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

===== 5.5.2.1.4 Ecosystem-based adaptation =====

There is a growing body of literature regarding the effectiveness and economics of EbA. In addition to building resilience to climate change, EbA is expected to bring a wide range of co-benefits that include increasing ecological complexity, with multiple ecosystem services, and other economic co-benefits (Perkins et al., 2015 <sup>[[#fn:r2027|2027]]</sup> ; Perry, 2015 <sup>[[#fn:r2028|2028]]</sup> ; Moosavi, 2017 <sup>[[#fn:r2029|2029]]</sup> ; Scarano, 2017 <sup>[[#fn:r2030|2030]]</sup> ). The cost-effectiveness of EbA approaches varies between marine ecosystem types; for example, coral reefs (Perkins et al., 2015 <sup>[[#fn:r2031|2031]]</sup> ; Beetham et al., 2017 <sup>[[#fn:r2032|2032]]</sup> ; Elliff and Silva, 2017 <sup>[[#fn:r2033|2033]]</sup> ; Beck et al., 2018 <sup>[[#fn:r2034|2034]]</sup> ; Comte and Pendleton, 2018 <sup>[[#fn:r2035|2035]]</sup> ) and salt-marshes (Ondiviela et al., 2014 <sup>[[#fn:r2036|2036]]</sup> ; Miloshis and Fairfield, 2015 <sup>[[#fn:r2037|2037]]</sup> ; Schaeffer-Novelli et al., 2016 <sup>[[#fn:r2038|2038]]</sup> ; Wigand et al., 2017 <sup>[[#fn:r2039|2039]]</sup> ) performed best at reducing wave heights, whilst salt marshes and mangroves were two to five times cheaper than submerged breakwaters for wave heights of less than half a meter. Although low regrets, win-win approaches like EbA are supported in the literature (Watkiss et al., 2014 <sup>[[#fn:r2040|2040]]</sup> ; Barange et al. 2018 <sup>[[#fn:r2041|2041]]</sup> ), syntheses of experience from context-specific practical implementation of EbA and assessment of their cost-effectiveness are limited (Narayan et al., 2016). Therefore, EbA can be a cost-effective approach for securing climate change-related ecosystem services with multiple co-benefits ( ''medium evidence, high agreement'' ).

The application of EbA approaches can be more effective when incorporating local knowledge and Indigenous knowledge and cultural practices into adaptation responses (Ataur Rahman and Rahman, 2015 <sup>[[#fn:r2042|2042]]</sup> ; Perkins et al., 2015 <sup>[[#fn:r2043|2043]]</sup> ; Sutton-Grier et al., 2015 <sup>[[#fn:r2044|2044]]</sup> ; Sánchez-Arcilla et al., 2016 <sup>[[#fn:r2045|2045]]</sup> ; van der Nat et al., 2016 <sup>[[#fn:r2046|2046]]</sup> ). The application of synergistic combinations of adaptation responses in multiple ecosystems can provide a range of co-benefits, and this approach is strengthened when combined with socioinstitutional approaches (Kochnower et al., 2015 <sup>[[#fn:r2047|2047]]</sup> ; MacDonald et al., 2017 <sup>[[#fn:r2048|2048]]</sup> ). Research to improve and refine EbA approaches and increase their specificity to local context is important for their effectiveness in reducing climate risks and generating co-benefits (Sutton-Grier et al., 2015 <sup>[[#fn:r2049|2049]]</sup> ). Conversely, a lack of inclusion of local communities and economic undervaluation of specific coastal and marine ecosystems, compounded by gaps in scientific data, can undermine the potential effectiveness of EbA approaches (Perkins et al., 2015 <sup>[[#fn:r2050|2050]]</sup> ; Hernández-González et al.; Narayan et al., 2016 <sup>[[#fn:r2051|2051]]</sup> ; Roberts et al., 2017 <sup>[[#fn:r2052|2052]]</sup> ).

Despite the abundance of EbA examples in the literature, knowledge gaps pertaining to their implementation and limitations remain. Developing this literature could help with understanding context specific application of EbA and improve their effectiveness ( ''medium confidence'' ).

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