Editing IPCC:AR6/SROCC/SPM (section)

==== Projected Physical Changes <sup>[[#fn:25|25]]</sup> '''''' ====

'''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''' [[File:d36c4e81147e753b78bf397873d1c249 SPM-Icon-xoxo.png]] 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''' [[File:d36c4e81147e753b78bf397873d1c249 SPM-Icon-xoxo.png]] 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''' [[File:7dd9d5f1c0e829eec2bf341c5154813e SPM-Icon-xxoo.png]] 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''' [[File:7dd9d5f1c0e829eec2bf341c5154813e SPM-Icon-xxoo.png]] 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 CO 2 <sup>[[#fn:26|26]]</sup> 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''' [[File:4d299f9da92412c8279a7422468e6e12 SPM-Icon-xooo.png]] 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''' [[File:7dd9d5f1c0e829eec2bf341c5154813e SPM-Icon-xxoo.png]] 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 [[File:7dd9d5f1c0e829eec2bf341c5154813e SPM-Icon-xxoo.png]] 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}

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'''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''' [[File:aa4c791c8b6f965d8de1653e5ac59fbc SPM-Icon-ooox.png]] 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 stratification 14 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''' [[File:aa4c791c8b6f965d8de1653e5ac59fbc SPM-Icon-ooox.png]] 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''' [[File:aa4c791c8b6f965d8de1653e5ac59fbc SPM-Icon-ooox.png]] 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''' [[File:aa4c791c8b6f965d8de1653e5ac59fbc SPM-Icon-ooox.png]] 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''' [[File:37d9ca019c63e0a7a080aaca0b2016e4 SPM-Icon-oxox.png]] 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''' [[File:aa4c791c8b6f965d8de1653e5ac59fbc SPM-Icon-ooox.png]] 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''' [[File:aa4c791c8b6f965d8de1653e5ac59fbc SPM-Icon-ooox.png]] 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}

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'''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''' [[File:f83f15a29ea2d8a2d2ddc3ce832f4aaa SPM-Icon-oxxo.png]] 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''' [[File:c2dab058529f43e723961cf4dccd97c2 SPM-Icon-ooxx.png]] 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''' [[File:f83f15a29ea2d8a2d2ddc3ce832f4aaa SPM-Icon-oxxo.png]] 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''' [[File:3dcc514bf2acf9f1b7861bf877ef79a9 SPM-Icon-ooxo.png]] 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''' [[File:22af16650531e42ab6972bf52565981a SPM-Icon-oxxx.png]] 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''' [[File:3dcc514bf2acf9f1b7861bf877ef79a9 SPM-Icon-ooxo.png]] 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}

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