Editing IPCC:AR6/WGI/Chapter-4 (section)

==== 4.3.2.4 Ocean and Land Carbon Uptake ====

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The AR5 concluded with ''very high confidence'' that ocean carbon uptake of anthropogenic CO <sub>2</sub> will continue under all RCPs through the 21st century, with higher uptake corresponding to higher concentration pathways. The future evolution of the land carbon uptake was assessed to be much more uncertain than for ocean carbon uptake, with a majority of CMIP5 models projecting a continued cumulative carbon uptake.

Based on results from the CMIP6 models, we conclude that the flux of carbon from the atmosphere into the ocean increases continually through most of 21st century in the two highest emissions and decreases continually under the other emissions scenarios (Figure 4.7a). The flux of carbon from the atmosphere to land shows a similar 21st century behaviour across the scenarios but with much higher year-to-year variation than ocean carbon flux (Figure 4.7b). A more in-depth assessment and discussion of the mechanism involved can be found in [[IPCC:Wg1:Chapter:Chapter-5|Chapter 5]] (Section 5.4.5).

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[[File:09581ff5c63fc03bfc618b5f774488cc IPCC_AR6_WGI_Figure_4_7.png]]

'''Figure''' '''4.7 |''' '''CMIP6 carbon uptake in historical and scenario simulations. (a)''' Atmosphere to ocean carbon flux (PgC yr <sup>–1</sup> ). '''(b)''' Atmosphere to land carbon flux (PgC yr <sup>–1</sup> ). The curves show ensemble averages and the shadings show the 5–95% ranges across the SSP1-2.6 and SSP3-7.0 ensembles. The numbers inside each panel are the number of model simulations. The land uptake is taken as Net Biome Productivity (NBP) and so includes any modelled net land-use change emissions. Results are from concentration-driven simulations. Further details on data sources and processing are available in the chapter data table (Table 4.SM.1).

In summary, we assess that the cumulative uptake of carbon by the ocean and by land will increase through the 21st century irrespective of the considered emissions scenarios except SSP1-1.9 ( ''very high confidence'' ).

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