Impact of increasing stratospheric water vapor on ozone depletion and temperature change

Abstract

Using a detailed, fully coupled chemistry climate model (CCM), the effect of increasing stratospheric H₂O on ozone and temperature is investigated. Different CCM time-slice runs have been performed to investigate the chemical and radiative impacts of an assumed 2 ppmv increase in H₂O. The chemical effects of this H₂O increase lead to an overall decrease of the total column ozone (TCO) by ∼1% in the tropics and by a maximum of 12% at southern high latitudes. At northern high latitudes, the TCO is increased by only up to 5% due to stronger transport in the Arctic. A 2-ppmv H₂O increase in the model’s radiation scheme causes a cooling of the tropical stratosphere of no more than 2 K, but a cooling of more than 4 K at high latitudes. Consequently, the TCO is increased by about 2%–6%. Increasing stratospheric H₂O, therefore, cools the stratosphere both directly and indirectly, except in the polar regions where the temperature responds differently due to feedbacks between ozone and H₂O changes. The combined chemical and radiative effects of increasing H₂O may give rise to more cooling in the tropics and middle latitudes but less cooling in the polar stratosphere. The combined effects of H₂O increases on ozone tend to offset each other, except in the Arctic stratosphere where both the radiative and chemical impacts give rise to increased ozone. The chemical and radiative effects of increasing H₂O cause dynamical responses in the stratosphere with an evident hemispheric asymmetry. In terms of ozone recovery, increasing the stratospheric H₂O is likely to accelerate the recovery in the northern high latitudes and delay it in the southern high latitudes. The modeled ozone recovery is more significant between 2000–2050 than between 2050–2100, driven mainly by the larger relative change in chlorine in the earlier period.