Editing IPCC:AR6/SROCC/Chapter-5 (section)

=== 5.5.2 Ocean-based Adaptation ===

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The AR5 concluded, with ''high agreement'' but ''limited evidence'' , that climate change impacts on coastal human settlements and communities could be reduced through coastal adaptation activities (Wong et al., 2014a). The limited evidence of the context-specific application of adaptation principles to support the assessment was highlighted as a knowledge gap for future research. This assessment reports progress made with developing such evidence and assesses human adaptation response to climate change in ecosystems, coastal communities and marine environments.

Components of human adaptation responses include risk assessment, risk reduction, and pathways towards resilience (Cross-Chapter Box 2; Chapter 1.6). Residual risk remains where hazard, vulnerability and exposure intersect, subsequent to an adaptation pathway response. Here we focus on adaptation responses within ecosystems and in human systems, as framed in Chapter 1, and defined by:

* ''Nature-based'' or ''ecosystem-based adaptation'' (5.5.2.1). The use of biodiversity and ecosystem services as part of an overall adaptation strategy to help people to adapt to the adverse effects of climate change. EbA uses the range of opportunities for the sustainable management, conservation, and restoration of ecosystems to provide services that enable people to adapt to the impacts of climate change (Narayan et al., 2016; Moosavi, 2017).
* ''Human systems – Built environment adaptation'' (5.5.2.3.1) Adaptation solutions pertaining to coastal built infrastructure and the systems that support such infrastructure (Mutombo and Ölçer, 2016; Forzieri et al., 2018).
* ''Human systems – Socioinstitutional adaptation'' (5.5.2.3) Adaptation responses within human social, governance and economic systems and sectors (Oswald Beiler et al., 2016; Thorne et al., 2017). This includes, but is not limited to ''community-based adaptation'' by coastal communities (5.5.2.3.2) based on empowering and promoting the adaptive capacity of communities, through appropriate use of context, culture, knowledge, agency, and community preferences (Archer et al., 2014; Shaffiril et al., 2017)

To avoid duplication, detailed consideration of adaptation responses to SLR and extreme events (including heat waves, and compound and cascading events) are avoided here, as they are covered by Chapter 4 and Chapter 6, respectively. Tables 5.7 and 5.8 provide a summary assessment of climate change impacts, human adaptation response and benefits in ecosystems and human systems respectively. Details of the assessed literature are in SM Table 5.7. Climate drivers and impacts reported in the adaptation literature are consistent with those reported in Sections 5.2 and 5.3. Physical impacts include the disruption of physical coastal processes, like sediment dynamics, leading to, for example, erosion, flooding and coastal infrastructure damage (see Tables 5.7 and 5.8). Ecological impacts include the loss of ecosystems and biodiversity (Sections 5.2.3, 5.2.4, 5.3), which affected provision of ecosystem services, like coastal protection or food provision. The most commonly reported non-climate human drivers are growing human coastal populations (Elliff and Silva, 2017; van Oppen et al., 2017a; Gattuso et al., 2018) with poorly planned or managed urban development (Barbier, 2015; Wigand et al., 2017), land use change (Robins et al., 2016), loss of ecosystems (Runting et al., 2017), socioeconomic vulnerability (Broto et al., 2015; Bennett et al., 2016) of many coastal communities, ineffective governance and knowledge gaps for implementation.

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==== 5.5.2.1 Ecosystem-based Adaptation ====

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This section assesses adaptation response in coastal ecosystems, beginning with biological adaptation in species, and followed by a summary assessment of EbA as a response to climate change.

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===== 5.5.2.1.1 Biological adaptation =====

There are many studies on biological climate change adaptation responses (Crozier and Hutchings, 2014 <sup>[[#fn:r1844|1844]]</sup> ; Miller et al., 2017 <sup>[[#fn:r1845|1845]]</sup> ; Diamond, 2018 <sup>[[#fn:r1846|1846]]</sup> ). Sections 5.2.3 and 5.3.3 discuss three main types of biological adaptation, broadly defined: evolutionary (genetic) adaptation through natural selection; phenotypic plasticity (acclimatisation), within an organism’s lifetime; and individual or population mobility towards more favourable conditions. There are, however, expected to be limits to such natural adaptation, and large variations between species and populations (Gienapp and Merilä, 2018 <sup>[[#fn:r1847|1847]]</sup> ).

An accurate understanding of climate change impacts upon species, their sensitivity and adaptive capacity and consequent ecological effects (considering both indirect as well as direct impacts) is used to estimate extinction risk, so that an appropriate management response can be developed (Butt et al., 2016 <sup>[[#fn:r1848|1848]]</sup> ). EbA takes these complex interactions into account (Hobday et al., 2015 <sup>[[#fn:r1849|1849]]</sup> ), including the disruptive impacts of alien invasive species (Ondiviela et al., 2014 <sup>[[#fn:r1850|1850]]</sup> ; Wigand et al., 2017 <sup>[[#fn:r1851|1851]]</sup> ) . Effective adaptation action, therefore, contains a broader consideration than historical conservation practices ( ''medium evidence, high agreement'' ), including the development of international collaborations and databases to improve ocean-scale understanding of climate change impacts (Okey et al., 2014 <sup>[[#fn:r1852|1852]]</sup> ; Young et al., 2015 <sup>[[#fn:r1853|1853]]</sup> ). A key knowledge gap relates to the critical thresholds for irreversible change for species (Powell et al., 2017 <sup>[[#fn:r1854|1854]]</sup> ).

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'''Table 5.7'''
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Summary of reported Adaptation responses (A), the Impacts (I) they aimed to address, and the expected Benefits (B) in coastal ecosystems within Physical, Ecological, Social, Governance, Economic and Knowledge categories. For further details of impacts on ecosystems see Section 5.3. Legend: a + sign indicates ''robust evidence'' , a triangle indicates ''medium evidence'' and an underline indicates ''limited evidence'' . Dark blue cells indicate ''high agreement'' , blue indicates ''medium agreement'' and light blue indicates either ''low agreement'' (denoted by presence of a sign) if sufficient papers were reviewed for an assessment or no assessment (if less than three papers were assessed per cell). The papers used for this assessment can be found in SM5.5.

[[File:7d39cdbf3aab3eb42035a9db2c3f1367 table5.7-a.png]]<br />
[[File:995d701e2b1eb3c4eb9b8539bb2d5ab5 table5.7-b.png]]<br />
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[[File:2493b73e56fe1a2359445f0abd7692fc table5.7-d.png]]

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===== 5.5.2.1.2 Adaptation in coral reefs =====

Coral reefs are currently threatened by the continuous global degradation of warm water coral reef ecosystems and the failure of traditional conservation actions to revive most of the degrading reefs (Rinkevich, 2008 <sup>[[#fn:r1855|1855]]</sup> ; Miller and Russ, 2014 <sup>[[#fn:r1856|1856]]</sup> ). Interventions to rehabilitate degraded coral reef ecosystems can be categorised as preventive (‘passive’ restoration) or adaptive (‘active’ restoration) (Miller and Russ, 2014 <sup>[[#fn:r1857|1857]]</sup> ; Linden and Rinkevich, 2017 <sup>[[#fn:r1858|1858]]</sup> ) (see Box 5.5).

Inspired by silviculture (forestation) approaches to terrestrial ecosystem restoration, studies (Rinkevich, 1995 <sup>[[#fn:r1859|1859]]</sup> ; Rinkevich, 2005 <sup>[[#fn:r1860|1860]]</sup> ; Rinkevich, 2006 <sup>[[#fn:r1861|1861]]</sup> ; Rinkevich, 2008 <sup>[[#fn:r1862|1862]]</sup> ; Bongiorni et al., 2011 <sup>[[#fn:r1863|1863]]</sup> ) have proposed a two step restoration strategy for warm water coral reefs termed gardening of denuded coral reefs. In the first step, a large pool of coral colonies (derived from coral nubbins and fragments, and from sexually derived spat) are farmed in underwater nurseries, preferably on mid-water floating devices installed in sheltered zones, in which coral material can be cultured for up to several years. In the second step, nursery-grown coral colonies, together with recruited associated biota, are transplanted to degraded reef sites (Shafir and Rinkevich, 2008 <sup>[[#fn:r1864|1864]]</sup> ; Mbije et al., 2010 <sup>[[#fn:r1865|1865]]</sup> ; Shaish et al., 2010b <sup>[[#fn:r1866|1866]]</sup> ; Shaish et al., 2010a <sup>[[#fn:r1867|1867]]</sup> ; Bongiorni et al., 2011 <sup>[[#fn:r1868|1868]]</sup> ; Horoszowski-Fridman et al., 2011 <sup>[[#fn:r1869|1869]]</sup> ; Linden and Rinkevich, 2011 <sup>[[#fn:r1870|1870]]</sup> ; Mbije et al., 2013 <sup>[[#fn:r1871|1871]]</sup> ; Cruz et al., 2014 <sup>[[#fn:r1872|1872]]</sup> ; Chavanich et al., 2015 <sup>[[#fn:r1873|1873]]</sup> ; Horoszowski-Fridman et al., 2015 <sup>[[#fn:r1874|1874]]</sup> ; Lirman and Schopmeyer, 2016 <sup>[[#fn:r1875|1875]]</sup> ; Montoya Maya et al., 2016 <sup>[[#fn:r1876|1876]]</sup> ; Ng et al., 2016; Lohr and Patterson, 2017 <sup>[[#fn:r|]]</sup> ; Rachmilovitz and Rinkevich, 2017 <sup>[[#fn:r1878|1878]]</sup> ). Active restoration of coral reefs, while still in its infancy and facing a variety of challenges (Rinkevich, 2015b <sup>[[#fn:r1879|1879]]</sup> ; Hein et al., 2017 <sup>[[#fn:r1880|1880]]</sup> ), has been suggested to potentially improve the ecological status of degraded coral reefs and the socioeconomic benefits that the reefs provide (Rinkevich, 2014 <sup>[[#fn:r1881|1881]]</sup> ; Rinkevich, 2015b <sup>[[#fn:r1882|1882]]</sup> ; Linden and Rinkevich, 2017 <sup>[[#fn:r1883|1883]]</sup> ).

Ecological engineering approaches may promote coral reef adaptation (Rinkevich, 2014 <sup>[[#fn:r1884|1884]]</sup> ; Forsman et al., 2015 <sup>[[#fn:r1885|1885]]</sup> ; Coelho et al., 2017 <sup>[[#fn:r1886|1886]]</sup> ; Horoszowski-Fridman and Rinkevich, 2017 <sup>[[#fn:r1887|1887]]</sup> ; Linden and Rinkevich, 2017 <sup>[[#fn:r1888|1888]]</sup> ; Rachmilovitz and Rinkevich, 2017 <sup>[[#fn:r1889|1889]]</sup> ). They also include: augmenting functional diversity, including that of the microbiome (Casey et al., 2015 <sup>[[#fn:r1890|1890]]</sup> ; Horoszowski-Fridman and Rinkevich, 2017 <sup>[[#fn:r1891|1891]]</sup> ; Shaver and Silliman, 2017 <sup>[[#fn:r1892|1892]]</sup> ); transplantating whole habitats (Shaish et al., 2010b <sup>[[#fn:r1893|1893]]</sup> ; Gómez et al., 2014 <sup>[[#fn:r1894|1894]]</sup> ); and enhancing genetic diversity (Iwao et al., 2014 <sup>[[#fn:r1895|1895]]</sup> ; Drury et al., 2016 <sup>[[#fn:r1896|1896]]</sup> ; Horoszowski-Fridman and Rinkevich, 2017 <sup>[[#fn:r1897|1897]]</sup> ). Active restoration can contribute to reef rehabilitation in all major reef regions (Rinkevich, 2014 <sup>[[#fn:r1898|1898]]</sup> ; Rinkevich, 2015b <sup>[[#fn:r1899|1899]]</sup> ). However, there is ''limited evidence'' on how resistant these manipulated corals are to global change drivers (Shaish et al., 2010b <sup>[[#fn:r1900|1900]]</sup> ; Shaish et al., 2010a <sup>[[#fn:r1901|1901]]</sup> ) or how the nursery time affects biological traits like reproduction in coral transplants (Horoszowski-Fridman et al., 2011 <sup>[[#fn:r1902|1902]]</sup> ). Coral epigenetics may also be used as an adaptive management tool for reef rehabilitation ( ''low confidence'' ), as suggested by studies on coral adaptation (Brown et al., 2002 <sup>[[#fn:r1903|1903]]</sup> ; Horoszowski-Fridman et al., 2011 <sup>[[#fn:r1904|1904]]</sup> ; Palumbi et al., 2014 <sup>[[#fn:r1905|1905]]</sup> ; Putnam and Gates, 2015 <sup>[[#fn:r1906|1906]]</sup> ; Putnam et al., 2016 <sup>[[#fn:r1907|1907]]</sup> ).

Research on active coral reef restoration (Box 5.5) suggests the potential to help rehabilitate degraded coral reefs, provided that the underlying drivers of the impacts are mitigated ( ''high confidence'' ). Ongoing and new research in active coral reef restoration may further improve active reef restoration outcomes (Box 5.5) ( ''low confidence'' ). However, these coral reef restoration options may be ineffectual if global warming exceeds 1.5 o C relative to pre-industrial levels (Hoegh-Guldberg et al., 2018 <sup>[[#fn:r1908|1908]]</sup> ; IPCC, 2018 <sup>[[#fn:r1909|1909]]</sup> ).

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