A new method of assessing Climate Sensitivity.

Chris Barnes

Abstract— The IPCC regards carbon dioxide as the most relevant driver of climate warming and their Sixth Assessment Report (AR6) refines this to a likely range of 2.5°C to 4.0°C and a very likely range of 2.0°C to 5.0°C for climate sensitivity to a doubling of present levels of atmospheric carbon dioxide. Since this is a very large range the need exists to find a method to better quantify climate sensitivity. Previous methods do not consider that there could be other hitherto undiscovered climate drivers, which may be heavily inter-correlated with carbon dioxide. Such a driver is magnetic pole shift, which via energetic particle precipitation impacts on cloud albedo, which would be expected to mimic the effect of a non-constant climate feedback. Climate sensitivity is usually estimated by direct observation of SST and cloud tops or by Global Climate models. The question posited here is concerned with how much the temperature increase is due to pole shift induced albedo reduction and how much it is due to CO2. Granger causality is employed to confirm the validity of the method and independent paleo-climate data is employed together with the GISTEMP v4 dataset to develop a simple new method to estimate climate sensitivity, which works because carbon dioxide concentration was almost flat in the two warm periods preceding the industrial era. The model yields a range of climate sensitivities for a doubling of CO2 of between .105K and .318K depending on the date range of the modern warming data set employed. Higher sensitivity occurs post 1970. A sensitivity of .372 K for doubling was required to produce the best retrospective model data fit. This is probably an overestimate, as other warming factors were not modelled