There is general concern that the rapid increase in atmospheric CO₂ concentration will lead to reduced stomatal conductance and subsequent increases in leaf temperature. Such an increase in leaf temperature is expected to adversely impact a plethora of processes connected to leaf metabolism and microbial/fungal communities on leaves. A model is proposed that combines the leaf energy balance with leaf gas exchange and photosynthesis to explore such issues. The model represents a hybrid ecological/physiological approach described by systems of equations based on steady-state leaf-gas exchange theories and leaf energy/radiation balance, equilibrium thermodynamics within the leaf, stomatal data, and atmospheric CO₂ concentration. The model allows separating air from leaf temperatures thereby permitting exploration of the dependence of leaf cooling or heating for any combination of environmental conditions (e.g., wind velocity, atmospheric humidity, and atmospheric CO₂ level), anatomic leaf properties (e.g., leaf size), and physiologic quantities (e.g., assimilation rate and transpiration rate). The model permits to distinguish whether leaf cooling or heating is to be expected if these parameters are varied. Based on model calculations, it is shown that leaf temperature is far more impacted by leaf size or wind speed than reduction in stomatal conductance caused by elevated atmospheric CO₂. The model results are consistent with measurements of leaf cooling and heating.