Estimations of climate feedbacks based on top-of-atmosphere net radiation

There are large uncertainties in the predictions of the Earth's future climate in current climate models. To reduce the uncertainties, an energy balance model constrained by top-of-atmosphere (TOA) net radiation is explored. The net radiation estimated from various observational methods has considerable uncertainties and is assumed to be 0.85 W/m2 in this study. Instead of solving the initial condition problem in previous energy balance analysis, current study focuses on boundary conditions. The climate system memory and deep ocean heat transports are also considered. The estimated feedback factor for the current climate system ranges from –1.3 to –1.0 W/m2/K. The feedback range is caused by the uncertainties in the climate memory length. The estimated time constant of the climate is about 100 years, implying that the climate may be not in an equilibrium state in the last century. For the doubled-CO2 atmosphere, the estimated global warming would be 3.1 K if the estimate of TOA net radiation were correct. These results are consistent with some other model predictions. The significant difference is that the uncertainties of current feedback estimates are basically dependent on observational errors while those of other model predictions are the differences among models. This study suggests that long-term measurements of the TOA radiation with both high precision and high absolute accuracy are crucial. With long-term, accurate global TOA energy imbalance measurements and the analysis method suggested here, a great potential in accurate climate predictions could be realized, and a physically-based tool in determination of climate change policies could be provided to the public and policymakers.