Editing IPCC:AR6/SROCC/Chapter-1 (section)

=== 1.4.1 Observed and Projected Changes in the Ocean ===

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Increasing greenhouse gases in the atmosphere cause heat uptake in the Earth system (Section 1.2) and as reported since 1970, there is ''high confidence <sup>[[#fn:3|3]]</sup>'' that the majority (more than 90%) of the extra thermal energy in the Earth’s system is stored in the global ocean (IPCC, 2013 <sup>[[#fn:r96|96]]</sup> ). Mean ocean surface temperature has increased since the 1970s at a rate of 0.11 (0.09 – 0.13)°C per decade ( ''high confidence'' ), and forms part of a long-term warming of the surface ocean since the mid-19th century. The upper ocean (0 – 700 m, ''virtually certain'' ) and intermediate ocean (700 to 2,000 m, ''likely'' ) have warmed since the 1970s. Ocean heat uptake has continued unabated since AR5 (Sections 3.2.1.2.1, 5.2 ), increasing the risk of marine heat waves and other extreme events (Section 6.4). During the 21st century, ocean warming is projected to continue even if anthropogenic greenhouse gas emissions cease (Sections 1.3, 5.2). The global water cycle has been altered, resulting in substantial regional changes in sea surface salinity ( ''high confidence'' ; Rhein et al., 2013 <sup>[[#fn:r97|97]]</sup> ), which is expected to continue in the future (Sections 5.2.2, 6.3, 6.5).

The rate of sea level rise since the mid-19th century has been larger than the mean rate of the previous two millennia ( ''high confidence'' ). Over the period 1901 to 2010, global mean sea level rose by 0.19 (0.17 – 0.21) m ( ''high confidence)'' (Church et al., 2013 <sup>[[#fn:r98|98]]</sup> ; Table SM1.1). Sea level rise continues due to freshwater added to the ocean by melting of glaciers and ice sheets, and as a result of ocean expansion due to continuous ocean warming, with a projected acceleration and century to millennial-scale commitments for ongoing rise (Section 4.2.3). In SROCC, recent developments of ice sheet modelling are assessed (Sections 1.8, 4.3, Cross-Chapter Box 8 in Chapter 3) and the projected sea level rise at the end of 21st century is higher than reported in AR5 but with a larger uncertainty range (Sections 4.2.3.2, 4.2.3.3).

By 2011, the ocean had taken up about 30 ± 7% of the anthropogenic CO 2 that had been released to the atmosphere since the industrial revolution (Ciais et al., 2013 <sup>[[#fn:r99|99]]</sup> ; Section 5.2). In response, ocean pH decreased by 0.1 since the beginning of the industrial era ( ''high confidence'' ), corresponding to an increase in acidity of 26% (Table SM1.1) and leading to both positive and negative biological and ecological impacts ( ''high confidence'' ) (Gattuso et al., 2014 <sup>[[#fn:r100|100]]</sup> ) . Evidence is increasing that the ocean’s oxygen content is declining (Oschlies et al., 2018 <sup>[[#fn:r101|101]]</sup> ). AR5 did not come to a final conclusion with regard to potential long-term changes in ocean productivity due to short observational records and divergent scientific evidence (Boyd et al., 2014 <sup>[[#fn:r102|102]]</sup> ; Section 5.2.2). Ocean acidification and deoxygenation are projected to continue over the next century with ''high confidence'' (Sections 3.2.2.3, 5.2.2).

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