Photosynthetic responses of C4 leaves are less sensitive to high CO2 than that of C3 leaves while reduction in stomatal conductance (gs) is consistent between C3 and C4 plants. Lowered gs might be a response of both lowered stomatal density and opening, and can result in increased foliage temperatures which may alter the dependence of photosynthesis to air temperature under elevated CO2. Acclimation responses such as reduced carboxylation efficiency (CE) may occur in response to high CO2. Reduced CE is thought to be a result of decreased C4 enzyme activities, primarily of PEP carboxylase. In order to make predictions of these complex gas exchange responses in C4 plants under climate change scenarios, a model that takes into account physical and biochemical mechanisms of gas exchange processes is necessary. We developed a comprehensive model of gas exchange processes in C4 leaves by combining a biochemical model of C4 photosynthesis, stomatal conductance models and the energy balance equation. Whole-canopy gas exchange processes were scaled up from the leaf responses based on the sun-shade leaf classes method. Here we present a synopsis of the model and its behavior as well as model predictions of the effects of elevated CO2 and increased atmospheric temperature on photosynthesis and water relations in C4 maize.