Editing IPCC:AR6/WGII/Chapter-3 (section)

=== 3.6.3 Implementation and Effectiveness of Adaptation and Mitigation Measures ===

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This section assesses implemented adaptations introduced in [[#3.6.2|Section 3.6.2]] for selected marine sectors ( [[#3.6.3.1|Section 3.6.3.1]] ) and ecosystems ( [[#3.6.3.2|Section 3.6.3.2]] ), using case studies to emphasise characteristics that enable or inhibit adaptation ( [[#3.6.3.3|Section 3.6.3.3]] ). The feasibility and effectiveness of these adaptations are assessed in Figure 3.24.

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[[File:249b35bf2d448ba466510a4f2992ed36 IPCC_AR6_WGII_Figure_3_024.png]]

'''Figure 3.24 |''' '''Assessment of feasibility and effectiveness of adaptation solutions for ocean and coastal ecosystems.''' Feasibility dimensions assessed include: technical and economic capacity to deliver and implement the solution; the institutional and geophysical capacity to implement a solution; and associated social and ecological implications that make a solution more feasible. The general feasibility level is obtained from assessment of the three dimensions together. Note that feasibility is assessed for marine and coastal ecosystems as a whole and not by ecosystem type or region. Feasibility dimensions and assessment are updated and adapted from [[#IPCC--2018|IPCC (2018)]] and [[#Singh--2020|Singh et al. (2020)]] . Effectiveness: ability of the adaptation solution to reduce climate-change mid-term risks. The main solutions are assessed per sector. (Underlying data are available in Table 3.SM.3.)

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==== 3.6.3.1 Degree of Implementation and Evidence of Effectiveness Across Sectors ====

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===== 3.6.3.1.1 Coastal community development and settlement =====

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Coastal adaptation often addresses the risk of flooding and erosion from SLR, changes in storm activity and degradation of coastal ecosystems and their services ( ''high confidence'' ) (Sections 3.4.2, 3.5; [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ). Without coastal protection, people and property will be increasingly exposed to coastal flooding after 2050, especially under RCP8.5 (Cross-Chapter Box SLR in Chapter 3; [[#Bevacqua--2020|Bevacqua et al., 2020]] ; [[#Kirezci--2020|Kirezci et al., 2020]] ). This section assesses adaptation responses for coastal ecosystems, addressing loss of natural coastal protection (Sections 3.4.2.1, 3.4.2.4–3.4.2.6), and the need for relocation ( [[#3.6.2.1|Section 3.6.2.1.2]] ). Adaptation responses specific to SLR are assessed in detail in Cross-Chapter Box SLR in Chapter 3, while adaptation in coastal cities and settlements is assessed in Chapter 6.

Coastal conservation tends to involve cost-effective, low-impact actions that aim to support both adaptation and mitigation by conserving a wide array of ecosystem functions and services ( [[#Gattuso--2018|Gattuso et al., 2018]] ; [[#Gattuso--2021|Gattuso et al., 2021]] ), and that are achievable by nations with extensive coastlines or low-income status ( [[#Herr--2017|Herr et al., 2017]] ; [[#Taillardat--2018|Taillardat et al., 2018]] ). Where coastlines are undeveloped, the lowest-risk option is to avoid new development, but elsewhere, coastal conservation includes protection of key assets, accommodation of SLR, advancing defences seawards or upwards, or planned retreat from the coast (Cross-Chapter Box SLR in Chapter 3).

Hard-engineered structures like seawalls are generally more costly than nature-based adaptations ( ''high confidence'' ) ( [[#Hérivaux--2018|Hérivaux et al., 2018]] ; [[#Haasnoot--2019|Haasnoot et al., 2019]] ; [[#Nicholls--2019|Nicholls et al., 2019]] ; [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ) and can lock communities into engineered responses in the future (Cross-Chapter Box SLR in Chapter 3), creating trade-offs with mitigation goals, which constitutes maladaptation ( [[#Nunn--2021|Nunn et al., 2021]] ) that carries ecological and cultural costs (Sections 3.4.2.4, 3.4.2.6, 3.5.6). As a result, there is ''high agreement'' on the importance of shifting from hard infrastructure to soft infrastructure for coastal defence ( [[#Toimil--2020|Toimil et al., 2020]] ; [[#Nunn--2021|Nunn et al., 2021]] ). The common remedy for beach erosion is beach nourishment ( [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ; [[#Pinto--2020|Pinto et al., 2020]] ; [[#Elko--2021|Elko et al., 2021]] ), which provides rapid results but poorly quantified trade-offs between efficacy, long-term cost, utility to beach users and ecological damage ( [[#de%20Schipper--2021|de Schipper et al., 2021]] ).

Since SROCC, coastal adaptation using NbS, like restoration of coastal vegetation, has advanced substantially ( [[#Cohen-Shacham--2019|Cohen-Shacham et al., 2019]] ; [[#Kuhl--2020|Kuhl et al., 2020]] ; [[#Kumar--2020|Kumar et al., 2020]] ; [[#Morris--2020a|Morris et al., 2020a]] ). Field and modelling studies confirm that wetland restoration and preservation are key actions to restore coastal protection and reduce community vulnerability to flooding ( ''very high confidenc'' e) (see also [[#3.6|Section 3.6]] ; Chapter 15; Cross-Chapter Box SLR in Chapter 3; [[#Jones--2020|Jones et al., 2020]] ; [[#Menéndez--2020|Menéndez et al., 2020]] ; [[#Van%20Coppenolle--2020|Van Coppenolle and Temmerman, 2020]] ), while maintaining coastal ecosystem services ( [[#3.5|Section 3.5]] ). Restoring coral reefs, oyster reefs and mangroves ( [[#3.6.2.1|Section 3.6.2.1]] ) and protecting macrophyte meadows dissipates wave energy ( [[#3.4.2.1|Section 3.4.2.1]] ; [[#Yates--2017|Yates et al., 2017]] ; [[#Beck--2018|Beck et al., 2018]] ; [[#Wiberg--2019|Wiberg et al., 2019]] ; [[#Menéndez--2020|Menéndez et al., 2020]] ), accretes sediment and elevate shorelines, which reduces exposure to waves and storm surges, and offsets erosional losses ( ''medium confidence'' ) ( [[#Kench--2017|Kench and Mann, 2017]] ; [[#Pomeroy--2018|Pomeroy et al., 2018]] ; [[#Dasgupta--2019|Dasgupta et al., 2019]] ; [[#James--2019|James et al., 2019]] ; [[#Morris--2019|Morris et al., 2019]] ; [[#David--2020|David and Schlurmann, 2020]] ; [[#Masselink--2020|Masselink et al., 2020]] ). However, irreversible regime shifts in ocean ecosystems due to SLR and extreme events, such as MHWs, can limit or compromise restoration in the long term ( ''high confidence'' ) ( [[#3.4.3.3.3|Section 3.4.3.3.3]] ; Cross-Chapter Box SLR in Chapter 3; [[#Marzloff--2016|Marzloff et al., 2016]] ; [[#Johnson--2017a|Johnson et al., 2017a]] ). Under all warming scenarios, coastal wetlands will be impacted by warming and MHWs (Sections 3.2.2.1, 3.2.4.5; Cross-Chapter Box 9.1 in WGI Chapter 9; [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ), while also being pressed inland by RSLR ( [[#3.4.2.5|Section 3.4.2.5]] ; Cross-Chapter Box SLR in Chapter 3). Therefore, restoration and conservation are more successful when non-climate drivers are also minimised ( ''high confidence'' ) ( [[#Brodie--2020|Brodie et al., 2020]] ; [[#Duarte--2020|Duarte et al., 2020]] ; [[#Liu--2021|Liu et al., 2021]] ).

For highly exposed human settlements, migration is an adaptation option (e.g., for some island populations under extreme circumstances), but there are important uncertainties ( [[IPCC:Wg2:Chapter:Chapter-15#15.3.4.6|Section 15.3.4.6]] ), as international regimes develop around human rights, migration ( [[#Scobie--2019a|Scobie, 2019a]] ), displacement (George [[#Puthucherril--2012|Puthucherril, 2012]] ) and the implications for national sovereignty ( [[#Yamamoto--2014|Yamamoto and Esteban, 2014]] ) of disappearing land spaces caused by climate change. Colonial power dynamics can influence climate-change responses (Chapter 18), for example, when external funders favour migration over local desires to adapt in place to preserve national identity and sovereignty ( [[#Bordner--2020|Bordner et al., 2020]] ). Examples of relocation within livelihoods’ customary land show some successes ( [[IPCC:Wg2:Chapter:Chapter-15#15.3.4.6|Section 15.3.4.6]] ).

Evidence since SROCC (Section, 5.5.2.3.3; [[#Bindoff--2019a|Bindoff et al., 2019a]] ) continues to show that built infrastructure cannot address all of the adaptation challenges that coastal communities face. Coastal squeeze creates tensions between coastal development, armouring and habitat management (Sections 3.4.2.4–3.4.2.6). Managed realignment is the best option to reduce risks from SLR ( ''high confidence'' ) (Cross-Chapter Box SLR in Chapter 3) but requires transformative changes in coastal development and settlement (Felipe [[#Pérez--2021|Pérez and Tomaselli, 2021]] ; [[#Fitton--2021|Fitton et al., 2021]] ; [[#Mach--2021|Mach and Siders, 2021]] ; [[#Siders--2021|Siders et al., 2021]] ). Implementation of protective measures varies among nations and lack of financial resources limits the options available ( ''very high confidence'' ) (Cross-Chapter Box SLR in Chapter 3; [[#Hinkel--2018|Hinkel et al., 2018]] ; [[#Klöck--2019|Klöck and Nunn, 2019]] ).

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===== 3.6.3.1.2 Fisheries and mariculture =====

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SROCC ( [[#Bindoff--2019a|Bindoff et al., 2019a]] ) assessed adaptation in fisheries and mariculture (marine aquaculture), and socioeconomically focused updates are provided in [[IPCC:Wg2:Chapter:Chapter-5#5.8.4|Section 5.8.4]] and Cross-Chapter Box MOVING SPECIES in Chapter 5. Here, we present a brief synthesis of how fisheries and mariculture adaptations interact with the natural environment, with further detail and supporting material in SM3.5.2.

Mobility allows fishing fleets and fishers to adapt to shifts in marine species distributions ( ''high agreement'' ) (Sections 3.4.3.1, 3.5.3; [[#Peck--2018|Peck and Pinnegar, 2018]] ; [[#Pinsky--2018|Pinsky et al., 2018]] ; [[#Frazão%20Santos--2020|Frazão Santos et al., 2020]] ) but with limits and unintended consequences ( [[#Pinsky--2012|Pinsky and Fogarty, 2012]] ; [[#Bell--2021|Bell et al., 2021]] ). Diversification of target species, harvest tactics and employment sectors, including transitions from fisheries to mariculture and ecotourism, allows some fishers to accommodate some impacts on their livelihoods ( [[#Miller--2018|Miller et al., 2018]] ; [[#Robinson--2020|Robinson et al., 2020]] ; [[#Gonzalez-Mon--2021|Gonzalez-Mon et al., 2021]] ). Technology and infrastructure adaptations can improve marine harvest efficiency, reduce risk and support resource management goals ( [[#Friedman--2020|Friedman et al., 2020]] ; [[#Bell--2021|Bell et al., 2021]] ; [[#Melbourne-Thomas--2021|Melbourne-Thomas et al., 2021]] ), but their ability to overcome climate-change impacts remains uncertain ( [[#Bell--2020|Bell et al., 2020]] ). Improving capacity to predict anomalous conditions in coastal and marine ecosystems ( [[#Jacox--2019|Jacox et al., 2019]] ; [[#Holbrook--2020|Holbrook et al., 2020]] ; [[#Jacox--2020|Jacox et al., 2020]] ), storm-driven flooding in reef-lined coasts ( [[#Scott--2020|Scott et al., 2020]] ; [[#Winter--2020|Winter et al., 2020]] ) and fisheries stocks ( [[#Payne--2017|Payne et al., 2017]] ; [[#Tommasi--2017|Tommasi et al., 2017]] ; [[#Muhling--2018|Muhling et al., 2018]] ) can improve forecasts of coastal and marine resources; these can enhance sustainability of wild-capture fisheries under climate change ( ''high confidence'' ) ( [[#Blanchard--2017|Blanchard et al., 2017]] ; [[#Tommasi--2017|Tommasi et al., 2017]] ; [[#Pinsky--2020a|Pinsky et al., 2020a]] ; [[#Bell--2021|Bell et al., 2021]] ). Limiting overexploitation is the central goal of fishery management, and it ''very likely'' benefits fisheries adaptation to climate change ( [[#Burden--2019|Burden and Fujita, 2019]] ; [[#Free--2019|Free et al., 2019]] ; [[#Sumaila--2020|Sumaila and Tai, 2020]] ). Conventional tools include catch and size limits, spatial management and adaptive management. Ecosystem-based fisheries management outperforms single-species management ( [[#Fulton--2019|Fulton et al., 2019]] ), is widely legislated ( [[#Bryndum-Buchholz--2021|Bryndum-Buchholz et al., 2021]] ) and can reduce climate impacts in fisheries in the near-term, especially under low-emission scenarios ( [[#Karp--2019|Karp et al., 2019]] ; [[#Holsman--2020|Holsman et al., 2020]] ). Transboundary agreements on shifting fisheries will reduce the risk of overharvesting ( ''medium confidence'' ) ( [[#Gaines--2018|Gaines et al., 2018]] ). Permits tradable across political boundaries could also address this challenge, but ''limited evidence'' is available regarding their efficacy (Cross-Chapter Box MOVING SPECIES in Chapter 5; [[#Pinsky--2018|Pinsky et al., 2018]] ). Climate-smart conservation ( [[#3.6.3|Section 3.6.3]] 2.1) under the negotiations on areas beyond national jurisdiction (ABNJ) ( [[#Pinsky--2018|Pinsky et al., 2018]] ; [[#Tittensor--2019|Tittensor et al., 2019]] ; [[#Frazão%20Santos--2020|Frazão Santos et al., 2020]] ), and in the Convention on Biological Diversity (CBD) areas designed as other effective area-based conservation measures (OECMs) ( [[#Tittensor--2019|Tittensor et al., 2019]] ), provide further benefits. Despite the potential for adaptive management to achieve sustainable fisheries, outcomes will ''very likely'' be inequitable ( [[#Gaines--2018|Gaines et al., 2018]] ; [[#Lam--2020|Lam et al., 2020]] ), with lower-income countries suffering the greater biomass and economic losses, increasing inequalities, especially under higher-emission scenarios ( ''high confidence'' ) ( [[#Boyce--2020|Boyce et al., 2020]] ). Flexible and polycentric governance approaches have facilitated some short-term successes in achieving equitable, sustainable fisheries practices, but these may be challenging to implement where other governance systems, especially hierarchical systems, are well established ( [[#Cvitanovic--2018|Cvitanovic et al., 2018]] ; [[#Bell--2020|Bell et al., 2020]] ).

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===== 3.6.3.1.3 Tourism =====

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Coastal areas, coastal infrastructure and beaches, sustaining tourism that contributes significantly to local economies ( [[#James--2019|James et al., 2019]] ; [[#Ruiz-Ramírez--2019|Ruiz-Ramírez et al., 2019]] ), are under threat from development, SLR and increased wave energy during storms ( ''high confidence'' ) (Sections 3.4.2.4–3.4.2.6, 3.5.6, SM3.3.1; [[#Lithgow--2019|Lithgow et al., 2019]] ; [[#Ruiz-Ramírez--2019|Ruiz-Ramírez et al., 2019]] ). Engineered solutions, such as seawalls and revetments, have traditionally been used to address coastal erosion ( [[#3.6.3.1.1|Section 3.6.3.1.1]] ), but soft infrastructure approaches, including beach nourishment, submerged breakwaters and groins, and NbS ( [[#3.6.2.1|Section 3.6.2.1]] ), are becoming more common, partly due to demand from the tourism industry ( ''medium confidence'' ) ( [[#Pranzini--2018|Pranzini, 2018]] ; [[#Pranzini--2018|Pranzini et al., 2018]] ).

Elsewhere, interactions between tourism and climate impacts worsen outcomes for coastal and ocean environments ( [[#3.6.3.1.4|Section 3.6.3.1.4]] ). Climate change is opening up new cruise-ship routes in the Arctic ( [[#Sun--2018|Sun et al., 2018]] ), increasing the number of visitors and associated stressors, such as litter, to previously undisturbed areas ( [[#Anfuso--2020|Anfuso et al., 2020]] ; [[#Hovelsrud--2020|Hovelsrud et al., 2020]] ; [[#Suaria--2020|Suaria et al., 2020]] ). Risk reduction for cruise-ship tourism includes disaster response management, improved mapping and passenger codes of conduct ensuring social, cultural and ecological sustainability ( [[#Stewart--2015|Stewart et al., 2015]] ; [[#Dawson--2016|Dawson et al., 2016]] ).

Marine ecotourism, integrating conservation, education and provision of benefits to local communities ( [[#Donohoe--2006|Donohoe and Needham, 2006]] ) can provide significant economic benefits ( [[#Wabnitz--2019|Wabnitz, 2019]] ) and is among the most common livelihood alternatives to support both marine conservation and climate-change adaptation ( [[#Kutzner--2019|Kutzner, 2019]] ; [[#Pham--2020|Pham, 2020]] ; [[#Prasetyo--2020|Prasetyo et al., 2020]] ). Ecotourism can enhance social and political will for marine conservation ( [[#Cisneros-Montemayor--2014|Cisneros-Montemayor and Sumaila, 2014]] ) and facilitates integration of local and Indigenous Peoples in employment, ownership and industry governance. The community of Cabo Pulmo, Mexico, self-imposed an MPA and replaced fishing with ecotourism, which now generates millions of USD yr –1 , sustains locally owned and operated tour companies and has increased some fish populations tenfold ( [[#Knowlton--2020|Knowlton, 2020]] ). In Misool, Indonesia, local ecotourism incorporates IK by including local communities’ preferences and sustainable resource use ( [[#Prasetyo--2020|Prasetyo et al., 2020]] ).

Unintended consequences of ecotourism, such as detrimental ecological impacts on reefs ( [[#Giglio--2020|Giglio et al., 2020]] ), sharks, marine birds ( [[#Monti--2018|Monti et al., 2018]] ) and whales ( [[#Higham--2016|Higham et al., 2016]] ; [[#Barra--2020|Barra et al., 2020]] ; [[#Hoarau--2020|Hoarau et al., 2020]] ), can be minimised by relying on evidence-based management of associated activities ( [[#Blumstein--2017|Blumstein et al., 2017]] ). Public perception of climate-change connections to tourism can create obstacles ( [[#Meynecke--2017|Meynecke et al., 2017]] ; [[#Atzori--2018|Atzori et al., 2018]] ) such as deterring long-term investment in SIDS tourism initiatives ( [[#Santos-Lacueva--2017|Santos-Lacueva et al., 2017]] ), or benefits like inclining tourists to participate in conservation projects ( [[#Curnock--2019|Curnock et al., 2019]] ; [[#Miller--2020b|Miller et al., 2020b]] ; [[#Ziegler--2021|Ziegler et al., 2021]] ). Social and cultural networks may decrease climate vulnerability, as with Indigenous tourism operators in SIDS ( [[#Parsons--2018|Parsons et al., 2018]] ). Tourism-based adaptation can also be improved by equitable access to resources as well as recognition and inclusion of all stakeholders during policy planning and implementation. The principles of marine spatial planning ( [[#Papageorgiou--2016|Papageorgiou, 2016]] ) provide for effectively incorporating stakeholders and could inform development of activities to assess climate-associated risks (e.g., [[#Tzoraki--2018|Tzoraki et al., 2018]] ; [[#Loehr--2020|Loehr, 2020]] ). The recent decrease in global tourism due to the COVID-19 pandemic may offer opportunities to transform existing practices to more sustainable approaches (Cross-Chapter Box COVID in Chapter 7; [[#Gössling--2021|Gössling et al., 2021]] ).

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===== 3.6.3.1.4 Maritime transport =====

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Increased maritime transport and cruise-ship tourism in the Arctic are already impacting local and Indigenous Peoples, revealing conflicts over the uses of the ocean and the governance needed to support local people and a sustainable blue economy ( ''high confidence'' ) ( [[#Debortoli--2019|Debortoli et al., 2019]] ; [[#Palma--2019|Palma et al., 2019]] ; [[#Berman--2020|Berman et al., 2020]] ; [[#Dundas--2020|Dundas et al., 2020]] ). While shipping and its associated environmental impacts are projected to grow ( [[#Palma--2019|Palma et al., 2019]] ; [[#Dawson--2020|Dawson et al., 2020]] ), adaptation efforts are only at the planning stage ( [[#Debortoli--2019|Debortoli et al., 2019]] ). Increased Arctic traffic due to ice loss can benefit trade, transportation and tourism ( ''medium confidence'' ), but will also affect Arctic marine ecosystems and livelihoods ( ''high confidence'' ) ( [[#Palma--2019|Palma et al., 2019]] ; [[#Dawson--2020|Dawson et al., 2020]] ). Increasing search-and-rescue activities ( [[#Ford--2019|Ford and Clark, 2019]] ) reveal capacity gaps to support future demands ( [[#Ford--2019|Ford and Clark, 2019]] ; [[#Palma--2019|Palma et al., 2019]] ). The Low-Impact Shipping Corridors initiative has been developed as an adaptation strategy in the Arctic, although with limited inclusion of IKLK ( [[#Dawson--2020|Dawson et al., 2020]] ).

Relative SLR and the increased frequency and severity of storms are already affecting port activity, infrastructure and supply chains, sometimes disrupting trade and transport ( [[#Monios--2020|Monios and Wilmsmeier, 2020]] ), but these hazards are not systematically incorporated into adaptation planning ( ''medium evidence'' ) ( [[#Monios--2020|Monios and Wilmsmeier, 2020]] ; [[#O’Keeffe--2020|O’Keeffe et al., 2020]] ). Climate-change impacts that increase food insecurity, income loss and poverty can exacerbate maritime criminal activity, including illegal fishing, drug trafficking or piracy ( ''medium evidence'' ) ( [[#Germond--2019|Germond and Mazaris, 2019]] ). A transformational adaptation approach to address climate impacts on maritime activities and increase security ( [[#Germond--2019|Germond and Mazaris, 2019]] ) would relocate ports, change centres of demand, reduce shipping distances or shorten supply chains ( ''medium agreement'' ) ( [[#Walsh--2019|Walsh et al., 2019]] ; [[#Monios--2020|Monios and Wilmsmeier, 2020]] ) as well as decrease marginalisation of vulnerable groups, develop polycentric governance systems and eliminate maladaptive environmental policies and resource loss ( [[#Belhabib--2020|Belhabib et al., 2020]] ; [[#O’Keeffe--2020|O’Keeffe et al., 2020]] ).

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===== 3.6.3.1.5 Human health =====

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Health-focused adaptations to climate-driven changes in ocean and coastal water quality ( [[#3.5.5.3|Section 3.5.5.3]] ) leverage mainly technology and infrastructure ( [[#3.6.2.2|Section 3.6.2.2]] ) to improve water-quality monitoring and forecasting to inform socio-institutional adaptation ( [[#3.6.2.1|Section 3.6.2.1]] ) and NbS ( [[#3.6.2.3|Section 3.6.2.3]] ). Seafood quality and safety are decreasing due to climate-driven increases in marine-borne diseases (Cross-Chapter Box ILLNESS in Chapter 2), toxic HABs or toxin bioaccumulation ( ''high agreement'' ) ( [[#Karagas--2012|Karagas et al., 2012]] ; [[#Krabbenhoft--2013|Krabbenhoft and Sunderland, 2013]] ; [[#Rafaj--2013|Rafaj et al., 2013]] ; [[#Curtis--2019|Curtis et al., 2019]] ; [[#Schartup--2019|Schartup et al., 2019]] ; [[#Thackray--2019|Thackray and Sunderland, 2019]] ). Future exposure to seafood-borne contaminants also depends partly on consumers’ seafood preferences ( [[#Elsayed--2020|Elsayed et al., 2020]] ) and seafood supply ( [[#Sunderland--2018|Sunderland et al., 2018]] ). Reducing this risk by decreasing seafood consumption increases the risk of eating less nutritious foods, and loss of cultural practices (Chapter 5; Cross-Chapter Box MOVING SPECIES in Chapter 5; [[#Donatuto--2011|Donatuto et al., 2011]] ; [[#Bindoff--2019a|Bindoff et al., 2019a]] ). Models incorporating high-resolution satellite images, field survey data, meteorological observations and historical records can provide early-warning forecasts of HABs or conditions that favour microbial pathogen outbreaks (Cross-Chapter Box ILLNESS in Chapter 2; [[#Semenza--2017|Semenza et al., 2017]] ; [[#Franks--2018|Franks, 2018]] ; [[#Hattenrath-Lehmann--2018|Hattenrath-Lehmann et al., 2018]] ; [[#Borbor-Cordova--2019|Borbor-Cordova et al., 2019]] ; [[#Davis--2019|Davis et al., 2019]] ; [[#Campbell--2020a|Campbell et al., 2020a]] ; [[#Davidson--2021|Davidson et al., 2021]] ). Forecasts facilitate preventive public health measures ( [[#World%20Health%20Organisation%20and%20United%20Nations%20Children’s%20Fund--2017|World Health Organisation and United Nations Children’s Fund, 2017]] ), or seafood harvest guidance ( [[#Maguire--2016|Maguire et al., 2016]] ; [[#Leadbetter--2018|Leadbetter et al., 2018]] ; [[#Anderson--2019|Anderson et al., 2019]] ; [[#Bolin--2021|Bolin et al., 2021]] ), reducing risks of disease outbreaks, waste and contaminated seafood entering the market ( ''medium confidence'' ) (Cross-Chapter Box ILLNESS in Chapter 2; [[#Nichols--2018|Nichols et al., 2018]] ). Monitoring of water quality and seafood safety (Cross-Chapter Box ILLNESS in Chapter 2), paired with effective public communication and education ( [[#Ekstrom--2020|Ekstrom et al., 2020]] ), inform individual and local adaptations, including use of (a) personal protective equipment, (b) seafood selection and preparation ( [[#Elsayed--2020|Elsayed et al., 2020]] ; [[#Froelich--2020|Froelich and Daines, 2020]] ; [[#Fielding--2021|Fielding et al., 2021]] ), (c) income diversification ( [[#3.6.2.1|Section 3.6.2.1]] ; [[#Moore--2020b|Moore et al., 2020b]] ), (d) public education ( [[#Borbor-Cordova--2019|Borbor-Cordova et al., 2019]] ) or (e) community-level actions to decrease risk from coastal aquifer and soil salinisation ( [[#Slama--2020|Slama et al., 2020]] ; [[#Mastrocicco--2021|Mastrocicco and Colombani, 2021]] ), HAB toxins ( [[#Ekstrom--2020|Ekstrom et al., 2020]] ) and other contaminants (e.g., methylmercury, metals, persistent organic pollutants) in seafood ( [[#Chan--2021|Chan et al., 2021]] ). A full assessment of climate-change impacts on human health is found in [[IPCC:Wg2:Chapter:Chapter-7|Chapter 7]] and Cross-Chapter Box ILLNESS in Chapter 2.

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==== 3.6.3.2 Cross-Cutting Solutions for Coastal and Ocean Ecosystems ====

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SROCC concluded that protection, restoration and pollution reduction can support ocean and coastal ecosystems ( ''high confidence'' ), and that EbA lowers climate risks locally and provides multiple societal benefits ( ''high confidence'' ) ( [[#IPCC--2019c|IPCC, 2019c]] ). This section updates the assessment of the effectiveness of these strategies for addressing climate impacts.

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===== 3.6.3.2.1 Area-based protection: MPAs for adapting to climate change =====

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Marine protected areas are the most widely implemented area-based management approach ( [[#3.6.2.3|Section 3.6.2.3.2]] ), commonly intended to conserve, preserve or restore biodiversity and habitats, protect species or manage resources (especially fisheries) ( [[#National%20Research%20Council--2001|National Research Council, 2001]] ). By August 2021, 7.74% of the ocean was protected (in both MPAs and OECMs) ( [[#UNEP-WCMC%20and%20IUCN--2021|UNEP-WCMC and IUCN, 2021]] ), primarily within nations’ exclusive economic zones (EEZs). These MPAs support adaptation by sustaining nearshore ecosystems that provide natural erosion barriers (Sections 3.4.2.1–3.4.2.5; Cross-Chapter Box SLR in Chapter 3), ecosystem function ( [[#Cheng--2019|Cheng et al., 2019]] ), habitat, natural filtration, carbon storage, livelihoods and cultural opportunities (Sections 3.5.5, 3.5.6; [[#Erskine--2021|Erskine et al., 2021]] ), and help ecosystems and livelihoods recover after extreme events ( [[#Roberts--2017|Roberts et al., 2017]] ; [[#Aalto--2019|Aalto et al., 2019]] ; [[#Wilson--2020a|Wilson et al., 2020a]] ). However, in 2021 only 2.7% of the ocean was in fully or highly protected MPAs ( [[#Marine%20Conservation%20Institute--2021|Marine Conservation Institute, 2021]] ), the hard-to-achieve states that most effectively rebuild biomass and fish community structure ( [[#Sala--2017|Sala and Giakoumi, 2017]] ; [[#Bergseth--2018|Bergseth, 2018]] ; [[#Zupan--2018|Zupan et al., 2018]] ; [[#Ohayon--2021|Ohayon et al., 2021]] ). Only 1.18% of ABNJ is protected ( [[#UNEP-WCMC%20and%20IUCN--2021|UNEP-WCMC and IUCN, 2021]] ), mostly due to governance limitations ( [[#O’Leary--2017|O’Leary and Roberts, 2017]] ; [[#Vijayaraghavan--2021|Vijayaraghavan, 2021]] ), but calls to protect more ABNJ emphasise the need to protect the habitats of long-range pelagic fish and marine mammals, maintain the ocean’s regulating functions and minimise impacts from uses such as maritime shipping or deep-sea mining (Table 3.30).

Marine protected areas are theorised to facilitate ecological climate adaptation and contribute to SDG14 (Life Below Water) (Table 3.30; Figure 3.26; [[#Bates--2014|Bates et al., 2014]] ; [[#Lubchenco--2015|Lubchenco and Grorud-Colvert, 2015]] ; [[#Gattuso--2018|Gattuso et al., 2018]] ) because they alleviate non-climate drivers and promote biodiversity (i.e., ‘managed resilience hypothesis’) ( [[#Bruno--2019|Bruno et al., 2019]] ; [[#Maestro--2019|Maestro et al., 2019]] ; [[#Cinner--2020|Cinner et al., 2020]] ). Current MPAs offer conservation benefits such as increases in biomass and diversity of habitats, populations and communities ( ''high confidence'' ) ( [[#Pendleton--2018|Pendleton et al., 2018]] ; [[#Bates--2019|Bates et al., 2019]] ; [[#Stevenson--2020|Stevenson et al., 2020]] ; [[#Lenihan--2021|Lenihan et al., 2021]] ; [[#Ohayon--2021|Ohayon et al., 2021]] ), and these benefits may last after some (possibly climate-enhanced) disturbances (e.g., tropical cyclones) ( [[#McClure--2020|McClure et al., 2020]] ). But current MPAs do not provide resilience against observed warming and heatwaves in tropical-to-temperate ecosystems ( ''medium confidence'' ) ( [[#Bates--2019|Bates et al., 2019]] ; [[#Bruno--2019|Bruno et al., 2019]] ; [[#Freedman--2020|Freedman et al., 2020]] ; [[#Graham--2020|Graham et al., 2020]] ; [[#Rilov--2020|Rilov et al., 2020]] ). There is ''robust evidence'' that processes around MPA design and implementation strongly influence whether outcomes are beneficial or harmful for adjacent human communities (Mc [[#Neill--2018|Neill et al., 2018]] ; [[#Zupan--2018|Zupan et al., 2018]] ; [[#Ban--2019|Ban et al., 2019]] ).

Current placement and extent of MPAs will not provide substantial protections against projected climate change past 2050 ( ''high confidence'' ), as the placement of MPAs has been driven more often by political expediency (e.g., [[#Leenhardt--2013|Leenhardt et al., 2013]] ) than by managing key drivers of biodiversity loss ( [[#Cockerell--2020|Cockerell et al., 2020]] ; [[#Stevenson--2020|Stevenson et al., 2020]] ) or climate-induced drivers ( [[#Bruno--2018|Bruno et al., 2018]] ). Only 3.5% of the area currently protected will provide refuges from both SST and deoxygenation by 2050 under both RCP4.5 and RCP8.5 ( [[#Bruno--2018|Bruno et al., 2018]] ), and MPAs are more exposed to climate change under RCP8.5 than non-MPAs ( [[#3.4.3.3.4|Section 3.4.3.3.4]] ; Figure 3.20d). Community thermal tolerances will be exceeded by 2050 in the tropics and by 2150 for many higher-latitude MPAs ( [[#Bruno--2018|Bruno et al., 2018]] ). Most MPA design has focused on the surface ocean, but MPAs are assumed to protect the entire water column and benthos. Climate-induced drivers ( [[#3.2|Section 3.2]] ) throughout the water column and rapidly accelerating climate velocities at depths below 200 m ( [[#Johnson--2018|Johnson et al., 2018]] ; [[#Brito-Morales--2020|Brito-Morales et al., 2020]] ) are projected to affect virtually all North Atlantic deep-water and open-ocean area-based management zones in the next 20–50 years ( [[#Johnson--2018|Johnson et al., 2018]] ), and the conservation goals of benthic MPAs in the North Sea are not expected to be fulfilled ( [[#Weinert--2021|Weinert et al., 2021]] ). Heightened risk of non-indigenous species immigration from vessel traffic plus climate change further endangers MPA success ( [[#Iacarella--2020|Iacarella et al., 2020]] ), a particular concern in the Mediterranean ( [[#D’Amen--2020|D’Amen and Azzurro, 2020]] ; [[#Mannino--2021|Mannino and Balistreri, 2021]] ), where the current MPA network is already highly vulnerable to climate change ( [[#Kyprioti--2021|Kyprioti et al., 2021]] ). This new evidence supports SROCC’s ''high confidence'' assessment that present governance arrangements, including MPAs, are too fragmented to provide integrated responses to the increasing and cascading risks from climate change in the ocean (SROCC SPMC1.2; [[#IPCC--2019c|IPCC, 2019c]] ).

Strategic conservation planning can yield future MPA networks substantially more ready for climate change (e.g., [[#3.6.3.1.5|Section 3.6.3.1.5]] ; SROCC SPM C2.1; [[#IPCC--2019c|IPCC, 2019c]] ; [[#Frazão%20Santos--2020|Frazão Santos et al., 2020]] ; [[#Rassweiler--2020|Rassweiler et al., 2020]] ). Global protection is increasing ( [[#Worm--2017|Worm, 2017]] ; [[#Claudet--2020b|Claudet et al., 2020b]] ) as nations pursue international targets (e.g., SDG14, Life Below Water aimed to conserve 10% of the ocean by 2020), and the UN CBD proposes to protect 30% by 2030 ( [[#3.6.4|Section 3.6.4]] ; SM3.5.3; [[#CBD--2020|CBD, 2020]] ). A growing body of evidence ( [[#Tittensor--2019|Tittensor et al., 2019]] ; [[#Zhao--2020a|Zhao et al., 2020a]] ; [[#Pörtner--2021b|Pörtner et al., 2021b]] ; [[#Sala--2021|Sala et al., 2021]] ) underscores the urgent need to pursue biodiversity, ecosystem-service provision and climate-adaptation goals simultaneously, while acknowledging inherent trade-offs ( [[#Claudet--2020a|Claudet et al., 2020a]] ; [[#Sala--2021|Sala et al., 2021]] ). Frameworks to create ‘climate-smart’ MPAs ( [[#Tittensor--2019|Tittensor et al., 2019]] ) generally include: (a) defining conservation goals that embrace resource vulnerabilities and co-occurring hazards; (b) carefully selecting adaptation strategies that include IKLK while respecting Indigenous rights and accommodating human behaviour ( [[#Kikiloi--2017|Kikiloi et al., 2017]] ; [[#Thomas--2018|Thomas, 2018]] ; [[#Yates--2019|Yates et al., 2019]] ; [[#Failler--2020|Failler et al., 2020]] ; [[#Wilson--2020a|Wilson et al., 2020a]] ; [[#Croke--2021|Croke, 2021]] ; Reimer et al., 2021; [[#Vijayaraghavan--2021|Vijayaraghavan, 2021]] ); (c) developing protection that is appropriate for all ocean depths ( [[#Brito-Morales--2018|Brito-Morales et al., 2018]] ; [[#Frazão%20Santos--2020|Frazão Santos et al., 2020]] ; [[#Wilson--2020a|Wilson et al., 2020a]] ), especially considering climate velocity ( [[#Arafeh-Dalmau--2021|Arafeh-Dalmau et al., 2021]] ); (d) using dynamic national and international management tools to accommodate extreme events or species distribution shifts ( [[#Gaines--2018|Gaines et al., 2018]] ; [[#Pinsky--2018|Pinsky et al., 2018]] ; [[#Bindoff--2019a|Bindoff et al., 2019a]] ; [[#Scheffers--2019|Scheffers and Pecl, 2019]] ; [[#Tittensor--2019|Tittensor et al., 2019]] ; [[#Cashion--2020|Cashion et al., 2020]] ; [[#Crespo--2020|Crespo et al., 2020]] ; [[#Frazão%20Santos--2020|Frazão Santos et al., 2020]] ; [[#Maxwell--2020b|Maxwell et al., 2020b]] ), which could build on dynamic regulations already in place for fishing or ship strikes ( [[#Maxwell--2020b|Maxwell et al., 2020b]] ); and (e) seeking to increase connectivity ( [[#Wilson--2020a|Wilson et al., 2020a]] ), using genomic or multi-species model insights ( [[#Xuereb--2020|Xuereb et al., 2020]] ; [[#Friesen--2021|Friesen et al., 2021]] ; [[#Lima--2021|Lima et al., 2021]] ).

There is growing international support for a 30% conservation target for 2030 ( [[#Gurney--2021|Gurney et al., 2021]] ), which will need efforts beyond protected areas. For example, OECMs recognise management interventions that sustain biodiversity, irrespective of their main objective ( [[#Maxwell--2020b|Maxwell et al., 2020b]] ; [[#Gurney--2021|Gurney et al., 2021]] ). There is ''high agreement'' on the potential of OECMs to contribute to conservation and equity, for example, by recognising Indigenous territories as OECMs ( [[#Maxwell--2020b|Maxwell et al., 2020b]] ; [[#Gurney--2021|Gurney et al., 2021]] ); however, the capacity of these conservation tools to provide adaptation outcomes remains unexplored.

In summary, MPAs and other marine spatial-planning tools have great potential to address climate-change mitigation and adaptation in ocean and coastal ecosystems, if they are designed and implemented in a coordinated way that takes into account ecosystem vulnerability and responses to projected climate conditions, considers existing and future ecosystem uses and non-climate drivers, and supports effective governance ( ''high confidence'' ).

<div id="3.6.3.2.2" class="h4-container"></div>

<span id="ecological-restoration-interventions-and-their-limitations"></span>
===== 3.6.3.2.2 Ecological restoration, interventions and their limitations =====

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Restoration of degraded ecosystems is a common NbS increasingly deployed at local scales in response to climate change (Cross-Chapter Box NATURAL in Chapter 2; [[#Duarte--2020|Duarte et al., 2020]] ; [[#Bertolini--2021|Bertolini and da Mosto, 2021]] ; [[#Braun%20de%20Torrez--2021|Braun de Torrez et al., 2021]] ). Despite covering limited areas and having uncertain efficacy under future climate change ( [[#Gordon--2020|Gordon et al., 2020]] ), these actions have successfully restored marine populations and ecosystems at regional to global scales ( [[#Duarte--2020|Duarte et al., 2020]] ), and enhanced livelihoods and the well-being of coastal peoples as well as the biodiversity and resilience of ecological communities ( [[#Silver--2019|Silver et al., 2019]] ; [[#Gordon--2020|Gordon et al., 2020]] ; [[#Braun%20de%20Torrez--2021|Braun de Torrez et al., 2021]] ). Technology-based approaches, such as active restoration, assisted evolution and ecological forecasting, can aid in moving beyond restoring ecosystems ( [[#3.6.2.3|Section 3.6.2.3]] ) towards enhancing resilience, reviving biodiversity and guarding against loss of foundational, ornamental or iconic species ( [[#Bulleri--2018|Bulleri et al., 2018]] ; [[#Collins--2019a|Collins et al., 2019a]] ; [[#da%20Silva--2019|da Silva et al., 2019]] ; [[#National%20Academies%20of%20Sciences--2019|National Academies of Sciences, 2019]] ; [[#Boström-Einarsson--2020|Boström-Einarsson et al., 2020]] ; [[#Fredriksen--2020|Fredriksen et al., 2020]] ; [[#Morris--2020c|Morris et al., 2020c]] ; [[#Kleypas--2021|Kleypas et al., 2021]] ).

Local restoration projects often target vegetated ecosystems like mangroves, seagrasses and salt marshes that are valued and used by coastal communities ( [[#Veettil--2019|Veettil et al., 2019]] ; [[#Duarte--2020|Duarte et al., 2020]] ; [[#Wu--2020a|Wu et al., 2020a]] ; [[#Bertolini--2021|Bertolini and da Mosto, 2021]] ). Detail on mangroves and corals as EbA and protection/restoration hotspots is provided in SM3.8. Common and effective actions ( [[#Sasmito--2019|Sasmito et al., 2019]] ; [[#Duarte--2020|Duarte et al., 2020]] ; [[#Oreska--2020|Oreska et al., 2020]] ) include securing accommodation space (Sections 3.4.2.4–3.4.2.5), restoring hydrological ( [[#Kroeger--2017|Kroeger et al., 2017]] ; [[#Al-Haj--2020|Al-Haj and Fulweiler, 2020]] ) and sediment dynamics; managing harvesting (particularly in mangroves); reducing pollution (especially in seagrasses) ( [[#de%20los%20Santos--2019|de los Santos et al., 2019]] ); and replanting appropriate species in suitable environmental settings ( [[#Wodehouse--2019|Wodehouse and Rayment, 2019]] ; [[#Friess--2020a|Friess et al., 2020a]] ). Although efficacy is context dependent ( [[#Zeng--2020|Zeng et al., 2020]] ; [[#Krause-Jensen--2021|Krause-Jensen et al., 2021]] ) and implementation is most often local ( [[#Alongi--2018a|Alongi, 2018a]] ), such projects facilitate tangible community engagement in climate action. Moreover, because these ecosystems sequester disproportionate amounts of carbon (blue carbon) (Annex II: Glossary; see Box 3.4), restoration supports climate-change mitigation ( [[#Lovelock--2020|Lovelock and Reef, 2020]] ; [[#Gattuso--2021|Gattuso et al., 2021]] ). Yet, constraints remain. For instance, Southeast Asia has 1.21 million km 2 of terrestrial, freshwater and mangrove area biophysically suitable for reforestation, which could mitigate 3.43 ± 1.29 Pg CO 2 e yr −1 through 2030; however, reforestation is only feasible in a small fraction of this area (0.3–18%) given financial, land-use and operational constraints ( [[#Zeng--2020|Zeng et al., 2020]] ). Nevertheless, the multiple benefits offered by ecosystem restoration will ''likely'' outweigh competing costs and increase its relevance as part of adaptation-strategy portfolios ( [[#Silver--2019|Silver et al., 2019]] ; [[#Wedding--2021|Wedding et al., 2021]] ), national carbon-accounting systems and nationally determined contributions by parties to the Paris Agreement ( [[#Friess--2020a|Friess et al., 2020a]] ; [[#Wu--2020a|Wu et al., 2020a]] ).

Restoration efficacy of coral reefs, kelp forests and other habitat-forming coastal ecosystems (Sections 3.4.2.2–3.4.2.6) are jeopardised by the near-term nature of climate-driven risks ( [[#McLeod--2019|McLeod et al., 2019]] ; [[#National%20Academies%20of%20Sciences--2019|National Academies of Sciences, 2019]] ; [[#Coleman--2020b|Coleman et al., 2020b]] ). Modelling studies indicate that available practices will not prevent degradation of coral reefs from &gt;1.5°C of global average surface warming (Figure 3.25; [[#National%20Academies%20of%20Sciences%20Engineering%20and%20Medicine--2019|National Academies of Sciences Engineering and Medicine, 2019]] ; [[#Condie--2021|Condie et al., 2021]] ; [[#Hafezi--2021|Hafezi et al., 2021]] ). Proposed interventions include assisted migration ( [[#Boström-Einarsson--2020|Boström-Einarsson et al., 2020]] ; [[#Fredriksen--2020|Fredriksen et al., 2020]] ; [[#Morris--2020c|Morris et al., 2020c]] ), assisted evolution ( [[#Bay--2019|Bay et al., 2019]] ; [[#National%20Academies%20of%20Sciences--2019|National Academies of Sciences, 2019]] ) and other engineering solutions like artificial shading and enhanced upwelling ( [[#Condie--2021|Condie et al., 2021]] ; [[#Kleypas--2021|Kleypas et al., 2021]] ).

<div id="_idContainer117" class="Figure"></div>

[[File:d481dbbb29b57218790cb7abc53fb919 IPCC_AR6_WGII_Figure_3_025.png]]

'''Figure 3.25 |''' '''Implemented and potential future adaptations in ocean and coastal ecosystems.'''

'''(a)''' Global implementation since 1970 of (top) cumulative habitat-restoration projects ( [[#Duarte--2020|Duarte et al., 2020]] ), (middle) cumulative area-based conservation protected area (MPA total) ( [[#Boonzaier--2016|Boonzaier and Pauly, 2016]] ), no-take areas (UN Environment World Conservation Monitoring Centre et al., 2018; [[#UNEP-WCMC--2019|UNEP-WCMC, 2019]] ) and (bottom) percentage of total fish stocks rebuilt ( [[#Kleisner--2013|Kleisner et al., 2013]] ).

'''(b)''' Adaptation pathways for coral reefs to maintain healthy cover (line weight: solid lines, ''likely'' effectiveness; dashed lines, ''more likely'' ''than not'' to ''likely ;'' dotted lines = ''unlikely to more likely than not'' ), with confidence noted for each intervention ( [[#3.4.2.1|Section 3.4.2.1]] , 3.6.3.2; [[#Anthony--2019|Anthony et al., 2019]] ; [[#National%20Academies%20of%20Sciences--2019|National Academies of Sciences, 2019]] )

'''(c)''' As in (b), but for mangrove ecosystems. (Underlying data are available in Tables SM3.4–3.6.)

Transplanting heat-tolerant coral colonies can increase reef resistance to bleaching ( [[#Morikawa--2019|Morikawa and Palumbi, 2019]] ; [[#Howells--2021|Howells et al., 2021]] ) but potentially lower species diversity and alter ecosystem function ( [[#3.4.2.1|Section 3.4.2.1]] ). Genetic manipulation or assisted evolution that propagates genes from heat-tolerant populations could enhance restoration of corals ( [[#Anthony--2017|Anthony et al., 2017]] ; [[#Epstein--2019|Epstein et al., 2019]] ) and kelp ( ''medium agreement, limited evidence'' ) ( [[#Coleman--2019|Coleman and Goold, 2019]] ; [[#Coleman--2020b|Coleman et al., 2020b]] ; [[#Fredriksen--2020|Fredriksen et al., 2020]] ; [[#Wade--2020|Wade et al., 2020]] ). Managed breeding of corals has also had limited success in the laboratory and at small local scales ( [[#National%20Academies%20of%20Sciences--2019|National Academies of Sciences, 2019]] ). There is also ''limited evidence'' that physiological interventions, such as algal-symbiont or microbiome manipulation, could increase coral thermal tolerance in the field ( [[#National%20Academies%20of%20Sciences--2019|National Academies of Sciences, 2019]] ). Employing the natural adaptive capacity of species or individuals in active restoration for corals and kelps with current technology involves fewer risks than assisted evolution or long-distance relocation ( ''high confidence'' ) ( [[#Filbee-Dexter--2019|Filbee-Dexter and Smajdor, 2019]] ; [[#National%20Academies%20of%20Sciences--2019|National Academies of Sciences, 2019]] ). More ambitious engineered interventions like reef shading remain theoretical and not scalable to the reef level ( [[#Condie--2021|Condie et al., 2021]] ). Debate continues on how to apply planned adaptation in cost-effective ways that will accomplish the intended goals ( [[#National%20Academies%20of%20Sciences--2019|National Academies of Sciences, 2019]] ; [[#Duarte--2020|Duarte et al., 2020]] ; [[#Kleypas--2021|Kleypas et al., 2021]] ).

Models show that a combination of available management approaches (restoration, reducing non-climate drivers) and speculative interventions (e.g., enhanced corals, reef shading) can contribute to sustaining some coral reefs beyond 1.5°C of global warming with declining effectiveness beyond 2°C of global warming ( ''medium confidence'' ) (Figure 3.25; WGII Chapter 17). These proposed interventions are also currently theoretical and impractical over large scales; for example, engineered solutions like reef shading are untested and not scalable at the reef level ( [[#Condie--2021|Condie et al., 2021]] ). Existing projects suggest that restoration and ecological interventions to habitat-forming ecosystems have the additional benefits of raising local awareness, promoting tourism, and creating jobs and economic benefits ( [[#Fadli--2012|Fadli et al., 2012]] ; [[#Boström-Einarsson--2020|Boström-Einarsson et al., 2020]] ; [[#Hafezi--2021|Hafezi et al., 2021]] ), provided communities are involved in planning, operation and monitoring ( [[#Boström-Einarsson--2020|Boström-Einarsson et al., 2020]] ).

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<span id="enablers-barriers-and-limitations-of-adaptation-and-mitigation"></span>
==== 3.6.3.3 Enablers, Barriers and Limitations of Adaptation and Mitigation ====

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Not only is mitigation necessary to support ocean and coastal adaptation ( [[#Pörtner--2014|Pörtner et al., 2014]] ; [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ), but the global emission pathways also impose limits to ocean and coastal adaptation, with lower warming levels enabling greater effectiveness of adaptations ( ''high confidence'' ) (Figure 3.25). [[IPCC:Wg2:Chapter:Chapter-17|Chapter 17]] broadly assesses the limits to adaptation, while this section focuses on barriers and limits to adaptation imposed by cultural ( [[#3.6.3.3.1|Section 3.6.3.3.1]] ), economic ( [[#3.6.3.3.2|Section 3.6.3.3.2]] ) and governance ( [[#3.6.3.3.3|Section 3.6.3.3.3]] ) dimensions ( [[#Hinkel--2018|Hinkel et al., 2018]] ). Globally, these factors more strongly influence ocean development than does local natural resource availability ( [[#Cisneros-Montemayor--2021|Cisneros-Montemayor et al., 2021]] ), and are key to avoiding maladaptation. This section also assesses enablers and limits to mitigation ( [[#3.6.3.3.4|Section 3.6.3.3.4]] ).

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<span id="sociocultural-dimensions-culture-ethics-identity-behaviour"></span>
===== 3.6.3.3.1 Sociocultural dimensions (culture, ethics, identity, behaviour) =====

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Every coastal community values marine ecosystems for more than the material and intangible resources they deliver, or the physical protection they offer ( [[#Díaz--2018|Díaz et al., 2018]] ). Cultural services that provide identity, spiritual and cultural continuity, religious meaning or options for the future (e.g., genetic or mineral resources) ( [[#Bindoff--2019a|Bindoff et al., 2019a]] ) are not substitutable. Furthermore, interactions between climate impacts and existing inequalities can threaten the human rights of already-marginalised peoples by disrupting livelihoods and food security, which further erodes people’s social, economic and cultural rights ( [[#Finkbeiner--2018|Finkbeiner et al., 2018]] ). For instance, European colonisation and ongoing development blocked the Cucapá Indigenous People’s access and rights to resources in the Colorado River Delta, USA, over the 20th century. Recent reallocation of water rights and fishing access is allowing the Cucapá people to reconstruct their cultural identity ( [[#Sangha--2019|Sangha et al., 2019]] ), but future climate-change impacts could reverse the community’s recovery of their cultural heritage. Adaptations that consider local needs may help sustain cultural services ( [[#Ortíz%20Liñán--2021|Ortíz Liñán and Vázquez Solís, 2021]] ).

Interactions with oceans are fundamental to the identities of many coastal Indigenous Peoples ( [[#Norman--2017|Norman, 2017]] ), and this influences Indigenous responses to climate hazards and adaptation. Around 30 million Indigenous Peoples live along coasts ( [[#Cisneros-Montemayor--2016|Cisneros-Montemayor et al., 2016]] ). Seafood consumption among Indigenous Peoples is much higher than for non-Indigenous populations, and marine species support many cultural, medicinal and traditional activities contributing to public health ( [[#3.5.3|Section 3.5.3.1]] ; [[#Kenny--2018|Kenny et al., 2018]] ). Perpetuation of Indigenous cultures depends on protecting marine ecosystems and on adapting to changes in self-led ways ( [[#3.5.6|Section 3.5.6]] ; [[#Sangha--2019|Sangha et al., 2019]] ) that promote self-determination ( [[#von%20der%20Porten--2019|von der Porten et al., 2019]] ). Indigenous resurgence, or reinvigorating Indigenous ways of life and traditional management, can include marine resource protection and ocean-sector development founded on culturally appropriate strategies and partnerships that are consistent with traditional norms and beneficial to local communities ( [[#von%20der%20Porten--2019|von der Porten et al., 2019]] ). Successful adaptation would simultaneously improve ecosystem health and address current and historical inequities ( [[#Bennett--2018|Bennett, 2018]] ). Examples include practicing traditional resource management, protecting traditional territories, engaging with monitoring, collaborations with non-Indigenous partners and reinvesting benefits into capacity-building within communities ( [[#von%20der%20Porten--2019|von der Porten et al., 2019]] ; [[#Equator%20Initiative--2020|Equator Initiative, 2020]] ). The legitimacy of different adaptation strategies depends on local and Indigenous Peoples’ acceptance, which is based on cultural values ( [[#Adger--2017|Adger et al., 2017]] ); financial gain cannot compensate for loss of IK or LK ( [[#Wilson--2020b|Wilson et al., 2020b]] ). Palau’s recent goal of shifting seafood consumption away from reef fishes (Remengesau Jr., 2019) as well as limiting and closely monitoring the expansion of ecotourism was prompted by the cultural importance of protecting these reefs and associated traditional fisheries for local consumption, a recognition of the importance of tourism and the hazard of climate change ( [[#Wabnitz--2018a|Wabnitz et al., 2018a]] ).

Adaptations implemented at the local level that consider IKLK systems are beneficial ( ''high confidence'' ) ( [[#Nalau--2018|Nalau et al., 2018]] ; [[#Sultana--2019|Sultana et al., 2019]] ). Studies in SIDS and the Arctic have shown how IKLK facilitate the success of EbA ( [[#Nalau--2018|Nalau et al., 2018]] ; [[#Peñaherrera-Palma--2018|Peñaherrera-Palma et al., 2018]] ; [[#Raymond-Yakoubian--2018|Raymond-Yakoubian and Daniel, 2018]] ), reinforce and improve institutional approaches and enhance the provision of ecosystem services ( [[#Ross--2019|Ross et al., 2019]] ; [[#Terra%20Stori--2019|Terra Stori et al., 2019]] ). Perspectives on adaptation also vary among groups of age, race, (dis)ability, class, caste and gender ( [[#Wilson--2020b|Wilson et al., 2020b]] ), so engaging different groups results in more robust and equitable adaptation to climate change (Cross-Chapter Box GENDER in Chapter 18; [[#McLeod--2018|McLeod et al., 2018]] ). Some coastal communities have developed substantial social capital and dense local networks based on trust and reciprocity ( [[#Petzold--2015|Petzold and Ratter, 2015]] ), with individual and community flexibility to learn, adapt and organise themselves to help local adaptation governance ( [[#Silva--2020|Silva et al., 2020]] ). Recent evidence suggests that policies supporting local institutions can improve adaptation outcomes ( ''medium confidence'' ) ( [[#Berman--2020|Berman et al., 2020]] ). Coastal communities can be engaged using novel approaches to co-generate adaptation solutions ( [[#van%20der%20Voorn--2017|van der Voorn et al., 2017]] ; [[#Flood--2018|Flood et al., 2018]] ) that benefit education ( [[#Koenigstein--2020|Koenigstein et al., 2020]] ) and engagement in adaptation processes ( [[#Rumore--2016|Rumore et al., 2016]] ). Successful adaptation implementation in line with climate resilient development pathways (WGII Chapter 18) depends on bottom-up, participatory and inclusive processes ( [[#3.6.1|Section 3.6.1.2.1]] ) that engage diverse stakeholders ( [[#Basel--2020|Basel et al., 2020]] ; [[#McNamara--2020|McNamara et al., 2020]] ; [[#Ogier--2020|Ogier et al., 2020]] ; [[#Williams--2020|Williams et al., 2020]] ) and protect Indigenous customary rights ( [[#Farbotko--2019|Farbotko and McMichael, 2019]] ; [[#Ford--2020|Ford et al., 2020]] ), empower women and give rights to climate refugees ( [[#McLeod--2018|McLeod et al., 2018]] ).

<div id="3.6.3.3.2" class="h4-container"></div>

<span id="economic-dimensions-planning-finance-costs"></span>
===== 3.6.3.3.2 Economic dimensions (planning, finance, costs) =====

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Finance is a key barrier globally for ocean health, governance and adaptation to climate change ( ''high agreement'' ) (Annex II: Glossary; Cross-Chapter Box FINANCE in Chapter 17; [[#Hinkel--2018|Hinkel et al., 2018]] ; [[#Miller--2018|Miller et al., 2018]] ; [[#Wabnitz--2019|Wabnitz and Blasiak, 2019]] ; [[#Woodruff--2020|Woodruff et al., 2020]] ; [[#Sumaila--2021|Sumaila et al., 2021]] ). Global adaptation finance was estimated to total 30 billion USD yr –1 in 2017–2018, or 5% of all climate finance ( [[#CPI--2019|CPI, 2019]] ), with no tracking specifically for coastal or marine adaptation in low- to middle-income countries. Marine-focused adaptation finance is difficult to trace and label due to the cross-sectoral nature of many projects ( [[#Blasiak--2018|Blasiak and Wabnitz, 2018]] ) and the lack of clear definitions about what qualifies as adaptation or as new and additional finance ( [[#Donner--2016|Donner et al., 2016]] ; [[#Weikmans--2019|Weikmans and Roberts, 2019]] ). Finance for marine conservation from Overseas Development Assistance doubled between 2003 and 2016, reaching 634 million USD in 2016, similar to the level provided by philanthropic foundations ( [[#Berger--2019|Berger et al., 2019]] ). Yet coastal adaptation to SLR alone is projected to cost hundreds of billions of USD yr –1 , depending on the model and emission scenario (e.g., [[#Wong--2014|Wong et al., 2014]] ; [[#Nicholls--2019|Nicholls et al., 2019]] ). Economic and financing barriers to marine adaptation are often higher in low- to middle-income countries, where resources influence governance and constrain options for implementation and maintenance ( ''high confidence'' ) ( [[#Hinkel--2018|Hinkel et al., 2018]] ; [[#Klöck--2019|Klöck and Nunn, 2019]] ; [[#Tompkins--2020|Tompkins et al., 2020]] ), and impacts on their coastal and marine ecosystems could total several percentage points of their gross domestic product ( [[#Wong--2014|Wong et al., 2014]] ). Current financial flows are insufficient to meet the costs of coastal and marine impacts of climate change ( ''very high confidence'' ) and ocean-focused finance is unevenly distributed, with higher flows within, and to, developed countries ( ''very high confidence'' ).

Development assistance can help resolve resource constraints, but additional governance and coordination challenges can arise from short-term, project-based funding, shifting the priorities of donor institutions and the pressures placed on human resources in the receiving nation ( [[#Parsons--2019|Parsons and Nalau, 2019]] ; [[#Nunn--2020|Nunn et al., 2020]] ). Innovative policy instruments, such as concessional loans, tax-policy reforms, climate bonds and public-debt forgiveness, can supplement traditional financial instruments ( [[#Bisaro--2018|Bisaro and Hinkel, 2018]] ; [[#McGowan--2020|McGowan et al., 2020]] ). Mechanisms for solving the persistent problem of securing upfront investments for coastal protection and other adaptation measures ( [[#Bisaro--2018|Bisaro and Hinkel, 2018]] ; [[#Moser--2019|Moser et al., 2019]] ; [[#Kok--2021|Kok et al., 2021]] ) include integrating adaptation investments into insurance schemes ( [[#Reguero--2020|Reguero et al., 2020]] ) and using debt financing to bridge the time until benefits are realised ( [[#Ware--2020|Ware and Banhalmi-Zakar, 2020]] ). Insurance mechanisms that link payments to losses from a trigger event (e.g., MHW) can confer resilience to marine-dependent communities ( [[#Sumaila--2021|Sumaila et al., 2021]] ). All innovative financial instruments are most effective when they are inclusive and reach vulnerable groups and marginalised communities ( ''low evidence, high agreement'' ) ( [[#Claudet--2020a|Claudet et al., 2020a]] ; [[#Sumaila--2021|Sumaila et al., 2021]] ).

Countries with large ocean areas within their EEZs have opportunities to develop ‘blue–green economies’ to reduce emissions and finance adaptation pathways ( [[#Chen--2018a|Chen et al., 2018a]] ; [[#Lee--2020|Lee et al., 2020]] ). Shifting from grants to results-based financing can help attract more private capital to ocean adaptation ( [[#Lubchenco--2016|Lubchenco et al., 2016]] ; [[#Claudet--2020a|Claudet et al., 2020a]] ). Public–private partnerships can also increase ocean adaptation finance ( [[#Goldstein--2019|Goldstein et al., 2019]] ; [[#Sumaila--2021|Sumaila et al., 2021]] ). For example, the financial benefits that biodiversity conservation confers to seafood harvest resilience could be used to leverage industry participation in adaptation and conservation finance ( [[#Barbier--2018|Barbier et al., 2018]] ). Connecting restoration of blue carbon ecosystems with offset markets (e.g., [[#Vanderklift--2019|Vanderklift et al., 2019]] ) shows potential, but uncertainties remain about the international emissions trading under the UN Framework Convention on Climate Change and climate impacts on blue carbon ecosystems ( [[#3.6.3.1|Section 3.6.3.1.6]] ; [[#Lovelock--2017a|Lovelock et al., 2017a]] ; [[#Macreadie--2019|Macreadie et al., 2019]] ).

Transparency, coherence between different actors and initiatives, and project monitoring and evaluation enhance success in adapting and achieving SDG14 (Life Below Water) ( [[#Blasiak--2019|Blasiak et al., 2019]] ). Maladaptation (WGII Chapter 16; [[#Magnan--2016|Magnan et al., 2016]] ) is a common risk of current project-based funding due to the pressure to produce concrete results ( ''medium confidence'' ) ( [[#Parsons--2019|Parsons and Nalau, 2019]] ; [[#Nunn--2020|Nunn et al., 2020]] ; [[#Nunn--2021|Nunn et al., 2021]] ). Maladaptation can be avoided through a focus on building adaptive capacity, community-based management, drivers of vulnerability and site-specific measures ( ''low confidence'' ) ( [[#Magnan--2018|Magnan and Duvat, 2018]] ; [[#Piggott-McKellar--2020|Piggott-McKellar et al., 2020]] ; [[#Schipper--2020|Schipper, 2020]] ). More research is needed to identify ways that governance and financing agreements can help overcome financial barriers and sociocultural constraints to avoid maladaptation in coastal ecosystems ( ''high confidence'' ) ( [[#Hinkel--2018|Hinkel et al., 2018]] ; [[#Miller--2018|Miller et al., 2018]] ; [[#Piggott-McKellar--2020|Piggott-McKellar et al., 2020]] ; [[#Schipper--2020|Schipper, 2020]] ).

<div id="3.6.3.3.3" class="h4-container"></div>

<span id="governance-dimension-institutional-settings-decision-making"></span>
===== 3.6.3.3.3 Governance dimension (institutional settings, decision making) =====

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Ocean governance has become increasingly complex as new initiatives, new international agreements, institutions and scientific evidence arise at global, national and subnational scales ( ''high agreement'' ) ( [[#Bindoff--2019a|Bindoff et al., 2019a]] ; [[#Scobie--2019b|Scobie, 2019b]] ), limiting the present effectiveness of adaptation ( [[#IPCC--2019c|IPCC, 2019c]] ). Marine climate governance is within the normatively contested marine governance space ( [[#Frazão%20Santos--2020|Frazão Santos et al., 2020]] ), which is influenced by geopolitics ( [[#Gray--2020|Gray et al., 2020]] ) and profit maximisation ( [[#Flannery--2016|Flannery et al., 2016]] ; [[#Haas--2021|Haas et al., 2021]] ) in ways that can entrench exclusionary processes in decision making, science management and funding ( [[#Levin--2018|Levin et al., 2018]] ). This limits just and inclusive ocean governance ( [[#Bennett--2018|Bennett, 2018]] ), perpetuates historical and cultural extractive practices and climate inaction, and leaves little space for Indigenous-led adaptation frameworks and approaches ( [[#Nursey-Bray--2019|Nursey-Bray et al., 2019]] ). At the national level, ocean governance for climate-change adaptation is often transversal, requiring consideration of biophysical and environmental conditions ( [[#Furlan--2020|Furlan et al., 2020]] ) while fitting into existing economic ( [[#Kim--2020|Kim, 2020]] ) and political processes. Adaptation governance that couples existing top-down structures with decentralised and participatory approaches generates shared goals and unlocks required resources and monitoring ( [[#Gupta--2016|Gupta et al., 2016]] ; [[#Haas--2021|Haas et al., 2021]] ).

Communities and governments at all levels increasingly use decision-making frameworks (e.g., structured decision making) or decision-analysis tools to evaluate trade-offs between different responses, rather than applying generic best practices to different physical, technical or cultural contexts ( ''high confidence'' ) ( [[#Watkiss--2015|Watkiss et al., 2015]] ; [[#Haasnoot--2019|Haasnoot et al., 2019]] ; [[#Palutikof--2019|Palutikof et al., 2019]] ). Increased effort has also been devoted to developing climate services (actionable information and data products) that bridge the gap between climate prediction and decision making ( [[#Hewitt--2020|Hewitt et al., 2020]] ). Climate services have the potential to inform decision making related to disaster-risk reduction, adaptation responses, marine environmental management (e.g., fisheries management and MPA management) and ocean-based climate mitigation (e.g., renewable-energy installations) ( [[#Le%20Cozannet--2017|Le Cozannet et al., 2017]] ; [[#Gattuso--2019|Gattuso et al., 2019]] ; [[#Gattuso--2021|Gattuso et al., 2021]] ). Although improving observational and modelling capacity is important to developing ocean-focused services, particularly in high-risk regions like SIDS where regional climate projections are scarce (WGI AR6 Chapter 9; [[#Morim--2019|Morim et al., 2019]] ; [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ), data are not the only limiting factor in decision making ( [[#Weichselgartner--2019|Weichselgartner and Arheimer, 2019]] ). Focusing on user engagement, relationship building and the decision-making context ensures that climate services are useful to, and used by, different stakeholders ( ''high confidence'' ) ( [[#Soares--2018|Soares et al., 2018]] ; [[#Mackenzie--2019|Mackenzie et al., 2019]] ; [[#Weichselgartner--2019|Weichselgartner and Arheimer, 2019]] ; [[#Findlater--2021|Findlater et al., 2021]] ; [[#West--2021|West et al., 2021]] ).

<div id="3.6.3.3.4" class="h4-container"></div>

<span id="mitigation"></span>
===== 3.6.3.3.4 Mitigation =====

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Ocean and coastal NbS can contribute to global mitigation efforts, especially with ocean renewable energy and restoration and preservation of carbon ecosystems (see Box 3.4; [[#3.6.2.3|Section 3.6.2.3]] ). Technological, economic and financing barriers presently hamper development of renewable ocean energy (AR6 WGIII Chapter 6). Such development could help small nations reliant on imported fuel meet their climate-mitigation goals and decrease risk from global fuel-supply dynamics ( [[#Millar--2017|Millar et al., 2017]] ; [[#Chen--2018a|Chen et al., 2018a]] ), but progress is limited by lack of investment ( [[#Millar--2017|Millar et al., 2017]] ; [[#Lee--2020|Lee et al., 2020]] ) or equipment ( [[#Aderinto--2018|Aderinto and Li, 2018]] ; [[#Rusu--2018|Rusu and Onea, 2018]] ). Wave-energy installations, possibly co-located with wind turbines ( [[#Perez-Collazo--2018|Perez-Collazo et al., 2018]] ), are promising for both low- to middle-income nations and areas with significant island or remote coastal geographies ( [[#Lavidas--2016|Lavidas and Venugopal, 2016]] ; [[#Bergillos--2018|Bergillos et al., 2018]] ; [[#Jakimavičius--2018|Jakimavičius et al., 2018]] ; [[#Kompor--2018|Kompor et al., 2018]] ; [[#Penalba--2018|Penalba et al., 2018]] ; [[#Saprykina--2018|Saprykina and Kuznetsov, 2018]] ; [[#Lavidas--2019|Lavidas, 2019]] ). Wave-energy capture may also diminish storm-induced coastal erosion ( [[#Abanades--2018|Abanades et al., 2018]] ; [[#Bergillos--2018|Bergillos et al., 2018]] ). Tidal energy is a relatively new technology ( [[#Haslett--2018|Haslett et al., 2018]] ; [[#Liu--2018|Liu et al., 2018]] ; [[#Neill--2018|Neill et al., 2018]] ) with limiting siting requirements ( [[#Mofor--2013|Mofor et al., 2013]] ). Ocean renewable-energy expansion faces other technological obstacles including lack of implementable or scalable energy-capture devices, access to offshore sites, competing coastal uses, potential environmental impacts and lack of power-grid infrastructure at the coast ( [[#Aderinto--2018|Aderinto and Li, 2018]] ; [[#Neill--2018|Neill et al., 2018]] ).

<div id="cross-chapter-box-slr" class="h2-container box-container"></div>

'''Cross-Chapter Box SLR | Sea Level Rise'''
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Authors: Gonéri Le Cozannet (France, Chapter 13, CCP4), Judy Lawrence (New Zealand, Chapter 11), David S. Schoeman (Australia, Chapter 3), Ibidun Adelekan (Nigeria, Chapter 9), Sarah R. Cooley (USA, Chapter 3), Bruce Glavovic (New Zealand/South Africa, Chapter 18, CCP2), Marjolijn Haasnoot (The Netherlands, Chapter 13, CCP2), Rebecca Harris (Australia, Chapter 2), Wolfgang Kiessling (Germany, Chapter 3), Robert E. Kopp (USA, WGI), Aditi Mukherji (Nepal, Chapter 4), Patrick Nunn (Australia, Chapter 15), Dieter Piepenburg (Germany, Chapter 13), Daniela Schmidt (UK/Germany, Chapter 13), Craig T. Simmons (Australia), Chandni Singh (India, Chapter 10, CCP2), Aimée Slangen (The Netherlands, WGI), Seree Supratid (Thailand, Chapter 4).

Sea level rise is already impacting ecosystems, human livelihoods, infrastructure, food security and climate mitigation at the coast and beyond. Ultimately, it threatens the existence of cities and settlements in low-lying areas, and some island nations and their cultural heritage (Chapters 9–15; Cross-Chapter Papers 2, 4; [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ). The challenge can be addressed by mitigation of climate change and coastal adaptation.

'''Current impacts of sea level rise'''
The rate of global mean SLR was 1.35 mm yr –1 (0.78–1.92 mm yr –1 , ''very likely'' range) during 1901–1990, faster than during any century in at least 3000 years ( ''high confidence'' ) (WGI AR6 Chapter 9; [[#Stanley--1994|Stanley and Warne, 1994]] ; [[#Woodroffe--2016|Woodroffe et al., 2016]] ; [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ). Global mean SLR has accelerated to 3.25 mm yr –1 (2.88–3.61 mm yr –1 , ''very likely'' range) during 1993–2018 ( ''high confidence'' ). Extreme sea levels have increased consistently across most regions (WGI AR6 Chapter 9; [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ). The largest observed changes in coastal ecosystems are being caused by the concurrence of human activities, waves, current-induced sediment transport and extreme storm events ( ''medium confidence'' ) (Chapters 3, 15, 16; [[#Takayabu--2015|Takayabu et al., 2015]] ; [[#Mentaschi--2018|Mentaschi et al., 2018]] ; [[#Duvat--2019|Duvat, 2019]] ; [[#Murray--2019|Murray et al., 2019]] ; [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ). Early impacts of accelerating SLR detected at sheltered or subsiding coasts include chronic flooding at high tides, wetland salinisation and ecosystem transitions, increased erosion and coastal flood damage (Chapters 3, 11, 13–16; WGI AR6 Chapter 9; [[#Sweet--2014|Sweet and Park, 2014]] ; [[#Moftakhari--2015|Moftakhari et al., 2015]] ; [[#Nunn--2017|Nunn et al., 2017]] ; [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ; [[#Sharples--2020|Sharples et al., 2020]] ; [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ; [[#Strauss--2021|Strauss et al., 2021]] ). The exposure of many coastal populations and ecosystems to SLR is high: economic development is disproportionately concentrated in and around coastal cities and settlements ( ''virtually certain'' ) (Chapters 3, 9–15; Cross-Chapter Papers 2, 4).

'''Projected risks to coastal communities, infrastructure and ecosystems'''
Risks from SLR are ''very likely'' to increase by one order of magnitude well before 2100 without adaptation and mitigation action as agreed by parties to the Paris Agreement ( ''very high confidence'' ). Global mean SLR is ''likely'' to continue accelerating under SSP1-2.6 and more strongly forced scenarios (Figure BoxSLR1; WGI AR6 Chapter 9; [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ; [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ), increasing the risk of chronic coastal flooding at high tide, serious flooding during extreme events such as swells, storms and hurricanes, and erosion, and coastal ecosystem losses across many low-lying and erodible coasts ( ''very high confidence'' ) (Chapters 3, 9–15; Cross-Chapter Paper 2; [[#Hinkel--2014|Hinkel et al., 2014]] ; [[#McLachlan--2018|McLachlan and Defeo, 2018]] ; [[#Kulp--2019|Kulp and Strauss, 2019]] ; [[#Vousdoukas--2020b|Vousdoukas et al., 2020b]] ). The compounding of rainfall, river flooding, rising water tables, coastal surges and waves are projected to exacerbate SLR impacts on low-lying areas and rivers further inland (Chapters 4, 11–15; [[#Bevacqua--2020|Bevacqua et al., 2020]] ).

There is ''high confidence'' that coastal risks will increase by at least one order of magnitude over the 21st century due to committed SLR ( [[#Hinkel--2013|Hinkel et al., 2013]] ; [[#Hinkel--2014|Hinkel et al., 2014]] ; [[#IPCC--2019b|IPCC, 2019b]] ). Exposure of population and economic assets to coastal hazards is projected to increase over the next decades, particularly in coastal regions with fast-growing populations in Africa, Southeast Asia and Small Islands ( ''medium evidence'' ) (Chapters 9–15; Cross-Chapter Papers 2, 4; [[#Neumann--2015|Neumann et al., 2015]] ; [[#Jones--2016|Jones and O’Neill, 2016]] ; [[#Merkens--2016|Merkens et al., 2016]] ; [[#Merkens--2018|Merkens et al., 2018]] ; [[#Rasmussen--2020|Rasmussen et al., 2020]] ). For RCP8.5, 2.5–9% of the global population and 12–20% of the global gross domestic product is projected to be exposed to coastal flooding by 2100 ( [[#Kulp--2019|Kulp and Strauss, 2019]] ; [[#Kirezci--2020|Kirezci et al., 2020]] ; [[#Rohmer--2021|Rohmer et al., 2021]] ). Above 3°C global warming levels (GWL) and with low adaptation, SLR may cause disruptions to ports and coastal infrastructure ( [[#Camus--2019|Camus et al., 2019]] ; [[#Christodoulou--2019|Christodoulou et al., 2019]] ; [[#Verschuur--2020|Verschuur et al., 2020]] ; [[#Yesudian--2021|Yesudian and Dawson, 2021]] ), which in turn may cascade and amplify across sectors and regions, generating impacts to financial systems (Chapters 11, 13; [[#Mandel--2021|Mandel et al., 2021]] ). Depending on the hydrogeological context, SLR causes salinisation of groundwater, estuaries, wetlands and soils, adding constraints to water management and livelihoods in agriculture sectors, for example, in deltas (Chapters 9, 15; Cross-Chapter Paper 4; [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ; [[#Nicholls--2020|Nicholls et al., 2020]] ).

Coastal ecosystems can migrate landward or grow vertically in response to SLR, but their resilience and capacity to keep up with SLR will be compromised by ocean warming and other drivers, depending on regions and species, for example, above 1.5°C for coral reefs ( ''high confidence'' ) (Chapters 3, 16; [[#IPCC--2018|IPCC, 2018]] ; [[#Melbourne--2018|Melbourne et al., 2018]] ; [[#Perry--2018|Perry et al., 2018]] ; [[#IPCC--2019b|IPCC, 2019b]] ; [[#Cornwall--2021|Cornwall et al., 2021]] ). Sediments and space for landward retreat are crucial for mangroves, salt marshes and beach ecosystems ( ''high confidence'' ) (Chapter 3; [[#Peteet--2018|Peteet et al., 2018]] ; [[#Schuerch--2018|Schuerch et al., 2018]] ; [[#FitzGerald--2019|FitzGerald and Hughes, 2019]] ; [[#Friess--2019|Friess et al., 2019]] ; [[#Leo--2019|Leo et al., 2019]] ; [[#Schuerch--2019|Schuerch et al., 2019]] ). Loss of habitat is accompanied by loss of associated ecosystem services, including wave-energy attenuation, habitat provision for biodiversity, food production and carbon storage (Chapter 3; Cross-Chapter Box NATURAL in Chapter 2).

Under a high-emissions, low-likelihood/high-impact scenario, where ''low confidence'' ice-sheet mass loss occurs, global mean SLR could exceed the ''likely'' range by more than one additional metre in 2100 (Figure BoxSLR1b; Cross-Chapter Box DEEP in Chapter 17; WGI AR6 Technical Summary and Chapter 9; [[#Arias--2021|Arias et al., 2021]] ; [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ). This is a reason for concern given that rapid SLR after the last glacial–interglacial transition caused a drowning of coral reefs ( ''high confidence'' ) ( [[#Camoin--2015|Camoin and Webster, 2015]] ; [[#Sanborn--2017|Sanborn et al., 2017]] ; [[#Webster--2018|Webster et al., 2018]] ), extensive loss of coastal land and islands, habitats and associated biodiversity ( ''high confidence'' ) (AR6 WGI Chapter 9; [[#Fruergaard--2015|Fruergaard et al., 2015]] ; [[#Fernández-Palacios--2016|Fernández-Palacios et al., 2016]] ; [[#Hamilton--2019|Hamilton et al., 2019]] ; [[#Helfensdorfer--2019|Helfensdorfer et al., 2019]] ; [[#Kane--2020|Kane and Fletcher, 2020]] ; [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ), and triggered Neolithic migrations in Europe and Australia ( ''medium confidence'' ) (Cross-Chapter Box PALEO in Chapter 1; [[#Turney--2007|Turney and Brown, 2007]] ; [[#Brisset--2018|Brisset et al., 2018]] ; [[#Williams--2018|Williams et al., 2018]] ).

<div id="_idContainer108" class="Box_Header-continued"></div>

Cross-Chapter Box SLR

At centennial time scales, projected SLR represents an existential threat for island nations, low-lying coastal zones and the communities, infrastructure, and cultural heritage therein (Chapters 9–15; Cross-Chapter Paper 4). Even if climate warming is stabilised at 2°C to 2.5°C GWL, coastlines will continue to reshape over millennia, affecting at least 25 megacities and drowning low-lying areas where 0.6–1.3 billion people lived in 2010 ( ''medium confidence'' ) (WGI AR6 Chapter 9; [[#Marzeion--2014|Marzeion and Levermann, 2014]] ; [[#Clark--2016|Clark et al., 2016]] ; [[#Kulp--2019|Kulp and Strauss, 2019]] ; [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ; [[#Strauss--2021|Strauss et al., 2021]] ).

'''Solutions, opportunities and limits to adaptation'''
The ability to adapt to current coastal impacts, to cope with future coastal risks and to prevent further acceleration of SLR beyond 2050 depends on immediate mitigation and adaptation actions ( ''very high confidence'' ). The most urgent adaptation challenge is chronic flooding at high tide (Chapters 10, 11, 13–15). Reducing the acceleration of SLR beyond 2050 will only be achieved with fast and profound mitigation of climate change ( [[#Nicholls--2018|Nicholls et al., 2018]] ; [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ). Until 2050, adaptation planning and implementation needs are projected to increase significantly in most inhabited coastal regions (see Figure BoxSLR1; WGI AR6 Chapter 9; [[#IPCC--2019b|IPCC, 2019b]] ; [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ). For SSP1-2.6 and more strongly forced scenarios, SLR rates continue to increase (WGI AR6 Chapter 9; [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ), and so do the scale and frequency of adaptation interventions needed in coastal zones (Figure BoxSLR1; [[#Haasnoot--2020|Haasnoot et al., 2020]] ).

Risks can be anticipated, planned and decided upon, and adaptation interventions can be implemented over the coming decades considering their often long lead- and lifetimes, irrespective of the large uncertainty about SLR beyond 2050 ( ''high confidence'' ) (Figure BoxSLR1; Cross-Chapter Box DEEP in Chapter 17; Cross-Chapter Paper 2; Chapters 11, 13; [[#Haasnoot--2018|Haasnoot et al., 2018]] ; [[#Stephens--2018|Stephens et al., 2018]] ; [[#Stammer--2019|Stammer et al., 2019]] ). Adaptation capacity and governance to manage risks from projected SLR typically require decades to implement and institutionalise ( ''high confidence'' ) (Chapters 11, 13; [[#Haasnoot--2021|Haasnoot et al., 2021]] ). Without considering both short- and long-term adaptation needs, including beyond 2100, communities are increasingly confronted with a shrinking solution space, and adverse consequences are disproportionately borne by exposed and socially vulnerable people (Chapters 1, 8). Sea level rise is ''likely'' to compound social conflict in some settings ( ''high confidence'' ) ( [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ).

Coastal impacts of SLR can be avoided by preventing new development in exposed coastal locations (Chapters 3, 9–15; Cross-Chapter Paper 2; [[#Doberstein--2019|Doberstein et al., 2019]] ; [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ). For existing developments, a range of near-term adaptation options exists, including: (a) engineered, sediment- or ecosystem-based protection; (b) accommodation and land-use planning, to reduce the vulnerability of people and infrastructure; (c) advance through, for example, land reclamation; and (d) retreat through planned relocation or displacements and migrations due to SLR (Chapters 9–15; Cross-Chapter Paper 2; [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ). Only avoidance and relocation can remove coastal risks for the coming decades, while other measures only delay impacts for a time, have increasing residual risk or perpetuate risk and create ongoing legacy effects and ''virtually certain'' property and ecosystem losses ( ''high confidence'' ) (Cross-Chapter Paper 2; [[#Siders--2019|Siders et al., 2019]] ). Large-scale relocation has immense cultural, political, social and economic costs, and equity implications, which can be reduced by fast implementation of climate mitigation and adaptation policies (Chapter 8; Cross-Chapter Paper 2; [[#Gibbs--2015|Gibbs, 2015]] ; [[#Haasnoot--2021|Haasnoot et al., 2021]] ). While relocation may currently appear socially unacceptable, economically inefficient or technically infeasible today ( [[#Lincke--2021|Lincke and Hinkel, 2021]] ), it becomes the only feasible option as protection costs become unaffordable and the limits to accommodation become obvious (Chapters 11, 13, 15; [[#Hino--2017|Hino et al., 2017]] ; [[#Siders--2019|Siders et al., 2019]] ; [[#Strauss--2021|Strauss et al., 2021]] ). Effective responses to rising sea level involve locally applicable combinations of decision analysis, land-use planning, public participation and conflict resolution approaches; together these can anticipate change and help to chart adaptation pathways, over time addressing the governance challenges due to rising sea level ( ''high confidence'' ) ( [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ).

Ecosystem-based adaptation can reduce impacts on human settlements and bring substantial co-benefits, such as ecosystem services restoration and carbon storage, but they require space for sediment and ecosystems and have site-specific physical limits, at least above 1.5°C GWL ( ''high confidence'' ) (Cross-Chapter Box NATURAL in Chapter 2; Chapters 3, 9, 11, 15; [[#Herbert--2015|Herbert et al., 2015]] ; [[#Brown--2019|Brown et al., 2019]] ; [[#Van%20Coppenolle--2019|Van Coppenolle and Temmerman, 2019]] ; [[#Watanabe--2019|Watanabe et al., 2019]] ; [[#Neijnens--2021|Neijnens et al., 2021]] ). For example, planting and conserving vegetation helps sediment accumulation by dissipating wave energy and reducing impacts of storms, at least at present-day sea levels ( ''high confidence'' ) ( [[#Temmerman--2013|Temmerman et al., 2013]] ; [[#Narayan--2016|Narayan et al., 2016]] ; [[#Romañach--2018|Romañach et al., 2018]] ; [[#Laengner--2019|Laengner et al., 2019]] ; [[#Leo--2019|Leo et al., 2019]] ). Coastal wetlands and ecosystems can be preserved by landward migration ( [[#Schuerch--2018|Schuerch et al., 2018]] ; [[#Schuerch--2019|Schuerch et al., 2019]] ) or sediment supply ( [[#VanZomeren--2018|VanZomeren et al., 2018]] ), but they can be seriously damaged by coastal defences designed to protect infrastructure (Chapters 3, 13; [[#Cooper--2020b|Cooper et al., 2020b]] ). Sediment nourishment can prevent erosion, but it can also negatively impact beach amenities and ecosystems through ongoing dredging, pumping and deposition of sand and silts ( [[#VanZomeren--2018|VanZomeren et al., 2018]] ; [[#de%20Schipper--2021|de Schipper et al., 2021]] ; [[#Harris--2021|Harris et al., 2021]] ).

[[File:9d7ef33b97d234e8d52d2d6d35c26042 IPCC_AR6_WGII_Figure_3_Cross-Chapter_Box_SLR_1.png]]

'''Figure Cross-Chapter BoxSLR.1 |''' '''The challenge of coastal adaptation in the era of sea level rise (SLR):''' '''(a)''' '''typical time scales for the planning, implementation (grey triangles) and operational lifetime of current coastal risk-management measures (blue bars);''' '''(b)''' '''global sea level projections, which are representative of relative SLR projected for 60–70% of global shorelines, within ±20% errors (WGI AR6 Chapter 9; Fox-Kemper et al.''' ''',''' 2021); '''(c)''' frequency of illustrative adaptation decisions to +0.5 m of SLR under different SSP-RCP scenarios. In response to accelerated SLR, adaptation either occurs earlier and faster, or accounts for higher amounts of SLR (e.g., to +1 m instead of to +0.5 m). Adaptation to +0.5 m from today’s sea levels have a lifetime of 90 years for SSP1-2.6, but lifetime is reduced to 60 years for SSP5-8.5 and 30 years for a high-end scenario involving ''low confidence'' processes. Adaptations to +0.5 m are comparable to, for example, the Thames Barrier in the United Kingdom or the Delta Works in the Netherlands, which primarily had an intended lifetime of 100–200 years. Adaptation measures to +0.2 m may include nourishment or wetland or setback zones.

There is increasing evidence that current governance and institutional arrangements are unable to address the escalating risks in low-lying coastal areas worldwide ( ''high confidence'' ). Barriers to adaptation, such as decision making driven by short-term thinking or vested interests, funding limitations and inadequate financial policies and insurance, can be addressed equitably and sustainably through implementation of suites of adaptation options and pathways (Chapters 11, 13, 17–18; Cross-Chapter Paper 2). Improved coastal adaptation governance can be supported by approaches that consider changing risks over time, such as ‘dynamic adaptation pathways’ planning (Chapters 11, 13, 18; Cross-Chapter Box DEEP in Chapter 17). Integrated coastal zone management and land-use and infrastructure planning are starting to consider SLR by, for example, monitoring early signals ( [[#Haasnoot--2018|Haasnoot et al., 2018]] ; [[#Stephens--2018|Stephens et al., 2018]] ; [[#Kool--2020|Kool et al., 2020]] ), updating sea level projections ( [[#Stephens--2017|Stephens et al., 2017]] ; [[#Hinkel--2019|Hinkel et al., 2019]] ; [[#Kopp--2019|Kopp et al., 2019]] ; [[#Stammer--2019|Stammer et al., 2019]] ), considering uncertainties of sea level projections and coastal impacts (e.g., [[#Stephens--2017|Stephens et al., 2017]] ; [[#Jevrejeva--2019|Jevrejeva et al., 2019]] ; [[#Rohmer--2019|Rohmer et al., 2019]] ), as well as engaging with communities, practitioners and scientists, recognising the values of current and future generations (e.g., [[#Nicholls--2014|Nicholls et al., 2014]] ; [[#Buchanan--2016b|Buchanan et al., 2016b]] ). While there is ''high agreement'' that the majority of adaptation needs are not met yet, there is ''robust evidence'' of SLR increasingly being considered in coastal adaptation decision making and being embedded in national and local guidance and regulations ( [[#Nicholls--2014|Nicholls et al., 2014]] ; [[#Le%20Cozannet--2017|Le Cozannet et al., 2017]] ; [[#Lawrence--2018|Lawrence et al., 2018]] ; [[#Kopp--2019|Kopp et al., 2019]] ; [[#McEvoy--2021|McEvoy et al., 2021]] ).

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Cross-Chapter Box SLR

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