Energetics of climate models: Net energy balance and meridional enthalpy transport

We analyze the publicly released outputs of the simulations performedby climate models (CMs) in preindustrial (PI) and Special Reporton Emissions Scenarios A1B (SRESA1B) conditions. In the PI simulations,most CMs feature biases of the order of 1 W m−2 for the net globaland the net atmospheric, oceanic, and land energy balances. Thisdoes not result from transient effects but depends on the imperfectclosure of the energy cycle in the fluid components and on inconsistenciesover land. Thus, the planetary emission temperature is underestimated,which may explain the CMs' cold bias. In the PI scenario, CMs agreeon the meridional atmospheric enthalpy transport's peak location(around 40\,^∘N/S), while discrepancies of ∼20% exist on the intensity.Disagreements on the oceanic transport peaks' location and intensityamount to ∼10\,^∘ and ∼50%, respectively. In the SRESA1B runs, the atmospherictransport's peak shifts poleward, and its intensity increases upto ∼10% in both hemispheres. In most CMs, the Northern Hemisphericoceanic transport decreases, and the peaks shift equatorward in bothhemispheres. The Bjerknes compensation mechanism is active both onclimatological and interannual time scales. The total meridionaltransport peaks around 35\,^∘ in both hemispheres and scenarios, whereasdisagreements on the intensity reach ∼20%. With increased CO2 concentration,the total transport increases up to ∼10%, thus contributing to polaramplification of global warming. Advances are needed for achievinga self-consistent representation of climate as a nonequilibrium thermodynamicalsystem. This is crucial for improving the CMs' skill in representingpast and future climate changes