The validity of the hypothesis that galactic cosmic ray flux (CRF) may be driving global climate through an effect on low-clouds was investigated. A literature review revealed uncertainty regarding almost all aspects of the hypothesis, particularly the apparent CRF-low cloud correlations and the proposed mechanisms. While the hypothesis has potential, there is currently insufficient evidence to accept it as a climate driver. A radiative-convective climate model was developed to test the relative importance of greenhouse gases and the proposed CRF-Cloud-Climate Hypothesis to the global warming experienced over the past century. It was found that a CRF-low cloud link could explain some of the small-scale variability in the global temperature trend, but not the large-scale global warming. It should be noted that there is significant uncertainty in the results of such a simple climate model. Further investigation into the CRF-Cloud-Climate Hypothesis, through atmospheric, laboratory and modelling experiments, is recommended.