There are many ways to calculate how plants take up carbon. The challenge, in part, is scaling these approaches to global levels. Why? Because of the hypotheses behind each approach. Often, the hypothesis relies on data at such a small scale (molecules) that it is hard to scale up. To see how the different ways of determining carbon uptake affect global models, the team compared hypotheses for the maximum photosynthetic carboxylation rate. The rate is one of two plant traits that closely determine the photosynthetic rate. Scientists compared how various hypotheses calculated the carboxylation rate. Each method varied. The resultant variability in predictions has not yet been investigated in detail.