A model of carbon dioxide emissions of the USA is presented. The model consists of population, income per capita, economic structure, final and primary energy intensity per sector, primary fuel mix, and emission coefficients. The model is simple enough to be calibrated to observations since 1850. The model is used to project emissions until 2100. Best guess carbon dioxide emissions are in the middle of the IPCC SRES scenarios, but incomes and energy intensities are on the high side, while carbon intensities are on the low side. The confidence interval suggests that the SRES scenarios do not span the range of not-implausible futures. Although the model can be calibrated to reflect structural changes in the economy, it cannot anticipate such changes. The data poorly constrain crucial scenario elements, particularly energy prices. This suggests that the range of future emissions is wider still.