Reply to Comment #1 on egusphere-2023-1647

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Abstract
After many years with little change in community views on Equilibrium Climate Sensitivity (ECS), in 2021 the IPCC concluded that it was much better known than previously, supported by a major assessment the previous year. This development underpinned increased confidence in long-term climate changes in that report. Here, we place this development in historical context, briefly assess progress since then, and discuss the challenges and opportunities for further improving our knowledge of this iconic concept. We argue that the probability distributions published in those assessments are still approximately valid; while various subsequent studies have claimed further narrowing, they have omitted important structural uncertainties that should be included. The distributions could nonetheless be narrowed in the future, particularly through better understanding of certain climate processes and paleoclimate proxies. Not all touted strategies are truly helpful, however. We also note that as increasingly strong mitigation (i.e., “net-zero”) scenarios are considered, ECS becomes less informative about future climate change compared to other factors such as aerosol radiative forcing, carbon cycle and vegetation processes, and influences on regional change such as ocean dynamics.

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