{WGI SPM D.1.3}
131 Uncertainties for total carbon budgets have not been assessed and could affect the speciﬁc calculated fractions. 
132 See footnote 131. 
133 These projected adjustments of carbon sinks to stabilisation or decline of atmospheric CO2 concentrations are accounted for in calculations of remaining carbon budgets. 
{WGI SPM footnote 32}
If the annual CO2 emissions between 2020–2030 stayed, on average, 
at the same level as 2019, the resulting cumulative emissions would 
almost exhaust the remaining carbon budget for 1.5°C (50%), and 
exhaust more than a third of the remaining carbon budget for 2°C 
(67%) (Figure 3.5). Based on central estimates only, historical cumulative 
net CO2 emissions between 1850 and 2019 (2400 ±240 GtCO2) amount 
to about four-ﬁfths131 of the total carbon budget for a 50% probability of 
limiting global warming to 1.5°C (central estimate about 2900 GtCO2) and 
to about two-thirds132 of the total carbon budget for a 67% probability 
to limit global warming to 2°C (central estimate about 3550 GtCO2). 
{WGI Table SPM.2; WGIII SPM B.1.3, WGIII Table 2.1}
In scenarios with increasing CO2 emissions, the land and ocean 
carbon sinks are projected to be less effective at slowing the 
accumulation of CO2 in the atmosphere (high conﬁdence). 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).