Carbon uptake and loss from the Arctic is highly sensitive to climate change, and these processes are poorly represented in computational models of the Earth. A key challenge is representing carbon dioxide uptake by plants in the Arctic. These models rely on details developed in warmer climates. This study provided the first Arctic dataset of two key photosynthetic parameters. The parameters were markedly lower in the models than the values measured on the coastal tundra of northern Alaska. In some case, the values were five-fold lower. On average, the capacity for carbon dioxide uptake by Arctic vegetation is double current model estimates.