Projected Physical Changes B.1. Global-scale glacier mass loss, permafrost thaw, and decline in snow cover and Arctic sea ice extent are projected to continue in the near-term (2031–2050) due to surface air temperature increases (high confidence), with unavoidable consequences for river runoff and local hazards (high confidence). The Greenland and Antarctic Ice Sheets are projected to lose mass at an increasing rate throughout the 21st century and beyond (high confidence). The rates and magnitudes of these cryospheric changes are projected to increase further in the second half of the 21st century in a high greenhouse gas emissions scenario (high confidence). Strong reductions in greenhouse gas emissions in the coming decades are projected to reduce further changes after 2050 (high confidence). {2.2, 2.3, Cross-Chapter Box 6 in Chapter 2, 3.3, 3.4, Figure SPM.1, SPM Box SPM.1} B.1.1 Projected glacier mass reductions between 2015 and 2100 (excluding the ice sheets) range from 18 ± 7% (likely range) for RCP2.6 to 36 ± 11% (likely range) for RCP8.5, corresponding to a sea level contribution of 94 ± 25 mm (likely range) sea level equivalent for RCP2.6, and 200 ± 44 mm (likely range) for RCP8.5 (medium confidence). Regions with mostly smaller glaciers (e.g., Central Europe, Caucasus, North Asia, Scandinavia, tropical Andes, Mexico, eastern Africa and Indonesia), are projected to lose more than 80% of their current ice mass by 2100 under RCP8.5 (medium confidence), and many glaciers are projected to disappear regardless of future emissions (very high confidence). {Cross-Chapter Box 6 in Chapter 2, Figure SPM.1} B.1.2 In 2100, the Greenland Ice Sheet’s projected contribution to GMSL rise is 0.07 m (0.04–0.12 m, likely range) under RCP2.6, and 0.15 m (0.08–0.27 m, likely range) under RCP8.5. In 2100, the Antarctic Ice Sheet is projected to contribute 0.04 m (0.01–0.11 m, likely range) under RCP2.6, and 0.12 m (0.03–0.28 m, likely range) under RCP8.5. The Greenland Ice Sheet is currently contributing more to sea level rise than the Antarctic Ice Sheet (high confidence), but Antarctica could become a larger contributor by the end of the 21st century as a consequence of rapid retreat (low confidence). Beyond 2100, increasing divergence between Greenland and Antarctica’s relative contributions to GMSL rise under RCP8.5 has important consequences for the pace of relative sea level rise in the Northern Hemisphere. {3.3.1, 4.2.3, 4.2.5, 4.3.3, Cross-Chapter Box 8 in Chapter 3, Figure SPM.1} B.1.3 Arctic autumn and spring snow cover are projected to decrease by 5–10%, relative to 1986–2005, in the near-term (2031–2050), followed by no further losses under RCP2.6, but an additional 15–25% loss by the end of century under RCP8.5 (high confidence). In high mountain areas, projected decreases in low elevation mean winter snow depth, compared to 1986–2005, are likely 10–40% by 2031–2050, regardless of emissions scenario (high confidence). For 2081–2100, this projected decrease is likely 10–40 % for RCP2.6 and 50–90% for RCP8.5. {2.2.2, 3.3.2, 3.4.2, Figure SPM.1} B.1.4 Widespread permafrost thaw is projected for this century (very high confidence) and beyond. By 2100, projected near-surface (within 3–4 m) permafrost area shows a decrease of 24 ± 16% (likely range) for RCP2.6 and 69 ± 20% (likely range) for RCP8.5. The RCP8.5 scenario leads to the cumulative release of tens to hundreds of billions of tons (GtC) of permafrost carbon as CO2 and methane to the atmosphere by 2100 with the potential to exacerbate climate change (medium confidence). Lower emissions scenarios dampen the response of carbon emissions from the permafrost region (high confidence). Methane contributes a small fraction of the total additional carbon release but is significant because of its higher warming potential. Increased plant growth is projected to replenish soil carbon in part, but will not match carbon releases over the long term (medium confidence). {2.2.4, 3.4.2, 3.4.3, Figure SPM.1, Cross-Chapter Box 5 in Chapter 1} B.1.5 In many high mountain areas, glacier retreat and permafrost thaw are projected to further decrease the stability of slopes, and the number and area of glacier lakes will continue to increase (high confidence). Floods due to glacier lake outburst or rain-on-snow, landslides and snow avalanches, are projected to occur also in new locations or different seasons (high confidence). {2.3.2} B.1.6 River runoff in snow-dominated or glacier-fed high mountain basins is projected to change regardless of emissions scenario (very high confidence), with increases in average winter runoff (high confidence) and earlier spring peaks (very high confidence). In all emissions scenarios, average annual and summer runoff from glaciers are projected to peak at or before the end of the 21st century (high confidence), e.g., around mid-century in High Mountain Asia, followed by a decline in glacier runoff. In regions with little glacier cover (e.g., tropical Andes, European Alps) most glaciers have already passed this peak (high confidence). Projected declines in glacier runoff by 2100 (RCP8.5) can reduce basin runoff by 10% or more in at least one month of the melt season in several large river basins, especially in High Mountain Asia during the dry season (low confidence). {2.3.1} B.1.7 Arctic sea ice loss is projected to continue through mid-century, with differences thereafter depending on the magnitude of global warming: for stabilised global warming of 1.5°C the annual probability of a sea ice-free September by the end of century is approximately 1%, which rises to 10–35% for stabilised global warming of 2°C (high confidence). There is low confidence in projections for Antarctic sea ice. {3.2.2, Figure SPM.1}

B.2. Over the 21st century, the ocean is projected to transition to unprecedented conditions with increased temperatures (virtually certain), greater upper ocean stratification (very likely), further acidification (virtually certain), oxygen decline (medium confidence), and altered net primary production (low confidence). Marine heatwaves (very high confidence) and extreme El Niño and La Niña events (medium confidence) are projected to become more frequent. The Atlantic Meridional Overturning Circulation (AMOC) is projected to weaken (very likely). The rates and magnitudes of these changes will be smaller under scenarios with low greenhouse gas emissions (very likely). {3.2, 5.2, 6.4, 6.5, 6.7, Box 5.1, Figures SPM.1, SPM.3} B.2.1 The ocean will continue to warm throughout the 21st century (virtually certain). By 2100, the top 2000 m of the ocean are projected to take up 5–7 times more heat under RCP8.5 (or 2–4 times more under RCP2.6) than the observed accumulated ocean heat uptake since 1970 (very likely). The annual mean density stratification14 of the top 200 m, averaged between 60°S and 60°N, is projected to increase by 12–30% for RCP8.5 and 1–9% for RCP2.6, for 2081–2100 relative to 1986–2005 (very likely), inhibiting vertical nutrient, carbon and oxygen fluxes. {5.2.2, Figure SPM.1} B.2.2 By 2081–2100 under RCP8.5, ocean oxygen content (medium confidence), upper ocean nitrate content (medium confidence), net primary production (low confidence) and carbon export (medium confidence) are projected to decline globally by very likely ranges of 3–4%, 9–14%, 4–11% and 9-16% respectively, relative to 2006–2015. Under RCP2.6, globally projected changes by 2081–2100 are smaller compared to RCP8.5 for oxygen loss (very likely), nutrient availability (about as likely as not) and net primary production (high confidence). {5.2.2, Box 5.1, Figures SPM.1, SPM.3} B.2.3 Continued carbon uptake by the ocean by 2100 is virtually certain to exacerbate ocean acidification. Open ocean surface pH is projected to decrease by around 0.3 pH units by 2081–2100, relative to 2006–2015, under RCP8.5 (virtually certain). For RCP8.5, there are elevated risks for keystone aragonite shell-forming species due to crossing an aragonite stability threshold year-round in the Polar and sub-Polar Oceans by 2081–2100 (very likely). For RCP2.6, these conditions will be avoided this century (very likely), but some eastern boundary upwelling systems are projected to remain vulnerable (high confidence). {3.2.3, 5.2.2, Box 5.1, Box 5.3, Figure SPM.1} B.2.4 Climate conditions, unprecedented since the preindustrial period, are developing in the ocean, elevating risks for open ocean ecosystems. Surface acidification and warming have already emerged in the historical period (very likely). Oxygen loss between 100 and 600 m depth is projected to emerge over 59–80% of the ocean area by 2031–2050 under RCP8.5 (very likely). The projected time of emergence for five primary drivers of marine ecosystem change (surface warming and acidification, oxygen loss, nitrate content and net primary production change) are all prior to 2100 for over 60% of the ocean area under RCP8.5 and over 30% under RCP2.6 (very likely). {Annex I: Glossary, Box 5.1, Box 5.1 Figure 1} B.2.5 Marine heatwaves are projected to further increase in frequency, duration, spatial extent and intensity (maximum temperature) (very high confidence). Climate models project increases in the frequency of marine heatwaves by 2081–2100, relative to 1850–1900, by approximately 50 times under RCP8.5 and 20 times under RCP2.6 (medium confidence). The largest increases in frequency are projected for the Arctic and the tropical oceans (medium confidence). The intensity of marine heatwaves is projected to increase about 10-fold under RCP8.5 by 2081–2100, relative to 1850–1900 (medium confidence). {6.4, Figure SPM.1} B.2.6 Extreme El Niño and La Niña events are projected to likely increase in frequency in the 21st century and to likely intensify existing hazards, with drier or wetter responses in several regions across the globe. Extreme El Niño events are projected to occur about as twice as often under both RCP2.6 and RCP8.5 in the 21st century when compared to the 20th century (medium confidence). Projections indicate that extreme Indian Ocean Dipole events also increase in frequency (low confidence). {6.5, Figures 6.5, 6.6} B.2.7 The AMOC is projected to weaken in the 21st century under all RCPs (very likely), although a collapse is very unlikely (medium confidence). Based on CMIP5 projections, by 2300, an AMOC collapse is about as likely as not for high emissions scenarios and very unlikely for lower ones (medium confidence). Any substantial weakening of the AMOC is projected to cause a decrease in marine productivity in the North Atlantic (medium confidence), more storms in Northern Europe (medium confidence), less Sahelian summer rainfall (high confidence) and South Asian summer rainfall (medium confidence), a reduced number of tropical cyclones in the Atlantic (medium confidence), and an increase in regional sea level along the northeast coast of North America (medium confidence). Such changes would be in addition to the global warming signal. {6.7, Figures 6.8–6.10}

B.3. Sea level continues to rise at an increasing rate. Extreme sea level events that are historically rare (once per century in the recent past) are projected to occur frequently (at least once per year) at many locations by 2050 in all RCP scenarios, especially in tropical regions (high confidence). The increasing frequency of high water levels can have severe impacts in many locations depending on exposure (high confidence). Sea level rise is projected to continue beyond 2100 in all RCP scenarios. For a high emissions scenario (RCP8.5), projections of global sea level rise by 2100 are greater than in AR5 due to a larger contribution from the Antarctic Ice Sheet (medium confidence). In coming centuries under RCP8.5, sea level rise is projected to exceed rates of several centimetres per year resulting in multi-metre rise (medium confidence), while for RCP2.6 sea level rise is projected to be limited to around 1 m in 2300 (low confidence). Extreme sea levels and coastal hazards will be exacerbated by projected increases in tropical cyclone intensity and precipitation (high confidence). Projected changes in waves and tides vary locally in whether they amplify or ameliorate these hazards (medium confidence). {Cross-Chapter Box 5 in Chapter 1, Cross-Chapter Box 8 in Chapter 3, 4.1, 4.2, 5.2.2, 6.3.1, Figures SPM.1, SPM.4, SPM.5} B.3.1 The global mean sea level (GMSL) rise under RCP2.6 is projected to be 0.39 m (0.26–0.53 m, likely range) for the period 2081–2100, and 0.43 m (0.29–0.59 m, likely range) in 2100 with respect to 1986–2005. For RCP8.5, the corresponding GMSL rise is 0.71 m (0.51–0.92 m, likely range) for 2081–2100 and 0.84 m (0.61–1.10 m, likely range) in 2100. Mean sea level rise projections are higher by 0.1 m compared to AR5 under RCP8.5 in 2100, and the likely range extends beyond 1 m in 2100 due to a larger projected ice loss from the Antarctic Ice Sheet (medium confidence). The uncertainty at the end of the century is mainly determined by the ice sheets, especially in Antarctica. {4.2.3, Figures SPM.1, SPM.5} B.3.2 Sea level projections show regional differences around GMSL. Processes not driven by recent climate change, such as local subsidence caused by natural processes and human activities, are important to relative sea level changes at the coast (high confidence). While the relative importance of climate-driven sea level rise is projected to increase over time, local processes need to be considered for projections and impacts of sea level (high confidence). {SPM A3.4, 4.2.1, 4.2.2, Figure SPM.5} B.3.3 The rate of global mean sea level rise is projected to reach 15 mm yr–1 (10–20 mm yr–1, likely range) under RCP8.5 in 2100, and to exceed several centimetres per year in the 22nd century. Under RCP2.6, the rate is projected to reach 4 mm yr-1 (2–6 mm yr–1, likely range) in 2100. Model studies indicate multi-meter rise in sea level by 2300 (2.3–5.4 m for RCP8.5 and 0.6–1.07 m under RCP2.6) (low confidence), indicating the importance of reduced emissions for limiting sea level rise. Processes controlling the timing of future ice-shelf loss and the extent of ice sheet instabilities could increase Antarctica’s contribution to sea level rise to values substantially higher than the likely range on century and longer time-scales (low confidence). Considering the consequences of sea level rise that a collapse of parts of the Antarctic Ice Sheet entails, this high impact risk merits attention. {Cross-Chapter Box 5 in Chapter 1, Cross-Chapter Box 8 in Chapter 3, 4.1, 4.2.3} B.3.4 Global mean sea level rise will cause the frequency of extreme sea level events at most locations to increase. Local sea levels that historically occurred once per century (historical centennial events) are projected to occur at least annually at most locations by 2100 under all RCP scenarios (high confidence). Many low-lying megacities and small islands (including SIDS) are projected to experience historical centennial events at least annually by 2050 under RCP2.6, RCP4.5 and RCP8.5. The year when the historical centennial event becomes an annual event in the mid-latitudes occurs soonest in RCP8.5, next in RCP4.5 and latest in RCP2.6. The increasing frequency of high water levels can have severe impacts in many locations depending on the level of exposure (high confidence). {4.2.3, 6.3, Figures SPM.4, SPM.5} B.3.5 Significant wave heights (the average height from trough to crest of the highest one-third of waves) are projected to increase across the Southern Ocean and tropical eastern Pacific (high confidence) and Baltic Sea (medium confidence) and decrease over the North Atlantic and Mediterranean Sea under RCP8.5 (high confidence). Coastal tidal amplitudes and patterns are projected to change due to sea level rise and coastal adaptation measures (very likely). Projected changes in waves arising from changes in weather patterns, and changes in tides due to sea level rise, can locally enhance or ameliorate coastal hazards (medium confidence). {6.3.1, 5.2.2} B.3.6 The average intensity of tropical cyclones, the proportion of Category 4 and 5 tropical cyclones and the associated average precipitation rates are projected to increase for a 2°C global temperature rise above any baseline period (medium confidence). Rising mean sea levels will contribute to higher extreme sea levels associated with tropical cyclones (very high confidence). Coastal hazards will be exacerbated by an increase in the average intensity, magnitude of storm surge and precipitation rates of tropical cyclones. There are greater increases projected under RCP8.5 than under RCP2.6 from around mid-century to 2100 (medium confidence). There is low confidence in changes in the future frequency of tropical cyclones at the global scale. {6.3.1}

Projected Risks for Ecosystems B.4 Future land cryosphere changes will continue to alter terrestrial and freshwater ecosystems in high mountain and polar regions with major shifts in species distributions resulting in changes in ecosystem structure and functioning, and eventual loss of globally unique biodiversity (medium confidence). Wildfire is projected to increase significantly for the rest of this century across most tundra and boreal regions, and also in some mountain regions (medium confidence). {2.3.3, Box 3.4, 3.4.3} B.4.1 In high mountain regions, further upslope migration by lower-elevation species, range contractions, and increased mortality will lead to population declines of many alpine species, especially glacier- or snow-dependent species (high confidence), with local and eventual global species loss (medium confidence). The persistence of alpine species and sustaining ecosystem services depends on appropriate conservation and adaptation measures (high confidence). {2.3.3} B.4.2 On Arctic land, a loss of globally unique biodiversity is projected as limited refugia exist for some High-Arctic species and hence they are outcompeted by more temperate species (medium confidence). Woody shrubs and trees are projected to expand to cover 24–52% of Arctic tundra by 2050 (medium confidence). The boreal forest is projected to expand at its northern edge, while diminishing at its southern edge where it is replaced by lower biomass woodland/shrublands (medium confidence). {3.4.3, Box 3.4} B.4.3 Permafrost thaw and decrease in snow will affect Arctic and mountain hydrology and wildfire, with impacts on vegetation and wildlife (medium confidence). About 20% of Arctic land permafrost is vulnerable to abrupt permafrost thaw and ground subsidence, which is projected to increase small lake area by over 50% by 2100 for RCP8.5 (medium confidence). Even as the overall regional water cycle is projected to intensify, including increased precipitation, evapotranspiration, and river discharge to the Arctic Ocean, decreases in snow and permafrost may lead to soil drying with consequences for ecosystem productivity and disturbances (medium confidence). Wildfire is projected to increase for the rest of this century across most tundra and boreal regions, and also in some mountain regions, while interactions between climate and shifting vegetation will influence future fire intensity and frequency (medium confidence). {2.3.3, 3.4.1, 3.4.2, 3.4.3, SPM B.1}

B.5. A decrease in global biomass of marine animal communities, their production, and fisheries catch potential, and a shift in species composition are projected over the 21st century in ocean ecosystems from the surface to the deep seafloor under all emission scenarios (medium confidence). The rate and magnitude of decline are projected to be highest in the tropics (high confidence), whereas impacts remain diverse in polar regions (medium confidence) and increase for high emission scenarios. Ocean acidification (medium confidence), oxygen loss (medium confidence) and reduced sea ice extent (medium confidence) as well as non-climatic human activities (medium confidence) have the potential to exacerbate these warming-induced ecosystem impacts. {3.2.3, 3.3.3, 5.2.2, 5.2.3, 5.2.4, 5.4.1, Figure SPM.3} B.5.1 Projected ocean warming and changes in net primary production alter biomass, production and community structure of marine ecosystems. The global-scale biomass of marine animals across the foodweb is projected to decrease by 15.0 ± 5.9% (very likely range) and the maximum catch potential of fisheries by 20.5–24.1% by the end of the 21st century relative to 1986–2005 under RCP8.5 (medium confidence). These changes are projected to be very likely three to four times larger under RCP8.5 than RCP2.6. {3.2.3, 3.3.3, 5.2.2, 5.2.3, 5.4.1, Figure SPM.3} B.5.2 Under enhanced stratification reduced nutrient supply is projected to cause tropical ocean net primary production to decline by 7–16% (very likely range) for RCP8.5 by 2081–2100 (medium confidence). In tropical regions, marine animal biomass and production are projected to decrease more than the global average under all emissions scenarios in the 21st century (high confidence). Warming and sea ice changes are projected to increase marine net primary production in the Arctic (medium confidence) and around Antarctica (low confidence), modified by changing nutrient supply due to shifts in upwelling and stratification. Globally, the sinking flux of organic matter from the upper ocean is projected to decrease, linked largely due to changes in net primary production (high confidence). As a result, 95% or more of the deep sea (3000–6000 m depth) seafloor area and cold-water coral ecosystems are projected to experience declines in benthic biomass under RCP8.5 (medium confidence). {3.2.3, 5.2.2. 5.2.4, Figure SPM.1} B.5.3 Warming, ocean acidification, reduced seasonal sea ice extent and continued loss of multi-year sea ice are projected to impact polar marine ecosystems through direct and indirect effects on habitats, populations and their viability (medium confidence). The geographical range of Arctic marine species, including marine mammals, birds and fish is projected to contract, while the range of some sub-Arctic fish communities is projected to expand, further increasing pressure on high-Arctic species (medium confidence). In the Southern Ocean, the habitat of Antarctic krill, a key prey species for penguins, seals and whales, is projected to contract southwards under both RCP2.6 and RCP8.5 (medium confidence). {3.2.2, 3.2.3, 5.2.3} B.5.4 Ocean warming, oxygen loss, acidification and a decrease in flux of organic carbon from the surface to the deep ocean are projected to harm habitat-forming cold-water corals, which support high biodiversity, partly through decreased calcification, increased dissolution of skeletons, and bioerosion (medium confidence). Vulnerability and risks are highest where and when temperature and oxygen conditions both reach values outside species’ tolerance ranges (medium confidence). {Box 5.2, Figure SPM.3}

Figure SPM3(abc) Download Share

SROCC_SPM3(d)_Final_RGB Download Share Figure SPM.3 | Projected changes, impacts and risks for ocean regions and ecosystems. (a) depth integrated net primary production (NPP from CMIP5), (b) total animal biomass (depth integrated, including fishes and invertebrates from FISHMIP), (c) maximum fisheries catch potential and (d) impacts and risks for coastal and open ocean ecosystems. The three left panels represent […] Figure SPM.3 | Projected changes, impacts and risks for ocean regions and ecosystems. (a) depth integrated net primary production (NPP from CMIP5 ), (b) total animal biomass (depth integrated, including fishes and invertebrates from FISHMIP ), (c) maximum fisheries catch potential and (d) impacts and risks for coastal and open ocean ecosystems. The three left panels represent the simulated (a,b) and observed (c) mean values for the recent past (1986–2005), the middle and right panels represent projected changes (%) by 2081–2100 relative to recent past under low (RCP2.6) and high (RCP8.5) greenhouse gas emissions scenario {Box SPM.1}, respectively. Total animal biomass in the recent past (b, left panel) represents the projected total animal biomass by each spatial pixel relative to the global average. (c) *Average observed fisheries catch in the recent past (based on data from the Sea Around Us global fisheries database); projected changes in maximum fisheries catch potential in shelf seas are based on the average outputs from two fisheries and marine ecosystem models. To indicate areas of model inconsistency, shaded areas represent regions where models disagree in the direction of change for more than: (a) and (b) 3 out of 10 model projections, and (c) one out of two models. Although unshaded, the projected change in the Arctic and Antarctic regions in (b) total animal biomass and (c) fisheries catch potential have low confidence due to uncertainties associated with modelling multiple interacting drivers and ecosystem responses. Projections presented in (b) and (c) are driven by changes in ocean physical and biogeochemical conditions e.g., temperature, oxygen level, and net primary production projected from CMIP5 Earth system models. **The epipelagic refers to the uppermost part of the ocean with depth <200 m from the surface where there is enough sunlight to allow photosynthesis. (d) Assessment of risks for coastal and open ocean ecosystems based on observed and projected climate impacts on ecosystem structure, functioning and biodiversity. Impacts and risks are shown in relation to changes in Global Mean Surface Temperature (GMST) relative to pre-industrial level. Since assessments of risks and impacts are based on global mean Sea Surface Temperature (SST), the corresponding SST levels are shown . The assessment of risk transitions is described in Chapter 5 Sections 5.2, 5.3, 5.2.5 and 5.3.7 and Supplementary Materials SM5.3, Table SM5.6, Table SM5.8 and other parts of the underlying report. The figure indicates assessed risks at approximate warming levels and increasing climate-related hazards in the ocean: ocean warming, acidification, deoxygenation, increased density stratification, changes in carbon fluxes, sea level rise, and increased frequency and/or intensity of extreme events. The assessment considers the natural adaptive capacity of the ecosystems, their exposure and vulnerability. Impact and risk levels do not consider risk reduction strategies such as human interventions, or future changes in non-climatic drivers. Risks for ecosystems were assessed by considering biological, biogeochemical, geomorphological and physical aspects. Higher risks associated with compound effects of climate hazards include habitat and biodiversity loss, changes in species composition and distribution ranges, and impacts/risks on ecosystem structure and functioning, including changes in animal/plant biomass and density, productivity, carbon fluxes, and sediment transport. As part of the assessment, literature was compiled and data extracted into a summary table. A multi-round expert elicitation process was undertaken with independent evaluation of threshold judgement, and a final consensus discussion. Further information on methods and underlying literature can be found in Chapter 5, Sections 5.2 and 5.3 and Supplementary Material. {3.2.3, 3.2.4, 5.2, 5.3, 5.2.5, 5.3.7, SM5.6, SM5.8, Figure 5.16, Cross Chapter Box 1 in Chapter 1 Table CCB1}

B.6. Risks of severe impacts on biodiversity, structure and function of coastal ecosystems are projected to be higher for elevated temperatures under high compared to low emissions scenarios in the 21st century and beyond. Projected ecosystem responses include losses of species habitat and diversity, and degradation of ecosystem functions. The capacity of organisms and ecosystems to adjust and adapt is higher at lower emissions scenarios (high confidence). For sensitive ecosystems such as seagrass meadows and kelp forests, high risks are projected if global warming exceeds 2°C above pre-industrial temperature, combined with other climate-related hazards (high confidence). Warm-water corals are at high risk already and are projected to transition to very high risk even if global warming is limited to 1.5°C (very high confidence). {4.3.3, 5.3, 5.5, Figure SPM.3} B.6.1 All coastal ecosystems assessed are projected to face increasing risk level, from moderate to high risk under RCP2.6 to high to very high risk under RCP8.5 by 2100. Intertidal rocky shore ecosystems are projected to be at very high risk by 2100 under RCP8.5 (medium confidence) due to exposure to warming, especially during marine heatwaves, as well as to acidification, sea level rise, loss of calcifying species and biodiversity (high confidence). Ocean acidification challenges these ecosystems and further limits their habitat suitability (medium confidence) by inhibiting recovery through reduced calcification and enhanced bioerosion. The decline of kelp forests is projected to continue in temperate regions due to warming, particularly under the projected intensification of marine heatwaves, with high risk of local extinctions under RCP8.5 (medium confidence). {5.3, 5.3.5, 5.3.6, 5.3.7, 6.4.2, Figure SPM.3} B.6.2 Seagrass meadows and saltmarshes and associated carbon stores are at moderate risk at 1.5°C global warming and increase with further warming (medium confidence). Globally, 20–90% of current coastal wetlands are projected to be lost by 2100, depending on projected sea level rise, regional differences and wetland types, especially where vertical growth is already constrained by reduced sediment supply and landward migration is constrained by steep topography or human modification of shorelines (high confidence). {4.3.3, 5.3.2, Figure SPM.3, SPM A6.1} B.6.3 Ocean warming, sea level rise and tidal changes are projected to expand salinization and hypoxia in estuaries (high confidence) with high risks for some biota leading to migration, reduced survival, and local extinction under high emission scenarios (medium confidence). These impacts are projected to be more pronounced in more vulnerable eutrophic and shallow estuaries with low tidal range in temperate and high latitude regions (medium confidence). {5.2.2, 5.3.1, Figure SPM.3} B.6.4 Almost all warm-water coral reefs are projected to suffer significant losses of area and local extinctions, even if global warming is limited to 1.5°C (high confidence). The species composition and diversity of remaining reef communities is projected to differ from present-day reefs (very high confidence). {5.3.4, 5.4.1, Figure SPM.3}

Projected Risks for People and Ecosystem Services B.7. Future cryosphere changes on land are projected to affect water resources and their uses, such as hydropower (high confidence) and irrigated agriculture in and downstream of high mountain areas (medium confidence), as well as livelihoods in the Arctic (medium confidence). Changes in floods, avalanches, landslides, and ground destabilization are projected to increase risk for infrastructure, cultural, tourism, and recreational assets (medium confidence). {2.3, 2.3.1, 3.4.3} B.7.1 Disaster risks to human settlements and livelihood options in high mountain areas and the Arctic are expected to increase (medium confidence), due to future changes in hazards such as floods, fires, landslides, avalanches, unreliable ice and snow conditions, and increased exposure of people and infrastructure (high confidence). Current engineered risk reduction approaches are projected to be less effective as hazards change in character (medium confidence). Significant risk reduction and adaptation strategies help avoid increased impacts from mountain flood and landslide hazards as exposure and vulnerability are increasing in many mountain regions during this century (high confidence). {2.3.2, 3.4.3, 3.5.2} B.7.2 Permafrost thaw-induced subsidence of the land surface is projected to impact overlying urban and rural communication and transportation infrastructure in the Arctic and in high mountain areas (medium confidence). The majority of Arctic infrastructure is located in regions where permafrost thaw is projected to intensify by mid-century. Retrofitting and redesigning infrastructure has the potential to halve the costs arising from permafrost thaw and related climate-change impacts by 2100 (medium confidence). {2.3.4, 3.4.1, 3.4.3} B.7.3 High mountain tourism, recreation and cultural assets are projected to be negatively affected by future cryospheric changes (high confidence). Current snowmaking technologies are projected to be less effective in reducing risks to ski tourism in a warmer climate in most parts of Europe, North America, and Japan, in particular at 2°C global warming and beyond (high confidence). {2.3.5, 2.3.6}

B.8. Future shifts in fish distribution and decreases in their abundance and fisheries catch potential due to climate change are projected to affect income, livelihoods, and food security of marine resource-dependent communities (medium confidence). Long-term loss and degradation of marine ecosystems compromises the ocean’s role in cultural, recreational, and intrinsic values important for human identity and well-being (medium confidence). {3.2.4, 3.4.3, 5.4.1, 5.4.2, 6.4} B.8.1 Projected geographical shifts and decreases of global marine animal biomass and fish catch potential are more pronounced under RCP8.5 relative to RCP2.6 elevating the risk for income and livelihoods of dependent human communities, particularly in areas that are economically vulnerable (medium confidence). The projected redistribution of resources and abundance increases the risk of conflicts among fisheries, authorities or communities (medium confidence). Challenges to fisheries governance are widespread under RCP8.5 with regional hotspots such as the Arctic and tropical Pacific Ocean (medium confidence). {3.5.2, 5.4.1, 5.4.2, 5.5.2, 5.5.3, 6.4.2, Figure SPM.3} B.8.2 The decline in warm-water coral reefs is projected to greatly compromise the services they provide to society, such as food provision (high confidence), coastal protection (high confidence) and tourism (medium confidence). Increases in the risks for seafood security (medium confidence) associated with decreases in seafood availability are projected to elevate the risk to nutritional health in some communities highly dependent on seafood (medium confidence), such as those in the Arctic, West Africa, and Small Island Developing States. Such impacts compound any risks from other shifts in diets and food systems caused by social and economic changes and climate change over land (medium confidence). {3.4.3, 5.4.2, 6.4.2} B.8.3 Global warming compromises seafood safety (medium confidence) through human exposure to elevated bioaccumulation of persistent organic pollutants and mercury in marine plants and animals (medium confidence), increasing prevalence of waterborne Vibrio pathogens (medium confidence), and heightened likelihood of harmful algal blooms (medium confidence). These risks are projected to be particularly large for human communities with high consumption of seafood, including coastal Indigenous communities (medium confidence), and for economic sectors such as fisheries, aquaculture, and tourism (high confidence). {3.4.3, 5.4.2, Box 5.3} B.8.4 Climate change impacts on marine ecosystems and their services put key cultural dimensions of lives and livelihoods at risk (medium confidence), including through shifts in the distribution or abundance of harvested species and diminished access to fishing or hunting areas. This includes potentially rapid and irreversible loss of culture and local knowledge and Indigenous knowledge, and negative impacts on traditional diets and food security, aesthetic aspects, and marine recreational activities (medium confidence). {3.4.3, 3.5.3, 5.4.2}

B.9. Increased mean and extreme sea level, alongside ocean warming and acidification, are projected to exacerbate risks for human communities in low-lying coastal areas (high confidence). In Arctic human communities without rapid land uplift, and in urban atoll islands, risks are projected to be moderate to high even under a low emissions scenario (RCP2.6) (medium confidence), including reaching adaptation limits (high confidence). Under a high emissions scenario (RCP8.5), delta regions and resource rich coastal cities are projected to experience moderate to high risk levels after 2050 under current adaptation (medium confidence). Ambitious adaptation including transformative governance is expected to reduce risk (high confidence), but with context-specific benefits. {4.3.3, 4.3.4, SM4.3, 6.9.2, Cross-chapter Box 9, Figure SPM.5} B.9.1 In the absence of more ambitious adaptation efforts compared to today, and under current trends of increasing exposure and vulnerability of coastal communities, risks, such as erosion and land loss, flooding, salinization, and cascading impacts due to mean sea level rise and extreme events are projected to significantly increase throughout this century under all greenhouse gas emissions scenarios (very high confidence). Under the same assumptions, annual coastal flood damages are projected to increase by 2–3 orders of magnitude by 2100 compared to today (high confidence). {4.3.3, 4.3.4, Box 6.1, 6.8, SM4.3, Figures SPM.4, SPM.5} B.9.2 High to very high risks are approached for vulnerable communities in coral reef environments, urban atoll islands and low-lying Arctic locations from sea level rise well before the end of this century in case of high emissions scenarios. This entails adaptation limits being reached, which are the points at which an actor’s objectives (or system needs) cannot be secured from intolerable risks through adaptive actions (high confidence). Reaching adaptation limits (e.g., biophysical, geographical, financial, technical, social, political, and institutional) depends on the emissions scenario and context-specific risk tolerance, and is projected to expand to more areas beyond 2100, due to the long-term commitment of sea level rise (medium confidence). Some island nations are likely to become uninhabitable due to climate-related ocean and cryosphere change (medium confidence), but habitability thresholds remain extremely difficult to assess. {4.3.4, 4.4.2, 4.4.3, 5.5.2, Cross-Chapter Box 9, SM4.3, SPM C.1, Glossary, Figure SPM.5} B.9.3 Globally, a slower rate of climate-related ocean and cryosphere change provides greater adaptation opportunities (high confidence). While there is high confidence that ambitious adaptation, including governance for transformative change, has the potential to reduce risks in many locations, such benefits can vary between locations. At global scale, coastal protection can reduce flood risk by 2–3 orders of magnitude during the 21st century, but depends on investments on the order of tens to several hundreds of billions of US$ per year (high confidence). While such investments are generally cost efficient for densely populated urban areas, rural and poorer areas may be challenged to afford such investments with relative annual costs for some small island states amounting to several percent of GDP (high confidence). Even with major adaptation efforts, residual risks and associated losses are projected to occur (medium confidence), but context-specific limits to adaptation and residual risks remain difficult to assess. {4.1.3, 4.2.2.4, 4.3.1, 4.3.2, 4.3.4, 4.4.3, 6.9.1, 6.9.2, Cross-Chapter Boxes 1–2 in Chapter 1, SM4.3, Figure SPM.5}