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

==== 1.8.1.1 Ocean and Cryosphere Observations  ====

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Long-term sustained observations are critical for detecting and understanding the processes of ocean and cryosphere change (Rhein et al., 2013 <sup>[[#fn:r392|392]]</sup> ; Vaughan et al., 2013 <sup>[[#fn:r393|393]]</sup> ). Scientific knowledge of the ocean and cryosphere has increased through time and geographical space (Figure 1.3). ''In situ'' ocean subsurface temperature and salinity observations have increased in spatial and temporal coverage since the middle of the 19th century (Abraham et al., 2013 <sup>[[#fn:r394|394]]</sup> ), and near global coverage (60°S–60°N) of the upper 2,000 m has been achieved since 2007 due to the international Argo network (Riser et al., 2016 <sup>[[#fn:r395|395]]</sup> ; Figure 1.3). Improved data quality and data analysis techniques have reduced uncertainties in global ocean heat uptake estimates (Sections 1.4.1, 5.2.2). In addition to providing deep ocean measurements, repeated hydrographic physical and biogeochemical observations since AR5 have led to improved estimates of ocean carbon uptake and ocean deoxygenation (Sections 1.4.1, 5.2.2.3, 5.2.2.4). Targeted observational programmes have improved scientific knowledge for specific regions and physical processes of particular concern in a warming climate, including the Greenland and West Antarctic ice sheets (Section 3.3), and the AMOC (Section 6.7). Ocean and cryosphere mass changes and sea level studies have benefited from sustained or newly implemented satellite-based remote sensing technologies, complemented by ''in situ'' data such as tide gauges measurements (Sections 3.3, 4.2; Dowell et al., 2013 <sup>[[#fn:r396|396]]</sup> ; Raup et al., 2015 <sup>[[#fn:r397|397]]</sup> ; PSMSL, 2016 <sup>[[#fn:r398|398]]</sup> ). Glacier length measurements in some locations go back many centuries (Figure 1.3), but it is the systematic high resolution satellite monitoring of a large number of the world’s glaciers since the late 1970s that has improved global assessments of glacier mass loss (Sections 2.2.3, 3.3.2).

L imitations in knowledge of ocean and cryosphere change remain, creating knowledge gaps for the SROCC assessment. Ocean and cryosphere datasets are frequently short, and do not always span the key IPCC assessment time intervals (Cross-Chapter Box 1 in Chapter 1), so for many parameters the full magnitude of changes since the pre-industrial period is not observed (Figure 1.3). The brevity of ocean and cryosphere measurements also means that some expected changes cannot yet be detected with confidence in direct observations (e.g., Antarctic sea ice loss in Section 3.2.1, AMOC weakening in Section 6.7.1), or other observed changes cannot yet be robustly attributed to anthropogenic factors (e.g., ice sheet mass loss in Section 3.3.1). Observations for many key ocean variables (Bojinski et al., 2014 <sup>[[#fn:r399|399]]</sup> ), such as ocean currents, surface heat fluxes, oxygen, inorganic carbon, subsurface salinity, phytoplankton biomass and diversity, etc., do not yet have global coverage or have not reached the required density or accuracy for detection of change. Some ocean and cryosphere areas remain difficult to observe systematically, for example, the ocean under sea ice, subsurface permafrost, high mountain areas, marginal seas, coastal areas (Section 4.2.2.3) and ocean boundary currents (Hu and Sprintall, 2016 <sup>[[#fn:r400|400]]</sup> ), basin interconnections (Section 6.6) and the Southern Ocean (Sections 3.2, 5.2.2). Measurements that reflect ecosystem change are often location or species specific, and assessments of long-term ocean ecosystem changes are currently only feasible for a limited subset of variables, for example coral reef health (e.g., coral reef health) (Section 5.3; Miloslavich et al., 2018 <sup>[[#fn:r401|401]]</sup> ). The deep ocean below 2,000 m is still rarely observed (Talley et al., 2016 <sup>[[#fn:r402|402]]</sup> ), limiting (for example) the accurate estimate of deep ocean heat uptake and, consequently the full magnitude of Earth’s energy imbalance (e.g., von Schuckmann et al., 2016 <sup>[[#fn:r403|403]]</sup> ; Johnson et al., 2018 <sup>[[#fn:r404|404]]</sup> ; Sections 1.2, 1.4, 5.2.2).

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