Comments on ``Variation of cosmic ray flux and global cloud coverageAa missing link in solar-climate relationships'' by Henrik Svensmark and Eigil Friis-Christensen [Journal of Atmospheric and Solar-Terrestrial Physics 59 (1997) 1225-1232]

An often used method in geophysical investigations is to correlate the time series of two phenomena, and if a ``good'' correlation is found, a cause-effect relation is implied. In their search for a physical mechanism that might explain the correlations between solar activity and the Earth's climate which have been reported in innumerable papers during the past two centuries (see Hoyt and Schatten, 1997 and references therein) Svensmark and Friis-Christensen (1997) [henceforth SF-C], compared observations of cloud cover and cosmic particles and concluded that variation in global cloud cover was correlated with the cosmic ray flux from 1980 to 1995. They proposed that the observed variation in cloud cover seemed to be caused by the varying solar activity related cosmic ray flux and postulated that an accompanying change in the Earth's albedo could explain the observed correlations between solar activity and climate. In this paper we claim that an observed change in cloud cover can be attributed to a change in the flux of cosmic particles only if (1) there is a significant correlation between the flux of cosmic particles and the observed impact on cloud cover, (2) the impact has a physical basis, and (3) other explanations can be ruled out. We will show that neither of these requirements are fulfilled, and accordingly that evidence supporting the mechanism of cosmic rays affecting the cloud cover and hence climate does not exist.