More convincing than a hypothesized cosmic ray effect which, if so large and significant, should be relatively easy to measure in some way. (climate-skeptic.com)
Solar irradiance change has a strong spectral dependence [Lean, 2000], and resulting climate changes may include indirect effects of induced ozone change [RFCR; Haigh, 1999; Shindell et al., 1999a] and conceivably even cosmic ray effects on clouds [Dickinson, 1975]. (realclimate.org)
Many scientists doubt the significance of these cosmic ray effects, but Svensmark sees the question as ripe for investigation. (discovermagazine.com)