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

==== 7.4.3.3 Synthesis of State-dependence of Feedbacks from Modelling and Paleoclimate Records ====

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Overall, independent lines of evidence from models ( [[#7.4.3.1|Section 7.4.3.1]] ) and from the paleoclimate proxy record ( [[#7.4.3.2|Section 7.4.3.2]] ) lead to ''high confidence'' that the net feedback parameter, α , increases (i.e., becomes less negative) as temperature increases; that is, that sensitivity to forcing increases as temperature increases (Figure 7.11). This temperature-dependence should be considered when estimating ECS from ESM simulations in which CO <sub>2</sub> is quadrupled ( [[#7.5.5|Section 7.5.5]] ) or from paleoclimate observations from past time periods colder or warmer than today ( [[#7.5.4|Section 7.5.4]] ). Although individual lines of evidence give only ''medium confidence'' , the overall high confidence comes from the multiple models that show the same sign of the temperature-dependence of α , the general agreement in evidence from the paleo proxy and modelling lines of evidence, and the agreement between proxy evidence from both cold and warm past climates. However, due to the large range in estimates of the magnitude of the temperature-dependence of α across studies (Figure 7.11), a quantitative assessment cannot currently be given, which provides a challenge for including this temperature-dependence in emulator-based future projections (Cross-Chapter Box 7.1). Greater confidence in the modelling lines of evidence could be obtained from simulations carried out for several hundreds of years ( [[#Rugenstein--2020|Rugenstein et al., 2020]] ), substantially longer than in many studies, and from more models carrying out simulations at multiple CO <sub>2</sub> concentrations. Greater confidence in the paleoclimate lines of evidence would be obtained from stronger constraints on atmospheric CO <sub>2</sub> concentrations, ice-sheet forcing, and temperatures, during past warm climates.

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