Editing IPCC:AR6/WGII/Cross-Chapter-Paper-2 (section)

== Executive Summary ==

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<span id="cities-and-settlements-cs-by-the-sea-are-on-the-frontline-of-climate-changethey-face-climate-compounded-risks-that-are-amongst-the-highest-but-are-a-key-source-of-innovation-in-climate-resilient-development-high-confidence-1-sections-6.1-6.2-chapter-7-box-15.2-cross-chapter-box-covid-in-chapter-7-cross-chapter-box-slr-in-chapter-3-ccp2.2-smccp2.1-."></span>

'''Cities and settlements (C&amp;S) by the sea are on the frontline of climate change—they face climate-compounded risks that are amongst the highest, but are a key source of innovation in climate resilient development (''' '''''high confidence''''' [[#footnote-002|1]] ''') {Sections 6.1, 6.2; Chapter 7; Box 15.2; Cross-Chapter Box COVID in Chapter 7; Cross-Chapter Box SLR in Chapter 3; CCP2.2; SMCCP2.1} .'''

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Much of the world’s population, economic activities and critical infrastructure are concentrated near the sea ( ''high confidence'' ), with nearly 11% of the global population, or 896 million people, already living on low-lying coasts directly exposed to interacting climatic and non-climatic coastal hazards ( ''very high confidence'' ). Low-lying cities and settlements (C&amp;S) by the sea are experiencing adverse climate impacts that are superimposed on extensive and accelerating anthropogenic coastal change ( ''very high confidence'' ). Depending on coastal C&amp;S characteristics, continuing existing patterns of coastal development will worsen exposure and vulnerability ( ''high confidence'' ). With accelerating sea level rise (SLR) and worsening climate-driven risks in a warming world, prospects for achieving the Sustainable Development Goals (SDGs) and charting climate resilient development (CRD) pathways are dismal ( ''high confidence'' ). However, coastal C&amp;S are also the source of SDG and CRD solutions, because they are centres of innovation with long histories of place-based livelihoods, many of which are globally connected through maritime trade and exchange ( ''medium confidence'' ) {CCP2.1, CCP2.2 CCP2.3, CCP2.4; SMCCP2.1; Chapters 16, 18} .

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'''Regardless of climate and socioeconomic scenarios, many C&amp;S face severe disruption to coastal ecosystems and livelihoods by 2050—extending to all C&amp;S by 2100 and beyond—caused by compound and cascading risks, including submergence of some low-lying island states (''' '''''very high confidence''''' ''') {CCP2.1; CCP2.2; SROCC SPM, Chapter 4; 6.2} .'''

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There is ''high confidence'' that projected climate risks will increase with (i) exposure to climate- and ocean-driven hazards manifest at the coast, such as heat waves, droughts, pluvial floods and impacts due to SLR, tropical cyclones, marine and land heatwaves, and ocean acidification; (ii) with increasing vulnerability driven by inequity and (iii) increasing exposure driven by urban growth in at-risk locations. Compounded and cascading climate risks, such as to coastal C&amp;S infrastructure and supply chain networks, are also expected to increase. These risks are acute for C&amp;S on subsiding and/or low-lying small islands, the Arctic, and open, estuarine and deltaic coasts ( ''high confidence'' ). By 2050, more than a billion people located in low-lying C&amp;S will be at risk from coast-specific climate hazards, influenced by coastal geomorphology, geographical location and adaptation action ( ''high confidence'' ). Between USD 7 and 14 trillion of coastal infrastructure assets will be exposed by 2100, depending on warming levels and socioeconomic development trajectories ( ''medium confidence'' ). Historically rare extreme sea level events will occur annually by 2100, with some atolls being uninhabitable by 2050. The coastal flood risk will rapidly increase during coming decades, possibly by 2–3 orders of magnitude by 2100 in the absence of effective adaptation and mitigation, with severe impacts on coast-dependent livelihoods and socioecological systems ( ''high confidence'' ). Impacts reach far beyond C&amp;S; for example damage to ports severely compromising global supply chains and maritime trade, with local–global geopolitical and economic ramifications. Global investment costs to accommodate port growth and adapt to SLR will amount to USD 223–768 billion before 2050, presenting opportunities for C&amp;S by the sea to build climate resilience ( ''medium evidence'' , ''high agreement'' ). Severely accelerated SLR resulting from rapid continental ice mass loss would bring impacts forward by decades, and adaptation would need to occur much faster and on a much greater scale than ever performed in the past ( ''medium confidence'' ) {Table SMCCP2.1; CCP2.1; CCP2.2; Cross-Chapter Box SLR in Chapter 3; Chapter 4; Sections 6.2.7} ''.''

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'''A mix of interventions is necessary to manage coastal risks and build resilience over time. An adaptation-pathways approach sets out near-term ‘low-regret’ actions that align with societal goals, facilitates implementation of a locally appropriate sequence of interventions in the face of uncertain climate and development futures, and enables necessary transformation (''' '''''high confidence''''' ''') {CCP2.3; Cross-Chapter Box DEEP in Chapter 17, Cross-Chapter Box SLR in Chapter 3} .'''

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A mix of infrastructural, nature-based, institutional and sociocultural interventions are needed to reduce the multifaceted risk facing C&amp;S, including vulnerability-reducing measures, avoidance (i.e., disincentivising developments in high-risk areas), hard and soft protection, accommodation, advance (i.e., building up and out to sea) and retreat (i.e., landward movement of people and development) ( ''very high confidence'' ). Depending on the C&amp;S archetype, technical limits for hard protection may be reached beyond 2100 under high-emission scenarios, with socioeconomic and governance barriers reached before then ( ''medium confidence'' ). However, hard protection can set up lock-in of assets and people to risks and, in some cases, may reach limits—due to technical and financial constraints—by 2100 or sooner depending on the scenario, local SLR effects and community tolerance thresholds ( ''medium confidence'' ) ''.'' Where sufficient space and adequate habitats are available, nature-based solutions can help to reduce coastal hazard risks and provide other benefits, but biophysical limits may be reached before end-century ( ''medium confidence'' ). Accommodation is easier, faster and cheaper to implement than hard protection, but limits may be reached by 2100, or sooner in some settings. An adaptation-pathways planning approach demonstrates how the solution space can expand or shrink depending on the type and timing of adaptation interventions. As SLR is relentless on human timescales, the solution space will shrink without adoption of an adaptation-pathways planning approach ( ''high confidence'' ). Due to long implementation lead times and the need to avoid maladaptive lock-in, particularly in localities facing rapid SLR and climate-compounded risk, adaptation will be more successful if timely action is taken accounting for long-term (committed) SLR, and if this is underpinned by sustained and ambitious mitigation to slow greenhouse gas emission rates ( ''high confidence'' ) { &lt;a class='section-link' data-title='Adaptation and Solutions' href='/report/ar6/wg2/chapter/ccp2#CCP1.3'&gt;CCP1.3.1.2&lt;/a&gt;; CCP2.3; CCP2.4; Cross-Chapter Box SLR in Chapter 3} .

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'''Individual and collective choices founded on public-centred values and norms, as well as pro-social behaviour, help to foster climate-resilient coastal development in C&amp;S (''' '''''high confidence''''' ''') {CCP2.4.1} .'''

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The effectiveness of different approaches (e.g., awareness and education, market-based and legal strategies) is mediated by how well they address contextual and psychosocial factors influencing adaptation choices in coastal C&amp;S ( ''medium confidence'' ). Adaptation options accounting for risk perceptions and aligning with public values tend to be more socioculturally acceptable, and consequently facilitate pro-social behavioural change {CCP2.4.1} .

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'''Locally appropriate institutional capabilities, including regulatory provisions and finances dedicated to maintaining healthy coastal socioecological systems, build adaptive capacity in C&amp;S by the sea (''' '''''high confidence''''' ''') {CCP2.4} .''' 

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Implementing integrated multi-level coastal zone governance, pre-emptive planning, enabling behavioural change and alignment of financial resources with a wide set of values will provide C&amp;S with greater flexibility to open up the solution space to adapt to climate change ( ''high confidence'' ). Insufficient financial resources are a key constraint for coastal adaptation, particularly in the Global South ( ''high confidence'' ). Engaging the private sector in coastal adaptation action with a range of financial tools is crucial to address the coastal adaptation funding gap ( ''high confidence'' ). Considering the full range of economic and non-economic values will improve adaptation effectiveness and equity across C&amp;S archetypes ( ''high confidence'' ). Aligning adaptation in C&amp;S with socioeconomic development, infrastructure maintenance and COVID-19 recovery investments will provide additional co-benefits. Urgency is also driven by the need to avoid lock-in to new and additional risks, for example to avoid C&amp;S sprawl into fragile ecosystems and the most exposed coastal localities {CCP2.3; CCP2.4.2; CCP2.4.4 } .

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

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'''Realising global aspirations for CRD depends on the extent to which coastal C&amp;S institutionalise key enabling conditions and chart place-based adaptation pathways to close the coastal adaptation gap, and on the extent to which they take urgent action to mitigate greenhouse gas emissions (''' '''''medium confidence''''' ''') {CCP2.4; Table CCP2.1 } .'''

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Extensive adaptation planning has been undertaken since the IPCC Fifth Assessment Report (AR5), but there has not been widespread effective implementation, thus giving rise to a ‘coastal adaptation gap’ ( ''high confidence'' ). To date, most interventions have been reactive and often rely on protective works alone ( ''high confidence'' ). The effectiveness of alternative interventions differs among C&amp;S archetypes, while their feasibility is influenced by geomorphology and socioeconomic conditions as well as cultural, political and institutional considerations ( ''very high confidence'' ). Mismatches between adaptation needs and patterns of physical development are commonplace in many coastal C&amp;S, with particularly adverse impacts on poor and marginalised communities in the Global North and Global South ( ''high confidence'' ). Overcoming this gap is key to transitioning towards CRD ( ''medium confidence'' ). Under higher warming levels and higher SLR, increasingly dichotomous coastal futures will become more entrenched ( ''medium confidence'' ), with stark differences between more urbanised, resource-rich coastal C&amp;S dependent on hard protection, and more rural, resource-poor C&amp;S facing displacement and migration {CCP2.3; CCP2.4, Chapter 18} .

Coastal adaptation innovators adopt more flexible, anticipatory and integrative strategies, combining technical and non-technical interventions that account for uncertainties and facilitate effective resolution of conflicting interests and worldviews ( ''limited evidence'' , ''high agreement'' ). Moreover, a core set of critical enablers is foundational for C&amp;S to chart CRD pathways. These include building and strengthening governance capabilities to tackle complex problems; taking a long-term perspective in making short-term decisions; enabling more effective coordination across scales, sectors and policy domains; reducing injustice, inequity, and social vulnerability; and unlocking the productive potential of coastal conflict while strengthening local democracy ( ''medium evidence'' , ''high agreement'' ) {Table CCP2.1, Table CCP2.2; CCP2.3; CCP2.4; Chapters 17, 18; Cross-Chapter Box DEEP in Chapter 17} .

C&amp;S play a pivotal role in global aspirations to implement the Paris Agreement, advance the SDGs and foster CRD. Progress towards these ends depends on the extent to which C&amp;S mobilise urgent and transformational changes to institutionalise enabling conditions, close the coastal adaptation gap by addressing the drivers and root causes of exposure and vulnerability to climate-compounded coastal hazard risks, and drastically reduce greenhouse gas emissions ( ''medium confidence'' ) {CCP2.4; Chapter 18}

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