Download PDF Spring Bridge Issue on Engineering and Climate Change March 15, 2020 Volume 50 Issue 1 The seven articles in this issue cannot cover all engineering-related aspects of climate change, but they highlight several areas of concern. Responding to Sea Level Rise Monday, March 16, 2020 Author: Jochen Hinkel and Robert J. Nicholls Global mean sea levels are rising because of human-induced global warming (Oppenheimer et al. 2019). The recent Special Report on the Ocean and Cryosphere in a Changing Climate of the Intergovernmental Panel on Climate Change (IPCC) projects that if greenhouse gas emissions continue to rise unabated (i.e., RCP8.5) there is a 66 percent chance that global mean sea level will rise 0.6–1.1 meters by 2100 and 2.3–5.4 m by 2300 (Oppenheimer et al. 2019) (figure 1). Figure 1 Stringent reduction of greenhouse gas emissions may substantially reduce global sea level rise (SLR). The IPCC Special Report finds that if emissions are reduced to meet the Paris Agreement goal of limiting global warming “well below 2°C” (i.e., RCP2.6), there is a 66 percent chance that global mean sea level will rise 0.3–0.6 m by 2100 and 0.6–1.1 m by 2300. These ranges, like most in the SLR literature, are probabilistic, which means that sea levels may turn out to be above (or below) these ranges. Current scientific understanding does not enable projection of an upper bound for SLR (Hinkel et al. 2019; Stammer et al. 2019). Potential Impacts of Sea Level Rise Sea level rise threatens the world’s coasts through a range of impacts (Oppenheimer et al. 2019): permanent submergence of land by mean sea levels or mean high tides; more frequent or intense coastal flooding; enhanced coastal erosion; loss, degradation, and change of coastal ecosystems; salinization of soils and of ground and surface water; and impeded drainage. These biophysical impacts will in turn have socio-economic impacts on coastal residents and their livelihoods, such as significant flood damage to buildings, disruption of economic activities, and degraded coastal agriculture. Three points about SLR impacts that are often obscured in the SLR literature are important to note upfront. First, SLR impacts are due to local relative sea level change, which differs from the global mean because of both climatic and nonclimatic factors, and this must be considered when evaluating future impacts and adaptation needs. One key nonclimatic factor is land sub-sidence; in densely populated sedimentary coastal plains human-induced land subsidence due to groundwater withdrawal and related processes can produce large relative rises in local sea levels (Kaneko and Toyota 2011). Second, most of the impacts of SLR will be felt not through the gradual increase of mean sea level but rather through increases in extreme sea level (ESL) events such as combinations of tides, surges, and waves that rise with mean sea levels (Wahl et al. 2017). The notion that sea levels gradually submerge large coastal areas, as often depicted in the SLR literature and media coverage (e.g., Lu and Flavelle 2019), is misleading. Third, in most cases potential SLR impacts are countered or strongly reduced by adaptation, especially where coastal zones are densely populated. Many coastal societies have a long history of adapting to local SLR and this is almost certain to continue. For example, a number of coastal megacities have experienced and adapted to relative SLR of several meters caused by human-induced land subsidence during the 20th century (Kaneko and Toyota 2011). A realistic picture of SLR risk and impacts requires consideration of adaptation responses, which are the focus of this article. Adaptation Responses Options Table 1 Adapting to SLR can be done in fundamentally different ways (table 1). Protection reduces the likelihood of coastal impacts and includes (i) hard engineered structures such as dikes, seawalls, breakwaters, and surge barriers, and (ii) sediment-based measures such as beach and shore nourishment and dunes (also referred to as soft protection). Advance creates new land by building seaward and upward. It includes land reclamation above sea levels and polderisation, the gain of new low land with the construction of dike enclosures. Ecosystem-based adaptation (EbA) uses coastal ecosystems such as coral and oyster reefs, mangroves, marshes, and seagrass meadows as protective buffers that attenuate extreme water levels (surges, waves), reduce rates of erosion, and raise elevation or create new land by trapping sediments and building up organic matter and detritus (Pontee et al. 2016; Spalding et al. 2014; Temmerman et al. 2013). Accommodation involves implementing early warning systems for floods and floodproofing and elevating houses. It does not prevent coastal impacts but reduces the vulnerability of coastal residents, infrastructure, and human activities. Planned or managed retreat reduces exposure to coastal impacts by moving people, infrastructures, and human activities out of the exposed coastal area (Hino et al. 2017)—or by avoiding development of the coastal floodplain in the first place. These physical responses are combined with or initiated through institutional arrangements such as regulations for design heights for dikes, building codes for floodproofing homes, monetary incentives for risk management (e.g., subsidized insurance), or the timely provision of information through flood early warning systems. Advantages and Disadvantages All types of response options have advantages and disadvantages and thus have complementary roles to play in an integrated response to SLR. Hard protection measures need less space and their effectiveness is more predictable than EbA approaches, which exhibit high natural variability in time and space (Narayan et al. 2016; Pinsky et al. 2013; Quataert et al. 2015). Advantages of EbA measures for protecting the coast include their contribution to other ecosystem services, such as carbon sequestration or improved water quality, and to conservation and related goals. Furthermore, EbA approaches may autonomously maintain their effectiveness over time by naturally adapting to rising sea levels by raising land and migrating inland, provided sufficient sediment and inland space are available. In practice EbA measures are often combined with hard defenses. Advance is widely practiced around coastal -cities where land is scarce and valuable. Globally, about 34,000 km2 of land has been gained from the sea during the last 30 years, with the biggest gains in Dubai, Singapore, and China (Donchyts et al. 2016; Martín-Antón et al. 2016). Over longer timescales, this has occurred around nearly all major coastal cities to some degree, even if only for the creation of port and harbor areas. Accommodation measures such as floodproofing have high benefit-cost ratios: implementing them is less expensive than doing nothing. Early warning systems for coastal floods and storms have one of the highest benefit-cost ratios and should be universally adopted. However, these measures alone are effective only for current conditions and small rises in sea level; if SLR rises substantially they will need to be combined and/or replaced with other approaches. It is also important to note that protection always leaves a residual risk—ESL events can exceed protection standards—and hence flood damage cannot necessarily be completely prevented. For example, a global analysis of flooding of coastal megacities under SLR found fewer but bigger flood disasters (Hallegatte et al. 2013). Only retreat and advance can avoid residual risks if ground is sufficiently high or can be reclaimed, or at least these options can buy time until residual risks reach unacceptable levels—and new adaptation decisions are necessary. Different Adaptation Responses in Different Contexts Coastal areas are diverse and there is no “silver bullet” adaptation. Rather, adaptation will vary in time and space depending on the context. Context-Specific Examples In deltas and sedimentary lowlands, especially urban areas, rates of human-induced subsidence may exceed climate-induced SLR by an order of magnitude. The most urgent response needed in this context is to mitigate human-induced subsidence. While in some cities such as Tokyo subsidence has been stopped by reducing the pumping of ground water, the problem continues at alarming rates of 3 to 17 cm/year in other Asian megacities such as Bangkok, Jakarta, and Manila (Kaneko and Toyota 2011) and is likely to emerge in other susceptible cities. For cities and densely populated low-elevation areas, hard protection will continue to play a central role in adaptation. Many cities around the world are protected by hard defense infrastructure and if there is limited space and large human assets (e.g., buildings, infrastructure) are at risk, hard protection should be continued for the coming decades, at least until more is known about possible high-end SLR, which may require a change in adaptation strategy. Planned retreat does not yet need to be implemented widely but must be considered in the longer term if protection ceases to be affordable or feasible (Nicholls et al. 2013). However, if major coastal floods cause significant damage, it makes sense to consider opportunities for retreat instead of rebuilding. If safe land is available, development should be steered away from coastal floodplains to avoid future damages and/or the need for adaptation investments. Economic Considerations In most cases, it is technologically feasible to protect cities against multiple meters of sea level rise. Providing global protection for densely populated coasts would require investments during the 21st century on the order of $2.8–$13.4 trillion under an SLR scenario that is consistent with the Paris Agreement (i.e., RCP2.6) and $4.4–$18.2 trillion under unmitigated greenhouse gas emissions (i.e., RCP8.5), considering capital and maintenance costs of coastal dikes, river dikes, and storm surge barriers (Nicholls et al. 2019). While this is a lot of money, the benefit-cost ratios of protecting cities (i.e., the cost of avoided damages divided by the cost of protection) are generally high (Lincke and Hinkel 2018). Further, the required investment is only a small fraction of local GDP (Diaz 2016; Hinkel et al. 2013; Lincke and Hinkel 2018). Economically productive cities should therefore be able to afford protection. For rural and sparsely populated coasts, understanding of the future is less clear and the range of adaptation options appears more constrained. Hard coastal protection is less economically feasible because benefit-cost ratios are often less than one (Lincke and Hinkel 2018) and the required annual investments in coastal protection can amount to several percent of GDP, in particular for small island states (Diaz 2016; Wong et al. 2014). An alternative strategy is to protect rural coasts through EbA measures. Where sediment budgets and human activity allow, land can be elevated through managed morphodynamics; for example, controlled flooding of low-lying areas in deltas can raise land surfaces through flood-deposited sediments (Amir et al. 2013). Designing and Planning Adaptation Responses Many coastal decisions with time horizons of decades to over a century—for example, concerning critical infrastructure, coastal protection works, city planning—are being made today and factoring in SLR, even with the large uncertainty about it (figure 1), can improve these decisions. Guiding Principles Figure 2 Two guiding principles are specifically relevant for such decisions (Hinkel et al. 2019). The first calls for increasing flexibility by delaying or splitting decisions into multiple steps. For example, in the federal state of Schleswig Holstein in Germany coastal dikes that are upgraded are equipped with a wider crest than necessary (figure 2), allowing further raising of the dikes if SLR turns out to be higher than anticipated (MELUR-SH 2012). In the Netherlands sediment-based instead of hard measures are used for coastal protection, because the former provide the flexibility to increase protection (e.g., by applying more sand) as the consequences of SLR and other changes unfold, without the need to decide today on the construction of hard measures that would last decades (Kabat et al. 2009). The second, related principle concerns adaptive decision making, which means that SLR monitoring systems are established to identify future decision points when a new strategy may need to be implemented. An important prerequisite for this approach is that the monitoring system can detect sea level signals (e.g., an acceleration in SLR) sufficiently early for implementation of adequate responses (Haigh et al. 2014; Stephens et al. 2018). One approach that illustrates this second principle is dynamic adaptive policy pathways (Haasnoot et al. 2013), or simply adaptation pathways. This approach has, for example, been integrated in national guidance for coastal hazard and climate change decision making in New Zealand (Lawrence et al. 2018). Even when no long-term SLR-related decisions are immediately needed, it is beneficial to prepare a long-term strategy to ensure that options, and sufficient time to implement them, are available even in the case of high SLR estimates (Hinkel et al. 2019). Stakeholders’ Risk Tolerance There is no objective way to provide SLR information for adaptation planning, because the range of SLR relevant to a decision depends on the risk tolerance of the relevant stakeholders (Hinkel et al. 2019). As such, the IPCC SLR ranges do not necessarily provide the required information. Risk-tolerant stakeholders may prefer an adaptation response based on the 66 percent range of SLR in the latest IPCC report cited above (i.e., up to 1.1 m of SLR by 2100). Stakeholders with a lower risk tolerance should also consider SLR above this range because there is a 17 percent chance that global mean SLR will exceed 1.1 m under the RCP8.5 scenario by 2100. Studies using and combining multiple lines of evidence—such as observations, paleo records, model sensitivity studies, scenario studies, and expert -judgment—provide higher SLR estimates. For example, in the United Kingdom the so-called H++ scenario range extends to about 2 m SLR by 2100 (Lowe et al. 2009; Nicholls et al. 2014) (figure 1) and has been considered in coastal adaptation planning for London (i.e., the Thames Estuary 2100 project; Ranger et al. 2013) and for nuclear power station design (Wilby et al. 2011). While the confidence in these estimates is lower than for those of the IPCC, the higher estimates should be taken into account in decision making when stakeholders have a low risk tolerance (Hinkel et al. 2015). Social Challenges in Implementing Adaptations Implementation of adaptations raises social concerns that can be much more difficult to deal with than many of the biophysical and technical issues reported above (Esteban et al. 2019; Hinkel et al. 2018). For example, financing the upfront investment in an adaptation is often prohibitively difficult, because the benefits of protection are public goods stochastically (i.e., benefits are felt only when a flood occurs) dispersed across diverse actors over a long period of time. In such situations beneficiaries may be unwilling to pay taxes or levees for uncertain benefits, and politicians do not have strong incentives to realize such long-term projects because of short electoral cycles and reputational risks that arise if investments are made and no flood occurs for a long time (Bisaro and Hinkel 2018). For these and related reasons, many parts of the world are not adapted to today’s ESL regimes let alone those under SLR. For urban areas, advance can be a way to overcome the financing gap, because upfront investments in protection can be recuperated within a few years through real estate revenues generated from newly created land. But this approach raises equity issues associated with access to the new land (Bisaro et al. 2019). Retreat is often politically contested because of vested coastal interests (e.g., of the tourism and real estate sectors), difficult questions around equity and compensation (e.g., for forfeited property), and adverse outcomes such as disruption of livelihoods and loss of culture and identity (Hauer et al. 2019; Siders et al. 2019). While EbA seems to be an attractive solution, the large-scale implementation required to address SLR in rural areas is a huge challenge, not least because coastal ecosystems currently experience the highest rates of human destruction. For example, annual global losses of mangroves and corals are 1–3 percent and 4–9 percent, respectively—much larger than for tropical forests (0.5 percent) (Duarte et al. 2008). The major driver is human development such as the conversion of mangroves into agriculture, shrimp farming, and industrial uses that provide short-term profits (Li et al. 2014). Maintaining wetlands and raising land through sediment management in river deltas also conflict with trends such as river-dam construction, which, if continued, could lead to a decline in sediment supply of up to 83 percent by 2100 (Dunn et al. 2019). The extent to which these and other conflicts can be resolved and adaptation advanced depends on the extent to which governance arrangements are in place or can be established to mitigate conflicts between different interests (e.g., development versus ecosystem conservation). Areas that have long been dealing with coastal risks and extreme sea levels, such as Northwestern Europe, China, and Japan, will find it easier to implement appropriate responses, and are already doing so, as governance arrangements are already in place. However, for many other places, SLR is a new phenomenon, preparation for it is generally less advanced, and new governance arrangements are required to address it. Conclusions The scale of the SLR challenge is immense and strong mitigation efforts are needed to avoid multiple meters of SLR within the next few centuries, which will be unmanageable for many coastal regions of the world. But even with such efforts, sea levels will continue to rise for decades and centuries to come. Thus coastal adaptation is essential in any future, but it will be much easier and more likely to be successful when combined with stringent mitigation. The important thing is to start exploring long-term adaptive strategies now if they are not already initiated. Diverse adaptation measures are available and, depending on the coastal setting, quite different options will be selected. Protection appears likely in many urban contexts, but should be combined with other measures as much as possible, and residual risk needs to be considered. In the longer run, retreat appears likely in many less developed areas; there is a need for more analysis of this and other options. Research is needed to determine to what extent ecosystem-based approaches are effective in different areas. Irrespective of technical considerations, coastal adaptation is much more constrained by economic, financial, and other social factors. Long before technical limits to coastal adaptation are reached, societies will probably be economically unable or socially unwilling to invest in such adaptation. This points to the need for research on appropriate governance structures for mitigating social conflicts around these issues to ensure progress on adaptation. Importantly, such constraints will have a greater impact on poorer and rural areas, exacerbating inequalities between rich and poor coastal communities. Richer and more densely populated areas are likely to be well protected behind hard structures, while poorer and less densely populated areas are not likely to be able to afford investments in coastal protection and so will suffer ever more frequent damages from ESL events and eventually have to retreat from the coast. These social and economic issues should be discussed extensively in international climate change negotiations. References Amir MSII, Khan MSA, Khan MMK, Rasul MG, Akram F. 2013. Tidal river sediment management: A case study in Southwestern Bangladesh. International Journal of Environmental, Chemical, Ecological, Geological and Geophysical Engineering 7(3):174–85. Bamber JL, Oppenheimer M, Kopp RE, Aspinall WP, Cooke RM. 2019. Ice sheet contributions to future sea-level rise from structured expert judgment. Proceedings, National Academy of Sciences 116:11195–200. Bisaro A, Hinkel J. 2018. Mobilizing private finance for coastal adaptation: A literature review. Wiley Climate Change 9:1–15. Bisaro A, de Bel M, Hinkel J, Kok S, Bouwer LM. 2019. Leveraging public adaptation finance through urban land reclamation: Cases from Germany, the Netherlands and the Maldives. Climatic Change. Diaz DB. 2016. Estimating global damages from sea level rise with the Coastal Impact and Adaptation Model (CIAM). Climatic Change 137:143–56. Donchyts G, Baart F, Winsemius H, Gorelick N, Kwadijk J, van de Giesen N. 2016. Earth’s surface water change over the past 30 years. Nature Climate Change 6:810–13. Duarte CM, Dennison WC, Orth RJW, Carruthers TJB. 2008. The charisma of coastal ecosystems: Addressing the imbalance. Estuaries and Coasts 31(2):233–38. Dunn FE, Darby SE, Nicholls RJ, Cohen S, Zarfl C, Fekete BM. 2019. Projections of declining fluvial sediment delivery to major deltas worldwide in response to climate change and anthropogenic stress. Environmental Research Letters 14(8):084034. Esteban M, Jamero L, Nurse L, Yamamoto L, Takagi H, Thao ND, Mikami T, Kench P, Onuki M, Nellas A, and 6 -others. 2019. Adaptation to sea level rise on low coral islands: -Lessons from recent events. Ocean & Coastal Management 168:35–40. Haasnoot M, Kwakkel JH, Walker WE, ter Maat J. 2013. Dynamic adaptive policy pathways: A method for crafting robust decisions for a deeply uncertain world. Global Environmental Change 23:485–98. Haigh ID, Wahl T, Rohling EJ, Price RM, Pattiaratchi CB, Calafat FM, Dangendorf S. 2014. Timescales for detecting a significant acceleration in sea level rise. Nature Communications 5:3635. Hallegatte S, Green C, Nicholls RJ, Corfee-Morlot J. 2013. Future flood losses in major coastal cities. Nature Climate Change 3:802–806. Hauer ME, Fussell E, Mueller V, Burkett M, Call M, Abel K, McLeman R, Wrathall D. 2019. Sea-level rise and human migration. Nature Reviews Earth & Environment 1:28–39. Hinkel J, van Vuuren DP, Nicholls RJ, Klein RJT. 2013. The effects of mitigation and adaptation on coastal impacts in the 21st century. Climatic Change 117:783–94. Hinkel J, Jaeger CC, Nicholls RJ, Lowe J, Renn O, Peijun S. 2015. Sea-level rise scenarios and coastal risk management. Nature Climate Change 5:188–90. Hinkel J, Aerts JCJH, Brown S, Jiménez JA, Lincke D, -Nicholls RJ, Scussolini P, Sanchez-Arcilla A, Vafeidis A, Addo KA. 2018. The ability of societies to adapt to twenty-first-century sea-level rise. Nature Climate Change 8:570–578. Hinkel J, Church JA, Gregory JM, Lambert E, Le Cozannet G, Lowe J, McInnes KL, Nicholls RJ, Pol TD, van de Wal R. 2019. Meeting user needs for sea level rise information: A decision analysis perspective. Earth’s Future 7(6804):320–37. Hino M, Field CB, Mach KJ. 2017. Managed retreat as a response to natural hazard risk. Nature Climate Change 7:364–70. IPCC [Intergovernmental Panel on Climate Change]. 2014. Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects. Contribution of Working Group II to the Fifth Assessment Report of the IPCC, eds Field CB, Barros VR, Dokken DJ, Mach KJ, Mastrandrea MD, Bilir TE, Chatterjee M, Ebi KL, Estrada YO, Genova RC, and 6 others. New York: Cambridge University Press. IPCC. 2019. Summary for policymakers. In: Special Report on the Ocean and Cryosphere in a Changing Climate. New York: Cambridge University Press. Kabat P, Fresco LO, Stive MJF, Veerman CP, van Alphen JSLJ, Parmet BWAH, Hazeleger W, Katsman CA. 2009. Dutch coasts in transition. Nature Geoscience 2:450–52. Kaneko S, Toyota T. 2011. Long-term urbanization and land subsidence in Asian megacities: An indicators system approach. In: Groundwater and Subsurface Environments: Human Impacts in Asian Coastal Cities, ed Taniguchi M. Tokyo: Springer. Lawrence J, Bell R, Blackett P, Stephens S, Allan S. 2018. National guidance for adapting to coastal hazards and sea-level rise: Anticipating change, when and how to change pathway. Environmental Science & Policy 82:100–107. Li Y, Shi Y, Zhu X, Cao H, Yu T. 2014. Coastal wetland loss and environmental change due to rapid urban expansion in Lianyungang, Jiangsu, China. Regional Environmental Change 14:1175–88. Lincke D, Hinkel J. 2018. Economically robust protection against 21st century sea-level rise. Global Environmental Change 51:67–73. Lowe JA, Howard TP, Pardaens A, Tinker J, Holt J, Wakelin S, Milne G, Leake J, Wolf J, Horsburgh K, and 5 others. 2009. UK Climate Projections Science Report: Marine and Coastal Projections. Exeter UK: Met Office Hadley Centre. Lu D, Flavelle C. 2019. Rising seas will erase more cities by 2050, new research shows. New York Times, Oct 29. Martín-Antón M, Negro V, del Campo JM, López-Gutiérrez JS, Esteban MD. 2016. Review of coastal land reclamation situation in the world. Journal of Coastal Research 75:667–71. MELUR-SH [Ministerium für Energiewende, Landwirtschaft, Umwelt und ländliche Räume des Landes Schleswig-Holstein]. 2012. Generalplan Küstenschutz des Landes Schleswig-Holstein—Fortschreibung 2012. Kiel. Narayan S, Beck MW, Reguero BG, Losada IJ, van -Wesenbeeck B, Pontee N, Sanchirico JN, Ingram JC, Lange G-M, Burks-Copes KA. 2016. The effectiveness, costs and coastal protection benefits of natural and nature-based defences. PLoS One 11:e0154735. Nicholls RJ, Townend IH, Bradbury AP, Ramsbottom D, Day SA. 2013. Planning for long-term coastal change: Experiences from England and Wales. Ocean Engineering 71:3–16. Nicholls RJ, Hanson SE, Lowe JA, Warrick RA, Lu X, Long AJ. 2014. Sea-level scenarios for evaluating coastal impacts. WIREs Climate Change 5:129–50. Nicholls RJ, Hinkel J, Lincke D, van der Pol T. 2019. Global Investment Costs for Coastal Defense through the 21st Century (No. WPS8745). Washington: World Bank. Oppenheimer M, Glavovic B, Hinkel J, van de Wal R, Magnan AK, Abd-Elgawad A, Cai R, Cifuentes-Jara M, Deconto RM, Ghosh T, and 5 others. 2019. Sea level rise and implications for low lying islands, coasts and communities. In: Special Report on the Ocean and Cryosphere in a Changing Climate, eds Pörtner H-O, Roberts DC, Masson-Delmotte V, Zhai P, Tignor M, Poloczanska E, Mintenbeck K, Alegría A, Nicolai M, Okem A, and 3 others. Geneva: Intergovernmental Panel on Climate Change. Pinsky ML, Guannel G, Arkema KK. 2013. Quantifying wave attenuation to inform coastal habitat conservation. -Ecosphere 4(8):95. Pontee N, Narayan S, Beck MW, Hosking AH. 2016. Nature-based solutions: Lessons from around the world. Maritime Engineering 169(1):29–36. Quataert E, Storlazzi C, van Rooijen A, Cheriton O, van Dongeren A. 2015. The influence of coral reefs and climate change on wave‐driven flooding of tropical coastlines. Geophysical Research Letters 42:6407–15. Ranger N, Reeder T, Lowe J. 2013. Addressing “deep” uncertainty over long-term climate in major infrastructure -projects: Four innovations of the Thames Estuary 2100 -Project. EURO Journal on Decision Processes 1(3-4):233–62. Siders AR, Hino M, Mach KJ. 2019. The case for strategic and managed climate retreat. Science 365(6455):761–63. Spalding MD, McIvor AL, Beck MW, Koch EW, Möller I, Reed DJ, Rubinoff P, Spencer T, Tolhurst TJ, Wamsley TV, and 3 others. 2014. Coastal ecosystems: A critical element of risk reduction. Conservation Letters 7:293–301. Stammer D, van de Wal RSW, Nicholls RJ, Church JA, Le Cozannet G, Lowe JA, Horton BP, White K, Behar D, -Hinkel J. 2019. Framework for high-end estimates of sea level rise for stakeholder applications. Earth’s Future 7(8):923–38. Stephens SA, Bell RG, Lawrence J. 2018. Developing signals to trigger adaptation to sea-level rise. Environmental Research Letters 13(10):104004. Temmerman S, Meire P, Bouma TJ, Herman PMJ, Ysebaert T, Vriend HJD. 2013. Ecosystem-based coastal defence in the face of global change. Nature 504:79–83. Wahl T, Haigh ID, Nicholls RJ, Arns A, Dangendorf S, -Hinkel J, Slangen ABA. 2017. Understanding extreme sea -levels for broad-scale coastal impact and adaptation analysis. Nature Communications 8:16075. Wilby RL, Nicholls RJ, Warren R, Wheater HS, Clarke D, Dawson RJ. 2011. Keeping nuclear and other coastal sites safe from climate change. Civil Engineering 164:129–36. Wong PP, Losada IJ, Gattuso J-P, Hinkel J, Khattabi A, McInnes KL, Saito Y, Sallenger A. 2014. Coastal systems and low-lying areas. In: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects. Contribution of Working Group II to the Fifth Assessment Report of the IPCC, eds Field CB, -Barros VR, Dokken DJ, Mach KJ, Mastrandrea MD, Bilir TE, -Chatterjee M, Ebi KL, Estrada YO, Genova RC, and 6 -others. Geneva: Inter-governmental Panel of Climate Change.  The IPCC (2014) defines four Representative Concentration Pathways (RCPs) to characterize greenhouse gas concentration trajectories, from a low of 2.6 to a high of 8.5.  Amounts are in US dollars and are not discounted. About the Author:Jochen Hinkel is senior researcher and head of adaptation and social learning research at the Global Climate Forum and a lecturer in the Division of Resource Economics at Albrecht Daniel Thaer Institute, Humboldt University, Berlin. Robert Nicholls is director of the Tyndall Centre for Climate Change Research at the University of East Anglia.