Radiative Feedbacks on Global Precipitation

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Environmental Research Letters
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The radiative kernel technique is employed to quantify twenty-first century changes to the tropospheric energy budget in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) models in order to better understand changes in global-mean precipitation. The strongest feedbacks on the tropospheric radiative cooling are found to be associated with increases in temperature and water vapor, with the water vapor feedback offsetting a significant portion (~39%) of the increase in radiative cooling due to higher temperatures. Cloud and surface sensible heat flux feedbacks, though not as large in magnitude as the temperature and water vapor feedbacks, are important contributors to the intermodel difference in the global precipitation response to warming, or hydrological sensitivity. The direct effects of radiative forcing agents on the tropospheric energy budget are also important. Rising CO2 levels reduce tropospheric radiative cooling and hence limit the increase in global rainfall. Additionally, in some of the models, further reductions in radiative cooling occur due to increases in absorbing aerosol, suggesting that differences in aerosol forcing can explain part of the difference in hydrological sensitivity between models.