Editing IPCC:AR6/WGI/Chapter-3 (section)

=== Human Influence on the Ocean ===

<div id="h2-4-siblings" class="h2-siblings"></div>

'''It is''' extremely likely '''that human influence was the main driver''' '''of the ocean heat content increase observed since the 1970s, which extends into the deeper ocean''' ( very high confidence ''').''' Since AR5, there is improved consistency between recent observed estimates and model simulations of changes in upper (&lt;700 m) ocean heat content, when accounting for both natural and anthropogenic forcings. Updated observations and model simulations show that warming extends throughout the entire water column ( ''high confidence'' ), with CMIP6 models simulating 58% of industrial-era heat uptake (1850–2014) in the upper layer (0–700 m), 21% in the intermediate layer (700–2000 m) and 22% in the deep layer (&gt;2000 m). The structure and magnitude of multi-model mean ocean temperature biases have not changed substantially between CMIP5 and CMIP6 ( ''medium confidence'' ). {3.5.1}

'''It is''' extremely likely '''that human influence has contributed''' '''to observed near-surface and subsurface ocean salinity''' '''changes since the mid-20th century.''' The associated pattern of change corresponds to fresh regions becoming fresher and salty regions becoming saltier ( ''high confidence'' ). Changes to the coincident atmospheric water cycle and ocean-atmosphere fluxes (evaporation and precipitation) are the primary drivers of the observed basin-scale salinity changes ( ''high confidence'' ). The observed depth-integrated basin-scale salinity changes have been attributed to human influence, with CMIP5 and CMIP6 models able to reproduce these patterns only in simulations that include greenhouse gas increases ( ''medium confidence'' ). The basin-scale changes are consistent across models and intensify through the historical period ( ''high confidence'' ). The structure of the biases in the multi-model mean has not changed substantially between CMIP5 and CMIP6 ( ''medium confidence'' ). {3.5.2}

'''Combining the attributable contributions from glaciers,''' '''i''' '''ce-she''' '''et surface mass balance and thermal expansion, it is''' very likely '''that human influence was the main driver of the observed global mean sea level rise since at least 1971.''' Since AR5, studies have shown that simulations that exclude anthropogenic greenhouse gases are unable to capture the sea level rise due to thermal expansion (thermosteric) during the historical period and that model simulations that include all forcings (anthropogenic and natural) most closely match observed estimates. It is ''very likely'' that human influence was the main driver of the observed global mean thermosteric sea level increase since 1970. {3.5.3, 3.5.1, 3.4.3}

'''While observations show that the Atlantic Meridional Overturning Circulation (AMOC) has weakened from the mid-2000s to the mid-2010s''' ( high confidence ) '''and the Southern Ocean upper overturning cell has strengthened since the 1990s''' ( low confidence '''), observational records are too short to determine the relative contributions of internal variability, natural forcing, and anthropogenic forcing to these changes''' ( high confidence ''').''' No changes in Antarctic Circumpolar Current transport or meridional position have been observed. The mean zonal and overturning circulations of the Southern Ocean and the mean overturning circulation of the North Atlantic (the Atlantic Meridional Overturning Circulation, AMOC) are broadly reproduced by CMIP5 and CMIP6 models. However, biases are apparent in the modelled circulation strengths ( ''high confidence'' ) and their variability ( ''medium confidence'' ). {3.5.4}

<span id="human-influence-on-the-biosphere"></span>