Editing IPCC:AR6/SROCC/SPM (section)

== A Observed changes and impacts ==

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==== Observed Physical Changes ====

'''A.1. Over 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 increased permafrost temperature ( ''very high confidence'' ). {2.2, 3.2, 3.3, 3.4, Figures SPM.1, SPM.2}'''

'''A.1.1 ''' [[File:83ce8208a5b1bfd831112dee0dcef7fd SPM-Icon-xxxo.png]]  Ice sheets and glaciers worldwide have lost mass ( ''very high confidence'' ). Between 2006 and 2015, the Greenland Ice Sheet <sup>[[#fn:9|9]]</sup> lost ice mass at an average rate of 278 ± 11 Gt yr–1 (equivalent to 0.77 ± 0.03 mm yr–1 of global sea level rise) <sup>[[#fn:10|10]]</sup> , mostly due to surface melting ( ''high confidence'' ). In 2006–2015, the Antarctic Ice Sheet lost mass 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 major outlet glaciers draining the West Antarctic Ice Sheet ( ''very high confidence'' ). Glaciers worldwide outside Greenland and 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) in 2006–2015. {3.3.1, 4.2.3, Appendix 2.A, Figure SPM.1}

'''A.1.2'''   [[File:7dd9d5f1c0e829eec2bf341c5154813e SPM-Icon-xxoo.png]]  Arctic June snow cover extent on land declined by 13.4 ± 5.4% per decade from 1967 to 2018, a total loss of approximately 2.5 million km 2 , 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 over recent decades, especially at lower elevation ( ''high confidence'' ). {2.2.2, 3.4.1, Figure SPM.1}

'''A.1.3''' [[File:7dd9d5f1c0e829eec2bf341c5154813e SPM-Icon-xxoo.png]] Permafrost temperatures have increased to record high levels (1980s-present) ( ''very high confidence'' ) including the recent increase by 0.29°C ± 0.12°C from 2007 to 2016 averaged across polar and high-mountain regions globally. Arctic and boreal permafrost contain 1460–1600 Gt organic carbon, almost twice the carbon in the atmosphere ( ''medium confidence'' ). There is ''medium'' ''evidence'' with ''low'' ''agreement'' whether northern permafrost regions are currently releasing additional net methane and CO 2 due to thaw. Permafrost thaw and glacier retreat 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.1.4''' [[File:37d9ca019c63e0a7a080aaca0b2016e4 SPM-Icon-oxox.png]] Between 1979 and 2018, Arctic sea ice extent has ''very likely'' decreased for all months of the year. September sea ice reductions are ''very likely'' 12.8 ± 2.3% per decade. These sea ice changes in September are ''likely'' 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 approximately 90% ( ''very high confidence'' ). Feedbacks from the loss of summer sea ice and spring snow cover on land have contributed to amplified warming in the Arctic ( ''high confidence'' ) where surface air temperature ''likely'' increased by more than double the global average over the last two decades. Changes in Arctic sea ice have the potential to influence mid-latitude weather ( ''medium confidence'' ), but there is ''low'' ''confidence'' in the detection of this influence for specific weather types. Antarctic sea ice extent overall has had no statistically significant trend (1979–2018) due to 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}

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'''Figure SPM.1'''

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'''Figure SPM.1 | Observed and modelled historical changes in the ocean and cryosphere since 1950, and projected future changes under low (RCP2.6) and high (RCP8.5) greenhouse gas emissions scenarios. {Box SPM.1} Changes are shown for: (a) Global mean surface air temperature change with likely range. {Box SPM.1, Cross-Chapter Box 1 in Chapter 1} Ocean-related changes […]'''
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[[File:a87e5a90b0c85f9fdd00964433c75b78 SROCC_SPM1_Final_RGB-2319x3000.jpg]]

Figure SPM.1 | Observed and modelled historical changes in the ocean and cryosphere since 1950 <sup>[[#fn:11|11]]</sup> , and projected future changes under low (RCP2.6) and high (RCP8.5) greenhouse gas emissions scenarios. {Box SPM.1} Changes are shown for: (a) Global mean surface air temperature change with likely range. {Box SPM.1, Cross-Chapter Box 1 in Chapter 1} Ocean-related changes with very likely ranges for (b) Global mean sea surface temperature change {Box 5.1, 5.2.2}; (c) Change factor in surface ocean marine heatwave days {6.4.1}; (d) Global ocean heat content change (0–2000 m depth). An approximate steric sea level equivalent is shown with the right axis by multiplying the ocean heat content by the global-mean thermal expansion coefficient (ε ≈ 0.125 m per 1024 Joules)12 for observed warming since 1970 {Figure 5.1}; (h) Global mean surface pH (on the total scale). Assessed observational trends are compiled from open ocean time series sites longer than 15 years {Box 5.1, Figure 5.6, 5.2.2}; and (i) Global mean ocean oxygen change (100–600 m depth). Assessed observational trends span 1970–2010 centered on 1996 {Figure 5.8, 5.2.2}. Sea level changes with likely ranges for (m) Global mean sea level change. Hashed shading reflects low confidence in sea level projections beyond 2100 and bars at 2300 reflect expert elicitation on the range of possible sea level change {4.2.3, Figure 4.2}; and components from (e,f) Greenland and Antarctic ice sheet mass loss {3.3.1}; and (g) Glacier mass loss {Cross-Chapter Box 6 in Chapter 2, Table 4.1}. Further cryosphere-related changes with very likely ranges for (j) Arctic sea ice extent change for September13 {3.2.1, 3.2.2 Figure 3.3}; (k) Arctic snow cover change for June (land areas north of 60oN) {3.4.1, 3.4.2, Figure 3.10}; and (l) Change in near-surface (within 3–4 m) permafrost area in the Northern Hemisphere {3.4.1, 3.4.2, Figure 3.10}. Assessments of projected changes under the intermediate RCP4.5 and RCP6.0 scenarios are not available for all variables considered here, but where available can be found in the underlying report. {For RCP4.5 see: 2.2.2, Cross-Chapter Box 6 in Chapter 2, 3.2.2, 3.4.2, 4.2.3, for RCP6.0 see Cross-Chapter Box 1 in Chapter 1}

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