Editing IPCC:AR6/WGI/Chapter-7 (section)

==== 7.5.3.2 Estimates of ECS from Glacial–Interglacial Cycles ====

<div id="h3-46-siblings" class="h3-siblings"></div>

Since AR5, several studies have extended the [[#Rohling--2012|Rohling et al. (2012)]] approach (described above for the LGM) to the glacial–interglacial cycles of the last approximately 1 to 2 million years ( [[#von%20der%20Heydt--2014|von der Heydt et al., 2014]] ; [[#Köhler--2015|Köhler et al., 2015]] , 2017, 2018; [[#Friedrich--2016|Friedrich et al., 2016]] ; [[#Royer--2016|Royer, 2016]] ; [[#Snyder--2019|Snyder, 2019]] ; [[#Stap--2019|Stap et al., 2019]] ; [[#Friedrich--2020|Friedrich and Timmermann, 2020]] ; see Table 7.11). Compared to the LGM, uncertainties in the derived ECS from these periods are in general greater, due to greater uncertainty in global surface temperature (due to fewer individual sites with proxy temperature records), ice-sheet forcing (due to a lack of detailed ice-sheet reconstructions), and CO <sub>2</sub> forcing (for those studies that include the pre-ice-core period, where CO <sub>2</sub> reconstructions are substantially more uncertain). Furthermore, accounting for varying orbital forcing in the traditional global mean forcing and response energy budget framework (Box 7.1) is challenging ( [[#Schmidt--2017b|Schmidt et al., 2017b]] ), due to seasonal and latitudinal components of the forcing that, despite a close-to-zero orbital forcing in the global annual mean, can directly result in responses in annual mean global surface temperature ( [[#Liu--2014|Liu et al., 2014]] ), ice volume ( [[#Abe-Ouchi--2013|Abe-Ouchi et al., 2013]] ), and feedback processes such as those associated with methane ( [[#Singarayer--2011|Singarayer et al., 2011]] ). In addition, for time periods in which the forcing relative to the modern era is small (interglacials), the inferred ECS has relatively large uncertainties because the forcing and temperature response (Δ ''F'' and Δ ''T'' in Equation 7.1, Box 7.1) are both close to zero.

<div id="7.5.3.3" class="h3-container"></div>

<span id="estimates-of-ecs-from-warm-periods-of-the-pre-quaternary"></span>