<P> Because of concerns that greenhouse experiments might not adequately simulate the actual environment (such as competing plants), scientists developed Free - air carbon dioxide enrichment (FACE) experiments . In this procedure, plants are grown outdoors, and the CO concentration of the surrounding air is artificially elevated . FACE experiments, using generally lower CO levels than the greenhouse studies, showed lower gains in growth than greenhouse studies, with the gains depending heavily on the species under study . A 2005 review of 12 experiments at 475 - 600 ppm showed an average gain of 17% in crop yield, with legumes typically showing a greater response than other species, and C4 plants generally showing less . The review also stated that the reviewed experiments have their own limitations . The studied CO levels were lower, and most of the experiments were carried out in temperate regions . </P> <P> A 2017 article describes research that shows how increased CO levels have a negative impact on a variety of human food crops, by increasing the levels of carbohydrates, such as glucose, while decreasing the levels of important nutrients such as protein, iron, and zinc . Crops experiencing a decrease in protein include rice, wheat, barley and potatoes . </P> <P> The Earth's oceans contain a large amount of CO in the form of bicarbonate and carbonate ions--much more than the amount in the atmosphere . The bicarbonate is produced in reactions between rock, water, and carbon dioxide . One example is the dissolution of calcium carbonate: </P> <Dl> <Dd> CaCO 3 + CO + H 2O ⇌ Ca 2 + + 2 HCO − </Dd> </Dl>

Where does the carbon dioxide go once it is in our atmosphere