CICERO - Center for International Climate Research

Hydrological sensitivity to greenhouse gases and aerosols in a global climate model

Maria Malene Kvalevåg, Bjørn Hallvard Samset, Gunnar Myhre

Changes in greenhouse gases and aerosols alter the atmospheric energy budget on different time scales and at different levels in the atmosphere. We study the relationship between global mean precipitation changes, radiative forcing, and surface temperature change since preindustrial times caused by several climate change components (CO2, CH4, sulphate and black carbon (BC) aerosols, and solar forcing) using the National Center for Atmospheric Research Community Earth System Model (CESM1.03). We find a fast response in precipitation due to atmospheric instability that correlates with radiative forcing associated with atmospheric absorption and a slower response caused by changes in surface temperature which correlates with radiative forcing at the top of the atmosphere. In general, global climate models show large differences in climate response to global warming, but here we find a strong relationship between global mean radiative forcing and global mean precipitation changes that is very consistent with other models, indicating that precipitation changes from a particular forcing mechanism are more robust than previously expected. In addition, we look at the precipitation response and relate it to changes in lifetime of atmospheric water vapor (t). BC aerosols have a significantly larger impact on changes in t related to surface temperature compared to greenhouse gases, sulphate aerosols, and solar forcing and are the dominating forcing mechanism affecting fast precipitation in this quantity.

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