Dr. Roy Spencer from The University of Alabama at Huntsville will be presenting a special seminar at CU Boulder in the CIRES Auditorium on Thursday, July 17th, based on the Journal of Climate paper (in press):
Spencer, R.W., and W.D. Braswell, 2008: Feedback vs. Chaotic Radiative Forcing: “Smoking Gun” Evidence for an Insensitive Climate System?
“A simple model and satellite observations are used to demonstrate that previous diagnoses of climate feedbacks from the satellite record have a strong bias in the direction of high climate sensitivity (positive feedback). The source of the bias is chaotic radiative forcing generated within the climate system, most likely due to low clouds. Through analysis of frequency histograms of local regression slopes computed throughout the low-pass filtered time series of temperature and total (reflected shortwave SW and emitted longwave LW) radiative fluxes, the radiative forcing signal is shown to have a unique signature separate from the feedback signature. The global oceanic averages of satellite CERES data during 2000 through 2005 reveal a net (SW+LW) feedback parameter of around 8 W m-2 K-1. This strong negative feedback signal exists independent of the low-pass filter time scale, from 10 day to 2 years. In stark contrast, IPCC AR4 models analyzed with the same method all exhibit positive feedbacks of various strengths. It is suggested that the unrealistically high sensitivity of the climate models is the result of a misinterpretation of the co-variability of clouds and temperature when specifying cloud parameterizations. Since only radiative feedback has been assumed in feedback analysis of natural variability (clouds being forced by temperature), the presence of chaotic radiative forcing of temperature by clouds causes the false appearance of positive feedback. In short, cause and effect have been confused. Finally, if such a strong negative feedback has indeed been operating on multi-decadal time scales, this means that the radiative forcing from anthropogenic greenhouse gas emissions is not nearly strong enough to explain the 1°C warming in the last century.”
The pdf of the ms powerpoint presentation is here.
Climate Science: Roger Pielke Sr. Research Group News: Special Guest Seminar at CU by Roy Spencer, July 17, 2008:Global Warming: Recent Evidence for Reduced Climate Sensitivity