Land dominates the regional response to CO2 direct radiative forcing

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 sea surface temperature warming must be reinterpreted to include the importance of increased CO₂ over land.