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

===== Blue carbon and mitigation co-benefits of adaptation actions =====

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The Paris Agreement recognises that mitigation co-benefits resulting from Parties’ adaptation actions and/or economic diversification plans can contribute to mitigation outcomes ( [[#UNFCCC--2015a|UNFCCC 2015a]] : Article 4.7). Blue carbon refers to biologically-driven carbon flux or storage in coastal ecosystems such as seagrasses, salt marshes, and mangroves ( [[#Wylie--2016|Wylie et al. 2016]] ; [[#Fennessy--2019|Fennessy et al. 2019]] ; [[#Fourqurean--2012|Fourqurean et al. 2012]] ; [[#Tokoro--2014|Tokoro et al. 2014]] ) (see Cross-Chapter Box 8 on blue carbon as a storage medium and removal process).

Restoring or protecting coastal ecosystems is a mitigation action with synergies with adaptation and development. Such restoration has been described as a ‘no regrets’ mitigation option in the Special Report on the Ocean and Cryosphere in a Changing Climate ( [[#Bindoff--2019|Bindoff et al. 2019]] ) and advocated as a climate solution at national scales ( [[#Bindoff--2019|Bindoff et al. 2019]] ; [[#Taillardat--2018|Taillardat et al. 2018]] ; [[#Fargione--2018|Fargione et al. 2018]] ) and global scales ( [[#Howard--2017|Howard et al. 2017]] ). On a per-area basis, carbon stocks in coastal ecosystems can be higher than in terrestrial forests ( [[#Howard--2017|Howard et al. 2017]] ), with below-ground carbon storage up to 1000 tC ha –1 ( [[#McLeod--2011|McLeod et al. 2011]] ; [[#Crooks--2018|Crooks et al. 2018]] ; [[#Bindoff--2019|Bindoff et al. 2019]] ). Overall, coastal vegetated systems have a mitigation potential of around 0.5% of current global emissions, with an upper limit of less than 2% ( [[#Bindoff--2019|Bindoff et al. 2019]] ).

Restoration or protection of coastal ecosystems is an important adaptation action with multiple benefits, with bounded global mitigation benefits ( [[#Gattuso--2018|Gattuso et al. 2018]] ; [[#Bindoff--2019|Bindoff et al. 2019]] ). Such restoration/preservation reduces coastal erosion and protects from storm surges, and otherwise mitigates impacts of sea level rise and extreme weather along the coast line ( [[#Siikamäki--2012|Siikamäki et al. 2012]] ; [[#Romañach--2018|Romañach et al. 2018]] ; Alongi 2008). Restoration of tidal flow to coastal wetlands inhibits methane emissions which occur in fresh and brackish water ( [[#Kroeger--2017|Kroeger et al. 2017]] ) ( [[IPCC:Wg3:Chapter:Chapter-7#7.4.2.8|Section 7.4.2.8]] describes a more inclusive set of ecosystem services provided by coastal wetlands). Coastal habitat restoration projects can also provide significant social benefits in the form of job creation (through tourism and recreation opportunities), as well as ecological benefits through habitat preservation ( [[#Edwards--2013|Edwards et al. 2013]] ; [[#Sutton-Grier--2015|Sutton-Grier et al. 2015]] ; [[#Sutton-Grier--2016|Sutton-Grier and Moore 2016]] ; [[#Wylie--2016|Wylie et al. 2016]] ; [[#Kairo--2018|Kairo et al. 2018]] ; [[#Bindoff--2019|Bindoff et al. 2019]] ).

Coastal ecosystem-based mitigation can be cost-effective, but interventions should be designed with care. One concern is to assure that actions remain effective at higher levels of climate change (Alongi 2015; [[#Bindoff--2019|Bindoff et al. 2019]] ). Also, methane emissions from ecosystems may partially reduce the benefit of the carbon sequestration ( [[#Rosentreter--2018|Rosentreter et al. 2018]] ) depending on the salinity ( [[#Poffenbarger--2011|Poffenbarger et al. 2011]] ; [[#Kroeger--2017|Kroeger et al. 2017]] ). As the main driver of mangrove forest loss is aquaculture/agriculture ( [[#Thomas--2017|Thomas et al. 2017]] ), there may be entrenched interests opposing restoration and protection actions.

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