We examined recent radial growth increases in western juniper trees using an 11-site chronology dating from AD 1000–2006. By various measures, radial growth during the late 20th/early 21st centuries was exceptional, with increases occurring absent of regional climatic change. We found that 54% of annual radial growth variability was explained by June Palmer Drought Severity Index (PDSI) values, but the inclusion of atmospheric CO₂ values accounted for a 14% increase in explanatory power. We reconstructed June PDSI both including and excluding CO₂, and found that PDSI values were overestimated at the end of the record with CO₂ omitted from the model. We conclude that: 1) western juniper radial growth was associated with rising CO₂ during the late 20th/early 21st centuries; and, 2) the use of CO₂-sensitive trees such as western juniper for dendroclimatic reconstructions may influence the results if the impacts of CO₂ fertilization are omitted.