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

===== Projections: vulnerabilities, risks and impacts =====

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'''Ocean conditions are projected to continue diverging from a pre-industrial state (''' '''''virtually certain''''' '''), with the magnitude of warming, acidification, deoxygenation, sea level rise and other climate-induced drivers depending on the emission scenario (''' '''''very high confidence''''' '''), and to increase risk of regional extirpations and global extinctions of marine species (''' '''''medium confidence''''' ''').''' Marine species richness near the equator and in the Arctic is projected to continue declining, even with less than 2°C warming by the end of the century ( ''medium confidence'' ). In the deep ocean, all global warming levels will cause faster movements of temperature niches by 2100 than those that have driven extensive reorganisation of marine biodiversity at the ocean surface over the past 50 years ( ''medium confidence'' ). At warming levels beyond 2°C by 2100, risks of extirpation, extinction and ecosystem collapse escalate rapidly ( ''high confidence'' ). Paleorecords indicate that at extreme global warming levels (&gt;5.2°C), mass extinction of marine species may occur ( ''medium confidence'' ). {Box 3.2, 3.2.2.1, 3.4.2.5, 3.4.2.10, 3.4.3.3, Cross-Chapter Box PALEO in Chapter 1}

'''Climate impacts on ocean and coastal ecosystems will be exacerbated by increases in intensity, reoccurrence and duration of marine heatwaves (''' '''''high confidence''''' '''), in some cases, leading to species extirpation, habitat collapse or surpassing ecological tipping points (''' '''''very high confidence''''' ''').''' Some habitat-forming coastal ecosystems including many coral reefs, kelp forests and seagrass meadows, will undergo irreversible phase shifts due to marine heatwaves with global warming levels &gt;1.5°C and are at high risk this century even in &lt;1.5°C scenarios that include periods of temperature overshoot beyond 1.5°C ( ''high confidence'' ). Under SSP1-2.6, coral reefs are at risk of widespread decline, loss of structural integrity and transitioning to net erosion by mid-century due to increasing intensity and frequency of marine heatwaves ( ''very high confidence'' ). Due to these impacts, the rate of sea level rise is ''very likely'' to exceed that of reef growth by 2050, absent adaptation. Other coastal ecosystems, including kelp forests, mangroves and seagrasses, are vulnerable to phase shifts towards alternate states as marine heatwaves intensify ( ''high confidence'' ). Loss of kelp forests are expected to be greatest at the low-latitude warm edge of species’ ranges ( ''high confidence'' ). {3.4.2.1, 3.4.2.3, 3.4.2.5, 3.4.4}

'''Escalating impacts of climate change on marine life will further alter biomass of marine animals (''' '''''medium confidence''''' '''), the timing of seasonal ecological events (''' '''''medium confidence''''' ''') and the geographic ranges of coastal and ocean taxa (''' '''''medium confidence''''' '''), disrupting life cycles (''' '''''medium confidence''''' '''), food webs (''' '''''medium confidence''''' ''') and ecological connectivity throughout the water column (''' '''''medium confidence''''' ''').''' Multiple lines of evidence suggest that climate-change responses are ''very likely'' to amplify up marine food webs over large regions of the ocean. Modest projected declines in global phytoplankton biomass translate into larger declines of total animal biomass (by 2080–2099 relative to 1995–2014) ranging from (mean ± ''very likely'' range) −5.7 ± 4.1% to −15.5 ± 8.5% under SSP1-2.6 and SSP5-8.5, respectively ( ''medium confidence'' ). Projected declines in upper-ocean nutrient concentrations, ''likely'' associated with increases in stratification, will reduce carbon export flux to the mesopelagic and deep-sea ecosystems ( ''medium confidence'' ). This will lead to a decline in the biomass of abyssal meio- and macrofauna (by 2081–2100 relative to 1995–2014) by −9.8% and −13.0% under SSP1-2.6 and SSP5-8.5, respectively ( ''limited evidence'' ). By 2100, 18.8 ± 19.0% to 38.9 ± 9.4% of the ocean will ''very likely'' undergo a change of more than 20 d (advances and delays) in the start of the phytoplankton growth period under SSP1-2.6 and SSP5-8.5, respectively ( ''low confidence'' ). This altered timing increases the risk of temporal mismatches between plankton blooms and fish spawning seasons ( ''medium to high confidence'' ) and increases the risk of fish-recruitment failure for species with restricted spawning locations, especially in mid-to-high latitudes of the Northern Hemisphere ( ''low confidence'' ). Projected range shifts among marine species ( ''medium confidence'' ) suggest extirpations and strongly decreasing tropical biodiversity. At higher latitudes, range expansions will drive increased homogenisation of biodiversity. The projected loss of biodiversity ultimately threatens marine ecosystem resilience ( ''medium to high confidence'' ), with subsequent effects on service provisioning ( ''medium to high confidence'' ). {3.2.2.3, 3.4.2.10, 3.4.3.1–3.4.3.5, 3.5, WGI AR6 &lt;a class='section-link' data-title='Hazards and Exposure' href='/report/ar6/wg2/chapter/chapter-2#2.3'&gt;Section 2.3.4.2.3&lt;/a&gt;}

'''Risks from sea level rise for coastal ecosystems and people are''' '''''very likely''''' '''to increase tenfold well before 2100 without adaptation and mitigation action as agreed by Parties to the Paris Agreement (''' '''''very high confidence''''' ''').''' Sea level rise under emission scenarios that do not limit warming to 1.5°C will increase the risk of coastal erosion and submergence of coastal land ( ''high confidence'' ), loss of coastal habitat and ecosystems ( ''high confidence'' ) and worsen salinisation of groundwater ( ''high confidence'' ), compromising coastal ecosystems and livelihoods ( ''high confidence'' ). Under SSP1-2.6, most coral reefs ( ''very high confidence'' ), mangroves ( ''likely'' , ''medium confidence'' ) and salt marshes ( ''likely'' , ''medium confidence'' ) will be unable to keep up with sea level rise by 2050, with ecological impacts escalating rapidly beyond 2050, especially for scenarios coupling high emissions with aggressive coastal development ( ''very high confidence'' ). Resultant decreases in natural shoreline protection will place increasing numbers of people at risk ( ''very high confidence'' ). The ability to adapt to current coastal impacts, cope with future coastal risks and prevent further acceleration of sea level rise beyond 2050 depends on immediate implementation of mitigation and adaptation actions ( ''very high confidence'' ). {3.4.2.1, 3.4.2.4, 3.4.2.5, 3.4.2.6, 3.5.5.3, Cross-Chapter Box SLR in Chapter 3}

'''Climate change will alter many ecosystem services provided by marine systems (''' '''''high confidence''''' '''), but impacts to human communities will depend on people’s overall vulnerability, which is strongly influenced by local context and development pathways (''' '''''very high confidence''''' ''').''' Catch composition and diversity of regional fisheries will change ( ''high confidence'' ), and fishers who are able to move, diversify and leverage technology to sustain harvests decrease their own vulnerability ( ''medium confidence'' ). Management that eliminates overfishing facilitates successful future adaptation of fisheries to climate change ( ''very high confidence'' ). Marine-dependent communities, including Indigenous Peoples and local peoples, will be at increased risk of losing cultural heritage and traditional seafood-sourced nutrition ( ''medium confidence'' ). Without adaptation, seafood-dependent people face increased risk of exposure to toxins, pathogens and contaminants ( ''high confidence'' ), and coastal communities face increasing risk from salinisation of groundwater and soil ( ''high confidence'' ). Early-warning systems and public education about environmental change, developed and implemented within the local and cultural context, can decrease those risks ( ''high confidence'' ). Coastal development and management informed by sea level rise projections will reduce the number of people and amount of property at risk ( ''high confidence'' ), but historical coastal development and policies impede change ( ''high confidence'' ). Current financial flows are globally uneven and overall insufficient to meet the projected costs of climate impacts on coastal and marine social–ecological systems ( ''very high confidence'' ). Inclusive governance that (a) accommodates geographically shifting marine life, (b) financially supports needed human transformations, (c) provides effective public education and (d) incorporates scientific evidence, Indigenous knowledge and local knowledge to manage resources sustainably shows greatest promise for decreasing human vulnerability to all of these projected changes in ocean and coastal ecosystem services ( ''very high confidence'' ). {3.5.3, 3.5.5, 3.5.6, 3.6.3, Box 3.4, Cross-Chapter Box ILLNESS in Chapter 2, Cross-Chapter Box SLR in Chapter 3}

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