The effect of global climate change on the regions of tropical convection in CSM1

The impact of enhanced carbon dioxide concentrations on deep tropical conve ction (DTC) is explored using the National Center for Atmospheric Research (NCAR) Climate System Model (CSM 1) model. A 134-year simulation in which C O concentrations increase 1 % year(-l) is analyzed. With approximately pres ent-day CO2 concentrations (367 ppmv) the CSM1 simulation captures the obse rved relationship between outgoing longwave radiation (OLR) and sea-surface temperature (SST) in the tropics. The temperature threshold for deep conve ction in the model is approximately 24.75 degrees C. As CO2 concentrations increase, the simulated threshold temperature for tropical convection progr essively increases to similar to 25.55 degrees C and 26.55 degrees C at 2xC O(2) (year 80) and 3.4xC0(2) (year 133). The fully coupled climate model re sponse to increased CO2 concentrations implies that the expansion of the 26 degrees C isotherm, the present-day observed threshold, wilt not yield an expansion of the regions of DTC.