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

== Box 5.3 Responses of Coupled Human-Natural Eastern Boundary Upwelling Systems to Climate Change ==

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Eastern Boundary Upwelling Systems (EBUS) are among the world’s most productive ocean ecosystems (Kämpf and Chapman, 2016). They directly support livelihoods in coastal communities and provide many wider benefits to human society (García-Reyes et al., 2015; Levin and Le Bris, 2015). The high productivity of EBUS is supported by the upwelling of cold and nutrient-rich waters, itself driven by equator-ward alongshore winds that cause the displacement of surface waters offshore and their replacement by deeper waters. Total annual fish catches from the four main EBUS (California Current, Humboldt Current, Canary Current and Benguela Current) were 16–24 tonnes yr -1 in the 2000s, providing around 17% of the global catch (Pauly and Zeller, 2016). These catches are consumed locally, as well as being processed and exported as seafood, fish meals and oils to support aquaculture and livestock production. Upwelling of cold deeper water also increases the condensation of humid air in coastal areas, benefitting coastal vegetation and agriculture and suppressing forest fires (Black et al., 2014). The high concentration of marine mammals attracted by the productive upwelling ecosystem support lucrative eco-tourism, such as whale watching in the California Current (Kämpf and Chapman, 2016). The total economic value of the goods and services provided by the Humboldt Current alone is estimated to be 19.45 billion USD per year (Gutiérrez et al.). Thus, although their area is small compared to other pelagic ecosystems, climate change impacts on EBUS will have disproportionately large consequences for human society ( ''very high confidence'' ).

The coupled human-natural EBUS are vulnerable to the multiple effects of climate change with large regional variation (Blasiak et al., 2017). Observations and modelling analyses suggest that winds have intensified in most EBUS (except the Canary Current) during the last 60 years, with several hypotheses proposed to explain the mechanisms (Sydeman et al., 2014; García-Reyes et al., 2015; Rykaczewski et al., 2015; Varela et al., 2015). ESMs predict reduction of wind and upwelling intensity in EBUS at low latitudes and enhancement at high latitudes for Representative Concentration Pathway (RCP)8.5, with an overall reduction in either upwelling intensity or extension (Belmadani et al., 2014; Rykaczewski et al., 2015; Sousa et al., 2017). However, coastal warming and wind intensification may lead to variable countervailing responses to upwelling intensification at local scales (García-Reyes et al., 2015; Wang et al., 2015a; Oyarzún and Brierley, 2018; Xiu et al., 2018). Local winds and mesoscale oceanographic features (not resolved in most global Earth System Models (ESMs)) are thought to have a greater impact on regional productivity than large-scale wind patterns (Renault et al., 2016; Xiu et al., 2018).

There is conflicting evidence in sea surface temperature (SST) trends in recent decades, even among the same EBUS, due to varying spatio-temporal resolution of SST data and the superimposed effects of interannual to multi-decadal variability (García-Reyes et al., 2015). Some EBUS are close to important thresholds in terms of oxygenation and ocean acidification (Gruber et al., 2012; Franco et al., 2018a; Levin, 2018). Large-scale coastal and offshore data for the California Current indicate that there have been decadal decreases in pH and dissolved oxygen affecting organisms and ecosystems (Alin et al., 2012; Bednaršek et al. 2014; Breitburg et al., 2018; Levin, 2018). Model projections for 2100 suggest strong effects of deoxygenation and reduced pH in the Humboldt Current and the California Current under RCP8.5 (Gruber et al., 2012; García-Reyes et al., 2015), affecting seafloor habitats and invertebrate fisheries (Marshall et al., 2017; Hodgson et al., 2018). For instance, the Humboldt Current is projected to experience widespread aragonite undersaturation within a few decades (Franco et al., 2018a), with strong impacts on calcified organisms. Such ocean acidification could be worsened by synergistic effects of ocean warming and deoxygenation (Lachkar, 2014).

The climate change impacts on ecosystem services from EBUS vary according to the biophysical and the socioeconomic characteristics of the upwelling systems (García-Reyes et al., 2015) (SM5.4). The fisheries are not only highly sensitive to upwelling conditions but also by fishing effects on the exploited populations. For example, the anchoveta population collapsed in the Humboldt Current after an El Niño in the 1970s (Gutiérrez et al., 2017). Because small pelagic fisheries from upwelling regions are the main source of the global fishmeal market, decreases in their catches increase the international fishmeal price, increasing the price of other food commodities (like aquaculture derived fish) that rely on fishmeal for their production (Merino et al., 2010; Carlson et al., 2017).

Any decrease in fish catches in EBUS will affect regional food security. For example, coastal fisheries in the Canary Current are an important source of micronutrients to nearby West African countries (Golden et al., 2016) that have particularly high susceptibility to climate change impacts and low adaptive capacity, because of their strong dependence on the fisheries resources, a rapidly growing population and regional conflicts. Decreased small pelagic fish stocks also increase the mortality and reduce reproduction of larger vertebrates such as hake (Guevara-Carrasco and Lleonart, 2008), whales and seabirds (Essington et al., 2015). Impacts on these organisms affect other non-fishing sectors that are dependent on EBUS, such as whale watching in the California Current, and generally degrade their intrinsic value .

Overall, EBUS have been changing with intensification of winds that drives the upwelling, leading to changes in water temperature and other ocean biogeochemistry ( ''medium confidence'' ). Three out of the four major EBUS have shown upwelling intensification in the past 60 years, with strongly increasing trends in ocean acidification and deoxygenation in the two Pacific EBUS in the last few decades ( ''high confidence'' ). The expanding oxygen minimum zone in the California EBUS has altered ecosystem structure and and fisheries catches ( ''medium confidence'' ). However, the direction and magnitude of observed changes vary among and within EBUS, with uncertainties regarding the driving mechanisms behind this variability. Moreover, the high natural variability of EBUS and their insufficient representation by global ESMs gives ''low confidence'' that these observed changes can be attributed to anthropogenic causes, which are predicted to emerge primarily in the second half of the 21st century ( ''medium confidence'' ) (Brady et al., 2017). Given the high sensitivity of the coupled human-natural EBUS to oceanographic changes, the future sustainable delivery of key ecosystem services from EBUS is at risk under climate change; those that are most at risk in the 21st century include fisheries ( ''high confidence'' ), aquaculture ( ''medium confidence'' ), coastal tourism ( ''low confidence'' ) and climate regulation ( ''low confidence'' ). For vulnerable human communities with a strong dependence on EBUS services and low adaptive capacity, such as those along the Canary Current system (Belhabib et al., 2016; Blasiak et al., 2017), unmitigated climate change effects on EBUS (complicated by other non-climatic stresses such as social unrest) have a high risk of altering their development pathways ( ''high confidence'' ).

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==== 5.4.1.2 Regulating Services ====

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Regulating services are those ecosystem functions, like climate regulation, that allow the environment to be in conditions conducive to human well-being and development (Costanza et al., 2017 <sup>[[#fn:r1304|1304]]</sup> ). AR5 WGII concluded that climate change will alter biological, chemical and physical processes in the ocean that provide feedback on the climate system through their effects on atmospheric composition ( ''high confidence'' ) (Pörtner et al., 2014 <sup>[[#fn:r1305|1305]]</sup> ). Sections 5.2 and 5.3 consider new evidence since AR5 regarding climate impacts on marine ecosystems and associated risks; their implications for regulating services are examined here.

A major regulating service provided by marine ecosystems is carbon sequestration. The observed net carbon uptake from the atmosphere to the global ocean varied between 1.0–2.5 GtC yr –1 between 2000 and 2012, with a ''very likely'' uptake of 30–38 Gt of anthropogenic C over the period 1994–2007 (Section 5.2.2.3, Gruber et al., 2019). Estimates of carbon sequestered in the deep ocean range from 0.4 GtC yr –1 (Rogers, 2015 <sup>[[#fn:r1306|1306]]</sup> ) to 1.6 GtC yr –1 (Armstrong et al., 2010) with the annual burial rate (permanent removal to sediment) around 0.2 GtC yr –1 (Armstrong et al., 2010 <sup>[[#fn:r1307|1307]]</sup> ).

Deep sea ecosystems also contribute to the removal of methane released from the beneath the seabed through microbial anaerobic oxidation and the sequestration of methane-derived carbon in carbonate (Marlow et al., 2014 <sup>[[#fn:r1309|1309]]</sup> ; Thurber et al., 2014 <sup>[[#fn:r1310|1310]]</sup> ). In coastal ecosystems, carbon is biologically sequestered in coastal sediments, commonly known as ‘blue carbon’ (Section 5.5.1). Tidal wetlands play disproportionately important roles in coastal carbon budgets, forming critical linkages between rivers, estuaries, and oceans (Najjar et al., 2018 <sup>[[#fn:r1311|1311]]</sup> ). Mean c arbon storage in the top meter of soil is estimated at 280 MgC ha –1 for mangroves, 250 MgC ha –1 for salt marshes, and 140 MgC ha –1 for seagrass meadows, with l ong-term rates of carbon accumulation in sediments of salt marshes, mangroves, and seagrasses ranging from 18–1713 gC m –2 yr –1 (Pendleton et al., 2012 <sup>[[#fn:r1312|1312]]</sup> ). These values are, however, highly variable (Section 5.5.1.2). The large space and time scales mean that there is a long time-lag between seafloor change and detectable changes in carbon sequestration. These large lags, in turn render assessment of climate impacts on regulatory services in the deep ocean having ''low confidence'' .

Under RCP2.6, CMIP5 ESMs project a reduced net ocean carbon uptake by 2080, to around 1.0 GtC yr –1 . Under RCP8.5, net ocean carbon uptake increases to a net sink of around 5.5 GtC yr –1 , but with variability between models (Lovenduski et al., 2016 <sup>[[#fn:r1313|1313]]</sup> ). Although the open ocean biological pump contributes only part of current carbon uptake (Boyd et al. 2019 <sup>[[#fn:r1314|1314]]</sup> ), the downward carbon flux at 1000 m is projected to decrease by 9–16% globally under RCP8.5 by 2100. A projected decrease in carbon sequestration in the North Atlantic by 27–41% has been estimated to represent a loss of 170‒3000 billion USD in abatement (mitigation) costs and 23–401 billion USD in social costs (Barange et al., 2017 <sup>[[#fn:r1315|1315]]</sup> ). Others have highlighted the declining value of open ocean carbon sequestration in the eastern tropical Pacific (Martin et al., 2016b <sup>[[#fn:r1316|1316]]</sup> ) and the Mediterranean (Melaku Canu et al., 2015 <sup>[[#fn:r1317|1317]]</sup> ). The open ocean therefore seems ''very likely'' to reduce its carbon uptake by the end of the 21st century, with the reduction ''very likely'' being greater under RCP8.5 than for RCP2.6; however, specific projections only have  ''medium confidence'' due to uncertainties associated with the structure of the models and with the future behaviour of the biological carbon pump (Section 5.2.2.3.1, 5.2.3) ''.''

Coastal blue carbon ecosystems provide climate regulatory services through their carbon removal and storage (Section 5.3.3). The current rates of loss of blue carbon ecosystems, partly due to climate change (Section 5.3) results in release of their stored CO 2 to the atmosphere (Section 5.5.1.2.2). However, increases in carbon sequestration are also possible; for example, temperature-driven displacement of salt marsh plants by mangrove trees may increase carbon uptake in coastal wetlands (Megonigal et al., 2016 <sup>[[#fn:r1318|1318]]</sup> ). Different rates of SLR may have opposite effects, with potential increases in net carbon uptake for slowly rising sea levels (assuming inland habitat migration is possible), but net carbon release for more rapid SLR (Figure 5.19). Such contrasting feedbacks between scenarios arise from the different responses of plant biomass, sediment accretion and inundation that control the overall response of vegetated coastal ecosystems to rising sea level (Gonneea et al., 2019 <sup>[[#fn:r1319|1319]]</sup> ). Thus, under high emission scenarios, SLR and warming are expected to reduce carbon sequestration by vegetated coastal ecosystems ( ''medium confidence'' ); however, under conditions of slow SLR, there may be net increase in carbon uptake by some coastal wetlands ( ''medium confidence'' )

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'''Figure 5.19'''

<span id="figure-5.19-biogeomorphic-climate-feedbacks-involving-plant-biomass-sediment-accretion-and-inundation-that-control-the-response-of-vegetated-coastal-ecosystems-to-rising-sea-levels.-a-under-high-rates-of-soil-formation-plants-are-able-to-offset-gradual-sea-level-rise-slr-and-may-produce-a-negative-feedback-by-increasing-the-uptake-of-atmospheric-co2."></span>
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'''Figure 5.19 | Biogeomorphic climate feedbacks involving plant biomass, sediment accretion and inundation that control the response of vegetated coastal ecosystems to rising sea levels. (A) Under high rates of soil formation plants are able to offset gradual sea level rise (SLR) and may produce a negative feedback by increasing the uptake of atmospheric CO2. […]'''
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[[File:131870d5877fecd198d24bd84b951618 IPCC-SROCC-CH_5_19.jpg]]

Figure 5.19 | Biogeomorphic climate feedbacks involving plant biomass, sediment accretion and inundation that control the response of vegetated coastal ecosystems to rising sea levels. (A) Under high rates of soil formation plants are able to offset gradual sea level rise (SLR) and may produce a negative feedback by increasing the uptake of atmospheric CO2. In addition, below ground root production contributes to the formation of new soils and consolidates the seabed substrates. (B) Under low rate of soil formation, and when SLRs exceed critical thresholds, plants become severely stressed by inundation leading to less organic accretion and below ground subsidence and decay, producing a positive feedback by net CO2 outgassing. This figure does not consider landward movements, controlled by topography and human land-use.

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Coastal vegetation-rich ecosystems such as mangrove, coral reefs and salt marshes reduce storm impacts, protect the coastline from erosion, and help buffer the impacts of SLR, wave action and even moderate-sized tsunamis (Orth et al., 2006 <sup>[[#fn:r1320|1320]]</sup> ; Ferrario et al., 2014 <sup>[[#fn:r1321|1321]]</sup> ; Rao et al., 2015 <sup>[[#fn:r1322|1322]]</sup> ) (Section 5.5.2.2). Their loss or degradation under climate change (Sections 5.3) would therefore reduce the benefits of these regulatory services to coastal human communities (Perry et al., 2018 <sup>[[#fn:r1323|1323]]</sup> ), increasing the risk of damage and mortality from natural disasters (Rao et al., 2015 <sup>[[#fn:r1324|1324]]</sup> ) ( ''high confidence'' ). In some locations where climate-induced range expansion of coastal wetlands occurs, regulatory services such as storm protection and nutrient storage may be enhanced; however, the replacement of an existing ecosystem by others (e.g., salt marshes replaced by mangroves) may reduce habitat availability for fauna requiring specific vegetation structure and consequently other types of ecosystem services (Kelleway et al., 2017b <sup>[[#fn:r1325|1325]]</sup> ; Sheng and Zou, 2017 <sup>[[#fn:r1326|1326]]</sup> ).

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==== 5.4.1.3 Supporting Services ====

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Supporting ecosystem services are structures and processes, such as habitats, biodiversity and productivity, that maintain the ecosystem functions that deliver other services (Costanza et al., 2017). Marine supporting services include: primary and secondary production; habitat provision for feeding, spawning or nursery grounds, and refugia; and biodiversity. All these provide essential support for provisioning, regulating or cultural services (Haines-Young and Potschin, 2013; Bopp et al., 2017). Therefore, climate change impacts on supporting services provided by marine ecosystems are directly dependent on the risks and impacts on their biodiversity and ecosystem functions, which are assessed in Sections 5.2.3, 5.2.4 and 5.3. Previously, AR5 highlighted the importance of the potential loss or degradation of habitat forming calcifying algae and corals, and the projected changes in waterways for Arctic shipping (Pörtner et al., 2014 <sup>[[#fn:r1327|1327]]</sup> ). The latter topic is considered in Chapter 3 and Section 5.4.2.4.

Publications since AR5 provide further evidence that coastal habitats are at risk from SLR, warming and other climate-related hazards (see Section 5.3). All these changes to supporting services have implications for other ecosystem services (Costanza et al., 2014 <sup>[[#fn:r1329|1329]]</sup> ), such as altering fish catches and their composition (Pratchett et al., 2014 <sup>[[#fn:r1330|1330]]</sup> ; Carrasquilla-Henao and Juanes, 2017 <sup>[[#fn:r1331|1331]]</sup> ; Maharaj et al., 2018 <sup>[[#fn:r1332|1332]]</sup> ) (Section 5.4.1.1) and carbon sequestration (Section 5.4.1.2). In the epipelagic ocean, climate change affects the pattern and magnitude of global NPP (Section 5.2.2.6) and the export of organic matter; both these processes support ecosystem services in the deep ocean (Section 5.2.4) and elsewhere. Projected ocean acidification and oxygen loss will also affect deep ocean biodiversity and habitats that are linked to provisioning services in the deep ocean (Section 5.2.3.2, 5.2.4). Overall, there is ''high confidence'' that marine habitat loss and degradation have already impacted supporting services from many marine ecosystems worldwide. The confidence on the attribution of those impacts to climate change depends on the assessment of the ocean and coastal ecosystems (Section 5.2.3, 5.2.4, 5.3). Projected climate-driven alterations of marine habitats will increase the future risks of impacts on supporting services ( ''high confidence'' ).

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==== 5.4.1.4 Cultural Services ====

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Cultural ecosystem services include recreation, tourism, aesthetic, cultural identity and spiritual experiences. These services are a product of humans experiencing nature and the availability of nature to provide the experiences (Chan et al., 2012). There is increasing evidence to support the conclusion in WGII AR5 that the intrinsic values and cultural importance of marine ecosystems, such as indigenous culture, recreational fishing and tourism, that are dependent on biodiversity and other ecosystem functions, are at risk from climate change. Since marine cultural services are inherently integrated with human well-being, their assessment is provided in Section 5.4.2.

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=== 5.4.2 Climate Risk, Vulnerability and Exposure of Human Communities and their Well-being ===

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Human communities heavily depend on the ocean through the goods and services provided by marine ecosystems (Section 5.4.1) (Hilmi et al., 2015). The values of ocean-based economic activities are estimated to be trillions of USD, generating hundreds of millions of jobs (Hoegh-Guldberg, 2015; Spalding, 2016). As climate change is impacting marine biodiversity and ecosystem services (Section 5.3.1), human communities and their well-being will also be affected. This section is based on diverse types of information, from quantitative modelling to qualitative studies, using expert opinion, local knowledge and Indigenous knowledge (Cross-Chapter Box 4 in Chapter 1). Projection and assessment of risk and vulnerabilities not only depend on climate change scenarios but are also strongly dependent on scenarios of future social-economic development (Cross-Chapter Box 1 in Chapter 1).

This assessment divides the linkages between ecosystem services and human communities and their well-being into the three pillars of sustainable development, as used by the World Commission on Environment and Development. The three pillars are social and cultural, economic and environmental. Table 5.6 lists the specific dimensions under these pillars that are assessed in this section. Synthesis of risks and opportunities of climate change on human communities and well-being is at the end of this section through the lens of ocean economy and the United Nations’ Sustainable Development Goals (SDGs).

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'''Table 5.6'''

The social, cultural and economic dimensions assessed in Section 5.4.2.

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{| class="wikitable"
|-
| '''Dimensions'''
| '''Sections under 5.4.2 '''
|-
| Human and environmental health
| Water-borne diseases (5.4.2.1.1)
Harmful algal blooms (HABs) (Box 5.4)

Interactions with contaminants (5.4.2.1.2)

Food security (5.4.2.1.3)

|-
| Culture and other social dimensions
| Cultural and aesthetic values (5.4.2.2.1)
Potential conflicts in resource utilisation (5.4.2.2.2)

|-
| Monetary and material wealth
| Fisheries (5.4.2.3.1)
Coastal and marine tourism (5.4.2.3.2)

Property values and coastal infrastructure (5.4.2.3.3)

|}
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==== 5.4.2.1 Human Health and Environmental Health ====

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===== 5.4.2.1.1 Water-borne diseases =====

SR15 concluded that climate change will result in an aerial expansion and increased risk of water-borne disease with regional differences ( ''high to very high confidence'' )(Hoegh-Guldberg et al., 2018). AR5 concluded that warming, excessive nutrient and seawater inundation due to SLR are projected to exacerbate the expansion and threat of cholera (Pörtner et al., 2014) ( ''medium confidence'' ). This assessment focuses on health risks caused by ''Vibrio'' bacteria and HABs. ''Vibrio cholerae'' (causing cholera) is estimated to be responsible for around 760,000 and 650,000 cases of human illness and death respectively in the world in 2010 (Kirk et al., 2015). An assessment of HABs is given in Box 5.4.

''Vibrio'' species naturally occur in warm, nutrient-rich and low salinity coastal waters. Since AR5, analysis of the the Continuous Plankton Recorder dataset (Section 5.2.3) has shown a significant increase in ''Vibrio'' abundance in the North Sea over the period 1958‒2011 related to sea surface warming (Vezzulli et al., 2016). Other time series data have confirmed a poleward expansion of ''Vibrio'' pathogens in mid- to high-latitude regions, ascribed at least partly to climate change (Baker-Austin et al., 2013; Baker-Austin et al., 2017). Extreme weather events such as flooding and tropical cyclones are also linked to increased incidences of ''Vibrio'' -related disease, suggested to be caused by the increased exposure of human populations to the pathogens during these extreme events (Baker-Austin et al., 2017). New evidence since AR5 therefore increases support for the linkages between warming, extreme weather events and increased risk of diseases caused by ''Vibrio'' bacteria ( ''very'' ''high confidence'' ).

Extrapolating from the observed relationship between environmental conditions and current ''Vibrio'' distributions, coastal areas that experience future warming, changes in precipitation and increases in nutrient inputs can be expected to see an increase in prevalence of ''Vibrio'' pathogens. These effects have been simulated in a global-scale model that relates occurrences of ''Vibrio'' with SST, pH, dissolved oxygen and chlorophyll ''a'' concentration under the SRES B1 scenario (Escobar et al., 2015). In the Baltic Sea, a nearly two-fold increase in the area suitable for ''Vibrio'' is projected between 2015 and 2050 for both RCP4.5 and RCP8.5 scenarios (relating to projected SST increase of 4°C‒5°C), resulting in an elevated risk of ''Vibrio'' infections (Semenza et al., 2017). Projected conditions of increased coastal flooding from storm surges and SLR (Section 5.2.2) will also increase exposure to waterborne disease (Ashbolt, 2019), such as ''Vibrio'' ( ''medium confidence'' ). However, uncertainty in the socioeconomic factors affecting the future vulnerabilities of human populations render quantitative projections of the magnitude of health impacts uncertain (Lloyd et al., 2016).

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