hide
Free keywords:
-
Abstract:
Water vapour in the atmosphere is the source of a major climate feedback mechanism and potential increases in the availability of water vapour could have important consequences for mean and extreme precipitation. Future precipitation changes further depend on how the hydrological cycle responds to different drivers of climate change, such as greenhouse gases and aerosols. Currently, neither the total anthropogenic influence on the hydrological cycle nor that from individual drivers is constrained sufficiently to make solid projections. We investigate how integrated water vapour (IWV) responds to different drivers of climate change. Results from 11 global climate models have been used, based on simulations where <span classCombining double low line"inline-formula">CO2</span>, methane, solar irradiance, black carbon (BC), and sulfate have been perturbed separately. While the global-mean IWV is usually assumed to increase by <span classCombining double low line"inline-formula">ĝ1/47</span> per kelvin of surface temperature change, we find that the feedback response of IWV differs somewhat between drivers. Fast responses, which include the initial radiative effect and rapid adjustments to an external forcing, amplify these differences. The resulting net changes in IWV range from <span classCombining double low line"inline-formula">6.4±0.9</span>K<span classCombining double low line"inline-formula">-1</span> for sulfate to <span classCombining double low line"inline-formula">9.8±2</span>K<span classCombining double low line"inline-formula">-1</span> for BC. We further calculate the relationship between global changes in IWV and precipitation, which can be characterized by quantifying changes in atmospheric water vapour lifetime. Global climate models simulate a substantial increase in the lifetime, from <span classCombining double low line"inline-formula">8.2±0.5</span> to <span classCombining double low line"inline-formula">9.9±0.7</span>d between 1986-2005 and 2081-2100 under a high-emission scenario, and we discuss to what extent the water vapour lifetime provides additional information compared to analysis of IWV and precipitation separately. We conclude that<span idCombining double low line"page12888"/> water vapour lifetime changes are an important indicator of changes in precipitation patterns and that BC is particularly efficient in prolonging the mean time, and therefore likely the distance, between evaporation and precipitation. © Author(s) 2019. This work is distributed under the Creative Commons Attribution 4.0 License.
