Consistent Differences in Climate Feedbacks Between 1 Atmosphere - Ocean GCMs and Atmospheric GCMs with 2 Slab - Ocean Models

5 Climate sensitivity is generally studied using two types of models. Atmosphere-ocean general 6 circulation models (AOGCMs) include interactive ocean dynamics and detailed heat uptake. 7 Atmospheric GCMs (AGCMs) with slab ocean models (SOMs) cannot fully simulate the 8 ocean’s response to and influence on climate. However, AGCMs are cheaper computation9 ally and thus are often used to quantify and understand climate feedbacks and sensitivity. 10 Here, physical climate feedbacks are compared between AOGCMs and SOM-AGCMs from 11 the Coupled Model Intercomparison Project phase 3 using the radiative kernel technique. 12 Both the global-average (positive) water vapor and (negative) lapse-rate feedbacks are con13 sistently stronger in AOGCMs. Water vapor feedback differences result from an essentially 14 constant relative humidity and peak in the tropics, where temperature changes are larger for 15 AOGCMs. Differences in lapse-rate feedbacks extend to midlatitudes and correspond to a 16 larger ratio of tropicalto global-average temperature changes. Global-average surface albedo 17 feedbacks are similar between models types due to a near cancellation of Arctic and Antarc18 tic differences. In AOGCMs, the northern high latitudes warm faster than the southern, 19 resulting in inter-hemispheric differences in albedo, water vapor, and lapse-rate feedbacks 20 lacking in the SOM-AGCMs. Meridional heat transport changes also depend on the model 21 type, though there is a large inter-model spread. However, there are no consistent global or 22 zonal differences in cloud feedbacks. Effects of the forcing scenario (SRESa1b or 1%to2x) 23 on feedbacks are model-dependent and generally of lesser importance than the model type. 24 Care should be taken when using SOM-AGCMs to understand AOGCM feedback behavior. 25