Editing IPCC:AR6/SROCC/SPM (section)

== Box SPM.1 Use of Climate Change Scenarios in SROCC ==

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Assessments of projected future changes in this report are based largely on CMIP5 <sup>[[#fn:14|14]]</sup> climate model projections using Representative Concentration Pathways (RCPs). RCPs are scenarios that include time series of emissions and concentrations of the full suite of greenhouse gases (GHGs) and aerosols and chemically active gases, as well as land use / land cover. RCPs provide only one set of many possible scenarios that would lead to different levels of global warming. {Annex I: Glossary}

This report uses mainly RCP2.6 and RCP8.5 in its assessment, reflecting the available literature. RCP2.6 represents a low greenhouse gas emissions, high mitigation future, that in CMIP5 simulations gives a two in three chance of limiting global warming to below 2°C by 2100 <sup>[[#fn:15|15]]</sup> . By contrast, RCP8.5 is a high greenhouse gas emissions scenario in the absence of policies to combat climate change, leading to continued and sustained growth in atmospheric greenhouse gas concentrations. Compared to the total set of RCPs, RCP8.5 corresponds to the pathway with the highest greenhouse gas emissions. The underlying chapters also reference other scenarios, including RCP4.5 and RCP6.0 that have intermediate levels of greenhouse gas emissions and result in intermediate levels of warming. {Annex I: Glossary, Cross-Chapter Box 1 in Chapter 1}

Table SPM.1 provides estimates of total warming since the pre-industrial period under four different RCPs for key assessment intervals used in SROCC. The warming from the 1850–1900 period until 1986–2005 has been assessed as 0.63°C (0.57 to 0.69°C ''likely'' range) using observations of near-surface air temperature over the ocean and over land . <sup>[[#fn:16|16]]</sup> Consistent with the approach in AR5, modelled future changes in global mean surface air temperature relative to 1986–2005 are added to this observed warming. {Cross-Chapter Box 1 in Chapter 1}

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'''Table SPM.1'''

Projected global mean surface temperature change relative to 1850–1900 for two time periods under four RCPs <sup>[[#fn:15|15]]</sup> . {Cross-Chapter Box 1 in Chapter 1}

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{| class="wikitable"
|-
|
| colspan="2"| '''Near-term: 2031''' – '''2050'''
| colspan="2"| '''End-of-century: 2081''' – '''2100'''
|-
| '''Scenario'''
| '''Mean (''' '''°''' '''C)'''
| '''''Likely''''' '''range (''' '''°''' '''C)'''
| '''Mean (''' '''°''' '''C)'''
| '''''Likely''''' '''range (''' '''°''' '''C)'''
|-
| RCP2.6
| 1.6
| 1.1 to 2.0
| 1.6
| 0.9 to 2.4
|-
| RCP4.5
| 1.7
| 1.3 to 2.2
| 2.5
| 1.7 to 3.3
|-
| RCP6.0
| 1.6
| 1.2 to 2.0
| 2.9
| 2.0 to 3.8
|-
| RCP8.5
| 2.0
| 1.5 to 2.4
| 4.3
| 3.2 to 5.4
|}
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'''A.2. It is ''virtually certain'' that the global ocean has warmed unabated since 1970 and has taken up more than 90% of the excess heat in the climate system ( ''high confidence'' ). Since 1993, the rate of ocean warming has more than doubled ( ''likely'' ). Marine heatwaves have ''very likely'' doubled in frequency since 1982 and are increasing in intensity ( ''very high confidence'' ). By absorbing more CO2, the ocean has undergone increasing surface acidification ( ''virtually certain'' ). A loss of oxygen has occurred from the surface to 1000 m ( ''medium confidence'' ). {1.4, 3.2, 5.2, 6.4, 6.7, Figures SPM.1, SPM.2}'''

'''A.2''' . '''1''' [[File:aa4c791c8b6f965d8de1653e5ac59fbc SPM-Icon-ooox.png]] The ocean warming trend documented in the IPCC Fifth Assessment Report (AR5) has continued. Since 1993 the rate of ocean warming and thus heat uptake has more than doubled ( ''likely'' ) from 3.22 ± 1.61 ZJ yr –1 (0–700 m depth) and 0.97 ± 0.64 ZJ yr –1 (700–2000 m) between 1969 and 1993, to 6.28 ± 0.48 ZJ yr –1 (0–700 m) and 3.86 ± 2.09 ZJ yr –1 (700–2000 m) between 1993 and 2017 <sup>[[#fn:17|17]]</sup> , and is attributed to anthropogenic forcing ( ''very likely'' ). {1.4.1, 5.2.2, Table 5.1, Figure SPM.1}

'''A.2.2''' [[File:37d9ca019c63e0a7a080aaca0b2016e4 SPM-Icon-oxox.png]] The Southern Ocean accounted for 35–43% of the total heat gain in the upper 2000 m global ocean between 1970 and 2017 ( ''high confidence'' ). Its share increased to 45–62% between 2005 and 2017 ( ''high confidence'' ). The deep ocean below 2000 m has warmed since 1992 ( ''likely'' ), especially in the Southern Ocean. {1.4, 3.2.1, 5.2.2, Table 5.1, Figure SPM.2}

'''A.2.3''' [[File:aa4c791c8b6f965d8de1653e5ac59fbc SPM-Icon-ooox.png]] Globally, marine heat-related events have increased; marine heatwaves <sup>[[#fn:18|18]]</sup> , defined when the daily sea surface temperature exceeds the local 99th percentile over the period 1982 to 2016, have doubled in frequency and have become longer-lasting, more intense and more extensive ( ''very likely'' ). It is ''very likely'' that between 84–90% of marine heatwaves that occurred between 2006 and 2015 are attributable to the anthropogenic temperature increase. {Table 6.2, 6.4, Figures SPM.1, SPM.2}

'''A.2.4''' [[File:aa4c791c8b6f965d8de1653e5ac59fbc SPM-Icon-ooox.png]] Density stratification <sup>[[#fn:19|19]]</sup> has increased in the upper 200 m of the ocean since 1970 ( ''very likely'' ). Observed surface ocean warming and high latitude addition of freshwater are making the surface ocean less dense relative to deeper parts of the ocean ( ''high confidence'' ) and inhibiting mixing between surface and deeper waters ( ''high confidence'' ). The mean stratification of the upper 200 m has increased by 2.3 ± 0.1% ( ''very likely'' range) from the 1971–1990 average to the 1998–2017 average. {5.2.2}

'''A.2.5''' [[File:37d9ca019c63e0a7a080aaca0b2016e4 SPM-Icon-oxox.png]] The ocean has taken up between 20–30% ( ''very likely'' ) of total anthropogenic CO 2 emissions since the 1980s causing further ocean acidification. Open ocean surface pH has declined by a ''very likely'' range of 0.017–0.027 pH units per decade since the late 1980s <sup>[[#fn:20|20]]</sup> , with the decline in surface ocean pH ''very likely'' to have already emerged from background natural variability for more than 95% of the ocean surface area. {3.2.1, 5.2.2, Box 5.1, Figures SPM.1, SPM.2}

'''A.2.6''' [[File:aa4c791c8b6f965d8de1653e5ac59fbc SPM-Icon-ooox.png]] Datasets spanning 1970–2010 show that t he open ocean has lost oxygen by a ''very likely'' range of 0.5–3.3% over the upper 1000 m, alongside a ''likely'' expansion of the volume of oxygen minimum zones by 3–8% ( ''medium confidence'' ). O xygen loss is primarily due to increasing ocean stratification, changing ventilation and biogeochemistry ( ''high confidence'' ). {5.2.2, Figures SPM.1, SPM.2}

'''A.2.7''' [[File:aa4c791c8b6f965d8de1653e5ac59fbc SPM-Icon-ooox.png]] Observations, both in situ (2004–2017) and based on sea surface temperature reconstructions, indicate that the Atlantic Meridional Overturning Circulation (AMOC) <sup>[[#fn:21|21]]</sup> has weakened relative to 1850–1900 ( ''medium confidence'' ). There is insufficient data to quantify the magnitude of the weakening, or to properly attribute it to anthropogenic forcing due to the limited length of the observational record. Although attribution is currently not possible, CMIP5 model simulations of the period 1850–2015, on average, exhibit a weakening AMOC when driven by anthropogenic forcing. {6.7}

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'''A.3. Global mean sea level (GMSL) is rising, with acceleration in recent decades due to increasing rates of ice loss from the Greenland and Antarctic ice sheets ( ''very'' ''high confidence'' ), as well as continued glacier mass loss and ocean thermal expansion. Increases in tropical cyclone winds and rainfall, and increases in extreme waves, combined with relative sea level rise, exacerbate extreme sea level events and coastal hazards ( ''high confidence'' ). {3.3, 4.2, 6.2, 6.3, 6.8, Figures SPM.1, SPM.2, SPM.4, SPM.5}'''

'''A.3.1''' [[File:83ce8208a5b1bfd831112dee0dcef7fd SPM-Icon-xxxo.png]] Total GMSL rise for 1902–2015 is 0.16 m ( ''likely'' range 0.12–0.21 m). The rate of GMSL rise for 2006–2015 of 3.6 mm yr –1 (3.1–4.1 mm yr –1 , ''very likely'' range), is unprecedented over the last century ( ''high confidence'' ), and about 2.5 times the rate for 1901–1990 of 1.4 mm yr –1 (0.8– 2.0 mm yr –1 , ''very likely'' range). The sum of ice sheet and glacier contributions over the period 2006–2015 is the dominant source of sea level rise (1.8 mm yr –1 , ''very likely'' range 1.7–1.9 mm yr –1 ), exceeding the effect of thermal expansion of ocean water (1.4 mm yr –1 , ''very likely'' range 1.1–1.7 mm yr –1 ) <sup>[[#fn:22|22]]</sup>   ( ''very high confidence'' ). The dominant cause of global mean sea level rise since 1970 is anthropogenic forcing ( ''high confidence'' ). {4.2.1, 4.2.2, Figure SPM.1}

'''A.3.2''' [[File:f83f15a29ea2d8a2d2ddc3ce832f4aaa SPM-Icon-oxxo.png]] Sea level rise has accelerated ( ''extremely likely'' ) due to the combined increased ice loss from the Greenland and Antarctic ice sheets ( ''very high confidence'' ). Mass loss from the Antarctic ice sheet over the period 2007–2016 tripled relative to 1997–2006. For Greenland, mass loss doubled over the same period ( ''likely, medium confidence'' ). {3.3.1, Figures SPM.1, SPM.2, SPM A1.1}

'''A.3.3''' [[File:f83f15a29ea2d8a2d2ddc3ce832f4aaa SPM-Icon-oxxo.png]] Acceleration of ice flow and retreat in Antarctica, which has the potential to lead to sea level rise of several metres within a few centuries, is observed in the Amundsen Sea Embayment of West Antarctica and in Wilkes Land, East Antarctica ( ''very high confidence'' ). These changes may be the onset of an irreversible <sup>[[#fn:23|23]]</sup>  ice sheet instability. Uncertainty related to the onset of ice sheet instability arises from limited observations, inadequate model representation of ice sheet processes, and limited understanding of the complex interactions between the atmosphere, ocean and the ice sheet. {3.3.1, Cross-Chapter Box 8 in Chapter 3, 4.2.3}

'''A.3.4''' [[File:f83f15a29ea2d8a2d2ddc3ce832f4aaa SPM-Icon-oxxo.png]] Sea level rise is not globally uniform and varies regionally. Regional differences, within ±30% of the global mean sea level rise, result from land ice loss and variations in ocean warming and circulation. Differences from the global mean can be greater in areas of rapid vertical land movement including from local human activities (e.g. extraction of groundwater). ( ''high confidence'' ) {4.2.2, 5.2.2, 6.2.2, 6.3.1, 6.8.2, Figure SPM.2 }

'''A.3.5''' [[File:f83f15a29ea2d8a2d2ddc3ce832f4aaa SPM-Icon-oxxo.png]] Extreme wave heights, which contribute to extreme sea level events, coastal erosion and flooding, have increased in the Southern and North Atlantic Oceans by around 1.0 cm yr –1 and 0.8 cm yr –1 over the period 1985–2018 ( ''medium confidence'' ). Sea ice loss in the Arctic has also increased wave heights over the period 1992–2014 ( ''medium confidence'' ). {4.2.2, 6.2, 6.3, 6.8, Box 6.1}

'''A.3.6''' [[File:3dcc514bf2acf9f1b7861bf877ef79a9 SPM-Icon-ooxo.png]] Anthropogenic climate change has increased observed precipitation ( ''medium confidence'' ), winds ( ''low confidence'' ), and extreme sea level events ( ''high confidence'' ) associated with some tropical cyclones, which has increased intensity of multiple extreme events and associated cascading impacts ( ''high confidence'' ). Anthropogenic climate change may have contributed to a poleward migration of maximum tropical cyclone intensity in the western North Pacific in recent decades related to anthropogenically-forced tropical expansion ( ''low confidence'' ). There is emerging evidence for an increase in annual global proportion of Category 4 or 5 tropical cyclones in recent decades ( ''low confidence'' ). {6.2, Table 6.2, 6.3, 6.8, Box 6.1}

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==== Observed Impacts on Ecosystems ====

'''A.4. Cryospheric and associated hydrological changes have impacted terrestrial and freshwater species and ecosystems in high mountain and polar regions through the appearance of land previously covered by ice, changes in snow cover, and thawing permafrost. These changes have contributed to changing the seasonal activities, abundance and distribution of ecologically, culturally, and economically important plant and animal species, ecological disturbances, and ecosystem functioning. ( ''high confidence'' ) {2.3.2, 2.3.3, 3.4.1, 3.4.3, Box 3.4, Figure SPM.2}'''

'''A.4.1''' [[File:7dd9d5f1c0e829eec2bf341c5154813e SPM-Icon-xxoo.png]] Over the last century some species of plants and animals have increased in abundance, shifted their range, and established in new areas as glaciers receded and the snow-free season lengthened ( ''high confidence'' ). Together with warming, these changes have increased locally the number of species in high mountains, as lower-elevation species migrate upslope ( ''very high confidence'' ). Some cold-adapted or snow-dependent species have declined in abundance, increasing their risk of extinction, notably on mountain summits ( ''high confidence'' ). In polar and mountain regions, many species have altered seasonal activities especially in late winter and spring ( ''high confidence'' ). {2.3.3, Box 3.4}

'''A.4.2''' [[File:7dd9d5f1c0e829eec2bf341c5154813e SPM-Icon-xxoo.png]] Increased wildfire and abrupt permafrost thaw, as well as changes in Arctic and mountain hydrology have altered frequency and intensity of ecosystem disturbances ( ''high confidence'' ). This has included positive and negative impacts on vegetation and wildlife such as reindeer and salmon ( ''high confidence'' ). {2.3.3, 3.4.1, 3.4.3}

'''A.4.3''' [[File:7dd9d5f1c0e829eec2bf341c5154813e SPM-Icon-xxoo.png]] Across tundra, satellite observations show an overall greening, often indicative of increased plant productivity ( ''high confidence'' ). Some browning areas in tundra and boreal forest are indicative that productivity has decreased ( ''high confidence'' ). These changes have negatively affected provisioning, regulating and cultural ecosystem services, with also some transient positive impacts for provisioning services, in both high mountains ( ''medium confidence'' ) and polar regions ( ''high confidence'' ). {2.3.1, 2.3.3, 3.4.1, 3.4.3, Annex I: Glossary}

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'''A.5. Since about 1950 many marine species across various groups have undergone shifts in geographical range and seasonal activities in response to ocean warming, sea ice change and biogeochemical changes, such as oxygen loss, to their habitats ( ''high confidence'' ). This has resulted in shifts in species composition, abundance and biomass production of ecosystems, from the equator to the poles. Altered interactions between species have caused cascading impacts on ecosystem structure and functioning ( ''medium confidence'' ). In some marine ecosystems species are impacted by both the effects of fishing and climate changes ( ''medium confidence'' ). {3.2.3, 3.2.4, Box 3.4, 5.2.3, 5.3, 5.4.1, Figure SPM.2} '''

'''A.5.1''' [[File:37d9ca019c63e0a7a080aaca0b2016e4 SPM-Icon-oxox.png]] Rates of poleward shifts in distributions across different marine species since the 1950s are 52 ± 33 km per decade and 29 ± 16 km per decade ( ''very likely'' ranges) for organisms in the epipelagic (upper 200 m from sea surface) and seafloor ecosystems, respectively. The rate and direction of observed shifts in distributions are shaped by local temperature, oxygen, and ocean currents across depth, latitudinal and longitudinal gradients ( ''high confidence'' ). Warming-induced species range expansions have led to altered ecosystem structure and functioning such as in the North Atlantic, Northeast Pacific and Arctic ( ''medium confidence'' ). {5.2.3, 5.3.2, 5.3.6, Box 3.4, Figure SPM.2}

'''A.5.2''' [[File:37d9ca019c63e0a7a080aaca0b2016e4 SPM-Icon-oxox.png]] In recent decades, Arctic net primary production has increased in ice-free waters ( ''high confidence'' ) and spring phytoplankton blooms are occurring earlier in the year in response to sea ice change and nutrient availability with spatially variable positive and negative consequences for marine ecosystems ( ''medium confidence'' ). In the Antarctic, such changes are spatially heterogeneous and have been associated with rapid local environmental change, including retreating glaciers and sea ice change ( ''medium confidence'' ). Changes in the seasonal activities, production and distribution of some Arctic zooplankton and a southward shift in the distribution of the Antarctic krill population in the South Atlantic are associated with climate-linked environmental changes ( ''medium confidence'' ). In polar regions, ice associated marine mammals and seabirds have experienced habitat contraction linked to sea ice changes ( ''high confidence'' ) and impacts on foraging success due to climate impacts on prey distributions ( ''medium confidence'' ). Cascading effects of multiple climate-related drivers on polar zooplankton have affected food web structure and function, biodiversity as well as fisheries ( ''high confidence'' ). {3.2.3, 3.2.4, Box 3.4, 5.2.3, Figure SPM.2}

'''A.5.3''' [[File:aa4c791c8b6f965d8de1653e5ac59fbc SPM-Icon-ooox.png]] Eastern Boundary Upwelling Systems (EBUS) are amongst the most productive ocean ecosystems. Increasing ocean acidification and oxygen loss are negatively impacting two of the four major upwelling systems: the California Current and Humboldt Current ( ''high confidence'' ). Ocean acidification and decrease in oxygen level in the California Current upwelling system have altered ecosystem structure, with direct negative impacts on biomass production and species composition ( ''medium confidence'' ). {Box 5.3, Figure SPM.2}

'''A.5.4''' [[File:aa4c791c8b6f965d8de1653e5ac59fbc SPM-Icon-ooox.png]] Ocean warming in the 20th century and beyond has contributed to an overall decrease in maximum catch potential ( ''medium confidence'' ), compounding the impacts from overfishing for some fish stocks ( ''high confidence'' ). In many regions, declines in the abundance of fish and shellfish stocks due to direct and indirect effects of global warming and biogeochemical changes have already contributed to reduced fisheries catches ( ''high confidence'' ). In some areas, changing ocean conditions have contributed to the expansion of suitable habitat and/or increases in the abundance of some species ( ''high confidence'' ). These changes have been accompanied by changes in species composition of fisheries catches since the 1970s in many ecosystems ( ''medium confidence'' ). {3.2.3, 5.4.1, Figure SPM.2}

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'''A.6. Coastal ecosystems are affected by ocean warming, including intensified marine heatwaves, acidification, loss of oxygen, salinity intrusion and sea level rise, in combination with adverse effects from human activities on ocean and land ( ''high confidence'' ). Impacts are already observed on habitat area and biodiversity, as well as ecosystem functioning and services ( ''high confidence'' ). {4.3.2, 4.3.3, 5.3, 5.4.1, 6.4.2, Figure SPM.2}'''

'''A.6.1''' [[File:c2dab058529f43e723961cf4dccd97c2 SPM-Icon-ooxx.png]] Vegetated coastal ecosystems protect the coastline from storms and erosion and help buffer the impacts of sea level rise. Nearly 50% of coastal wetlands have been lost over the last 100 years, as a result of the combined effects of localised human pressures, sea level rise, warming and extreme climate events ( ''high confidence'' ). Vegetated coastal ecosystems are important carbon stores; their loss is responsible for the current release of 0.04–1.46 GtC yr –1 ( ''medium'' ''confidence'' ). In response to warming, distribution ranges of seagrass meadows and kelp forests are expanding at high latitudes and contracting at low latitudes since the late 1970s ( ''high confidence'' ), and in some areas episodic losses occur following heatwaves ( ''medium confidence'' ). Large-scale mangrove mortality that is related to warming since the 1960s has been partially offset by their encroachment into subtropical saltmarshes as a result of increase in temperature, causing the loss of open areas with herbaceous plants that provide food and habitat for dependent fauna ( ''high confidence'' ). {4.3.3, 5.3.2, 5.3.6, 5.4.1, 5.5.1, Figure SPM.2}

'''A.6.2''' [[File:c2dab058529f43e723961cf4dccd97c2 SPM-Icon-ooxx.png]] Increased sea water intrusion in estuaries due to sea level rise has driven upstream redistribution of marine species ( ''medium confidence'' ) and caused a reduction of suitable habitats for estuarine communities ( ''medium confidence'' ). Increased nutrient and organic matter loads in estuaries since the 1970s from intensive human development and riverine loads have exacerbated the stimulating effects of ocean warming on bacterial respiration, leading to expansion of low oxygen areas ( ''high confidence'' ). {5.3.1}

'''A.6.3''' [[File:c2dab058529f43e723961cf4dccd97c2 SPM-Icon-ooxx.png]] The impacts of sea level rise on coastal ecosystems include habitat contraction, geographical shift of associated species, and loss of biodiversity and ecosystem functionality. Impacts are exacerbated by direct human disturbances, and where anthropogenic barriers prevent landward shift of marshes and mangroves (termed coastal squeeze) ( ''high confidence'' ). Depending on local geomorphology and sediment supply, marshes and mangroves can grow vertically at rates equal to or greater than current mean sea level rise ( ''high confidence'' ). {4.3.2, 4.3.3, 5.3.2, 5.3.7, 5.4.1}

'''A.6.4''' [[File:c2dab058529f43e723961cf4dccd97c2 SPM-Icon-ooxx.png]] Warm-water coral reefs and rocky shores dominated by immobile, calcifying (e.g., shell and skeleton producing) organisms such as corals, barnacles and mussels, are currently impacted by extreme temperatures and ocean acidification ( ''high confidence'' ). Marine heatwaves have already resulted in large-scale coral bleaching events at increasing frequency ( ''very high confidence'' ) causing worldwide reef degradation since 1997, and recovery is slow (more than 15 years) if it occurs ( ''high confidence'' ). Prolonged periods of high environmental temperature and dehydration of the organisms pose high risk to rocky shore e cosystems ( ''high confidence'' ). {SR1.5, 5.3.4, 5.3.5, 6.4.2, Figure SPM.2}

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'''Figure SPM.2'''

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'''Figure SPM.2 | Synthesis of observed regional hazards and impacts in ocean (top) and high mountain and polar land regions (bottom) assessed in SROCC. For each region, physical changes, impacts on key ecosystems, and impacts on human systems and ecosystem function and services are shown. For physical changes, yellow/green refers to an increase/decrease, respectively, in […]'''
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[[File:2df5b5912775f9eb3a0c94a3eaf6169e SROCC_SPM2_Final_RGB.jpg]]

Figure SPM.2 | Synthesis of observed regional hazards and impacts in ocean <sup>[[#fn:24|24]]</sup> (top) and high mountain and polar land regions (bottom) assessed in SROCC. For each region, physical changes, impacts on key ecosystems, and impacts on human systems and ecosystem function and services are shown. For physical changes, yellow/green refers to an increase/decrease, respectively, in amount or frequency of the measured variable. For impacts on ecosystems, human systems and ecosystems services blue or red depicts whether an observed impact is positive (beneficial) or negative (adverse), respectively, to the given system or service. Cells assigned ‘increase and decrease’ indicate that within that region, both increase and decrease of physical changes are found, but are not necessarily equal; the same holds for cells showing ‘positive and negative’ attributable impacts. For ocean regions, the confidence level refers to the confidence in attributing observed changes to changes in greenhouse gas forcing for physical changes and to climate change for ecosystem, human systems, and ecosystem services. For high mountain and polar land regions, the level of confidence in attributing physical changes and impacts at least partly to a change in the cryosphere is shown. No assessment means: not applicable, not assessed at regional scale, or the evidence is insufficient for assessment. The physical changes in the ocean are defined as: Temperature change in 0–700 m layer of the ocean except for Southern Ocean (0–2000 m) and Arctic Ocean (upper mixed layer and major inflowing branches); Oxygen in the 0–1200 m layer or oxygen minimum layer; Ocean pH as surface pH (decreasing pH corresponds to increasing ocean acidification). Ecosystems in the ocean: Coral refers to warm-water coral reefs and cold-water corals. The ‘upper water column’ category refers to epipelagic zone for all ocean regions except Polar Regions, where the impacts on some pelagic organisms in open water deeper than the upper 200 m were included. Coastal wetland includes salt marshes, mangroves and seagrasses. Kelp forests are habitats of a specific group of macroalgae. Rocky shores are coastal habitats dominated by immobile calcified organisms such as mussels and barnacles. Deep sea is seafloor ecosystems that are 3000–6000 m deep. Sea-ice associated includes ecosystems in, on and below sea ice. Habitat services refer to supporting structures and services (e.g., habitat, biodiversity, primary production). Coastal Carbon Sequestration refers to the uptake and storage of carbon by coastal blue carbon ecosystems. Ecosystems on Land: Tundra refers to tundra and alpine meadows, and includes terrestrial Antarctic ecosystems.

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<span id="observed-impacts-on-people-and-ecosystem-services"></span>
==== Observed Impacts on People and Ecosystem Services ====

'''A.7. Since the mid-20th century, the shrinking cryosphere in the Arctic and high-mountain areas has led to predominantly negative impacts on food security, water resources, water quality, livelihoods, health and well-being, infrastructure, transportation, tourism and recreation, as well as culture of human societies, particularly for Indigenous peoples ( ''high confidence'' ). Costs and benefits have been unequally distributed across populations and regions. Adaptation efforts have benefited from the inclusion of Indigenous knowledge and local knowledge ( ''high confidence'' ). {1.1, 1.5, 1.6.2, 2.3, 2.4, 3.4, 3.5, Figure SPM.2} '''

'''A.7.1''' [[File:7dd9d5f1c0e829eec2bf341c5154813e SPM-Icon-xxoo.png]] Food and water security have been negatively impacted by changes in snow cover, lake and river ice, and permafrost in many Arctic regions ( ''high confidence'' ). These changes have disrupted access to, and food availability within, herding, hunting, fishing, and gathering areas, harming the livelihoods and cultural identity of Arctic residents including Indigenous populations ( ''high confidence'' ). Glacier retreat and snow cover changes have contributed to localized declines in agricultural yields in some high mountain regions, including Hindu Kush Himalaya and the tropical Andes ( ''medium confidence'' ). {2.3.1, 2.3.7, Box 2.4, 3.4.1, 3.4.2, 3.4.3, 3.5.2, Figure SPM.2}

'''A.7.2''' [[File:7dd9d5f1c0e829eec2bf341c5154813e SPM-Icon-xxoo.png]] In the Arctic, negative impacts of cryosphere change on human health have included increased risk of food- and waterborne diseases, malnutrition, injury, and mental health challenges especially among Indigenous peoples ( ''high confidence'' ). In some high-mountain areas, water quality has been affected by contaminants, particularly mercury, released from melting glaciers and thawing permafrost ( ''medium confidence'' ). Health-related adaptation efforts in the Arctic range from local to international in scale, and successes have been underpinned by Indigenous knowledge ( ''high confidence'' ). {1.8, Cross-Chapter Box 4 in Chapter 1, 2.3.1, 3.4.3}

'''A.7.3''' [[File:219efacb8ac4464b2e76514065b22cc7 SPM-Icon-oxoo.png]] Arctic residents, especially Indigenous peoples, have adjusted the timing of activities to respond to changes in seasonality and safety of land, ice, and snow travel conditions. Municipalities and industry are beginning to address infrastructure failures associated with flooding and thawing permafrost and some coastal communities have planned for relocation ( ''high confidence'' ). Limited funding, skills, capacity, and institutional support to engage meaningfully in planning processes have challenged adaptation ( ''high confidence'' ). {3.5.2, 3.5.4, Cross-Chapter Box 9} ''' '''

'''A.7.4''' [[File:37d9ca019c63e0a7a080aaca0b2016e4 SPM-Icon-oxox.png]] Summertime Arctic ship-based transportation (including tourism) increased over the past two decades concurrent with sea ice reductions ( ''high confidence'' ). This has implications for global trade and economies linked to traditional shipping corridors, and poses risks to Arctic marine ecosystems and coastal communities ( ''high confidence'' ), such as from invasive species and local pollution. {3.2.1, 3.2.4, 3.5.4, 5.4.2, Figure SPM.2}

'''A.7.5''' [[File:4d299f9da92412c8279a7422468e6e12 SPM-Icon-xooo.png]] In past decades, exposure of people and infrastructure to natural hazards has increased due to growing population, tourism and socioeconomic development ( ''high confidence).'' Some disasters have been linked to changes in the cryosphere, for example in the Andes, high mountain Asia, Caucasus and European Alps ( ''medium confidence'' ). {2.3.2, Figure SPM.2} ''' '''

'''A.7.6''' [[File:4d299f9da92412c8279a7422468e6e12 SPM-Icon-xooo.png]] Changes in snow and glaciers have changed the amount and seasonality of runoff and water resources in snow dominated and glacier-fed river basins ( ''very high confidence'' ). Hydropower facilities have experienced changes in seasonality and both increases and decreases in water input from high mountain areas, for example, in central Europe, Iceland, Western USA/Canada, and tropical Andes ( ''medium confidence'' ). However, there is only ''limited evidence'' of resulting impacts on operations and energy production. {SPM B.1.4, 2.3.1}

'''A.7.7''' [[File:4d299f9da92412c8279a7422468e6e12 SPM-Icon-xooo.png]] High mountain aesthetic and cultural aspects have been negatively impacted by glacier and snow cover decline (e.g. in the Himalaya, East Africa, the tropical Andes) ( ''medium confidence'' ). Tourism and recreation, including ski and glacier tourism, hiking, and mountaineering, have also been negatively impacted in many mountain regions ( ''medium confidence'' ) ''.'' In some places, artificial snowmaking has reduced negative impacts on ski tourism ( ''medium confidence'' ). {2.3.5, 2.3.6, Figure SPM.2}

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'''A.8. Changes in the ocean have impacted marine ecosystems and ecosystem services with regionally diverse outcomes, challenging their governance ( ''high confidence'' ). Both positive and negative impacts result for food security through fisheries ( ''medium confidence'' ), local cultures and livelihoods ( ''medium confidence'' ), and tourism and recreation ( ''medium confidence'' ). The impacts on ecosystem services have negative consequences for health and well-being ( ''medium confidence'' ), and for Indigenous peoples and local communities dependent on fisheries ( ''high confidence'' ). {1.1, 1.5, 3.2.1, 5.4.1, 5.4.2, Figure SPM.2}'''

'''A.8.1''' [[File:37d9ca019c63e0a7a080aaca0b2016e4 SPM-Icon-oxox.png]] Warming-induced changes in the spatial distribution and abundance of some fish and shellfish stocks have had positive and negative impacts on catches, economic benefits, livelihoods, and local culture ( ''high confidence'' ). There are negative consequences for Indigenous peoples and local communities that are dependent on fisheries ( ''high confidence'' ). Shifts in species distributions and abundance has challenged international and national ocean and fisheries governance, including in the Arctic, North Atlantic and Pacific, in terms of regulating fishing to secure ecosystem integrity and sharing of resources between fishing entities ( ''high confidence'' ). {3.2.4, 3.5.3, 5.4.2, 5.5.2, Figure SPM.2}

'''A.8.2''' [[File:c2dab058529f43e723961cf4dccd97c2 SPM-Icon-ooxx.png]] Harmful algal blooms display range expansion and increased frequency in coastal areas since the 1980s in response to both climatic and non-climatic drivers such as increased riverine nutrients run-off ( ''high confidence'' ). The observed trends in harmful algal blooms are attributed partly to the effects of ocean warming, marine heatwaves, oxygen loss, eutrophication and pollution ( ''high confidence'' ). Harmful algal blooms have had negative impacts on food security, tourism, local economy, and human health ( ''high confidence'' ). The human communities who are more vulnerable to these biological hazards are those in areas without sustained monitoring programs and dedicated early warning systems for harmful algal blooms ( ''medium confidence'' ). {Box 5.4, 5.4.2, 6.4.2}

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'''A.9. Coastal communities are exposed to multiple climate-related hazards, including tropical cyclones, extreme sea levels and flooding, marine heatwaves, sea ice loss, and permafrost thaw ( ''high confidence'' ). A diversity of responses has been implemented worldwide, mostly after extreme events, but also some in anticipation of future sea level rise, e.g., in the case of large infrastructure. {3.2.4, 3.4.3, 4.3.2, 4.3.3, 4.3.4, 4.4.2, 5.4.2, 6.2, 6.4.2, 6.8, Box 6.1, Cross Chapter Box 9, Figure SPM.5}'''

'''A.9.1''' [[File:3dcc514bf2acf9f1b7861bf877ef79a9 SPM-Icon-ooxo.png]] Attribution of current coastal impacts on people to sea level rise remains difficult in most locations since impacts were exacerbated by human-induced non-climatic drivers, such as land subsidence (e.g., groundwater extraction), pollution, habitat degradation, reef and sand mining ( ''high confidence'' ). {4.3.2, 4.3.3}

'''A.9.2''' [[File:f83f15a29ea2d8a2d2ddc3ce832f4aaa SPM-Icon-oxxo.png]] Coastal protection through hard measures, such as dikes, seawalls, and surge barriers, is widespread in many coastal cities and deltas. Ecosystem-based and hybrid approaches combining ecosystems and built infrastructure are becoming more popular worldwide. Coastal advance, which refers to the creation of new land by building seawards (e.g., land reclamation), has a long history in most areas where there are dense coastal populations and a shortage of land. Coastal retreat, which refers to the removal of human occupation of coastal areas, is also observed, but is generally restricted to small human communities or occurs to create coastal wetland habitat. The effectiveness of the responses to sea level rise are assessed in Figure SPM.5. {3.5.3, 4.3.3, 4.4.2, 6.3.3, 6.9.1, Cross-Chapter Box 9}

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