Volume 4, Number 50: 12 December 2001
In a recent review of the scientific literature (165 references), Craig Idso (2001) describes a number of proven biological consequences of elevated atmospheric CO2 concentrations that are well worth recounting.
Idso begins his essay with an overview of basic plant responses to atmospheric CO2 enrichment. The best known of these biological impacts is probably CO2's aerial fertilization effect, which works its wonders on plants that utilize all three of the major biochemical pathways of photosynthesis (C3, C4, CAM). In the case of herbaceous plants, Idso notes this phenomenon typically boosts their productivity by about a third in response to a 300 ppm increase in the air's CO2 content, while it enhances the growth of woody plants by 50% or more.
Next comes plant water use efficiency, which may be defined as the amount of organic matter produced per unit of water transpired by the plant and lost to the atmosphere. This vegetative parameter is directly enhanced by the aerial fertilization effect of atmospheric CO2 enrichment, as well as by its anti-transpirant effect, which is produced by reductions in the number density and degree of openness of leaf stomatal openings that occur at higher atmospheric CO2 concentrations. Here, too, CO2-induced percentage increases as large as - or, more typically, even larger than - those exhibited by plant productivity are commonplace.
One of the important ramifications of this CO2-induced increase in plant water use efficiency, according to Idso, is the fact it enables plants to grow and reproduce in areas that were previously too dry for them. With consequent increases in ground cover in these regions, the adverse effects of wind- and water-induced soil erosion are also reduced, and there is a subsequent tendency for desertification to be reversed and vast tracts of previously unproductive land to become supportive of more abundant animal life, both above- and below-ground, in what could appropriately be called a "greening of the earth."
In addition to helping vegetation overcome the stress of limited water supplies, Idso's review indicates that elevated levels of atmospheric CO2 help plants to better cope with a number of other environmental stresses, such as low soil fertility, low light intensity, high soil and water salinity, high air temperature, high oxidative stress, and the stress of herbivory. When confronted with the specter of global warming, for example, many experiments reveal that concomitant enrichment of the air with CO2 tends to increase the temperature at which plants function at their optimum, often making them even better suited to the warmer environment than they were to the cooler environment to which they were originally adapted. Under the most extreme of stressful conditions, in fact, extra CO2 sometimes is the deciding factor in determining whether a plant lives or dies.
Idso notes that the many benefits of atmospheric CO2 enrichment apply to both agricultural and natural ecosystems; and in this regard he has a wonderful quote from Sylvan Wittwer (1995), the father of modern research in these areas: "The rising level of atmospheric CO2 could be the one global natural resource that is progressively increasing food production and total biological output, in a world of otherwise diminishing natural resources of land, water, energy, minerals, and fertilizer. It is a means of inadvertently increasing the productivity of farming systems and other photosynthetically active ecosystems. The effects know no boundaries and both developing and developed countries are, and will be, sharing equally."
As the air's CO2 content thus continues its upward trend, we can expect the carrying capacity of the planet for both human and other animal life to rise right along with it. Idso cites important studies that verify this expectation for fully 51 terrestrial ecosystems and 22 aquatic ecosystems, noting also that in a study of the vascular plants of 94 terrestrial ecosystems "it was found that ecosystem species richness is more positively correlated with ecosystem productivity than it is with anything else," which finding bodes well indeed for ecosystem biodiversity, which is currently under siege throughout the entire world.
Since trees appear to be the most responsive of all plants to atmospheric CO2 enrichment, it is only natural to expect we would already be seeing evidence of their benefiting from the 100 ppm increase in the air's CO2 content experienced since the inception of the Industrial Revolution. Idso confirms this expectation as well, with information gleaned from 33 publications originating from all parts of the world; and he cites a number of other studies that confirm the planet-wide range expansions that would be expected of woody plants under such circumstances.
An important side-effect of the CO2-stimulated growth of agricultural, forest, and other natural ecosystems is the returning of ever increasing amounts of carbon to the soil. Idso reviews this subject too, presenting evidence that suggests a good portion of the carbon thus sequestered may well be kept from the atmosphere for centuries, if not millennia. In addition to helping reduce the rate of rise of the air's CO2 content - for those who needlessly worry about the highly-hyped but fictional negative consequences of that phenomenon - Idso points out that enhanced soil organic matter storage also provides a host of real-world benefits for both agriculture and nature.
The final subject treated by Idso is the increasing amplitude of the atmosphere's seasonal CO2 cycle, which is evident in the results of multitudinous direct measurements of the air's CO2 concentration performed over the past forty-plus years at a number of locations around the world. Here he cites several studies that show this phenomenon to be primarily the consequence of a concomitant and ongoing increase in the amount and vigor of the totality of earth's vegetation, due, of course, to the growth-promoting effects of the ever-increasing CO2 content of the atmosphere.
In concluding his treatise, Idso sees nothing but a bright and shining future for earth's biosphere as a consequence of continued anthropogenic CO2 emissions. We agree. It should be acknowledged, however, that many of mankind's other activities are not so beneficial. In fact, they are often detrimental; and these negative phenomena must be dealt with appropriately wherever they occur, on a local case-by-case basis. Fortunately, elevated levels of atmospheric CO2 often help in this regard, such as when they reduce the apertures of stomates on plant leaves and thereby curtail the entry of harmful air pollutants into vegetation, as also described by Idso.
Yes, the benefits of atmospheric CO2 enrichment are truly incredible; and that is why we sometimes refer to this wonderful "greenearth gas" as the elixir of life. Please help us spread the word. Policy makers at all levels of government the world over have got to understand these important facts; and the only people who can make it happen are you, our many faithful readers.
Dr. Sherwood B. Idso
Dr. Keith E. Idso
Idso, C.D. 2001. Earth's rising atmospheric CO2 concentration: Impacts on the biosphere. Energy & Environment 12: 287-310.
Wittwer, S.H. 1995. Food, Climate, and Carbon Dioxide: The Global Environment and World Food Production. Lewis Publishers, Boca Raton, FL.