Editing IPCC:AR6/WGII/Chapter-14 (section)

==== 14.5.2.1 Observed Impacts and Projected Risks of Climate Change ====

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Warming of surface and subsurface ocean waters has been broadly observed across all North American marine ecosystems from the polar Arctic to the subtropics of Mexico ( ''virtually certain'' ) ( [[#Hobday--2016|Hobday et al., 2016]] ; [[#Jewett--2017|Jewett and Romanou, 2017]] ; [[#Pershing--2018|Pershing et al., 2018]] ; [[#Smale--2019|Smale et al., 2019]] ). Higher ocean temperatures have directly affected food-web structure ( [[#Gibert--2019|Gibert, 2019]] ) and altered physiological rates, distribution, phenology and behaviour of marine species with cascading effects on food-web dynamics ( ''very high confidence'' ) ( [[#Gattuso--2015|Gattuso et al., 2015]] ; Pinsky and Byler, 2015; [[#Sydeman--2015|Sydeman et al., 2015]] ; [[#Poloczanska--2016|Poloczanska et al., 2016]] ; [[#Frölicher--2018|Frölicher et al., 2018]] ; [[#Le%20Bris--2018|Le Bris et al., 2018]] ; [[#Free--2019|Free et al., 2019]] ; [[#Stevenson--2019|Stevenson and Lauth, 2019]] ; [[#Barbeaux--2020|Barbeaux et al., 2020]] ; [[#Dahlke--2020|Dahlke et al., 2020]] ). Pacific coastal waters from Mexico to Canada and US mid-Atlantic coastal waters have a high proportion of species (&gt;5% of all marine species) near their upper thermal limit, representing hotspots of risk from MHWs ( ''medium confidence'' ) ( [[#Smale--2019|Smale et al., 2019]] ; [[#Dahlke--2020|Dahlke et al., 2020]] ). Kelp, a macroalgae, forms important habitat for other marine species, and its biomass has decreased 85–99% in the past 40–60 years off Nova Scotia, Canada, replaced by invasive and turf algae; this is associated directly with warming waters ( [[#Filbee-Dexter--2016|Filbee-Dexter et al., 2016]] ).

Climate change has induced phenological and spatial shifts in primary productivity with cascading impacts on food webs ( ''high confidence'' ) ( [[#Siddon--2013|Siddon et al., 2013]] ; [[#Stortini--2015|Stortini et al., 2015]] ; [[#Sydeman--2015|Sydeman et al., 2015]] ; [[#Stanley--2018|Stanley et al., 2018]] ). This includes widespread starvation events of fish, birds (e.g., tufted puffins in Bering Sea in 2016–2017 and Cassin’s Auklets in British Columbia in 2014–2015) and marine mammals (grey whales along both coasts of North America) ( [[#Sydeman--2015|Sydeman et al., 2015]] ; Duffy- [[#Anderson--2019|Anderson et al., 2019]] ; [[#Jones--2019b|Jones et al., 2019b]] ; [[#Cheung--2020|Cheung and Frölicher, 2020]] ; [[#Piatt--2020|Piatt et al., 2020]] ), which challenge protected species and fisheries management ( [[#14.5.4|Section 14.5.4]] ; [[#Chasco--2017|Chasco et al., 2017]] ; [[#Wilson--2018|Wilson et al., 2018]] ; [[#Barbeaux--2020|Barbeaux et al., 2020]] ; [[#Free--2020|Free et al., 2020]] ; [[#Fisher--2021|Fisher et al., 2021]] ; [[#Cheung--2020|Cheung and Frölicher, 2020]] ). Climate change has altered foraging behaviour and distribution of North Atlantic right whales and their target copepod prey ( [[#Record--2019|Record et al., 2019]] ) increasing entanglement rates in lobster and snow crab fishing gear on the east coast of the USA and Canada as lobster and crab distributions also shift due to changing water temperatures ( [[#Meyer-Gutbrod--2018|Meyer-Gutbrod et al., 2018]] ; [[#Davies--2019|Davies and Brillant, 2019]] ). Similarly, whale entanglements in fishing gear along the Pacific coast has increased twentyfold ( [[#Hazen--2018|Hazen et al., 2018]] ). Projected shifts in the North Pacific Transition Zone by up to 1000 km northward (by the end of the century under RCP8.5) combined with changes in coastal upwelling ( [[#Polovina--2011|Polovina et al., 2011]] ; [[#Hazen--2013|Hazen et al., 2013]] ; [[#Rykaczewski--2015|Rykaczewski et al., 2015]] ) could alter up to 35% of elephant seal and bluefin tuna foraging habitat ( [[#Robinson--2009|Robinson et al., 2009]] ; [[#Kappes--2010|Kappes et al., 2010]] ).

In North American Arctic marine systems, rapid warming is significant, with cascading impacts beyond polar regions (CCP6), and presents limited opportunities (tourism, shipping, extractive) but high risks (shipping, fishing industries, Indigenous subsistence and cultural activities) ( ''high confidence'' ) (Sections 14.5.4, 14.5.9, 14.5.11; CCP6 [[#Gaines--2018|Gaines et al., 2018]] ; [[#IPCC--2019b|IPCC, 2019b]] ; [[#Samhouri--2019|Samhouri et al., 2019]] ; [[#Free--2020|Free et al., 2020]] ; [[#Holsman--2020|Holsman et al., 2020]] ). Both direct hazards and indirect food-web alterations from sea ice loss have imperilled seabirds, marine mammals, small-boat operators, subsistence hunters and coastal communities (CCP6; [[#Sigler--2014|Sigler et al., 2014]] ; [[#Allison--2015|Allison and Bassett, 2015]] ; [[#Huntington--2015|Huntington et al., 2015]] ; [[#Hauser--2018|Hauser et al., 2018]] ; [[#Raymond-Yakoubian--2018|Raymond-Yakoubian and Daniel, 2018]] ; [[#Dezutter--2019|Dezutter et al., 2019]] ). Increasingly favourable environmental conditions due to warming combined with shipping and other activities has raised the rate of invasive species movement into the Arctic ( [[#Mueter--2011|Mueter et al., 2011]] ). Sea ice loss due to climate change is expected to accelerate over the next century ( [[#14.2|Section 14.2]] , [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ).

Coral reefs in the Gulf of Mexico and along the coasts of Florida and the Yucatan Peninsula are facing increasing risk of bleaching and mortality from warming ocean waters interacting with non-climate stressors ( ''very high confidence'' ) ( [[#Cinner--2016|Cinner et al., 2016]] ; [[#Hughes--2018|Hughes et al., 2018]] ; [[#Sully--2019|Sully et al., 2019]] ; [[#Williams--2019b|Williams et al., 2019b]] ). Coral reefs are contracting in equatorial regions and expanding poleward ( [[#Lluch-Cota--2010|Lluch-Cota et al., 2010]] ; [[#Jones--2019a|Jones et al., 2019a]] ). Loss of coral habitat leads to loss of ecosystem structure, fish habitat, food for coastal communities and impacts tourism opportunities ( [[#14.5.7|Section 14.5.7]] ; [[#Weijerman--2015a|Weijerman et al., 2015a]] ; [[#Weijerman--2015b|Weijerman et al., 2015b]] ). Without mitigation to keep surface temperatures below a 2°C increase by the end of the century, up to 99% of coral reefs will be lost; however, 95% of reefs will still be lost even if warming is kept below 1.5°C ( ''high confidence'' ) ( [[#Hoegh-Guldberg--2018|Hoegh-Guldberg et al., 2018]] ; [[#Hoegh-Guldberg--2018|Hoegh-Guldberg et al., 2018]] ). In Florida, by 2100, an estimated 24–55 billion USD may be lost in recreational use and value derived by people knowing the reef exists and is healthy ( [[#Lane--2013|Lane et al., 2013]] ; [[#Hoegh-Guldberg--2019b|Hoegh-Guldberg et al., 2019b]] ) as coral reefs decline ( [[#14.5.9|Section 14.5.9]] ).

Sea level rise has led to flooding, erosion and damage to infrastructure along the western Gulf of Mexico, the southeast US coasts and the southern coast of the Gulf of St Lawrence ( ''very high confidence'' ) ( [[#14.2|Section 14.2]] ; [[#Daigle--2006|Daigle, 2006]] ; [[#Lemmen--2016|Lemmen et al., 2016]] ; [[#Frederikse--2020|Frederikse et al., 2020]] ). Mangroves, important nurseries for fish and climate refugia for corals ( [[#Yates--2014|Yates et al., 2014]] ), are under threat from climate change along the east coast of Mexico ( [[#Pedrozo%20Acuña--2012|Pedrozo Acuña, 2012]] ). This SLR, storm surge and attendant erosion of coastlines and barrier habitats are projected to have large impacts on coastal ecosystems, maritime industries ( [[#14.5.9|Section 14.5.9]] ), urban centres and cities ( [[#14.5.5|Section 14.5.5]] ) along the Gulf of Mexico, Caribbean Sea, southeast USA, southern Gulf of St Lawrence and Pacific Coast of Mexico (see Box 14.4; [[#Semarnat--2014|Semarnat, 2014]] ; [[#Sweet--2017|Sweet et al., 2017]] ; [[#Vousdoukas--2020|Vousdoukas et al., 2020]] ). Coastal archaeological and historical sites are especially vulnerable to SLR ( [[#Anderson--2017|Anderson et al., 2017]] ; [[#Hestetune--2018|Hestetune et al., 2018]] ; [[#Hollesen--2018|Hollesen et al., 2018]] ).

Future seawater CO 2 levels have been shown in laboratory studies to negatively impact Pacific and Atlantic squid, bivalve, crab and fish species (Pacific cod), and indirectly alter food-web dynamics ( ''high confidence'' ) ( [[#Kaplan--2013|Kaplan et al., 2013]] ; [[#Long--2013b|Long et al., 2013b]] ; [[#Gledhill--2015|Gledhill et al., 2015]] ; [[#Seung--2015|Seung et al., 2015]] ; [[#Punt--2016|Punt et al., 2016]] ; [[#Swiney--2017|Swiney et al., 2017]] ; [[#Hurst--2019|Hurst et al., 2019]] ; [[#Wilson--2020|Wilson et al., 2020]] ). Long-term exposure to CO 2 has reduced growth of Atlantic halibut ( [[#Gräns--2014|Gräns et al., 2014]] ), whereas some cultured oysters ( [[#Fitzer--2019|Fitzer et al., 2019]] ) and key Alaskan commercial fish species show tolerance for high CO 2 waters (i.e., juvenile walleye pollock) ( [[#Hurst--2012|Hurst et al., 2012]] ). Ocean acidification has already caused shellfish growers in the USA and Canada to modify hatchery procedures and farming locations to protect the most vulnerable life stages ( [[#Cross--2016|Cross et al., 2016]] ) and is projected to increasingly impact shellfish resources in the central and northeast Pacific and Atlantic coasts ( [[#14.5.4|Section 14.5.4]] ; [[#Seung--2015|Seung et al., 2015]] ; [[#Punt--2016|Punt et al., 2016]] ).

Open ocean oxygen minimum zones (OMZ) are expanding in the North Atlantic, the North Pacific California Current and tropical oceans due to warming waters, stratification and changes in precipitation ( ''medium confidence'' ) (WGI [[IPCC:Wg2:Chapter:Chapter-3#3.6.2|Section 3.6.2]] ; [[#Deutsch--2015b|Deutsch et al., 2015b]] ; [[#Breitburg--2018|Breitburg et al., 2018]] ; [[#Claret--2018|Claret et al., 2018]] ; [[#Ito--2019|Ito et al., 2019]] ). Hypoxic events along coasts, which are partially influenced by climate change, have been documented for all three countries, with events more prevalent on the east coast and around the Gulf of Mexico due to a regional oceanography dominated by rivers and estuaries carrying land-based nutrients ( [[#Breitburg--2018|Breitburg et al., 2018]] ). Hypoxia has directly caused large mortality events for fish and crabs in US estuaries in the Northwest Atlantic (Chesapeake Bay), Northeast Pacific (Puget Sound) and the Gulf of Mexico ( [[#Froehlich--2015|Froehlich et al., 2015]] ; [[#Rakocinski--2016|Rakocinski and Menke, 2016]] ; [[#Sato--2016|Sato et al., 2016]] ; [[#Kolesar--2017|Kolesar et al., 2017]] ). The OMZs and hypoxic events are projected to increase over the next century and may limit where fish can move ( ''medium confidence'' ) ( [[#Deutsch--2015b|Deutsch et al., 2015b]] ; [[#Stortini--2015|Stortini et al., 2015]] ; [[#Bianucci--2016|Bianucci et al., 2016]] ; [[#Li--2016|Li et al., 2016]] ).

Favourable conditions for harmful algal blooms (HABs) have expanded due to warming, more frequent extreme weather events ( [[#Gobler--2017|Gobler et al., 2017]] ; [[#Pershing--2018|Pershing et al., 2018]] ; [[#Trainer--2019|Trainer et al., 2019]] ) and increased stratification, CO 2 concentration and nutrient inputs ( ''high confidence'' ) ( [[#Wells--2015|Wells et al., 2015]] ; [[#Gobler--2017|Gobler et al., 2017]] ; [[#Griffith--2019|Griffith and Gobler, 2019]] ). Increased occurrence of HABs ( [[#McCabe--2016|McCabe et al., 2016]] ; [[#Yang--2016|Yang et al., 2016]] ; [[#Gobler--2017|Gobler et al., 2017]] ; [[#USGCRP--2018|USGCRP, 2018]] ) has induced ecological impacts and societal costs (see [[#14.5.4|Section 14.5.4]] for fishery closures). During the 2013–2016 Pacific MHW (see Box 14.3), a ''Pseudo-nitzschia'' diatom bloom off the west coast of the USA caused extensive closures of crab and razor clam fisheries (Fisher et al. 2021), with economic and sociocultural impacts beyond those in the fisheries sector ( [[#Ritzman--2018|Ritzman et al., 2018]] ).

Beaching of massive ''Sargassum'' seaweed mats ( ''Sargassum natans'' and ''S. fluitans'' ) have been reported across the Caribbean and Gulf of Mexico from 2011 to the present, affecting US and Mexico nearshore ecosystems, human health and the tourism industry ( [[#Franks--2016|Franks et al., 2016]] ; [[#Resiere--2018|Resiere et al., 2018]] ; [[#Wang--2019|Wang et al., 2019]] ). Costs of beach clean-up is high, with Texas spending over 2.9 million USD annually ( [[#Webster--2013|Webster and Linton, 2013]] ). Attribution of ''Sargassum'' blooms to climate change is still tenuous and complicated by multiple drivers and few observational data sources ( ''low confidence'' ) ( [[#Wang--2019|Wang et al., 2019]] ).

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