The 1973 “Miami Model” was the first global-scale empirical model of terrestrial net primary productivity (NPP), and its simplicity and relative accuracy has led to its continued use. However, improved techniques to measure NPP in the field and the expanded spatial and temporal range of observations have prompted this study, which re-examines the relationship of climatic variables to NPP. We developed several statistical models with paired climatic variables in order to investigate their relationships to terrestrial NPP. A reference dataset of 3034 NPP field observations was compiled for calibration and parameter optimization. In addition to annual-mean temperature and precipitation, as in the Miami Model, we chose more ecologically relevant climatic variables including growing degree-days, a soil moisture stress index, and surface photosynthetically active radiation (PAR). Calculated annual global NPP ranged from 50–60 Pg-C yr–1, within the estimates of previous studies. Comparisons of geographic patterns of NPP were made using biome and latitudinal averages, and model performance was evaluated using observed data.