocean Africa Indian Ocean Asia Indian Ocean Atlantic Ocean small islands Baltic Sea Central America Atlantic Central America Pacific Caribbean islands coasts of the C.I.S. east Asia coast Gulf states Indian Ocean small islands North America Atlantic North America Pacific northern Mediterranean north and west Europe Pacific Ocean large islands Pacific Ocean small islands South America Atlantic South America Pacific southeast Asia southern Mediterranean southern Atlantic small islands Figure 4. The annual protection cost by coastal region in 2100, as a percentage of global protection investment for a 0.5 m (grey bars) and a 2.0 m (black bars) rise in sea level by 2100. 4. Discussion Section 2 showed that a sea-level rise of between 0.5 and 2.0 m is not an implausible range of climate-induced global rise in sea level in a 4 ◦ C world. Owing to our poor understanding of the underlying processes driving climateinduced sea-level rise, we cannot associate any likelihood with this range, and we conclude that rises above 0.5 m and especially 1 m by 2100 are possible, rather than inevitable. However, it is important to consider what would happen and what responses are available if such large changes did occur: in effect, there is a poorly understood potential for a high-consequence rise in global sea-level rise that is of significant interest to those concerned about coastal impacts and adaptation. The results presented in §3 investigate the issue of impacts and adaptation assuming a rise in sea level between 0.5 and 2.0 m with or without upgraded protection by 2100. The results are indicative and are designed to provide an overview of their implications: they bracket the range of impacts and adaptation costs that might occur with intermediate sea-level-rise scenarios and partialprotection scenarios. They show that in addition to the uncertainty about sea-level rise, the outcome is very sensitive to our assumptions about protection. Without further upgrade to protection (no adaptation), sea-level rise will erode and more particularly flood and submerge extensive low-lying coastal areas displacing tens to millions of people or more by 2100. This would be a highly undesirable future world with many millions of forced environmental refugees owing to sea-level rise alone. In contrast, assuming a protection response, the impact of sea-level rise is mainly felt in terms of increasing protection costs. Hence, in developed coastal areas, a higher rise in sea level translates into a Phil. Trans. R. Soc. A (2011) Downloaded from rsta.royalsocietypublishing.org on November 30, 2010
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ISSN 1364-503X volume 369 number 19
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Phil. Trans. R. Soc. A (2011) 369,
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Editorial David Garner Phil. Trans.
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Four degrees and beyond: the potent
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Preface 5 commitments might give us
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8 M. New et al. In the final plenar
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10 M. New et al. supports the messa
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12 M. New et al. Table 1. Impacts a
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14 M. New et al. actors (NNSAs)—r
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16 M. New et al. as permanent crop
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18 M. New et al. 24 Boe, J. L., Hal
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Beyond 'dangerous' climate change:
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Beyond dangerous climate change 21
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(i) Energy and industrial process e
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(a) 50 (b) GtCO 2e yr -1 40 30 20 1
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Table 1. Summary of scenario pathwa
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Cumulative carbon emissions, emissi
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46 N. H. A. Bowerman et al. althoug
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48 N. H. A. Bowerman et al. a likel
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emissions (GtC) Review. Global warm
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Review. Global warming reaching 4
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global surface warming (°C) 6 5 4
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temperature (relative to 1861-1890
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°C above pre-industrial 8 7 6 5 4
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Water availability in +2 ◦ C and
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(ii) Water stress index Water avail
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(b) (c) (d) (a) Water availability
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(a) number of models, black line nu
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change in run-off (%) change in run
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Agriculture and food systems in sub
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118 P. K. Thornton et al. 1. Introd
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120 P. K. Thornton et al. increases
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122 P. K. Thornton et al. Table 1.
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spread in mosquitoborne disease may
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[89,94,95] further acidification by
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Editorial Editorial 3 D. Garner Pre
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