Editing IPCC:AR6/WGI/Chapter-5 (section)

===== 5.5.1.2.2 Sensitivity to the rate of CO <sub>2</sub> emissions =====

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Global average temperature increase responds over a time scale of about 10 years following the emission of a 100 PgC pulse of CO <sub>2</sub> ( [[#Joos--2013|Joos et al., 2013]] ; [[#Ricke--2014|Ricke and Caldeira, 2014]] ), with larger emission pulses associated with longer time scales and smaller pulses with shorter ones ( [[#Joos--2013|Joos et al., 2013]] ; [[#Matthews--2013|Matthews and Solomon, 2013]] ; [[#Zickfeld--2015|Zickfeld and Herrington, 2015]] ). This behaviour is confirmed in other studies, including those that calculate the temperature response to an instantaneous doubling or quadrupling of atmospheric CO <sub>2</sub> ( [[#Matthews--2009|Matthews et al., 2009]] ; [[#Gillett--2013|Gillett et al., 2013]] ; [[#Herrington--2014|Herrington and Zickfeld, 2014]] ; [[#Leduc--2015|Leduc et al., 2015]] ; [[#Hajima--2020b|Hajima et al., 2020b]] ). These findings suggest that the TCRE is sensitive to the rate of emissions, but studies assessing this sensitivity have found diverging results. For example, an increase in TCRE and its surrounding uncertainty was reported for experiments that imply a gradual decline in annual CO <sub>2</sub> emissions ( [[#Tachiiri--2019|Tachiiri et al., 2019]] ). These studies suggest that, in most cases, TCRE would be expected to increase in scenarios with decreasing annual emissions rates. This increase in TCRE for annual CO <sub>2</sub> emissions declining towards zero can be the result of the zero emissions commitment (ZEC) which is the amount of warming projected to occur following a complete cessation of emissions (see [[IPCC:Wg1:Chapter:Chapter-4#4.7.1.1|Section 4.7.1.1]] for its assessment), as well as Earth system processes that are unrepresented in current TCRE estimates ( [[#5.5.2.2.4|Section 5.5.2.2.4]] ) and other factors. When using TCRE to estimate CO <sub>2</sub> emissions consistent with a specific maximum warming level, these factors have to be taken into account (see Figure 5.31). Combined with recent literature on the ZEC ( [[#MacDougall--2020|MacDougall et al., 2020]] ) and emissions pathways ( [[#Huppmann--2018|Huppmann et al., 2018]] ) and noting the lack of literature that disentangles these various contributions, there is ''medium evidence'' and ''high agreement'' resulting in ''medium confidence'' that the TCRE remains a good predictor of CO <sub>2</sub> -induced warming when applied in the context of emissions reduction pathways, provided that ZEC and long-term Earth system feedbacks are adequately accounted for when emissions decline towards zero (see also [[#5.5.1.2.3|Section 5.5.1.2.3]] ).

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