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3,500
AR6_WGII
393
23
Projected range shifts among marine species
medium
1
train
3,501
AR6_WGII
393
27
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
2
train
3,502
AR6_WGII
393
28
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
3
train
3,503
AR6_WGII
393
29
Resultant decreases in natural shoreline protection will place increasing numbers of people at risk
very high
3
train
3,504
AR6_WGII
393
30
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
3
train
3,505
AR6_WGII
394
1
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
1
train
3,506
AR6_WGII
394
2
Management that eliminates overfishing facilitates successful future adaptation of fisheries to climate change
very high
3
train
3,507
AR6_WGII
394
3
Marine-dependent communities, including Indigenous Peoples and local peoples, will be at increased risk of losing cultural heritage and traditional seafood- sourced nutrition
medium
1
train
3,508
AR6_WGII
394
4
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
2
train
3,509
AR6_WGII
394
5
Early-warning systems and public education about environmental change, developed and implemented within the local and cultural context, can decrease those risks
high
2
train
3,510
AR6_WGII
394
6
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
2
train
3,511
AR6_WGII
394
7
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
3
train
3,512
AR6_WGII
394
8
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
3
train
3,513
AR6_WGII
394
10
Low-emission scenarios permit a wider array of feasible, effective and low-risk nature-based adaptation options (e.g., restoration, revegetation, conservation, early-warning systems for extreme events and public education)
high
2
train
3,514
AR6_WGII
394
11
Under high-emission scenarios, adaptation options (e.g., hard infrastructure for coastal protection, assisted migration or evolution, livelihood diversification, migration and relocation of people) are more uncertain and require transformative governance changes
high
2
train
3,515
AR6_WGII
394
12
Transformative climate adaptation will reinvent institutions to overcome obstacles arising from historical precedents, reducing current barriers to climate adaptation in cultural, financial and governance sectors
high
2
train
3,516
AR6_WGII
394
13
Without transformation, global inequities will likely increase between regions
high
2
train
3,517
AR6_WGII
394
15
Adaptation solutions implemented at appropriate scales, when combined with ambitious and urgent mitigation measures, can meaningfully reduce impacts
high
2
train
3,518
AR6_WGII
394
16
Increasing evidence from implemented adaptations indicates that multi-level governance, early-warning systems for climate-associated marine hazards, seasonal and dynamic forecasts, habitat restoration, ecosystem-based management, climate-adaptive management and sustainable harvesting tend to be both feasible and effective
high
2
train
3,519
AR6_WGII
394
17
Marine protected areas (MPAs), as currently implemented, do not confer resilience against warming and heatwaves (medium confidence) and are not expected to provide substantial protection against climate impacts past 2050
high
2
train
3,520
AR6_WGII
394
18
However, MPAs can contribute substantially to adaptation and mitigation if they are designed to address climate change, strategically implemented and well governed
high
2
train
3,521
AR6_WGII
394
19
Habitat restoration limits climate-change-related loss of ecosystem services, including biodiversity, coastal protection, recreational use and tourism (medium confidence), provides mitigation benefits on local to regional scales (e.g., via carbon-storing ‘blue carbon’ ecosystems)
high
2
train
3,522
AR6_WGII
394
20
Ambitious and swift global mitigation offers more adaptation options and pathways to sustain ecosystems and their services
high
2
train
3,523
AR6_WGII
394
22
Nature-based solutions, such as ecosystem-based management, climate-smart conservation approaches (i.e., climate- adaptive fisheries and conservation) and coastal habitat restoration, can be cost-effective and generate social, economic and cultural co- benefits while contributing to the conservation of marine biodiversity and reducing cumulative anthropogenic drivers
high
2
train
3,524
AR6_WGII
394
23
The effectiveness of nature-based solutions declines with warming; conservation and restoration alone will be insufficient to protect coral reefs beyond 2030 (high confidence) and to protect mangroves beyond the 2040s
high
2
train
3,525
AR6_WGII
394
24
The multidimensionality of climate-change impacts and their interactions with other anthropogenic stressors calls for integrated approaches that identify trade-offs and synergies across sectors and scales in space and time to build resilience of ocean and coastal ecosystems and the services they deliver
high
2
train
3,526
AR6_WGII
395
1
Furthermore, existing inequalities and entrenched practices limit effective and just responses to climate change in coastal communities
high
2
train
3,527
AR6_WGII
397
22
Previous IPCC assessments have established that many marine species ‘have shifted their geographic ranges, seasonal activities, migration patterns, abundances and species interactions in response to climate change’ (high confidence) (IPCC, 2014b; IPCC, 2014c), which has had global impacts on species composition, abundance and biomass, and on ecosystem structure and function
medium
1
train
3,528
AR6_WGII
397
23
Warming and acidification have affected coastal ecosystems in concert with non-climate drivers (high confidence), which have affected habitat area, biodiversity, ecosystem function and services
high
2
train
3,529
AR6_WGII
397
25
AR5 and SROCC assessed how physiological sensitivity to climate-induced drivers is the underlying cause of most marine organisms’ vulnerability to climate
high
2
train
3,530
AR6_WGII
403
9
MHWs became more frequent over the 20th century (high confidence) and into the beginning of the 21st century, approximately doubling in frequency (high confidence) and becoming more intense and longer since the 1980s
medium
1
train
3,531
AR6_WGII
404
11
RSL rise is driving a global increase in the frequency of extreme sea levels
high
2
train
3,532
AR6_WGII
406
1
The expected frequency of the current 1-in-100-year extreme sea level is projected to increase by a median of 20–30 times across tide-gauge sites by 2050, regardless of emission scenario
medium
1
train
3,533
AR6_WGII
406
2
In addition, extreme-sea-level frequency may be affected by changes in tropical cyclone climatology (low confidence), wave climatology (low confidence) and tides
high
2
train
3,534
AR6_WGII
406
8
Recent evidence has strengthened estimates of the rate of change (Yamaguchi and Suga, 2019; Li et al., 2020a; Sallée et al., 2021), with an estimated increase of 1.0 ± 0.3% (very likely range) per decade over the period 1970–2018
high
2
train
3,535
AR6_WGII
406
12
WGI AR6 assessed that only the California Current system has undergone large-scale upwelling-favourable wind intensification since the 1980s
medium
1
train
3,536
AR6_WGII
406
13
While no consistent pattern of contemporary changes in upwelling- favourable winds emerges from observation-based studies, numerical and theoretical work projects that summertime winds near poleward boundaries of upwelling zones will intensify, while winds near equatorward boundaries will weaken
high
2
train
3,537
AR6_WGII
406
14
Nevertheless, projected future annual cumulative upwelling wind changes at most locations and seasons remain within ±10–20% of present-day values
medium
1
train
3,538
AR6_WGII
406
16
Direct observational records since the mid-2000s remain too short to determine the relative contributions of internal variability, natural forcing and anthropogenic forcing to AMOC change
high
2
train
3,539
AR6_WGII
407
4
Ocean acidification is also developing in the ocean interior
very high
3
train
3,540
AR6_WGII
407
5
There, it leads to the shoaling of saturation horizons of aragonite and calcite
high
2
train
3,541
AR6_WGII
407
26
SROCC concluded that a loss of oxygen had occurred in the upper 1000 m of the ocean
medium
1
train
3,542
AR6_WGII
408
1
New findings since SROCC also confirm that the volume of oxygen minimum zones (OMZs) are expanding at many locations
high
2
train
3,543
AR6_WGII
408
3
Based on these CMIP6 projections, WGI AR6 concludes that the oxygen content of the subsurface ocean is projected to decline to historically unprecedented conditions over the 21st century
medium
1
train
3,544
AR6_WGII
408
8
Nitrogen availability tends to limit phytoplankton productivity throughout most of the low-latitude ocean, whereas dissolved iron availability limits productivity in high-nutrient, low- chlorophyll regions, such as in the main upwelling region of the Southern Ocean and the Eastern Equatorial Pacific
high
2
train
3,545
AR6_WGII
408
14
It is concluded that the surface ocean will encounter reduced nitrate concentrations in the 21st century
medium
1
train
3,546
AR6_WGII
408
16
The rates and magnitudes of these changes largely depend on the extent of future emissions
very high
3
train
3,547
AR6_WGII
408
22
The Arctic Ocean is characterised by the highest rates of acidification and warming, strong nutrient depletion, and it will likely become practically sea ice free in the September mean for the first time before the year 2050 in all SSP scenarios
high
2
train
3,548
AR6_WGII
408
23
In general, the projected changes in climate-induced drivers are less in absolute terms in the deep-sea (mesopelagic and bathypelagic domains and deep-sea habitats) than in the surface ocean and in shallow-water habitats (e.g., kelp ecosystems, warm-water corals)
very high
3
train
3,549
AR6_WGII
408
25
Significant differences in projected trends between the SSPs show that mitigation strategies will limit exposure of deep-sea ecosystems to potential warming, acidification and deoxygenation during the 21st century
very high
3
train
3,550
AR6_WGII
411
7
Ancient intervals of rapid climate warming that occurred between 300 and 50 million years ago (Ma) were triggered by the release of greenhouse gases
high
2
train
3,551
AR6_WGII
411
10
Warming and deoxygenation in the oceans were closely associated in hyperthermal events (high confidence), with anoxia reaching the photic zone and abyssal depths (Kaiho et al., 2014; Müller et al., 2017; Penn et al., 2018; Weissert, 2019), whereas ocean acidification has not been demonstrated consistently
medium
1
train
3,552
AR6_WGII
411
12
There is little evidence for ocean acidification in the past 2.6 Ma (low confidence) (Hönisch et al., 2012), but ocean ventilation was highly sensitive to even modest warming such as observed in the past 10,000 years
medium
1
train
3,553
AR6_WGII
411
17
Temperature affects the movement and transport of molecules and, thereby, the rates of all biochemical reactions; thus, ongoing and projected warming that remains below an organism’s physiological optimum will generally raise metabolic rates
very high
3
test
3,554
AR6_WGII
411
20
For example, organisms adapted to thermally stable environments (e.g., tropical, polar, deep sea) are often more sensitive to warming than those from thermally variable environments (e.g., estuaries)
very high
3
train
3,555
AR6_WGII
411
21
Heat tolerance also decreases with increasing organisational complexity (Storch et al., 2014; Pörtner and Gutt, 2016) and is lower in eggs, embryos and spawning fish than for their larval stages or adults outside the spawning season
high
2
train
3,556
AR6_WGII
411
22
By altering physiological responses, projected changes in ocean warming (Section 3.2.2.1) will modify growth, migration, distribution, competition, survival and reproduction
very high
3
train
3,557
AR6_WGII
412
2
Detrimental impacts of acidification include decreased growth and survival, and altered development, especially in early life stages
high
2
train
3,558
AR6_WGII
412
4
Calcifiers are generally more sensitive to acidification (e.g., for growth and survival) than non-calcifying groups
high
2
train
3,559
AR6_WGII
412
5
For calcifying primary producers, including phytoplankton and coralline algae, ocean acidification has different, often opposing effects, for example, decreasing calcification while photosynthetic rates increase
high
2
train
3,560
AR6_WGII
412
11
Under hypoxia (oxygen concentrations ≤2 mg l–1; Limburg et al., 2020), physiological and ecological processes are impaired and communities undergo species migration, replacement and loss, transforming community composition
very high
3
train
3,561
AR6_WGII
412
12
Hypoxia can lead to expanding OMZs, which will favour specialised microbes and hypoxia-tolerant organisms
medium
1
train
3,562
AR6_WGII
412
13
As respiration consumes oxygen and produces CO 2, lowered oxygen levels are often interlinked with acidification in coastal and tropical habitats (Rosa et al., 2013; Gobler and Baumann, 2016; Feely et al., 2018) and is an example of a compound hazard (Sections 3.2.4.1, 3.4.2.4).Increased density stratification and mixed-layer shallowing, caused by warming, freshening and sea ice decline, can alter light climate and nutrient availability within the surface mixed layer
high
2
train
3,563
AR6_WGII
412
15
Decreased upward nutrient supply is expected to decrease primary production in the low-latitude ocean
medium
1
train
3,564
AR6_WGII
412
16
Alternatively, higher mean underwater light levels resulting from changes in sea ice and/or mixed layer shallowing can increase primary production in high-latitude offshore regions, provided nutrient levels remain sufficiently high
medium
1
train
3,565
AR6_WGII
412
17
In some parts of the open Southern Ocean, where iron limitation largely controls primary productivity (Tagliabue et al., 2017), changes in wind fields will deepen the summer mixed-layer depth (Panassa et al., 2018), entrain more nutrients, and raise primary productivity in the future
medium
1
train
3,566
AR6_WGII
412
20
Marine heatwaves exacerbate the impacts of rising mean temperatures, with major ecological consequences
very high
3
train
3,567
AR6_WGII
412
25
The amplitude of diel and seasonal pH and CO 2 changes are projected to increase in the future due to lowered CO 2 seawater buffering capacity
very high
3
train
3,568
AR6_WGII
415
2
Non-climate drivers (Section 3.1) can dominate outcomes or amplify vulnerability to climate- induced drivers, with mostly detrimental effects such as extirpation
very high
3
train
3,569
AR6_WGII
415
7
Co-occurring environmental drivers often cause complex organismal responses
high
2
train
3,570
AR6_WGII
415
17
Ocean acidification poses a large risk for coralline algae that is further amplified by warming
medium
1
train
3,571
AR6_WGII
415
19
For seagrass, warming beyond a species’ thermal tolerance will limit growth and impact germination, but ocean acidification appears to increase thermal tolerance of some eelgrass species by increasing the photosynthesis-to-respiration ratio
medium
1
train
3,572
AR6_WGII
415
20
Thermal sensitivity of pelagic primary producers changes with nutrient supply
high
2
train
3,573
AR6_WGII
415
22
This trend may hold for open-ocean phytoplankton, which are often iron- limited
medium
1
train
3,574
AR6_WGII
415
26
Rising metabolic rates due to warming will be restricted to primary producers in high- nutrient regions
medium
1
test
3,575
AR6_WGII
415
28
The effects of ocean acidification on growth, metabolic rates or elemental composition of primary producers changes with nutrient availability and light conditions
high
2
train
3,576
AR6_WGII
417
2
Given the expected mixed-layer shallowing in some regions (Section 3.2.2.3), the exposure to overall higher mean irradiances could shift the effects of acidification from beneficial to detrimental for some primary producers, depending on species and organismal traits
medium
1
train
3,577
AR6_WGII
417
4
The few experimental studies that have addressed three or more drivers (Xu et al., 2014; Boyd et al., 2015b; Brennan and Collins, 2015; Brennan et al., 2017; Hoppe et al., 2018b; Moreno-Marín et al., 2018) indicate that one or two drivers generally dominate the cumulative outcome, with others playing a subordinate role
medium
1
train
3,578
AR6_WGII
417
7
Higher ocean CO 2 influences the thermal tolerance of species adapted to extreme but stable habitats in tropical and polar regions, more than that of thermally tolerant generalists
high
2
train
3,579
AR6_WGII
417
10
As with ocean acidification, reduced oxygen availability further alters the influence of warming on metabolic rates
high
2
train
3,580
AR6_WGII
417
17
In consequence, expansion of OMZs and other regions where warming, hypoxia and acidification combine will further reduce habitat for many fish and invertebrates
high
2
train
3,581
AR6_WGII
418
3
It is difficult to generalise to what extent co-occurring ocean warming ameliorates or exacerbates effects of acidification on behaviour (Laubenstein et al., 2019); outcomes depend upon species and life stage (Faleiro et al., 2015; Chan et al., 2016; Tills et al., 2016; Wang et al., 2018b; Jarrold et al., 2020), interactions between species (e.g., Paula et al., 2019) along with confounding factors including food availability and salinity
medium
1
test
3,582
AR6_WGII
418
5
Other influential drivers include ocean acidification, salinity (high confidence) (Lefevre, 2016; Whiteley et al., 2018; Reddin et al., 2020) or food availability/quality
medium
1
train
3,583
AR6_WGII
418
11
In highly fluctuating environments (e.g., upwelling regions, coastal zones), multiple drivers can change and interact across temporal and spatial scales, generating geographic mosaics of tolerances and sensitivities to environmental and climate change in marine organisms
medium
1
train
3,584
AR6_WGII
418
14
Some studies have documented higher phenotypic plasticity and tolerance to ocean warming and acidification in marine invertebrates (Dam, 2013; Kelly et al., 2013; Pespeni et al., 2013; Gaitán-Espitia et al., 2017a; Vargas et al., 2017; Li et al., 2018a), seaweeds (Noisette et al., 2013; Padilla-Gamiño et al., 2016; Machado Monteiro et al., 2019) and fish
medium
1
train
3,585
AR6_WGII
418
17
For instance, transgenerational effects and/or developmental acclimation, both ‘carry-over effects’ (where the early- life environment affects the expression of traits in later life stages or generations), can influence within- and cross-generational changes in the tolerances of marine organisms
medium
1
train
3,586
AR6_WGII
418
21
Although plasticity provides an adaptive mechanism, it is unlikely to provide a long-term solution for species undergoing sustained directional environmental change (e.g., global warming)
medium
1
train
3,587
AR6_WGII
419
5
Experimental evolution suggests that microbial populations can rapidly adapt (i.e., over 1–2 years) to environmental changes mimicking projected effects of climate change
medium
1
train
3,588
AR6_WGII
419
7
The evolutionary responses of microbes are conditioned by the number and characteristics of interacting drivers
low
0
train
3,589
AR6_WGII
420
9
Specifically, associations between vulnerabilities and traits of marine ectotherms in laboratory experiments correspond with organismal responses to ancient hyperthermal events
medium
1
train
3,590
AR6_WGII
420
14
On a global scale, ecosystem models project a −5.7 ± 4.1% (very likely range) to −15.5 ± 8.5% decline in marine animal biomass with warming under SSP1-2.6 and SSP5-8.5, respectively, by 2080–2099 relative to 1995–2014, albeit with significant regional variation in both trends and uncertainties
medium
1
train
3,591
AR6_WGII
420
16
For instance, trophic amplification (strengthening of responses to climate-induced drivers at higher trophic levels) may result from combined direct and indirect food-web-mediated effects
medium
1
train
3,592
AR6_WGII
420
17
Alternatively, compensatory species interactions can dampen strong impacts on species from ocean acidification, resulting in weaker responses at functional-group or community level than at species level
medium
1
train
3,593
AR6_WGII
420
18
Globally, the projected reduction of biomass due to climate-induced drivers is relatively unaffected by fishing pressure, indicating additive responses of fisheries and climate change
low
0
train
3,594
AR6_WGII
420
19
Regionally, projected interactions of climate-induced drivers, fisheries and other regional non-climate drivers can be both synergistic and antagonistic, varying across regions, functional groups and species, and can cause nonlinear dynamics with counterintuitive outcomes, underlining the importance of adaptations and associated trade-offs
high
2
train
3,595
AR6_WGII
423
3
Heat stress and mass bleaching events caused decreases in live coral cover (virtually certain) (Graham et al., 2014; Hughes et al., 2018b), loss of sensitive species (extremely likely) (Donner and Carilli, 2019; Lange and Perry, 2019; Toth et al., 2019; Courtney et al., 2020), vulnerability to disease (extremely likely) (van Woesik and Randall, 2017; Hadaidi et al., 2018; Brodnicke et al., 2019; Howells et al., 2020) and declines in coral recruitment in the tropics
medium
1
train
3,596
AR6_WGII
423
5
Changes in coral community structure due to bleaching have caused declines in reef carbonate production
high
2
train
3,597
AR6_WGII
423
7
Bleaching and other drivers promote phase shifts to ecosystems dominated by macroalgae or other stress-tolerant species (very high confidence) (Graham et al., 2015; Stuart-Smith et al., 2018), leading to changes in reef-fish species assemblages
high
2
train
3,598
AR6_WGII
423
8
Ocean acidification and associated declines in aragonite saturation state (Ω aragonite) decrease rates of calcification by corals and other calcifying reef organisms (very high confidence), reduce coral settlement (medium confidence) and increase bioerosion and dissolution of reef substrates
high
2
train
3,599
AR6_WGII
423
11
However, experimental evidence suggests that coral responses to ocean acidification are species specific
medium
1
train