The Effect of Global Climate Change on the Seasonal Cycle of the Global Energy Balance

There is a growing deficit in the outgoing LW flux due to the anthropogenic increase in atmospheric CO2 that produces an imbalance in the global annual-mean energy balance of the Earth. The small imbalance in the global annual-mean energy budget, which arises from the radiative properties of atmospheric CO2 and the large heat capacity of the ocean, is sometimes referred to as the ‘smoking gun’ of the observational consequences of the ongoing global warming phenomena. Currently amounting to somewhat less than 1 W/m2 in magnitude, this global annual-mean energy imbalance is a particularly difficult measurement to obtain with the accuracy and confidence that is needed to quantitatively diagnose climate model performance. Moreover, since the inter-annual variability of the global annual-mean energy balance is of the same order of magnitude, existing satellite measurements of the Earth’s global annual-mean energy imbalance would require the analysis of many decades of measurements in order to reach a definitive conclusion regarding changes in the Earth’s global energy imbalance. Accordingly, such measurements of the global energy imbalance cannot adequately provide the desired observational verification of the global warming effect on a near-term basis. On the other hand, with its 22 W/m2 amplitude, the seasonal cycle of the global-mean energy balance can serve as a more effective observational constraint for validating climate model performance. Because of the hemispheric land-ocean asymmetry, model results suggest that there should be a significant change in the shape of the seasonal global-mean energy balance cycle compared to that for pre-industrial climate conditions. Simulations with the GISS ModelE coupled climate model suggest that the climate-change-induced shift in the shape of the seasonal global-mean energy balance cycle provides a more effective diagnostic and informative measure of climate model performance than comparisons to the annual-mean of the global energy balance.