Editing IPCC:AR6/WGII/Chapter-11 (section)

==== 11.3.2.3 Adaptation ====

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Climate change adaptation opportunities and pathways have been identified across aquaculture, fisheries, conservation and tourism sectors in the region ( [[#MacDiarmid--2013|MacDiarmid et al., 2013]] ; [[#Fleming--2014|Fleming et al., 2014]] ; [[#MPI--2015|MPI, 2015]] ; [[#Jennings--2016|Jennings et al., 2016]] ; [[#MfE--2016|MfE, 2016]] ; [[#Royal%20Society%20Te%20Apārangi--2017|Royal Society Te Apārangi, 2017]] ; [[#Ling--2019|Ling and Hobday, 2019]] ), and some stakeholders are already autonomously adapting ( [[#Pecl--2019|Pecl et al., 2019]] ). Some fishing and aquaculture industries use seasonal forecasts of environmental conditions to improve decision-making, risk management and business planning ( [[#Hobday--2016|Hobday et al., 2016]] ), with the potential to use 5-yearly forecasts similarly ( [[#Champion--2019|Champion et al., 2019]] ). Shifts in the distribution and availability of target species (e.g., oceanic tuna) would impact the ability of domestic fishing vessels to continue current fishing practices, with potential social and economic adjustment costs ( [[#Dell--2015|Dell et al., 2015]] ), including disruption to supply chains ( [[#Fleming--2014|Fleming et al., 2014]] ; [[#Plagányi--2014|Plagányi et al., 2014]] ) (Cross-Chapter Box MOVING SPECIES in Chapter 5). Species abundance data are insufficient to enable projections of climate impacts on fishery productivity. However, fishery and aquaculture industries are considering adaptation strategies, such as changing harvests and relocating farms ( [[#Pinkerton--2017|Pinkerton, 2017]] ). Thus, while climate change is ''extremely likely'' to affect the abundance and distribution of marine species around New Zealand, insufficient monitoring means there is ''limited evidence'' of ecosystem level change in biodiversity to date and no quantitative projections of which species may win and lose to climate change (Table 11.6) ( [[#Law--2018a|Law et al., 2018a]] ; [[#Law--2018b|Law et al., 2018b]] ).

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'''Box 11.2 | The Great Barrier Reef in Crisis'''
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The GBR is the world’s largest coral reef system, comprising 3863 reefs over an area of 348,700 km 2 , stretching for 2300 km. The GBR is a central cornerstone of the beliefs, knowledges, lores, languages and ways of living for over 70 geographically and culturally diverse Traditional Owner groups spanning the length of the GBR ( [[#Dale--2018|Dale et al., 2018]] ), and it contributes an estimated AUD$6.4 billion per year (pre-COVID) to the Australian economy, mainly via tourism. As the world’s most extensive coral reef ecosystem, the GBR is a globally outstanding and significant entity, with practically the entire ecosystem inscribed as a World Heritage Site in 1981 (UNESCO, 1981).

The GBR is already severely impacted by climate change, particularly ocean warming, through more frequent and severe coral bleaching ( ''very high confidence'' ) ( [[#Hughes--2018b|Hughes et al., 2018b]] ; [[#Hughes--2019c|Hughes et al., 2019c]] ). The worst coral bleaching event on record affected over 90% of reefs in 2016 ( [[#Hughes--2018b|Hughes et al., 2018b]] ). In the most northern 700-km-long section of the GBR in which the heat exposure was the most extreme, 50% of the coral cover on reef crests was lost within 8 months ( [[#Hughes--2018c|Hughes et al., 2018c]] ). Throughout the entire GBR, including the southern third where heat exposure was minimal, the cover of corals declined by 30% between March and November 2016 ( [[#Hughes--2018b|Hughes et al., 2018b]] ). In 2017, the central third of the reef was the most severely affected and the back-to-back regional-scale bleaching events has led to an unprecedented shift in the composition of GBR coral assemblages, transforming the northern and middle sections of the reef system ( [[#Hughes--2018c|Hughes et al., 2018c]] ) to a highly degraded state ( ''very high confidence'' ). Coral recruitment to the GBR in 2018 was reduced to only 11% of the long-term average ( [[#Hughes--2019b|Hughes et al., 2019b]] ). A mass bleaching event also occurred in 2020, making it the third event in 5 years ( [[#BoM--2020|BoM, 2020]] ) (Figure Boxes 11.2.1 and 11.2.2).

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'''Figure Box 11.2.1 |''' '''Top panels: spatial patterns in heat exposure along the GBR in 2016 (left pair) and 2017 (right pair), measured from satellites as Degree Heating Weeks (DHW, °C-weeks).''' Middle panels: geographic footprint of recurrent coral bleaching in 2016 (left) and again in 2017 (right), measured by aerial assessments of individual reefs (adapted from ( [[#Hughes--2019c|Hughes et al., 2019c]] )]). Bottom panels: density of coral recruits (mean per recruitment panel on each reef), measured over three decades, from 1996 to 2016 ( ''n'' = 47 reefs, 1784 panels) (left), compared to the density of coral recruits in 2018 after the mass mortality of corals in 2016 and 2017 due to the back-to-back bleaching events ( ''n'' = 17 reefs, 977 panels) (right). The area of each circle is scaled to the overall recruit density of spawners and brooders combined. Yellow and blue indicate the proportion of spawners and brooders respectively (from ( [[#Hughes--2019b|Hughes et al., 2019b]] )]).

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'''Figure Box 11.2.2 | Variation in the severity of mass-bleaching episodes recorded on Australia’s GBR over the last four decades (1980–2020).''' The overall number of reefs surveyed was substantially higher in 1998, 2002, 2016, 2017 and 2020 when aerial surveys were undertaken, whereas the severity of other more localised bleaching episodes was documented with in-water surveys (adapted from ( [[#Pratchett--2021|Pratchett et al., 2021]] ). Extent of bleaching in 2020 was similar in severity to that of 2016 but more geographically widespread and included southern reefs.

Increased heat exposure also affects the abundance and distribution of associated fish, invertebrates and algae ( ''high confidence'' ) (Stuart- [[#Smith--2018|Smith et al., 2018]] ). Thus, coral bleaching is an indicator of thermal effects on coral habitat, fauna and flora. Bleaching is expected to continue for the GBR and Australia’s other coral reef systems ( ''virtually certain'' ). Bleaching conditions are projected to occur twice each decade from 2035, annually after 2044 under RCP8.5 and annually after 2051 under RCP4.5 ( [[#Heron--2017|Heron et al., 2017]] ). Global warming of 3°C would result in over six times the 2016 level of thermal stress ( [[#Lough--2018|Lough et al., 2018]] ).

Increases in cyclone intensity projected for this century, and other extreme weather events, will greatly accelerate coral reef degradation ( [[#Osborne--2017|Osborne et al., 2017]] ). Additionally, through interactions between elevated ocean temperature and coastal runoff (nutrient and sediment), extreme weather events may contribute to an increased frequency and/or amplitude of crown-of-thorns starfish outbreaks ( [[#Uthicke--2015|Uthicke et al., 2015]] ), further reducing the spatial distribution of coral.

Recovery of coral reefs following repeated disturbance events is slow ( [[#Hughes--2019b|Hughes et al., 2019b]] ; [[#IPCC--2019b|IPCC, 2019b]] ), and it takes at least a decade after each bleaching event for the very fastest growing corals to recover ( ''high confidence'' ) ( [[#Gilmour--2013|Gilmour et al., 2013]] ; [[#Osborne--2017|Osborne et al., 2017]] ). Estimates of future levels of thermal stress, measured as degree heating months, which incorporates both the magnitude and duration of warm season SST anomalies, suggest that achieving the 1.5°C Paris Agreement target would be insufficient to prevent more frequent mass bleaching events ( ''very high confidence'' ) ( [[#Lough--2018|Lough et al., 2018]] ), although it may reduce their occurrence ( [[#Heron--2017|Heron et al., 2017]] ), and occurrences of warming events similar to 2016 bleaching could be reduced by 25% ( [[#King--2017|King et al., 2017]] ).

Tourist motivations for visiting the GBR are changing, with a recent survey finding that two-thirds of tourists were visiting ‘before it was gone’ and a similar number were reporting damage to the reef—an example of ‘last chance tourism’ ( [[#Piggott-McKellar--2016|Piggott-McKellar and McNamara, 2016]] ). The Australian government is investing AUD$1.9 billion to support the GBR through science and practical environmental outcomes, including reducing other anthropogenic pressures, which can suppress natural adaptive capacity ( [[#CoA--2019b|CoA, 2019b]] ; [[#GBRMPA--2019|GBRMPA, 2019]] ). However, adaptation efforts on the GBR aimed specifically at climate impacts, for example coral restoration following marine heatwave impacts ( [[#Boström-Einarsson--2020|Boström-Einarsson et al., 2020]] ), may slow the impacts of climate change in small discrete regions of the reef or reduce short-term socioeconomic ramifications, but they will not prevent widespread bleaching (Condie et al. 2021).

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