An Analytic Study of Climate Sensitivity

According to IPCC, the climate sensitivity in the absence of feedbacks is T = 1 C. The evaluation is based on the Stefan-Boltzmann law. This naive picture is however doubtful. In the present work we have examined the climate sensitivity in the analytic model of radiative transfer and found that the IPCC is incorrect. The precise climate sensitivity is T = 1:4 C. The observed temperature anomaly is approximately reproduced even in the absence of feedbacks. It is likely that the feedbacks are rather weak. So as to con…rm this speculation, we have calculated the climate sensitivity with the water vapor feedback which is however obviously overestimated. The resultant feedback factor 1.65 is lower than 2 predicted by IPCC. In addition, we arti…cially reduce the water vapor feedback by half. The result reproduces the observed temperature anomaly fairly well. The resultant feedback factor 1.25 is much lower than 2. We can therefore conclude that the positive feedbacks are much weaker than the IPCC predictions.