Abstract. Abstract Justus von Liebig observed that one could greatly increase agricultural yields by adding relatively small quantities of nitrogen (N), phosphorus (P) and potassium (K) to soils. This finding led to the most recent agricultural revolution. But because most plants and microbes can be non-homeostatic with respect to their biomass elemental composition, adding nutrients can lead to disproportional increases in some macro-elements in organisms, while micronutrient content decreases. Increased CO2 in the atmosphere is an important driver of climate change, but it is also an important driver of changing biomass content and ecosystem stoichiometry. Increased CO2 has contributed to excess carbon in biomass and ecosystems, a state which could be contributing to changes in metabolism which I liken to metabolic diseases and ‘environmental obesity’. Here I defined environmental obesity as excess C accumulation relative to other elements in the environment. A warming climate is certainly motivation enough for humans to do whatever is necessary to decrease use of fossil fuels. However, increased carbon has detrimental health outcomes through effects on our food in natural and agricultural systems and suggests that CO2 is not ‘just an environmental problem’, but also a human health problem.