The Physics of Climate Sensitivity
I will first review the basic physics and chemistry underlying the influence of carbon dioxide on planetary temperature, and its multi-millennial duration of effect on climate, with a particular emphasis on observational confirmation of key aspects of the radiative transfer that can be considered to be understood with essentially 100% certainty. Leading off from this, I will discuss the prime aspects of climate physics (notably cloud feedbacks) that lead to uncertainty in climate sensitivity, and discuss current research on means of constraining climate sensitivity.
Decadal scale fluctuations in the rate of warming, such as have received much attention recently, have little or no implication for climate sensitivity, but a range of other approaches imply that it is extremely unlikely that climate sensitivity is so low that unrestrained industrial emissions pose insignificant risk. More importantly, no current constraint rules out values of the climate sensitivity high enough to cause absolutely catastrophic warming, in conjunction with fossil fuel emissions likely to occur in the next two centuries if we do not run out of coal first.