Question Are plant traits more closely correlated with mean annual temperature, or with mean annual precipitation? Location Global. Methods We quantified the strength of the relationships between temperature and precipitation and 21 plant traits from 447,961 species-site combinations worldwide. We used meta-analysis to provide an overall answer to our question. Results Mean annual temperature was significantly more strongly correlated with plant traits than was mean annual precipitation. Conclusions Our study provides support for some of the assumptions of classical vegetation theory, and points to many interesting directions for future research. The relatively low R2 values for precipitation might reflect the weak link between mean annual precipitation and the availability of water to plants.