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The role of stratospheric water vapor (SWV) changes, in response to increasing , as a feedback component of quantitative significance for climate sensitivity has remained controversial. Here, we calculate the SWV climate feedback under abrupt quadrupling in the CMIP5 ensemble of models. All models robustly show a moistening of the stratosphere, causing a global mean net stratosphere adjusted radiative perturbation of at the reference tropopause. The stratospheric temperature adjustment is a crucial component of this radiative perturbation. The associated climate feedback is , with a considerable inter-model range of 0.12–0.28 . Taking into account the rise in tropopause height under slightly reduces the feedback to , with a range of 0.10–. The SWV radiative perturbation peaks in the midlatitudes and not the …