Editing IPCC:AR6/SR15/Chapter-4 (section)

==== 4.3.2.3 Coastal systems ====

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'''Managing coastal stress.''' Particularly to allow for the landward relocation of coastal ecosystems under a transition to a 1.5°C warmer world, planning for climate change would need to be integrated with the use of coastlines by humans (Saunders et al., 2014; Kelleway et al., 2017) <sup>[[#fn:r277|277]]</sup> . Adaptation options for managing coastal stress include coastal hardening through the building of seawalls and the re-establishment of coastal ecosystems such as mangroves (André et al., 2016; Cooper et al., 2016) <sup>[[#fn:r278|278]]</sup> . While the feasibility of the solutions is high, they are expensive to scale ( ''robust evidence, medium agreement'' ).

There is ''low evidence'' and ''high agreement'' that reducing the impact of local stresses (Halpern et al., 2015) <sup>[[#fn:r279|279]]</sup> will improve the resilience of marine ecosystems as they transition to a 1.5°C world (O’Leary et al., 2017) <sup>[[#fn:r280|280]]</sup> .  Approaches to reducing local stresses are considered feasible, cost-effective and highly scalable. Ecosystem resilience may be increased through alternative livelihoods (e.g., sustainable aquaculture), which are among a suite of options for building resilience in coastal ecosystems. These options enjoy high levels of feasibility yet are expensive, which stands in the way of scalability ( ''robust evidence, medium agreement'' ) (Hiwasaki et al., 2015; Brugnach et al., 2017) <sup>[[#fn:r281|281]]</sup> .

Working with coastal communities has the potential for improving the resilience of coastal ecosystems. Combined with the advantages of using indigenous knowledge to guide transitions, solutions can be more effective when undertaken in partnership with local communities, cultures, and knowledge (See Box 4.3).

'''Restoration of coastal ecosystems and fisheries.''' Marine restoration is expensive compared to terrestrial restoration, and the survival of projects is currently low, with success depending on the ecosystem and site, rather than the size of the financial investment (Bayraktarov et al., 2016) <sup>[[#fn:r282|282]]</sup> . Mangrove replanting shows evidence of success globally, with numerous examples of projects that have established forests (Kimball et al., 2015; Bayraktarov et al., 2016) <sup>[[#fn:r283|283]]</sup> .

Efforts with reef-building corals have been attempted with a low level of success (Bayraktarov et al., 2016) <sup>[[#fn:r284|284]]</sup> . Technologies to help re-establish coral communities are limited (Rinkevich, 2014) <sup>[[#fn:r285|285]]</sup> , as are largely untested disruptive technologies (e.g., genetic manipulation, assisted evolution) (van Oppen et al., 2015) <sup>[[#fn:r286|286]]</sup> . Current technologies also have trouble scaling given the substantial costs and investment required (Bayraktarov et al., 2016) <sup>[[#fn:r287|287]]</sup> .

Johannessen and Macdonald (2016) <sup>[[#fn:r288|288]]</sup> report the ‘blue carbon’ sink to be 0.4–0.8% of global anthropogenic emissions. However, this does not adequately account for post-depositional processes and could overestimate removal potentials, subject to a risk of reversal. Seagrass beds will thus not contribute significantly to enabling 1.5°C-consistent pathways.

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