While 
natural land and ocean carbon sinks are projected to take up, in absolute 
terms, a progressively larger amount of CO2 under higher compared to 
lower CO2 emissions scenarios, they become less effective, that is, the 
proportion of emissions taken up by land and ocean decreases with 
increasing cumulative net CO2 emissions (high conﬁdence). Additional 
ecosystem responses to warming not yet fully included in climate models, 
such as GHG ﬂuxes from wetlands, permafrost thaw, and wildﬁres, 
would further increase concentrations of these gases in the atmosphere 
(high conﬁdence). In scenarios where CO2 concentrations peak and 
decline during the 21st century, the land and ocean begin to take up less 
carbon in response to declining atmospheric CO2 concentrations (high 
conﬁdence) and turn into a weak net source by 2100 in the very low 
GHG emissions scenario (medium confidence)133. {WGI SPM B.4, 
WGI SPM B.4.1, WGI SPM B.4.2, WGI SPM B.4.3}