Variation of cosmic ray flux and global cloud coverage-a missing link in solar-climate relationships

In the search for a physical mechanism that could account for reported correlations between solar activity parameters and climate, we have investigated the global cloud cover observed by satellites. We find that the observed variation of 3-4% of the global cloud cover during the recent solar cycle is strongly correlated with the cosmic ray flux. This, in turn, is inversely correlated with the solar activity. The effect is larger at higher latitudes in agreement with the shielding effect of the Earth's magnetic field on high-energy charged particles. The observed systematic variation in cloud cover will have a significant effect on the incoming solar radiation and may, therefore, provide a possible explanation of the tropospheric and stratospheric 10-12 year oscillations which have been reported. The above relation between cosmic ray flux and cloud cover should also be of importance in an explanation of the correlation between solar cycle length and global temperature, that has been found.