New results from the Coupled Model Intercomparison Project phase 5 (CMIP5) and multiple global reanalysis datasets are used to investigate the relationship between the mean and standard deviation (SD) in the surface air temperature (SAT) at intra- and inter-annual timescales. A combination of a land – sea mask and orographic filter was used to investigate the geographic region with the strongest correlation and in all cases this was found to be for low-lying over-land locations. This result is consistent with the expectation that differences in the effective heat capacity of the atmosphere are an important factor in determining the SAT response to forcing.