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

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Table 2. Implications of different combinations of decision lifetimes, driver uncertainty type and adaptation response types for decision-making strategies and tactics under diverging climate futures. decision lifetime, relative to rate of type of driver type of adaptation response characteristics of decision-making some options available to climate change uncertainty options about risk reduce decision riska monitor to ensure no regrets response still suffices ‘no regrets’: normal business planning to implement response same type and extent of response under all scenarios 1 short- or long-term monotonic or indeterminate cost-effectively monotonic or indeterminate 2 short-term (easily reassessed) Rethinking adaptation for a +4 ◦ C world 207 monitor rate of change to provide advanced warning of thresholds and need for ongoing, incremental adaptation in line with pace (and direction) of change little divergence between scenarios over short-term means considering only one set of Phil. Trans. R. Soc. A (2011) Downloaded from rsta.royalsocietypublishing.org on November 30, 2010 transformation responses reassess regularly to ensure rate of change still in risk envelope; real options, safety margins, shortened decisions precautionary risk management: use benefit–costs analysis to determine appropriate level of response now monotonic same type but different extent of response for different scenarios 3 long-term (implications may last for 50–100 years) high likelihood of need for transformation at some stage; reversible options, soft adaptations; shortened risk-hedging against alternative futures (with gradual transfer of resources as uncertainty diminishes); act now, given 4 different type (and extent) of response for different scenarios decisions often impossible monotonicity monitor change to identify if conditions are moving outside ‘robust space’; reversible options, safety margins, soft adaptations, shortened decisions all useful robust decision-making paradigm in the face of uncertainty about direction of change 5 indeterminate same type but different extent of response for different scenarios hardest combination: real options most likely to pay off if possible; likely to need support from higher levels of governance risk-hedging against alternative futures (with gradual transfer of resources as uncertainty diminishes); delay acting if possible 6 different type (and extent) of response for different scenarios aAbbreviated terms for some options from Hallegatte [8] and Dobes [49]: ‘real options’—conscious decision delay where benefits of improved information exceed risk of costs of delay; ‘reversible options’—favouring reversible and flexible options; ‘safety margins’—buying safety margins in new investments (e.g. bigger foundations pre-adapted to higher structures that are not yet built); ‘soft adaptations’—promoting changed behaviours and arrangements over physical infrastructure (e.g. reduced household water demand rather than a new dam); ‘shortened decisions’—reducing decision time horizons (e.g. housing with a short lifetime) within a long-term view.
208 M. Stafford Smith et al. These three factors—decision lifetime, the nature of driver uncertainty and the form of adaptation responses—combine to require different approaches to risk management. They also highlight where the various risk mitigation tactics outlined by Hallegatte [8] are most likely to be applicable, as well as how to think about transformative as opposed to incremental adaptation now and at what institutional scale of decision-making. We now illustrate some of these implications summarized in table 2. First (row 1 of table 2), where the adaptation response (same type and extent regardless of driver uncertainty) is no regrets, there is no reason to complicate decision-making any further. This is true for both short- and long-lifetime decisions, although decision-makers are probably already dealing successfully with the short-lifetime cases. We therefore devote no further space to these, other than noting that ongoing monitoring and reassessment are always required to ensure the decision space has not changed. Second (row 2 of table 2), while short-lifetime decisions do face uncertainty, in general, future scenarios do not diverge much over the coming 10 years. In both monotonic and indeterminate cases, incremental adaptation is appropriate, reacting to change as it emerges. Where adaptation responses are of the same type, whether the drivers are monotonic or indeterminate, the extent of response can be gradually adjusted over time (e.g. gradually altering the choice of crop cultivar to plant). However, it is important to establish monitoring processes that provide plenty of lead time for when a more transformative change may be needed (e.g. when the regional climate moves outside the tolerance of any available cultivars), and this monitoring may require the involvement of a higher level of governance. Where adaptation responses may be of different types as change increases, there is likely to be a strong justification for deliberatively delaying decisions, applying the concepts of real options [49]. However, our main focus here is on long-lifetime decisions, given the increasing prospects of a 4 ◦ C world. Four combinations of driver uncertainty and adaptation response remain (rows 3–6 of table 2), and each requires different treatment. — The key drivers may be monotonic, necessitating a variable extent of a fixed type of response; this is true for many aspects of setting design performance criteria and risk margins in engineering guidelines in the face of higher temperatures, and for standards such as concrete corrosion (e.g. [50,51]). For these decisions, risk management should adopt the precautionary principle, choosing a response extent (e.g. a new design extreme) through traditional benefit–cost analysis against the uncertainty in timing of change. Risks can be reduced by allowing extra safety margins where this is cheap to do, or deliberately shortening the lifetime of infrastructure where this is feasible and cost-effective. — The key drivers may be monotonic, but such that different levels of change necessitate fundamentally different types of response. Examples include implementing incremental coastal defences up to some level of sea-level rise but then needing to consider planned retreat, or gradually adapting farming system practices and cultivars to a drying climate but eventually having to change land use (or location) all together. The example of postfire management in the Victorian alpine forests given alternative future regional temperatures for trees establishing now, as noted above [25], also 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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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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98 M. G. Sanderson et al. 12 Betts,
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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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122 P. K. Thornton et al. Table 1.
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124 P. K. Thornton et al. century.
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Humid tropical forests on a warmer
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(a) Humid tropical forests on a war
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0 retraction risk 17 120 80 40 (a)
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0 retraction risk 17 120 80 40 0
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