Recent measurements by Stuiver and Quay1 on wood growth during the past millennium confirm in an impressive way the contention that, in addition to being affected by the geomagnetic dipole moment, the production rate of 14C is mediated by interplanetary modulation arising from solar activity, of which the sunspot index is a measure. But Stuiver2, like others before him, finds no statistically significant correlation with climate indicators, including ring-width data and δ14C. However, the data presented here show a case of an unusually convincing correlation between variations of cosmic ray-produced 14C activity of the CO2 in the terrestrial atmosphere during the past five millennia3,4 and annual growth ring widths for bristlecone pine wood from one particular area, that of Campito Mountain in eastern California.