The Intergovernmental Panel on Climate Change (IPCC) Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) is prepared following a decision of governments in preparation for the Sixth Assessment Cycle[1]. By assessing new scientific literature[2], this report expands the knowledge base for the United Nation Framework Convention on Climate Change (UNFCCC), building on the IPCC Fifth Assessment Report (AR5) and the IPCC Special Report on Global Warming of 1.5°C (SR1.5)[3].
The ocean and the cryosphere (snow, ice, glaciers, ice sheets, and frozen soil and ground) support human livelihoods and well-being in many ways. They are closely connected with the whole climate system. Global warming in response to increased emissions of greenhouse gases and other drivers due to human activities is associated with very clear and in some cases irreversible changes in the ocean and the cryosphere, altering living conditions for ecosystems and people. Organisms, ecosystems and people (societies) from mountains to oceans, and from poles to equator, will continue to experience novel, unprecedented environments and hazards as a result of climate-related changes in the ocean and cryosphere.
The SROCC assesses scientific knowledge about past, ongoing and future changes as well as their impacts in high mountain areas, polar regions, coasts, low-lying islands, and the open ocean. It gives particular attention to the issues of sea-level rise, extremes and abrupt events. Opportunities and risks as well as adaptation response options are also assessed, including nature-based solutions relevant for climate-resilient sustainable development pathways.
This Summary for Policymakers (SPM) synthesises key findings of the report and highlights new findings obtained since the AR5 (published 2013/2014). The level of confidence associated with each key finding in the three sections of this SPM is reported using IPCC calibrated language[4]. The underlying scientific basis of each paragraph can be traced back to chapter elements based on the references provided. Definitions for terms that are commonly used within the SROCC can be found in the glossary.
SPM. A ONGOING CHANGES IN THE OCEAN AND THE CRYOSPHERE ILLUSTRATE THEIR IMPORTANCE FOR CLIMATE, ECOSYSTEMS AND PEOPLE
A1. Changes to the ocean and cryosphere play a key role in the state of the climate at the global scale and impacts on ecosystems and human societies are now evident (very high confidence). Ongoing changes include unabated warming, acidification and deoxygenation of the ocean, reduced Northern Hemisphere snow cover and Arctic sea ice, worldwide retreat of mountain glaciers, reductions in the Greenland and Antarctic ice sheets, and permafrost degradation and thaw. Sea level rise has accelerated in the past decades due to increased contributions from ice sheets (very high confidence). Some of these changes are irreversible on timescales relevant to human societies (decades to centuries). {1.1, 1.2, 1.3, 1.4, 2.2, 3.2, 3.3, 3.4, 4.2, 5.2, Figure SPM.1}
A1.1 Ocean heat content is increasing at a steady rate; there is increased evidence from, and agreement between, observations and simulations since AR5 for increases in ocean heat content; these changes provide further support that the observed changes are largely caused by anthropogenic forcing (high confidence). ). The ocean heat uptake during the period 1970-2010 is equivalent to an energy imbalance of 0.42 W m-2 (with respect to the Earth surface area). {1.4.1, 5.2}
A1.2 The ocean is continuing to acidify in response to carbon dioxide uptake. It is very likely that the ocean has taken up about 25 ± 5% of total anthropogenic emissions in the past two decades. The anthropogenic pH signal has already emerged outside the range of natural variability over the entire surface ocean (high confidence). The ocean is observed to be losing oxygen and oxygen minimum zones have expanded. The largest reductions in oxygen have been observed in the Southern Ocean, South Atlantic and North Pacific (medium confidence), but there is low confidence for changes in the tropical ocean due to natural variability and limited agreement across studies. {3.2.1, 5.2.2}
A1.3 It is virtually certain that the Greenland ice sheet has lost mass and very likely that the Antarctic ice sheet has lost mass. The rate of mass loss from the Greenland Ice Sheet and polar glaciers has increased since around the year 2000 (high confidence). The rate of Antarctic Ice Sheet overall mass loss has increased since approximately 2005 (medium confidence), dominated by regions of West Antarctica (very high confidence). Because of a lack of long-term mass-change observations in both polar regions and incomplete representation of the full range of relevant processes in ice sheet models, attribution of mass loss from ice sheets to human-induced climate change is currently not possible. Glaciers and polar ice sheets are now the dominant source of sea level rise (very high confidence), and increasing losses from polar ice sheets are resulting in increasing rates of sea level rise. Anthropogenic forcing has been the dominant cause of global mean steric sea level rise since 1970 (high confidence). {1.4, 3.3.1, 3.3.2, 4.2}
A1.4 Arctic sea surface temperature has increased at approximately twice the rate of average global temperature (very high confidence). Continued substantial declines in Arctic summer sea ice extent (average rate –13.0% per decade in September; the month with the lowest sea ice cover over 1979–2017) and Arctic spring snow cover extent (–13.6% per decade in June; 1967–2018) have occurred (high confidence), with consequences for the global climate system, for example through changes in albedo. There is low confidence associated with the teleconnections between Arctic sea ice loss and changes in atmospheric circulation affecting weather patterns in mid-latitudes. Antarctic sea ice extent increased between 1979 and 2017 at an annual-mean rate of 20.2 ± 4.0 × 103 km2 yr–1, but with strong negative departures in 2016 and 2017 (very high confidence). The overall increase is composed of near-compensating regional changes, with rapid ice loss in the Amundsen and Bellingshausen seas outweighed by rapid ice gain in the Weddell and Ross seas. The regional pattern of observed Antarctic sea ice trends is closely related to meridional wind trends (high confidence). {3.2.1, Box 3.1}
A1.5 High mountain regions have experienced substantial warming; the extent and duration of snow cover have declined in many high mountain regions since the beginning of the 20th century, especially at lower snow elevations (very high confidence) although with high regional variability. The vast majority of glaciers in all high mountain regions have retreated and lost mass during the last two decades (very high confidence). Mass losses from the glaciers in 11 glaciated mountain regions (shown in Figure SPM.2) increased from 470 ± 80 kg m–2 yr–1 in the period 1986–2005 to 610 ± 90 kg m2 yr–1 during 2006–2015. Regional-scale average mass losses during 2006-2015 were largest in the southern Andes, the low latitudes and central Europe (>900 kg m2 yr–1) and smallest in High Mountain Asia (190 kg m2 yr–1). {2.2.1, 2.2.2, 2.2.3, Box 2.1}
A1.6 In situ measurements in the European Alps, Scandinavia and the Tibetan Plateau show that permafrost has undergone warming and thaw in the past two decades (high confidence). The observed rates of change in the 21st century are higher than in the late 20th century (medium confidence). Other mountain regions lack in-situ observations to assess trends. Permafrost temperatures have continued to increase (high confidence). Since 2000, the typical rate of increase in permafrost temperatures has been between 0.4°C and 0.7°C per decade for continuous permafrost monitoring at colder sites. The organic carbon pool stored in Arctic and boreal permafrost zone soils contains almost twice the carbon presently in the atmosphere (high confidence). Quantifying potential future greenhouse gas emissions (primarily carbon dioxide and methane) from thawing permafrost soils thus has global relevance. {2.2.4, 3.4.1; 3.4.2; 3.4.3}
A1.7 Glacier shrinkage and snow cover changes have led to changes in the amount and timing of river runoff in many mountain regions during the last two decades (high confidence). In some regions with predominantly small glaciers (e.g., western USA and Canada), runoff from glaciers has already decreased due to glacier shrinkage while in other regions, typically with larger glaciers (e.g., Alaska), runoff from glaciers has increased (medium confidence). Runoff changes from mountain glaciers have caused significant shifts in downstream nutrients (dissolved organic carbon, nitrogen, phosphorus) and influenced water quality through increases in heavy metals, particularly mercury and other contaminants that persist in the environment {2.2.3.2}
Figure SPM.1: Illustration of key findings on the ocean and cryosphere in a changing climate and the projected differences between low and high emission futures. Measured and projected carbon dioxide levels from 1850-2100 {Figure 1.3} are shown in the context of past and projected coastal and global population {1.1, 1.5} and global mean temperature change at key intervals since the pre-industrial {1.1, SR1.5}. Schematics for quantified observed and projected changes in the ocean and cryosphere are shown for ocean heat content {5.2.2.2}, global mean sea level rise {4.2.3.1}, mountain glacier mass {2.2.3.2}, mountain snow cover {2.2.2}, Arctic summer sea ice extent {3.3.1.1}, animal biomass in marine ecosystems {5.2.3.1} and coral reefs {SR1.5}. Colouring of schematics contrast the differing projected outcomes in a low emission/strong mitigation future (RCP2.6; blue) compared with a high emission/weak mitigation future (RCP8.5; red). [PLACEHOLDER FOR SECOND DRAFT: for further development of concept figure: incorporate more elements when quantified assessments become available (Antarctic and Greenland ice sheets, Antarctic sea ice, permafrost, ocean pH); incorporate more information on historical changes or change time axis scale to focus only on present day position and future projections; add confidence assessments; add visual representations of implications for natural, managed and human systems or for Sustainable Development Goals; committed responses beyond 2100]
A2. Ecosystems and people depend directly or indirectly on the multitude of services provided by the ocean and cryosphere. The local- to global-scale services supported by the ocean and cryosphere include heat and carbon uptake by the ocean, food and freshwater supplies, renewable energy generation, trade and transport, recreation, culture and well-being. These services are modified, degraded or eliminated under climate change (high confidence). {1.1, 1.5}
A2.1 Almost 13% of the global population lives in the Arctic or high mountain regions and face risks from climate-related changes in the cryosphere. Observed changes in the cryosphere have been exerting considerable impacts on agriculture, fisheries, hydropower, tourism and recreation activities and other sectors since the mid-20th century, while evidence on the long-term effectiveness of adaptation responses remains uneven and limited (medium confidence). The impacts on lives, livelihoods and infrastructure extend beyond the directly affected areas. For example, much larger populations and cities downstream of high mountain areas are also subject to cryosphere-change-related risks and impacts. {1.1, 1.5, 2.2.2, Figure SPM.2}
A2.2 In mountain terrestrial and freshwater environments, ecosystems are changing and shifting due to changes in snow cover, permafrost thaw and degradation as well as glacier retreat. Some populations of high-mountain species are in decline as climate changes and habitats, such as snowpack, are lost (high confidence). Multiple interacting cryosphere-related challenges, including survival under a shallower and denser snowpack, affect foraging and reproduction for high mountain species, such as wolverines (high confidence). {2.3.1, 2.3.3, Figure SPM.2}
A2.3 Adoption of new crops and irrigation techniques has reduced vulnerability of some high mountain agricultural communities to reduced stream flow linked to glacier retreat and changes in snow amounts. Managers of hydropower facilities incorporate projections of stream flow into planning to reduce their vulnerability to changing water amounts. Snow management, including snowmaking, has reduced the vulnerability of some mountain ski resorts to inter-annual variability and past decline of natural snow amounts. However, adaptation measures in agriculture, hydropower, tourism and other sectors are generally limited in scope, short-term and fragmented. The diverse priorities, conditions and mechanisms available for the implementation and evaluation of these measures place constraints on the available adaptation measures and assessment of their performance and limitations. {2.3.1, 2.3.4}
A2.4 Sea level rise, driven by changes in the ocean, glaciers and ice sheets, is a key concern for coastal areas which are the most densely populated areas on Earth; home to approximately 27% of the global population including more than half of the world’s megacities. Low-lying islands and coasts across latitudes are at high risk of climate-change related impacts, sharing physical, biological, and socio-economic characteristics and contexts in their exposure and vulnerability to climate change (high confidence). There is increasing evidence of changes caused by rising sea level at the coast with respect to ecosystems, ecosystem services, coastal infrastructure, habitability, community livelihoods, and cultural and aesthetic values. Attribution of local impacts to sea level rise, however, remains difficult due to the combined influence of non-climatic drivers and local processes unrelated to sea level rise (medium confidence). {4.3.3, 4.3.4, Cross-Chapter Box 7 on Low-lying Islands and Coasts}
A2.5 Emergence of novel ocean conditions for marine organisms from plankton to mammals are driving changes in physiology, biogeography and ecology that impact biodiversity and ecosystem functions (high confidence). Observed population declines of marine species in the lower-latitude range boundary (medium confidence), expansion in the poleward boundary (high confidence), earlier timing of biological events (high confidence), and overall shifts in biomass
A3. Ocean heat and carbon uptake, glacier and ice sheet loss and sea level rise are irreversible on timescales of centuries and beyond. Changes in the ocean and cryosphere have already affected the frequency and magnitude of multiple hazards that exacerbate environmental risks faced by many ecosystems and human systems. {1.5, 6.3, 6.4, 6.8}
A3.1 High mountain and Arctic systems as well as marine and coastal systems (including coral reefs) are at high to very high risk of adverse and potentially accelerated, larger and irreversible impacts as global temperatures approach or exceed 1.5°C to 2°C above pre-industrial. Committed ocean and cryosphere changes initiate the use of adaptation measures to reduce impacts on human and natural systems, alongside efforts to reduce greenhouse gas emissions. {1.1, 1.2, 1.3}
A3.2 Marine heatwaves (MHWs) have very likely doubled in frequency since the early 1980s (high confidence), with one quarter of the surface ocean experiencing either the longest or most intense events on record in 2015 and 2016. On a global scale, about 90% of the observed MHWs are attributable to human-induced global warming and some recent MHWs are unprecedented with respect to pre-industrial conditions (medium confidence). MHWs have occurred in all ocean basins over the last few decades with detrimental and potentially irreversible impacts on coral reefs and other marine ecosystems, and cascading impacts on economies and societies. {6.4, Figure 6.3, Figure 6.4}
A3.3 Retreat of mountain glaciers and thaw of mountain permafrost has decreased the stability of mountain slopes (high confidence). Glacier retreat has led to an increasing number and area of glacier lakes (high confidence). Over the past decades, there has been an increase in wet snow avalanches and a reduction in the size and run-out distance of dry snow avalanches (medium confidence). There is high confidence that the exposure of people and infrastructure to natural hazards in high mountain areas has increased. {2.3.2}
A3.4 Coastal ecosystems are under stress from the combination of climate change impacts in the ocean and from sources of stress originating on land such as water pollution and land use changes (high confidence). Extreme events such as marine heat waves and storms are exacerbating the rate of ecosystem changes, such as those observed in kelp forests and seagrass meadows (high confidence). {5.3.3, 6.4}
A3.5 Climate change-related impacts on the ocean and cryosphere are expected to compound the risks related to climatic and other environmental hazards already faced by many human and natural systems, particularly in coastal, polar and mountain areas. Enhanced climate change impacts on the ocean and cryosphere put sustainable development pathways at risk (medium confidence), and present particular challenges to communities living in close connection to polar, mountain and coastal environments, and to cities, states and nations whose territorial boundaries are being transformed by ongoing sea level rise {1.1, 1.2, 1.5}.
SPM.B PROJECTED CHANGES
B.1 Shifts in snowline, glacier retreat, permafrost thaw, and changing river runoff due to warming in high mountains are projected to continue causing natural hazards and risks for biodiversity, terrestrial and freshwater ecosystems, agriculture, hydropower, tourism, recreation activities, and infrastructure if adequate adaptation measures are not taken. Future changes are projected to pose challenges to livelihoods and other economic activities in and beyond mountain regions. {2.2, 2.3}
B1.1 Under all considered climate scenarios for the 21st century, air temperature in high mountain regions is projected to increase, exceeding average global warming rates and driving further reductions in snowfall below the mean snowline elevation (very high confidence). Elevation-dependent warming is projected to amplify in many mountain regions (medium confidence). Total precipitation is projected to show limited long-term changes, except at the highest elevations where it is projected to increase (medium confidence). {2.2.1; Box 2.1; 2.2.2}
B1.2 Glaciers in all mountain regions are projected to continue to lose mass throughout the 21st century (very likely). Projected mass reductions between 2015 and 2100 range from 29 ± 7% for Representative Concentration Pathway RCP2.6 to 47 ± 10% for RCP8.5[1]. In regions with relatively little ice cover (e.g., Central Europe, Caucasus, Low Latitudes, North Asia, Scandinavia), glaciers are projected to lose more than 80% of their current mass by 2100 under RCP8.5. {2.2.3}
B1.3 High mountain permafrost is expected to undergo increasing thaw and degradation in the 21st century in response to rising air temperature (high confidence). Quantitative projections are scarce and often limited to individual sites or small areas in some mountain regions. {2.2.4}
B1.4 There is high confidence that the structure and functioning of terrestrial and freshwater mountain ecosystems will change. Key future shifts may include further upslope migration of lower elevation species and changes in the timing and amount of plant growth, shifts in the characteristic traits of many terrestrial and freshwater species and increased potential for disturbance (e.g., increased fire and landslides) that could lead to loss or restriction in the range for high mountain taxa due to the changing cryosphere. Species extinctions may be slowed in terrestrial ecosystems by microclimate refugia (medium confidence) and accelerated in freshwater ecosystems due to greater variability in water resources (high confidence). Wide-ranging effects on large animals are projected to lead to population declines and smaller ranges (high confidence). {2.3.3; 2.3.5}
B1.5 Changes in the high-mountain cryosphere are likely to increase freshwater-related risks in some regions with high dependency on snow or glacier melt runoff by the end of the 21st century (medium confidence). However, projected effects of the changes in magnitude and seasonality of runoff on hydropower, irrigation and drinking water are subject to widespread regional variation. Current capacities to explicitly account for glacier changes especially in large-scale hydrological models are limited, thus increasing uncertainty in decision making and in taking adaptation measures {2.3.1}
B1.6 Agriculture, hydropower and tourism activities related to the mountain cryosphere are projected to undergo major changes in the 21st century as a result of cryospheric change (high confidence); however these changes may also be driven by potential changes in, inter alia, socio-economic, technological, policy, institutional and legal aspects on access, mobility and governance of resources. Existing local adaptation measures (e.g., extension of irrigation systems; current snowmaking technologies) are projected to approach their limits around 2°C of global warming above pre-industrial. Moreover, vulnerabilities of mountain societies are projected to increase because of limits to their adaptive capacity (medium confidence). {2.3.1; 2.3.4; 2.3.5}
B1.7 Human habitability in mountain regions relies on multiple and diverse means to secure basic needs and sustain livelihood options, which are increasingly challenged by climate-related cryosphere change. Recognition and integration of Indigenous knowledge and local knowledge with scientific knowledge promotes resilience and adaptation in a changing climate and cryosphere environment. There are limits to the adaptation capacity of socio-economic sectors under the influence of cryospheric change along with climate change (medium confidence). Integrated (cross-sectoral) governance approaches hold potential in promoting socio-economic sectors’ resilience and transformation, yet evidence on how these materialise to address cryosphere change in high mountain contexts remains low. {2.3.6}
B2 The oceanic and cryospheric environments of both the Arctic and Antarctica are projected to change during the course of this century. Climate change will affect ecosystems and biodiversity, with implications for internationally important fisheries and food security[2]. Polar ocean regions are changing more rapidly than the global ocean as a whole, with consequences for climate regulation and ecosystem services (high confidence). Warming will drive further loss of glacial ice in both polar regions, with implications for global sea level rise. {3.2.3; 3.3.1; 3.3.2; 3.4.1; 3.4.2; 3.4.3; Cross-Chapter Box 6 in Chapter 3}
B2.1 Major changes in the Arctic are projected to continue and accelerate in the coming decades. The decline in glaciers, snow, freshwater ice, sea ice, permafrost as well as ocean warming are affecting and will continue to affect hydrology, marine and terrestrial ecosystems, transportation and water and food security for Arctic people. While the retreat of Arctic sea ice provides opportunities for tourism and marine transportation, the expansion of shipping activities in a region where international regulation is limited can also cause risks for the polar environment and coastal communities, if regulation is not established. Climatic change in exposed regions of Antarctica and the Southern Ocean also opens possibilities for increased commercial activity such as tourism, though heightened risk of environmental damage emphasises the role of effective, long-term regulation. {3.2; 3.3; 3.4; 3.5}
B2.2 Climate-induced changes in the polar oceans and cryosphere are altering marine primary production, with impacts on marine food webs and ecosystems (high confidence). In the Arctic, changes in the timing, duration and intensity of primary production are affecting secondary production, with consequences for species composition, spatial distribution, abundance of higher trophic levels (zooplankton, fish, crustaceans and top predators), and impacts on ecosystem structure and biodiversity. In the Antarctic, primary production is projected to increase in regions near to the Antarctic continent, but the implications for higher trophic levels and for carbon export are not yet determined. {3.2.1; 3.2.3; 3.2.4; 3.3.3}
B2.3 Climate-driven shifts in the ranges and abundance of ecologically important marine species are occurring and are projected to continue (high confidence). Some of these species have global commercial and conservation value. Projected range expansion of sub-Arctic marine species will increase competition pressure for high-Arctic species (medium confidence), with regionally-variable impacts dependent on physical and ecological conditions, and regional benefits for fisheries (high confidence). On Arctic land, projections indicate a loss of globally unique biodiversity due to changes in terrestrial cryosphere as some high-Arctic species will be outcompeted by more southerly species and very limited refugia exist (medium confidence). {3.2.3; Box 3.3}
B2.4 Climate-related reductions in snow and freshwater ice and permafrost thaw and degradation continue to affect hydrology, disturbance regimes and vegetation, thereby decreasing water and food security for Arctic peoples (high confidence). These changes influence peoples’ access to hunting, fishing, foraging and gathering areas; they may alter food abundance and availability and affect the abundance and distribution of culturally and economically important species such as reindeer (high confidence), impacting health and cultural identity of Arctic peoples. Freshwater ecosystems, including fish for harvest, are impacted by changes in surface water conditions and lake ice regimes. There are limits to the success of adaptation measures, possibly constraining benefits from new opportunities for subsistence activities arising from ecosystem change. {3.4.1; 3.4.2; 3.4.3; 3.5.3}
B2.5 Warming will result in continued loss of Arctic sea ice and terrestrial snow, changes to permafrost, and reductions in the mass of glaciers. The current trend of permafrost temperatures reaching record high levels (high confidence) is projected to continue, with consequences for the global climate system due to the release of carbon dioxide and methane from the microbial breakdown of organic carbon in soils. The expected magnitude of these changes differs depending on future greenhouse gas emissions and mitigation measures (high confidence). {3.3.1; 3.3.2; 3.4}
B2.6 Evidence suggests substantial loss of permafrost carbon to the atmosphere by 2100 and beyond under RCP8.5, while scenarios limiting anthropogenic carbon emissions (e.g., RCP4.5) will result in lower losses (high confidence). There is low confidence concerning the level to which increased plant growth will compensate for these losses. Permafrost change will continue to impact infrastructure in urban and rural areas as well as distributed infrastructure for resource extraction and transportation (high confidence). 70% of Arctic circumpolar infrastructure is located in areas where permafrost is projected to thaw by 2050 under RCP4.5 (high confidence). Basing infrastructure design requirements and codes on past environmental records increases risk in a changing climate.{3.4.1; 3.4.2; 3.4.3}
B2.7 Limited knowledge, financial resources, human capital and organisational capacity continue to constrain adaptation in many human sectors of polar regions (high confidence). Harvesters of renewable natural resources are adjusting timing of activities to changes in seasonality and less safe ice travel conditions, municipalities and industry are addressing infrastructure failures associated with flooding and thawing permafrost, and coastal communities and cooperating agencies are now planning for relocation. In spite of these adaptations, many groups are making decisions without adequate knowledge to forecast near- and long-term conditions, and without the funding, skills and organizational support to engage fully in planning processes (high confidence). {3.5.3; 3.5.5; Cross-Chapter Box 7 on Low-lying Islands and Coasts}
B3 Ocean ecosystems are affected by ocean warming, acidification, and deoxygenation, which alter the distribution and availability of marine biological resources and consequently impact human communities that directly depend on the ocean. Impacts include reduced economic and food security and reduced viability of traditional livelihoods and cultures, as well as increased health risks from diseases and contaminants. {3.2.1; 5.4.1; 5.4.2}
B3.1 The overall warming of the ocean will continue this century even if radiative forcing stabilizes (e.g., RCP2.6, high confidence). By 2100 under the RCP2.6 and 8.5 scenarios, the ocean is likely to take up about 3 and 6 times, respectively, the roughly 500 × 1021 J that the ocean has already taken up since the start of the 20th century. {5.2.2}
B3.2 It is very likely that stratification in the upper few hundred meters of the ocean will increase significantly in the 21st century. This trend reduces surface exchange with the deep ocean, reducing heat and carbon uptake, as well as re-oxygenation of the ocean, affecting nutrient cycles. {5.2.2}
B3.3 Over the next century oxygen declines of 3.5% by 2100 are predicted globally (medium confidence), with low confidence at regional scales, especially in the tropics. The largest changes in the deep sea will occur after 2100. Where oxygen is already low, even very small declines in oxygen availability can lead to decreases in biodiversity, nutrient cycling, and ecosystem productivity. It is virtually certain that emissions will be the most important control of open ocean surface pH relative to internal variability for most of the 21st century at both global and local scale. Changes to the deep ocean are more complex as they are controlled by parallel changes to ocean circulation. {5.2.2; Cross-Chapter Box 5 in Chapter 3; 5.2.3; Box 5.1}
B3.4 Climate-induced changes in the oceans and cryosphere are altering marine primary production, with impacts on marine food webs and pelagic and seafloor ecosystems (high confidence). There is high confidence that future changes to ocean primary productivity will be driven by region specific changes in magnitude and ratio of nutrient supply. In general, models project a small decrease in global organic matter production (medium confidence) with increases at high-latitudes (low confidence) and decreases at low-latitudes (medium confidence) in response to changes in ocean nutrient supply (see also B2.2). {3.2.1; 3.2.2; 3.2.3; 3.2.4; 3.3.3; 5.2.2}
B3.5 Changes in biodiversity patterns and community structure are projected to continue in the 21st century (high confidence), with potential global biomass of marine animals projected to decrease by 4.8 ± 3.6% (standard deviation) and 17.2 ± 11.1% under RCP2.6 and 8.5, respectively, by 2090–2099 relative to 1990–1999 (likely). Climate projections also indicate loss of Antarctic seafloor biodiversity (medium confidence). Scope for adaptation for many organisms to cope with novel environmental conditions is limited (medium confidence), particularly those higher up in the ocean food web and for high carbon emission scenarios (RCP8.5). {3.2.3; Box 3.3; 5.2.2; 5.2.3; 5.3.3; Box 5.1}
B3.6 Almost all major coral reef systems (shallow and deep) are vulnerable to climate change with clear regional differences in their sensitivities and projected overall losses reaching more than 70% even under RCP2.6 (high confidence). Ocean warming, acidification, rising sea level and intensifying storms impede reef resilience on a global level and augment reef destruction (high confidence). Shallow coral reefs that are not degraded by other impacts such as extensive bottom trawling and nutrient enrichment could constitute an important refuge to reefs degraded by climate change. Loss of deep-water coral reef habitat is virtually certain under projected ocean acidification through dissolution and intensified bio-erosion of the non-living matrix. {5.3.3; 6.4.2}
B3.7 Benthic communities in deep-sea habitats will experience structural and functional changes that affect the carbon cycle this century under all emission scenarios (medium confidence). This is suggested by the strong positive relationship between annual Particulate Organic Carbon (POC) flux and oxygen consumption of abyssal sediment communities combined with projected changes in biomass. Much of the abyssal seafloor is expected to experience declines in food supply that will diminish benthic biomass, change community structure and rates of carbon burial (medium confidence). The majority (82%) of the mapped seamounts are predicted to experience reduced POC flux under RCP8.5 in 2100, resulting in declines in benthic biomass (medium confidence). {5.2.4}
B3.8 Across the globe, seafood provision from some fisheries and aquaculture will be impacted by climate change (high confidence), reducing their revenues and influencing the livelihood of the dependent communities and food security of vulnerable people (medium confidence). Fisheries catches and their composition are already affected by warming, deoxygenation and changes in primary production on growth, reproduction and survival of fish stocks (high confidence). Changes in these ocean conditions in the 21st century are projected by multiple models to cause decrease in global fisheries catches with increasing dominance of warmer water species under increasing CO2 emission (medium confidence), although the changes in realized catch will depend strongly on fishing intensity. Consequently, people who depend on fisheries and related sectors will experience substantial decline in their income, livelihood and availability of animal-sourced nutrients (medium confidence). Marine aquaculture is at risk under increasing carbon emissions. Shellfish aquaculture is sensitive to ocean acidification (high confidence). Farmed species will be exposed to increased risk of disease and harmful algal blooms, with adverse economic and social implications. {3.2.4; 3.5.3; 3.5.4; 5.4.1; 5.4.2, Figure SPM.3}
[1] A set of scenarios, the Representative Concentration Pathways (RCPs), was used under the framework of the Coupled Model Intercomparison Project Phase 5 (CMIP5) of the World Climate Research Programme. In all RCPs, atmospheric CO2 concentrations are higher in 2100 relative to present day as a result of a further increase of cumulative emissions of CO2 to the atmosphere during the 21st century. Levels of warming in this Summary for Policymakers refer to pre industrial (1850–1900) as a baseline, unless otherwise stated.
[2] See also B3.9