Carbon-climate feedback has been identified as one of the key areas of synthesis for the next Inter-governmental Panel on Climate Change (IPCC); however, most of the models on which the IPCC will rely are yet to consider vital interactions between nitrogen (N) and carbon (C) cycles. A major impediment to including N limitation in model predictions has been the lack of constraint to rates of N fixation worldwide. Here we use a theoretical framework that considers interactions of C and nutrients to estimate rates of terrestrial N fixation, and thereby examining how the constraints of N on land C uptake and global warming. We show that most global models without nutrient limitations significantly overestimated land C uptake, thus underestimating both the pace and magnitude of the predicted global warming. We suggest that the next IPCC assessment should consider nutrient constraints on carbon-climate feedback and the pace of global warming.