Some results relevant to the discussion of a possible link between cosmic rays and the Earth's climate

Based on a 16-year observation period (1980-1995), it was claimed recently that Earth's climate was linked to variations in the flux of cosmic rays penetrating into the atmosphere via their postulated effect on global cloud cover. Data from three independent studies yield information relevant to the ongoing discussion of the likelihood of the existence of such a link. (1) Model calculations show that the relative change in the ion production rate from a solar maximum to a solar minimum is of the same order as, or even greater than,the corresponding change in global cloud cover. (2) However, the smoothed combined flux of Be-10 and Cl-36 at Summit, Greenland, from 20-60 kyr B.P. (proportional to the geomagnetically modulated cosmic ray flux) is unrelated to the corresponding delta O-18 and CH4 data (interpreted as supraregional climate proxies). (3) Furthermore, although a comparison of the incoming neutron flux with cloud cover in Switzerland over the last 5 decades shows a significant correlation at times during the 1980s and 1990s, this does not occur during the rest of the period.