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

===== Cumulative CO 2 emissions and temperature goals =====

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The dominating role of CO 2 and its long lifetime in the atmosphere and some critical characteristics of the Earth System implies that there is a strong relationship between cumulative CO 2 emissions and temperature outcomes (Allen et al. 2009; [[#Matthews--2009|Matthews et al. 2009]] ; [[#Meinshausen--2009|Meinshausen et al. 2009]] ; [[#MacDougall--2015|MacDougall and Friedlingstein 2015]] ). This is illustrated in Figure 3.13, which plots the cumulative CO 2 emissions against the projected outcome for global mean temperature, both until peak temperature and through to end of century (or 2100). The deviations from a linear relationship in Figure 3.13 are mostly caused by different non-CO 2 emission and forcing levels (see also [[#Rogelj--2015b|Rogelj et al. 2015b]] ). This means that reducing non-CO 2 emissions can play an important role in limiting peak warming: the smaller the residual non-CO 2 warming, the larger the carbon budget. This impact on carbon budgets can be substantial for stringent warming limits. For 1.5°C pathways, variations in non-CO 2 warming across different emission scenarios have been found to vary the remaining carbon budget by approximately 220 GtCO 2 (AR6 WGI Chapter 5, [[IPCC:Wg3:Chapter:Chapter-5#5.5.2|Section 5.5.2]] .2). In addition to reaching net zero CO 2 emissions, a strong reduction in methane emissions is the most critical component in non-CO 2 mitigation to keep the Paris climate goals in reach ( [[#Collins--2018|Collins et al. 2018]] ; [[#van%20Vuuren--2018|van Vuuren et al. 2018]] ) (see also AR6 WGI, Chapters 5, 6 and 7). It should be noted that the temperature categories (C1–C7) generally aligned with the horizontal axis, except for the end-of-century values for C1 and C2 that coincide.

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[[File:097905b7b2683f470fa3f94df52d7591 IPCC_AR6_WGIII_Figure_3_13.png]]

'''Figure 3.13 | The near-linear relationship between cumulative CO''' 2 '''emissions and temperature.''' The left panel shows cumulative emissions until net zero emission is reached. The right panel shows cumulative emissions until the end of the century, plotted against peak and end-of-century temperature, respectively. Both are shown as a function of non-CO 2 forcing and cumulative net negative CO 2 emissions. Position temperature categories (circles) and IPs are also indicated, including two 2°C sensitivity cases for ''Neg'' (Neg-2.0) and ''Ren'' (Ren-2.0).

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