It has been widely observed that recent increases in atmospheric CO₂ concentrations have had, so far, a positive effect on the growth of plants. This is not surprising since CO₂ is an important nutrient for plant matter, being directly involved in photosynthesis. However, it is also known that the conditions which have accompanied this increase in atmospheric CO₂ concentration have also had significant effects on other environmental factors. It is possible that these other effects may emerge as limiting factors which could act to prevent plant growth. This may involve complex interactions between prevailing sunlight and water conditions, variable temperatures, the availability of essential nutrients and the type of synthetic pathway for the plant species. The issue of concern to this investigation is if we should be worried about a possible shift in the C₃-C₄ paradigm driven by changes in the atmospheric CO₂ concentration, or if some other factor, such as water scarcity, is much more relevant within a 30-year time frame. If an opinion is needed on what will have the worst effect on the survival of the planet between the scarcity of water or the reduced efficiency of C₃ plants to sequester CO₂, the issue of water is the more incisive.
Keywords: C3 species; C4 species; CO2 enrichment; carbon cycle; photosynthesis.