Abstract

Temperature feedbacks have hitherto been thought to contribute to equilibrium sensitivity up to ten times the direct warming or reference sensitivity that induced them, because it had been erroneously assumed that the Earth’s emission temperature would induce no feedbacks, though any subsequent direct warming, such as the response to the forcing caused by the presence of the naturally-arising, non-condensing greenhouse gases, would induce them. Accordingly, the large feedback-driven warming induced by emission temperature has been mistakenly counted as part of the feedback induced by the comparatively small direct warming from the non- condensing greenhouse gases, leading to substantial overstatements of the feedback fraction and thus of all climate sensitivities. The official estimate of equilibrium sensitivity to doubled CO2 (“Charney sensitivity”) had been 𝟑. 𝟑 [2.0, 4.5] K, implying a feedback fraction on 𝟎. 𝟔𝟕 [0.45, 0.75]. However, an empirical comparison of several published official estimates of industrial-era net anthropogenic forcings with observed warming coheres with two theoretical methods in finding the feedback fraction to be only 𝟎.𝟏𝟐 [0.08, 0.16], implying Charney sensitivity of order 𝟏. 𝟐𝟓 K.