Deep-seated, persistent uncertainty is a pernicious feature of climate change. One key parameter, equilibrium climate sensitivity, has eluded almost all attempts at pinning it down more precisely than a ‘likely’ range that has stalled at 1.5–4.5°C for over thirty-five years. The marginal...

Atmospheric CO2 concentrations and surface temperature reconstructions in the study period 1850-2017 are used to estimate observed equilibrium climate sensitivity. Comparison of climate sensitivities in the first and second halves of the study period and a study of climate sensitivities in a...