Transcription

Summary forPolicymakers

SPMSummaryfor PolicymakersDrafting Authors:Nerilie Abram (Australia), Carolina Adler (Switzerland/Australia), Nathaniel L. Bindoff (Australia),Lijing Cheng (China), So-Min Cheong (Republic of Korea), William W. L. Cheung (Canada),Matthew Collins (UK), Chris Derksen (Canada), Alexey Ekaykin (Russian Federation), ThomasFrölicher (Switzerland), Matthias Garschagen (Germany), Jean-Pierre Gattuso (France), BruceGlavovic (New Zealand), Stephan Gruber (Canada/Germany), Valeria Guinder (Argentina),Robert Hallberg (USA), Sherilee Harper (Canada), Nathalie Hilmi (Monaco/France), Jochen Hinkel(Germany), Yukiko Hirabayashi (Japan), Regine Hock (USA), Anne Hollowed (USA), Helene JacotDes Combes (Fiji), James Kairo (Kenya), Alexandre K. Magnan (France), Valérie Masson-Delmotte(France), J.B. Robin Matthews (UK), Kathleen McInnes (Australia), Michael Meredith (UK),Katja Mintenbeck (Germany), Samuel Morin (France), Andrew Okem (South Africa/Nigeria),Michael Oppenheimer (USA), Ben Orlove (USA), Jan Petzold (Germany), Anna Pirani (Italy), ElviraPoloczanska (UK/Australia), Hans-Otto Pörtner (Germany), Anjal Prakash (Nepal/India), GolamRasul (Nepal), Evelia Rivera-Arriaga (Mexico), Debra C. Roberts (South Africa), Edward A.G. Schuur(USA), Zita Sebesvari (Hungary/Germany), Martin Sommerkorn (Norway/Germany), MichaelSutherland (Trinidad and Tobago), Alessandro Tagliabue (UK), Roderik Van De Wal (Netherlands),Phil Williamson (UK), Rong Yu (China), Panmao Zhai (China)Draft Contributing Authors:Andrés Alegría (Honduras), Robert M. DeConto (USA), Andreas Fischlin (Switzerland),Shengping He (Norway/China), Miriam Jackson (Norway), Martin Künsting (Germany),Erwin Lambert (Netherlands), Pierre-Marie Lefeuvre (Norway/France), Alexander Milner (UK),Jess Melbourne-Thomas (Australia), Benoit Meyssignac (France), Maike Nicolai (Germany),Hamish Pritchard (UK), Heidi Steltzer (USA), Nora M. Weyer (Germany)This Summary for Policymakers should be cited as:IPCC, 2019: Summary for Policymakers. In: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate[H.-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, A. Alegría, M. Nicolai,A. Okem, J. Petzold, B. Rama, N.M. Weyer (eds.)]. In press.3

Summary for PolicymakersIntroductionThis Special Report on the Ocean and Cryosphere1 in a Changing Climate (SROCC) was prepared following an IPCC Paneldecision in 2016 to prepare three Special Reports during the Sixth Assessment Cycle2. By assessing new scientific literature3,the SROCC4 responds to government and observer organization proposals. The SROCC follows the other two Special Reportson Global Warming of 1.5ºC (SR1.5) and on Climate Change and Land (SRCCL)5 and the Intergovernmental Science PolicyPlatform on Biodiversity and Ecosystem Services (IPBES) Global Assessment Report on Biodiversity and Ecosystem Services.SPMThis Summary for Policymakers (SPM) compiles key findings of the report and is structured in three parts: SPM.A: ObservedChanges and Impacts, SPM.B: Projected Changes and Risks, and SPM.C: Implementing Responses to Ocean and CryosphereChange. To assist navigation of the SPM, icons indicate where content can be found. Confidence in key findings is reportedusing IPCC calibrated language6 and the underlying scientific basis for each key finding is indicated by references to sectionsof the underlying report.Key of icons to indicate contentHigh mountain cryospherePolar regionsCoasts and sea level riseOcean41The cryosphere is defined in this report (Annex I: Glossary) as the components of the Earth System at and below the land and ocean surface that arefrozen, including snow cover, glaciers, ice sheets, ice shelves, icebergs, sea ice, lake ice, river ice, permafrost, and seasonally frozen ground.2The decision to prepare a Special Report on Climate Change and Oceans and the Cryosphere was made at the Forty-Third Session of the IPCC inNairobi, Kenya, 11–13 April 2016.3Cut-off dates: 15 October 2018 for manuscript submission, 15 May 2019 for acceptance for publication.4The SROCC is produced under the scientific leadership of Working Group I and Working Group II. In line with the approved outline, mitigation options(Working Group III) are not assessed with the exception of the mitigation potential of blue carbon (coastal ecosystems).5The full titles of these two Special Reports are: “Global Warming of 1.5ºC. An IPCC special report on the impacts of global warming of 1.5ºC abovepre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat ofclimate change, sustainable development, and efforts to eradicate poverty”; “Climate Change and Land: an IPCC special report on climate change,desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystems”.6Each finding is grounded in an evaluation of underlying evidence and agreement. A level of confidence is expressed using five qualifiers: very low, low,medium, high and very high, and typeset in italics, e.g., medium confidence. The following terms have been used to indicate the assessed likelihood ofan outcome or a result: virtually certain 99–100% probability, very likely 90–100%, likely 66–100%, about as likely as not 33–66%, unlikely 0–33%,very unlikely 0–10%, exceptionally unlikely 0–1%. Assessed likelihood is typeset in italics, e.g., very likely. This is consistent with AR5 and the otherAR6 Special Reports. Additional terms (extremely likely 95–100%, more likely than not 50–100%, more unlikely than likely 0– 50%, extremelyunlikely 0–5%) are used when appropriate. This Report also uses the term ‘likely range’ or ‘very likely range’ to indicate that the assessed likelihoodof an outcome lies within the 17–83% or 5–95% probability range. {1.9.2, Figure 1.4}

Summary for PolicymakersStartup Box The Importance of the Ocean and Cryosphere for PeopleAll people on Earth depend directly or indirectly on the ocean and cryosphere. The global ocean covers 71% of theEarth surface and contains about 97% of the Earth’s water. The cryosphere refers to frozen components of the Earthsystem1. Around 10% of Earth’s land area is covered by glaciers or ice sheets. The ocean and cryosphere supportunique habitats, and are interconnected with other components of the climate system through global exchange ofwater, energy and carbon. The projected responses of the ocean and cryosphere to past and current human-inducedgreenhouse gas emissions and ongoing global warming include climate feedbacks, changes over decades to millenniathat cannot be avoided, thresholds of abrupt change, and irreversibility. {Box 1.1, 1.2}SPMHuman communities in close connection with coastal environments, small islands (including Small Island DevelopingStates, SIDS), polar areas and high mountains7 are particularly exposed to ocean and cryosphere change, such as sealevel rise, extreme sea level and shrinking cryosphere. Other communities further from the coast are also exposed tochanges in the ocean, such as through extreme weather events. Today, around 4 million people live permanently inthe Arctic region, of whom 10% are Indigenous. The low-lying coastal zone8 is currently home to around 680 millionpeople (nearly 10% of the 2010 global population), projected to reach more than one billion by 2050. SIDS are hometo 65 million people. Around 670 million people (nearly 10% of the 2010 global population), including Indigenouspeoples, live in high mountain regions in all continents except Antarctica. In high mountain regions, population isprojected to reach between 740 and 840 million by 2050 (about 8.4–8.7% of the projected global population).{1.1, 2.1, 3.1, Cross-Chapter Box 9, Figure 2.1}In addition to their role within the climate system, such as the uptake and redistribution of natural and anthropogeniccarbon dioxide (CO2) and heat, as well as ecosystem support, services provided to people by the ocean and/orcryosphere include food and water supply, renewable energy, and benefits for health and well-being, cultural values,tourism, trade, and transport. The state of the ocean and cryosphere interacts with each aspect of sustainabilityreflected in the United Nations Sustainable Development Goals (SDGs). {1.1, 1.2, 1.5}7High mountain areas include all mountain regions where glaciers, snow or permafrost are prominent features of the landscape. For a list of highmountain regions covered in this report, see Chapter 2. Population in high mountain regions is calculated for areas less than 100 kilometres fromglaciers or permafrost in high mountain areas assessed in this report. {2.1} Projections for 2050 give the range of population in these regions acrossall five of the Shared Socioeconomic Pathways. {Cross-Chapter Box 1 in Chapter 1}8Population in the low elevation coastal zone is calculated for land areas connected to the coast, including small island states, that are less than10 metres above sea level. {Cross-Chapter Box 9} Projections for 2050 give the range of population in these regions across all five of the SharedSocioeconomic Pathways. {Cross-Chapter Box 1 in Chapter 1}5

Summary for PolicymakersA.Observed Changes and ImpactsObserved Physical ChangesSPM6A.1Over the last decades, global warming has led to widespread shrinking of the cryosphere,with mass loss from ice sheets and glaciers (very high confidence), reductions in snow cover(high confidence) and Arctic sea ice extent and thickness (very high confidence), and increasedpermafrost temperature (very high confidence). {2.2, 3.2, 3.3, 3.4, Figures SPM.1, SPM.2}A.1.1Ice sheets and glaciers worldwide have lost mass (very high confidence). Between 2006 and2015, the Greenland Ice Sheet9 lost ice mass at an average rate of 278 11 Gt yr–1 (equivalent to 0.77 0.03 mm yr–1 ofglobal sea level rise) 10, mostly due to surface melting (high confidence). In 2006–2015, the Antarctic Ice Sheet lostmass at an average rate of 155 19 Gt yr–1 (0.43 0.05 mm yr–1), mostly due to rapid thinning and retreat of majoroutlet glaciers draining the West Antarctic Ice Sheet (very high confidence). Glaciers worldwide outside Greenlandand Antarctica lost mass at an average rate of 220 30 Gt yr–1 (equivalent to 0.61 0.08 mm yr–1 sea level rise) in2006–2015. {3.3.1, 4.2.3, Appendix 2.A, Figure SPM.1}A.1.2Arctic June snow cover extent on land declined by 13.4 5.4% per decade from 1967to 2018, a total loss of approximately 2.5 million km2, predominantly due to surface air temperature increase(high confidence). In nearly all high mountain areas, the depth, extent and duration of snow cover have declined overrecent decades, especially at lower elevation (high confidence). {2.2.2, 3.4.1, Figure SPM.1}A.1.3Permafrost temperatures have increased to record high levels (1980s–present)(very high confidence) including the recent increase by 0.29ºC 0.12ºC from 2007 to 2016 averaged across polarand high mountain regions globally. Arctic and boreal permafrost contain 1460–1600 Gt organic carbon, almost twicethe carbon in the atmosphere (medium confidence). There is medium evidence with low agreement whether northernpermafrost regions are currently releasing additional net methane and CO2 due to thaw. Permafrost thaw and glacierretreat have decreased the stability of high mountain slopes (high confidence). {2.2.4, 2.3.2, 3.4.1, 3.4.3, Figure SPM.1}A.1.4Between 1979 and 2018, Arctic sea ice extent has very likely decreased for all months of theyear. September sea ice reductions are very likely 12.8 2.3% per decade. These sea ice changes in September arelikely unprecedented for at least 1000 years. Arctic sea ice has thinned, concurrent with a transition to younger ice:between 1979 and 2018, the areal proportion of multi-year ice at least five years old has declined by approximately90% (very high confidence). Feedbacks from the loss of summer sea ice and spring snow cover on land havecontributed to amplified warming in the Arctic (high confidence) where surface air temperature likely increasedby more than double the global average over the last two decades. Changes in Arctic sea ice have the potential toinfluence mid-latitude weather (medium confidence), but there is low confidence in the detection of this influencefor specific weather types. Antarctic sea ice extent overall has had no statistically significant trend (1979–2018) dueto contrasting regional signals and large interannual variability (high confidence). {3.2.1, 6.3.1, Box 3.1, Box 3.2,SPM A.1.2, Figures SPM.1, SPM.2}9Including peripheral glaciers.10360 Gt ice corresponds to 1 mm of global mean sea level.

Summary for PolicymakersPast and future changes in the ocean and cryosphereHistorical changes (observed and modelled) and projections under RCP2.6 and RCP8.5 for key indicators5Projected (RCP2.6)Projected (RCP8.5)(a) Global mean surface air temperature8.1change relative to 1986 20054ºCHistorical (modelled)3(h) Surface ocean pH8.02low acidityhigh acidity7.91SPMpHHistorical (observed)7.80 125 (b) Global mean sea surface temperaturechange relative to 1986 20054ºC 221(i) Ocean oxygen (100 600 m depth)0multiplication factor 650(c) Marine heatwave daysfactor of change relative to 1986 2005150%10(j) Arctic sea ice extent(September)50.3and sea level equivalent (right axis)change relative to 1986 200516000.28000.1020002050yearchange relative to 1986 2005 1002100500%(e) Greenland ice sheet mass lossas sea level equivalent,change relative to 1986 20050.2 50(l) Near surface permafrost area0.10.3 50(k) Arctic snow cover extent (June)change relative to 1986 20050metres019502000year2050 1002100(f) Antarctic ice sheet mass lossas sea level equivalent,change relative to 1986 20050.25primary drivers0.140metres0.3*(m) Global mean sea level(g) Glacier mass lossas sea level equivalent,change relative to 1986 20050.23change relative to 1986 20050.84 mmetresmetres0.35