Geophysical Research Letters | Shaw and Voigt 
In Atmospheric General Circulation Models (AGCMs) direct radiative forcing (increased CO2 with fixed sea surface temperature) is an imperfect concept because land temperatures are not fixed. Here the response to direct radiative forcing is decomposed into increased CO2 over ocean and land using an AGCM with spatially dependent CO2. The land versus ocean response is mostly linear. Consistent with previous work, ocean direct radiative forcing decreases ocean-averaged outgoing longwave radiation, precipitation and tropical circulation intensity, however it cannot explain the regional response to direct radiative forcing. Increased CO2 over land dominates the regional response via energy input over land, e.g. over deserts where there is no cloud and water vapor masking, and a Rossby-wave teleconnection. This mechanism operates across a range of climate perturbations, including decreased CO2. Previous AGCM decompositions involving direct radiative forcing and indirect SST warming must be reinterpreted to include the importance of increased CO2 over land.
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