Richard Betts asked, “Can anyone point to any evidence in the peer-reviewed literature that the effect of galactic cosmic rays is large enough to influence global concentrations of cloud condensation nuclei, or their change over the last century or during a solar cycle?”
No, there is a paper I noticed on the shift of the tropical belt that may be germane. http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-11-00244.1
and also http://www.marine.usf.edu/PPBlaboratory/paleolab_pdfs/Poore_GRL04.pdf
With Spencer and Braswell’s recent “Cloud Forcing” dust up this looks like a likely candidate for amplifying solar impact.
GCR change may play a role, may not.