Constraining the Sensitivity of Regional Climate with the Use of Historical Observations

A novel method is presented for calculating how sensitive regional climate is to radiative forcings, based on global surface temperature observations. Forcings that originate in both the region of interest and outside of it are taken into account. It is found that the transient temperature sensitivity parameter (b, defined as the observed temperature response per unit forcing) can be better constrained for 508S–258N than for the rest of the globe. The average b in this region is 0.358C (W m22)21. The models used in the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4) 1% yr21 CO2 increase experiment exhibit a b in this region that, on average, is higher by 35%. The results show that for 508S–258N b may provide a more valuable constraint for model evaluation than global mean climate sensitivity.