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

=== CCP2.1.1 Introduction and Context ===

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This cross-chapter paper examines the distinctive roles played by C&amp;S by the sea in vulnerability and coastal hazard risk reduction, adaptation, resilience and sustainability in a changing climate. The paper builds upon evidence from AR5 ( [[#Wong--2014|Wong et al., 2014]] ), the Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC; [[#Magnan--2019|Magnan et al., 2019]] ; [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ) and draws material from across WGII AR6 (especially Chapters 3, 6, 9–15). It differs from the SLR-focused analysis of urban areas in SROCC ( [[IPCC:Wg2:Chapter:Chapter-4#4.3|Section 4.3]] ) through a more integrated assessment that distinguishes between archetypal coastal C&amp;S (Section CCP2.1.2), sectoral risks to C&amp;S by the sea (Section CCP2.2), responses to address these risks (Section CCP2.3) and enabling conditions and lessons learned (Section CCP2.4).

We define C&amp;S as concentrated human habitation centres, whether small or large, rural or urban ( [[IPCC:Wg2:Chapter:Chapter-6#6.1.3|Section 6.1.3]] ). We highlight the unique exposure and vulnerability of coastal C&amp;S resulting from rapid urbanisation at the narrow land–sea interface, and a high concentration of economic activity and at-risk people, many with long-standing cultural ties to the coast and dependence on coastal ecosystems that are prone to climate change impacts ( ''high confidence'' ; [[#He--2019|He and Silliman, 2019]] ; [[#Lau--2019|Lau et al., 2019]] ; [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ; [[#Sterzel--2020|Sterzel et al., 2020]] ) ''.''

Presently, the coastal C&amp;S population exposure to ocean-driven impacts from SLR and other climate-driven impacts is considerable by any measure ( [[#Buddemeier--2008|Buddemeier et al., 2008]] ; [[#Barragán--2015|Barragán and de Andrés, 2015]] ; [[#Kay--2017|Kay and Alder, 2017]] ; [[#Haasnoot--2019|Haasnoot et al., 2019]] ; [[#McMichael--2020|McMichael et al., 2020]] ; [[#Sterzel--2020|Sterzel et al., 2020]] ). In 2020, almost 11% of the global population—896 million people—resided in C&amp;S within the low-elevation coastal zone (LECZ; coastal areas below 10 m of elevation above sea level that are hydrologically connected to the sea; [[#Haasnoot--2021b|Haasnoot et al., 2021b]] ), a figure which will potentially increase beyond 1 billion by 2050 ( [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ). Infrastructural and economic assets worth USD 6,500–11,000 billion are also exposed in the 1-in-100-year floodplain for C&amp;S of all sizes ( [[#Neumann--2015|Neumann et al., 2015]] ; [[#Muis--2016|Muis et al., 2016]] ; [[#Brown--2018|Brown et al., 2018]] ; [[#Andrew--2019|Andrew et al., 2019]] ; [[#Kulp--2019|Kulp and Strauss, 2019]] ; [[#Kirezci--2020|Kirezci et al., 2020]] ; [[#Thomas--2020|Thomas et al., 2020]] ; [[#Haasnoot--2021b|Haasnoot et al., 2021b]] ; [[#Hooijer--2021|Hooijer and Vernimmen, 2021]] ).

Further, coastal cities located at higher elevations (e.g., São Paulo, Brazil) or distantly located inland along tidally influenced rivers (e.g., the Recife Metropolitan Region, Brazil) also have populations and infrastructure exposed to climate impacts. As such, the inclusion of C&amp;S beyond the LECZ is warranted when assessing climate impacts and associated exposure, vulnerabilities and risks. The coastal zone includes some of the world’s largest, most densely populated megacities, as well as the fastest-growing urban areas. However, vast coastal areas are sparsely populated, with populations in these regions concentrated in smaller C&amp;S, including along subsiding shorelines and in deltas ( [[#Nicholls--2002|Nicholls and Small, 2002]] ; [[#McGranahan--2007|McGranahan et al., 2007]] ; [[#Merkens--2018|Merkens et al., 2018]] ; [[#Edmonds--2020|Edmonds et al., 2020]] ; [[#Nicholls--2021|Nicholls et al., 2021]] ). From this wider perspective, climate change impacts on the coast directly or indirectly affect a large portion of the global population, economic activity and associated critical infrastructure. Some estimates suggest that 23–37% of the global population lives within 100 km of the shoreline ( [[#Nicholls--2002|Nicholls and Small, 2002]] ; [[#Shi--2003|Shi and Singh, 2003]] ; Christopher Small and Joel E. Cohen, 2004; [[#McMichael--2020|McMichael et al., 2020]] ).

C&amp;S by the sea are thus on the frontline of action to adapt to climate change, mitigate greenhouse gas emissions and chart CRD pathways for several distinct reasons. First, home to a concentrated (and growing) portion of the world’s population, many coastal C&amp;S are simultaneously exposed and vulnerable to climate-compounded hazards as well as being centres of creativity and innovation ( [[#Glavovic--2013|Glavovic, 2013]] ; [[#Crescenzi--2017|Crescenzi and Rodríguez-Pose, 2017]] ; [[#Druzhinin--2021|Druzhinin et al., 2021]] ; [[#Mariano--2021|Mariano et al., 2021]] ; [[#Storbjörk--2021|Storbjörk and Hjerpe, 2021]] ). Second, people in C&amp;S by the sea rely on coastal ecosystems, many of which are highly sensitive to climate change impacts that compound non-climatic risks and increase the precarity of coastal livelihoods ( [[#Lu--2018|Lu et al., 2018]] ; [[#He--2019|He and Silliman, 2019]] ; [[#Thrush--2021|Thrush et al., 2021]] ). Third, coastal C&amp;S are linked together through a network of ports and harbours that underpin global trade and exchange, but which are prone to climate change impacts, especially SLR, with significant implications for global CRD prospects ( [[#Becker--2018|Becker et al., 2018]] ; [[#Christodoulou--2019|Christodoulou et al., 2019]] ; [[#Walsh--2019|Walsh et al., 2019]] ; [[#Hanson--2020|Hanson and Nicholls, 2020]] ). For these reasons, this paper assesses responses, enabling conditions and lessons learned for addressing climate change in C&amp;S by the sea.

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