Editing IPCC:AR6/WGII/Chapter-3 (section)

===== 3.6.3.2.2 Ecological restoration, interventions and their limitations =====

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Restoration of degraded ecosystems is a common NbS increasingly deployed at local scales in response to climate change (Cross-Chapter Box NATURAL in Chapter 2; [[#Duarte--2020|Duarte et al., 2020]] ; [[#Bertolini--2021|Bertolini and da Mosto, 2021]] ; [[#Braun%20de%20Torrez--2021|Braun de Torrez et al., 2021]] ). Despite covering limited areas and having uncertain efficacy under future climate change ( [[#Gordon--2020|Gordon et al., 2020]] ), these actions have successfully restored marine populations and ecosystems at regional to global scales ( [[#Duarte--2020|Duarte et al., 2020]] ), and enhanced livelihoods and the well-being of coastal peoples as well as the biodiversity and resilience of ecological communities ( [[#Silver--2019|Silver et al., 2019]] ; [[#Gordon--2020|Gordon et al., 2020]] ; [[#Braun%20de%20Torrez--2021|Braun de Torrez et al., 2021]] ). Technology-based approaches, such as active restoration, assisted evolution and ecological forecasting, can aid in moving beyond restoring ecosystems ( [[#3.6.2.3|Section 3.6.2.3]] ) towards enhancing resilience, reviving biodiversity and guarding against loss of foundational, ornamental or iconic species ( [[#Bulleri--2018|Bulleri et al., 2018]] ; [[#Collins--2019a|Collins et al., 2019a]] ; [[#da%20Silva--2019|da Silva et al., 2019]] ; [[#National%20Academies%20of%20Sciences--2019|National Academies of Sciences, 2019]] ; [[#Boström-Einarsson--2020|Boström-Einarsson et al., 2020]] ; [[#Fredriksen--2020|Fredriksen et al., 2020]] ; [[#Morris--2020c|Morris et al., 2020c]] ; [[#Kleypas--2021|Kleypas et al., 2021]] ).

Local restoration projects often target vegetated ecosystems like mangroves, seagrasses and salt marshes that are valued and used by coastal communities ( [[#Veettil--2019|Veettil et al., 2019]] ; [[#Duarte--2020|Duarte et al., 2020]] ; [[#Wu--2020a|Wu et al., 2020a]] ; [[#Bertolini--2021|Bertolini and da Mosto, 2021]] ). Detail on mangroves and corals as EbA and protection/restoration hotspots is provided in SM3.8. Common and effective actions ( [[#Sasmito--2019|Sasmito et al., 2019]] ; [[#Duarte--2020|Duarte et al., 2020]] ; [[#Oreska--2020|Oreska et al., 2020]] ) include securing accommodation space (Sections 3.4.2.4–3.4.2.5), restoring hydrological ( [[#Kroeger--2017|Kroeger et al., 2017]] ; [[#Al-Haj--2020|Al-Haj and Fulweiler, 2020]] ) and sediment dynamics; managing harvesting (particularly in mangroves); reducing pollution (especially in seagrasses) ( [[#de%20los%20Santos--2019|de los Santos et al., 2019]] ); and replanting appropriate species in suitable environmental settings ( [[#Wodehouse--2019|Wodehouse and Rayment, 2019]] ; [[#Friess--2020a|Friess et al., 2020a]] ). Although efficacy is context dependent ( [[#Zeng--2020|Zeng et al., 2020]] ; [[#Krause-Jensen--2021|Krause-Jensen et al., 2021]] ) and implementation is most often local ( [[#Alongi--2018a|Alongi, 2018a]] ), such projects facilitate tangible community engagement in climate action. Moreover, because these ecosystems sequester disproportionate amounts of carbon (blue carbon) (Annex II: Glossary; see Box 3.4), restoration supports climate-change mitigation ( [[#Lovelock--2020|Lovelock and Reef, 2020]] ; [[#Gattuso--2021|Gattuso et al., 2021]] ). Yet, constraints remain. For instance, Southeast Asia has 1.21 million km 2 of terrestrial, freshwater and mangrove area biophysically suitable for reforestation, which could mitigate 3.43 ± 1.29 Pg CO 2 e yr −1 through 2030; however, reforestation is only feasible in a small fraction of this area (0.3–18%) given financial, land-use and operational constraints ( [[#Zeng--2020|Zeng et al., 2020]] ). Nevertheless, the multiple benefits offered by ecosystem restoration will ''likely'' outweigh competing costs and increase its relevance as part of adaptation-strategy portfolios ( [[#Silver--2019|Silver et al., 2019]] ; [[#Wedding--2021|Wedding et al., 2021]] ), national carbon-accounting systems and nationally determined contributions by parties to the Paris Agreement ( [[#Friess--2020a|Friess et al., 2020a]] ; [[#Wu--2020a|Wu et al., 2020a]] ).

Restoration efficacy of coral reefs, kelp forests and other habitat-forming coastal ecosystems (Sections 3.4.2.2–3.4.2.6) are jeopardised by the near-term nature of climate-driven risks ( [[#McLeod--2019|McLeod et al., 2019]] ; [[#National%20Academies%20of%20Sciences--2019|National Academies of Sciences, 2019]] ; [[#Coleman--2020b|Coleman et al., 2020b]] ). Modelling studies indicate that available practices will not prevent degradation of coral reefs from &gt;1.5°C of global average surface warming (Figure 3.25; [[#National%20Academies%20of%20Sciences%20Engineering%20and%20Medicine--2019|National Academies of Sciences Engineering and Medicine, 2019]] ; [[#Condie--2021|Condie et al., 2021]] ; [[#Hafezi--2021|Hafezi et al., 2021]] ). Proposed interventions include assisted migration ( [[#Boström-Einarsson--2020|Boström-Einarsson et al., 2020]] ; [[#Fredriksen--2020|Fredriksen et al., 2020]] ; [[#Morris--2020c|Morris et al., 2020c]] ), assisted evolution ( [[#Bay--2019|Bay et al., 2019]] ; [[#National%20Academies%20of%20Sciences--2019|National Academies of Sciences, 2019]] ) and other engineering solutions like artificial shading and enhanced upwelling ( [[#Condie--2021|Condie et al., 2021]] ; [[#Kleypas--2021|Kleypas et al., 2021]] ).

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[[File:d481dbbb29b57218790cb7abc53fb919 IPCC_AR6_WGII_Figure_3_025.png]]

'''Figure 3.25 |''' '''Implemented and potential future adaptations in ocean and coastal ecosystems.'''

'''(a)''' Global implementation since 1970 of (top) cumulative habitat-restoration projects ( [[#Duarte--2020|Duarte et al., 2020]] ), (middle) cumulative area-based conservation protected area (MPA total) ( [[#Boonzaier--2016|Boonzaier and Pauly, 2016]] ), no-take areas (UN Environment World Conservation Monitoring Centre et al., 2018; [[#UNEP-WCMC--2019|UNEP-WCMC, 2019]] ) and (bottom) percentage of total fish stocks rebuilt ( [[#Kleisner--2013|Kleisner et al., 2013]] ).

'''(b)''' Adaptation pathways for coral reefs to maintain healthy cover (line weight: solid lines, ''likely'' effectiveness; dashed lines, ''more likely'' ''than not'' to ''likely ;'' dotted lines = ''unlikely to more likely than not'' ), with confidence noted for each intervention ( [[#3.4.2.1|Section 3.4.2.1]] , 3.6.3.2; [[#Anthony--2019|Anthony et al., 2019]] ; [[#National%20Academies%20of%20Sciences--2019|National Academies of Sciences, 2019]] )

'''(c)''' As in (b), but for mangrove ecosystems. (Underlying data are available in Tables SM3.4–3.6.)

Transplanting heat-tolerant coral colonies can increase reef resistance to bleaching ( [[#Morikawa--2019|Morikawa and Palumbi, 2019]] ; [[#Howells--2021|Howells et al., 2021]] ) but potentially lower species diversity and alter ecosystem function ( [[#3.4.2.1|Section 3.4.2.1]] ). Genetic manipulation or assisted evolution that propagates genes from heat-tolerant populations could enhance restoration of corals ( [[#Anthony--2017|Anthony et al., 2017]] ; [[#Epstein--2019|Epstein et al., 2019]] ) and kelp ( ''medium agreement, limited evidence'' ) ( [[#Coleman--2019|Coleman and Goold, 2019]] ; [[#Coleman--2020b|Coleman et al., 2020b]] ; [[#Fredriksen--2020|Fredriksen et al., 2020]] ; [[#Wade--2020|Wade et al., 2020]] ). Managed breeding of corals has also had limited success in the laboratory and at small local scales ( [[#National%20Academies%20of%20Sciences--2019|National Academies of Sciences, 2019]] ). There is also ''limited evidence'' that physiological interventions, such as algal-symbiont or microbiome manipulation, could increase coral thermal tolerance in the field ( [[#National%20Academies%20of%20Sciences--2019|National Academies of Sciences, 2019]] ). Employing the natural adaptive capacity of species or individuals in active restoration for corals and kelps with current technology involves fewer risks than assisted evolution or long-distance relocation ( ''high confidence'' ) ( [[#Filbee-Dexter--2019|Filbee-Dexter and Smajdor, 2019]] ; [[#National%20Academies%20of%20Sciences--2019|National Academies of Sciences, 2019]] ). More ambitious engineered interventions like reef shading remain theoretical and not scalable to the reef level ( [[#Condie--2021|Condie et al., 2021]] ). Debate continues on how to apply planned adaptation in cost-effective ways that will accomplish the intended goals ( [[#National%20Academies%20of%20Sciences--2019|National Academies of Sciences, 2019]] ; [[#Duarte--2020|Duarte et al., 2020]] ; [[#Kleypas--2021|Kleypas et al., 2021]] ).

Models show that a combination of available management approaches (restoration, reducing non-climate drivers) and speculative interventions (e.g., enhanced corals, reef shading) can contribute to sustaining some coral reefs beyond 1.5°C of global warming with declining effectiveness beyond 2°C of global warming ( ''medium confidence'' ) (Figure 3.25; WGII Chapter 17). These proposed interventions are also currently theoretical and impractical over large scales; for example, engineered solutions like reef shading are untested and not scalable at the reef level ( [[#Condie--2021|Condie et al., 2021]] ). Existing projects suggest that restoration and ecological interventions to habitat-forming ecosystems have the additional benefits of raising local awareness, promoting tourism, and creating jobs and economic benefits ( [[#Fadli--2012|Fadli et al., 2012]] ; [[#Boström-Einarsson--2020|Boström-Einarsson et al., 2020]] ; [[#Hafezi--2021|Hafezi et al., 2021]] ), provided communities are involved in planning, operation and monitoring ( [[#Boström-Einarsson--2020|Boström-Einarsson et al., 2020]] ).

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