The long term variation of the cosmic ray ionization rate has been studied. This rate shows a cyclic variation with a period of roughly twice the 11 year cycle for the data available since the 1950s. The structures seen in the variation of the long term cosmic ray ionization rate with time are shown to be present in the variation of the mean daily sun spot number, solar irradiance and in the variation of the mean global surface temperature. Hence we report a possible observation of a cyclical variation in each of these quantities of a similar period. The cyclic variation of the global temperature is found to be in phase with the solar cycle as measured from the sun spot numbers and the solar irradiance and in antiphase with the cosmic ray variation. However, the cyclic variation of the CR cycle is delayed by 2–4 years. This indicates that, if it is real, the correlation is most likely caused by direct solar activity rather than by cosmic rays.
The long term variations of each of the cosmic ray rate and the solar irradiance are observed to be less than their cyclic variations. Therefore, assuming that there is a causal link between either of them with the mean global surface temperature, the long term variation of the temperature must be less than the amplitude of its cyclic variation of 0.07°C. Hence within our assumptions, the effect of varying solar activity, either by direct solar irradiance or by varying cosmic ray rates, must be less than 0.07°C since 1956 i.e. less than 14% of the observed global warming.
Add this to your quivers for the next time the Inhofe-Morano/Watts/ICECAP crowd tries to float the cosmic ray claim.