Our analysis of the new ISCCP (International Satellite Cloud Climatology Project) D2 cloud data reveals that there is a correspondence between the low cloud cover and the galactic cosmic ray flux. Using several proxies for solar activity and the radiative forcing for the ISCCP cloud types, we estimate the possible impact that such a solar-terrestrial connection may have on climate and find that much of the warming of the past century could be quantitatively accounted for by the direct and indirect effects of solar activity. We have also analysed the behaviour of the available proxies for cloud cover existing for the last century, searching for the cloud cover decrease predicted by the low cloud-cosmic ray flux correlation. The sunshine records and the synoptic cloud records both indicate that the total cloud cover over the oceans has increased during the past century but the evidence for a low cloud decrease is unclear.