Coastal Systems and Low-Lying Areas
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6 Coastal systems and low-lying areas Coordinating Lead Authors: Robert J. Nicholls (UK), Poh Poh Wong (Singapore) Lead Authors: Virginia Burkett (USA), Jorge Codignotto (Argentina), John Hay (New Zealand), Roger McLean (Australia), Sachooda Ragoonaden (Mauritius), Colin D. Woodroffe (Australia) Contributing Authors: Pamela Abuodha (Kenya), Julie Arblaster (USA/Australia), Barbara Brown (UK), Don Forbes (Canada), Jim Hall (UK), Sari Kovats (UK), Jason Lowe (UK), Kathy McInnes (Australia), Susanne Moser (USA), Susanne Rupp-Armstrong (UK), Yoshiki Saito (Japan), Richard S.J. Tol (Ireland) Review Editors: Job Dronkers (The Netherlands), Geoff Love (Australia), Jin-Eong Ong (Malaysia) This chapter should be cited as: Nicholls, R.J., P.P. Wong, V.R. Burkett, J.O. Codignotto, J.E. Hay, R.F. McLean, S. Ragoonaden and C.D. Woodroffe, 2007: Coastal systems and low-lying areas. Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E. Hanson, Eds., Cambridge University Press, Cambridge, UK, 315-356. Coastal systems and low-lying areas Chapter 6 Table of Contents .....................................................317 ......336 Executive summary 6.5 Costs and other socio-economic aspects 6.5.1 Methods and tools for characterising socio- 6.1 Introduction: scope, summary of TAR economic consequences ......................................337 ..............................318 conclusions and key issues 6.5.2 Socio-economic consequences under current climate conditions .................................................337 ...................318 6.2 Current sensitivity/vulnerability 6.5.3 Socio-economic consequences of climate 6.2.1 Natural coastal systems.........................................318 change...................................................................338 6.2.2 Increasing human utilisation of the coastal zone ...319 6.2.3 External terrestrial and marine influences ..............319 6.6 Adaptation: practices, options and ...........................................................340 6.2.4 Thresholds in the behaviour of coastal systems....320 constraints 6.6.1 Adaptation to changes in climate and sea level ...340 6.2.5 Observed effects of climate change on coastal systems .................................................................321 Box 6.5 Recent extreme events – lessons for coastal adaptation to climate change................................340 Box 6.1 Environmental thresholds and observed coral bleaching......................................................322 6.6.2 Costs and benefits of adaptation..........................342 6.6.3 Limits and trade-offs in adaptation .......................342 6.3 Assumptions about future trends for 6.6.4 Adaptive capacity..................................................344 .............322 coastal systems and low-lying areas 6.6.5 The links between adaptation and mitigation 6.3.1 Environmental and socio-economic trends ...........322 in coastal and low-lying areas...............................344 6.3.2 Climate and sea-level scenarios ............................322 6.7 Conclusions: implications for sustainable .......324 ........................................................345 6.4 Key future impacts and vulnerabilities development 6.4.1 Natural system responses to climate change drivers....................................................................324 6.8 Key uncertainties, research gaps and ..............................................................345 Box 6.2 Examples of extreme water level simulations priorities for impact studies..................................................325 Box 6.6 Long-term sea-level rise impacts (beyond 2100)........................................................346 Box 6.3 Deltas and megadeltas: hotspots for vulnerability ...........................................................327 ......................................................................347 6.4.2 Consequences for human society .........................330 References Box 6.4 Hurricane Katrina and coastal ecosystem services in the Mississippi delta............................332 6.4.3 Key vulnerabilities and hotspots ............................336 316 Chapter 6 Coastal systems and low-lying areas Executive Summary people by the 2080s, depending on assumptions about migration [6.3.1]. Increasing numbers of people and assets at risk at the coast are subject to additional stresses due to land-use and hydrological Since the IPCC Third Assessment Report (TAR), our changes in catchments, including dams that reduce sediment understanding of the implications of climate change for coastal supply to the coast [6.3.2]. Populated deltas (especially Asian systems and low-lying areas (henceforth referred to as ‘coasts’) megadeltas), low-lying coastal urban areas and atolls are key has increased substantially and six important policy-relevant societal hotspots of coastal vulnerability, occurring where the messages have emerged. stresses on natural systems coincide with low human adaptive capacity and high exposure [6.4.3]. Regionally, South, South-east Coasts are experiencing the adverse consequences of and East Asia, Africa and small islands are most vulnerable hazards related to climate and sea level (very high confidence). [6.4.2]. Climate change therefore reinforces the desirability of Coasts are highly vulnerable to extreme events, such as storms, managing coasts in an integrated manner [6.6.1.3]. which impose substantial costs on coastal societies [6.2.1, 6.2.2, Adaptation for the coasts of developing countries will be 6.5.2]. Annually, about 120 million people are exposed to more challenging than for coasts of developed countries, tropical cyclone hazards, which killed 250,000 people from 1980 due to constraints on adaptive capacity (high confidence). to 2000 [6.5.2]. Through the 20th century, global rise of sea level contributed to increased coastal inundation, erosion and While physical exposure can significantly influence ecosystem losses, but with considerable local and regional vulnerability for both human populations and natural systems, a variation due to other factors [6.2.5, 6.4.1]. Late 20th century lack of adaptive capacity is often the most important factor that effects of rising temperature include loss of sea ice, thawing of creates a hotspot of human vulnerability. Adaptive capacity is permafrost and associated coastal retreat, and more frequent largely dependent upon development status. Developing nations coral bleaching and mortality [6.2.5]. may have the political or societal will to protect or relocate people who live in low-lying coastal zones, but without the Coasts will be exposed to increasing risks, including coastal necessary financial and other resources/capacities, their erosion, over coming decades due to climate change and vulnerability is much greater than that of a developed nation in sea-level rise (very high confidence). an identical coastal setting. Vulnerability will also vary between Anticipated climate-related changes include: an accelerated rise developing countries, while developed countries are not in sea level of up to 0.6 m or more by 2100; a further rise in sea insulated from the adverse consequences of extreme events surface temperatures by up to 3°C; an intensification of tropical [6.4.3, 6.5.2]. and extra-tropical cyclones; larger extreme waves and storm Adaptation costs for vulnerable coasts are much less than surges; altered precipitation/run-off; and ocean acidification the costs of inaction (high confidence). [6.3.2]. These phenomena will vary considerably at regional and local scales, but the impacts are virtually certain to be Adaptation costs for climate change are much lower than overwhelmingly negative [6.4, 6.5.3]. damage costs without adaptation for most developed coasts, even considering only property losses and human deaths [6.6.2, Corals are vulnerable to thermal stress and have low adaptive 6.6.3]. As post-event impacts on coastal businesses, people, capacity. Increases in sea surface temperature of about 1 to 3°C housing, public and private social institutions, natural resources, are projected to result in more frequent coral bleaching events and the environment generally go unrecognised in disaster cost and widespread mortality, unless there is thermal adaptation or accounting, the full benefits of adaptation are even larger [6.5.2, acclimatisation by corals [Box 6.1, 6.4]. 6.6.2]. Without adaptation, the high-end sea-level rise scenarios, combined with other climate changes (e.g., increased storm Coastal wetland ecosystems, such as saltmarshes and intensity), are as likely as not to render some islands and low- mangroves, are especially threatened where they are sediment- lying areas unviable by 2100, so effective adaptation is urgently starved or constrained on their landward margin [6.4.1]. required [6.6.3]. Degradation of coastal ecosystems, especially wetlands and The unavoidability of sea-level rise, even in the longer-term, coral reefs, has serious implications for the well-being of frequently conflicts with present-day human development societies dependent on the coastal ecosystems for goods and patterns and trends (high confidence). services [6.4.2, 6.5.3]. Increased flooding and the degradation of freshwater, fisheries and other resources could impact Sea-level rise has substantial inertia and will continue beyond