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Center for the Study of Carbon Dioxid and Global Change

Atmospheric CO2 Enrichment Increases Quantity of Plant Biomass Without Sacrificing Quality 
Volume 4, Number 13: 28 March 2001

It goes without saying (but we'll say it anyway because of its great importance) that the more CO2 there is in the air, the bigger and better plants grow. Most of us learned this simple truth in elementary school; and it is reassuring to know that some things, like this particular fact, never change. Thousands upon thousands of experiments later, it still remains one of the fundamental verities of biology that plants just love CO2. And why shouldn't they? It's their food! 
But what about the rest of the biosphere? What about the herbivorous animals that feed on plants? The carnivorous animals that devour them? And we humans, who eat about everything imaginable? Is food grown in CO2-enriched air as desirable as food produced in ambient air? We know the quantity of vegetable biomass tends to rise with increases in atmospheric CO2 concentration. But what about quality? Are there any changes in the health-promoting or medicinal properties of plants when they're grown in air that is more highly endowed with CO2 than is currently the case?

In a comprehensive new review of this subject, Idso and Idso (2001) summarize what is known. They note, first of all, that significant increases in the air's CO2 concentration often lead to small reductions in the protein concentrations of animal-sustaining forage and human-sustaining cereal grains when soil nitrogen concentrations are sub-optimal. When these crops are supplied with adequate nitrogen, however, as is typical of modern farming techniques, the Idsos report that "no such reductions are observed."

But not all countries have ready access to commercial fertilizers. What happens in those cases? Does food quality decline? Probably not. The rate of rise of the atmosphere's CO2 concentration is only a couple parts per million per year, which is fully two orders of magnitude less than the CO2 increases employed in most experiments that show small reductions in plant protein contents when soil nitrogen concentrations are less than adequate; and there are many ways in which the tiny amount of extra nitrogen needed to maintain current crop protein concentrations in the face of such a small yearly increase in the air's CO2 concentration may be readily acquired.

For one thing, crops experiencing rising levels of atmospheric CO2 will likely produce larger and more-branching root systems (as they typically do in experiments when exposed to elevated CO2 concentrations), which should allow them to more effectively explore ever larger volumes of soil for the extra nitrogen and other nutrients the larger CO2-enriched crops will need as the air's CO2 content continues to rise. Also, tiny bacteria and algae that remove nitrogen from the air and make it directly available to plants are found nearly everywhere; and elevated atmospheric CO2 concentrations typically enhance their ability to perform this vital function. Hence, as these phenomena are gradually enhanced by the slowly rising CO2 content of the air, the slowly rising nutrient requirements of both crops and natural vegetation should be easily satisfied; and plant protein concentrations should therefore be maintained, at the very least, at their current levels.

In the case of other important plant constituents, atmospheric CO2 enrichment is much more than neutral; it clearly makes good things better. Elevated CO2 concentrations have been shown to increase the concentration of vitamin C in various fruits and vegetables, for example; and it increases the concentrations of disease-fighting substances in plants that are prized for their medicinal properties. In experiments with the woolly foxglove (Digitalis lanata), for example, in addition to increasing plant biomass by 63 to 83%, a near-tripling of the air's CO2 content increased the concentration of heart-helping digoxin by 11 to 14%. And in the tropical spider lily (Hymenocallis littoralis), in addition to increasing plant biomass by 56%, a 75% increase in the air's CO2 content increased the concentrations of five different substances proven effective in treating a number of human cancers (melanoma, brain, colon, lung, renal) and viral diseases (Japanese encephalitis and yellow, dengue, Punta Tora and Rift Valley fevers) by 6 to 28%.

After reviewing many other aspects of the impact of atmospheric CO2 enrichment on plant tissue composition, the Idsos conclude by saying it is likely that "the ongoing rise in the air's CO2 content will continue to increase food production around the world, while maintaining the nutritive quality of that food and enhancing the production of certain disease-inhibiting plant compounds." Yes, what's happening to the world in terms of its atmospheric CO2 concentration is not only helping to meet the caloric requirements of the planet's burgeoning human and animal populations; it's helping to meet their nutritional and medicinal requirements as well.

In the vernacular of nature, therefore, it is evident that when the atmosphere tells the biosphere "I love you," it says it with CO2. So why not do the same? Send the biosphere a love note. Rev up your clean-burning vehicle and take a trip through the countryside to admire the flowers. And take some pride in it. After all, the colorless, odorless, non-polluting CO2 coming from your vehicle's tailpipe helps make the flowers what they are: big and beautiful, and ever more nutritious to the humming birds, bees and other insects that depend on them for food.

Dr. Craig D. Idso
President Dr. Keith E. Idso
Vice President 

PS: We're not kidding! See Flowers in our Subject Index..

Idso, S.B. and Idso, K.E. 2001. Effects of atmospheric CO2 enrichment