A relationship is identified between the largest (top 5%) most rapid global increases in ISCCP retrieved IR cloud cover and statistically significant increases in the rate of galactic cosmic ray (GCR) flux across the globe; the cloud changes correspond both temporally and spatially to significant variations in a range of NCEP/NCAR reanalysis parameters, including: air temper-ature and pressure. We suggest that because the influence of GCR on cloud cover is likely a second order effect, the use of datasets internal to the climate system has allowed us to identify a strong relationship where previously none has been found. The cloud-climate interaction ob-served indicates an indirect forcing mechanism operating via an alteration to polar circulation. An attempt has been made to simulate the observed climate anomalies by modifying cloud cover directly within a general circulation model (GCM), thus allowing us to comment on the casual relationship between the observed cloud/climate changes.