In a broad review of the scientific literature, Idso (2001) describes a number of biological consequences of elevated atmospheric CO2 concentrations. The best known of these important 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 and CAM). In the case of herbaceous plants, this phenomenon typically boosts their productivities 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 (see our website's Plant Growth Data section).
Next comes plant water use efficiency, which may be defined as the amount of organic matter produced per unit of water transpired to the atmosphere. This 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 CO2-induced decreases in the number density and degree of openness of leaf stomatal apertures that occur at higher atmospheric CO2 concentrations. Here, too, CO2-induced percentage increases as large as, or 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 is the fact that 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. Hence, there is a tendency for desertification to be reversed and for 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, elevated levels of atmospheric CO2 help plants to better cope with other environmental stresses, such as low soil fertility, low light intensity, high soil and water salinity, high air temperature, various oxidative stresses and the stress of herbivory. When confronted with the specter of global warming, for example, many experiments have revealed 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 stressful of such conditions, in fact, extra CO2 sometimes is the deciding factor in determining whether a plant lives or dies.
These benefits of atmospheric CO2 enrichment apply to both agricultural and natural ecosystems; and as Wittwer (1995) has noted, "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." This phenomenon is thus a means, he says, "of inadvertently increasing the productivity of farming systems and other photosynthetically active ecosystems," and that "the effects know no boundaries and both developing and developed countries are, and will be, sharing equally."
In light of these several observations, plus the fact that the air's CO2 content has risen substantially over the past two centuries -- especially since 1950 -- one would expect to see some evidence of the "greening of the earth" (Idso, 1986) that they imply. Hence, in what follows, we summarize the results of some of the scientific journal articles we have reviewed on our website that deal with this phenomenon on the scale of the entire earth.
Each spring, when the Northern Hemisphere's vegetation awakens from the dormancy of winter and begins to grow again, it removes enough carbon dioxide from the atmosphere to reduce the air's CO2 content by several parts per million. Then, in the fall, when much of this vegetation dies and decays, it releases huge quantities of carbon dioxide back to the atmosphere, raising the air's CO2 content by a small amount. Together, these two phenomena produce a seasonal oscillation that is superimposed upon the yearly incremental rise in the air's mean CO2 concentration; and the greater the yearly growth of the planet's vegetation, the greater are the yearly down- and up-swings in the amount of carbon dioxide in the air. Consequently, the amplitude of the atmosphere's seasonal CO2 oscillation serves as a good relative measure of the planet's total vegetative productivity in any given year.
Detailed measurements of this phenomenon at Mauna Loa, Hawaii have revealed the biosphere's seasonal CO2 "inhalations" and "exhalations" to be growing more and more pronounced each year, as the atmosphere's mean CO2 content rises with time. Over the period 1958-1999, for example, this "breath of the biosphere" increased by approximately 20%, primarily as a direct result of atmospheric CO2 fertilization (Pearman and Hyson, 1981; Cleveland et al., 1983; Bacastow et al., 1985; Enting, 1987; Kohlmaier et al., 1989; Keeling et al., 1996), nitrogen-deposition-induced increases in the growth rates of earth's ecosystems (Shindler and Bayley, 1993; Hudson et al., 1994; Galloway et al., 1995), and CO2-induced expansions of some of their ranges (Idso, 1995). Modest temperature increases in some parts of the globe may also have augmented the phenomenon (Keeling et al., 1996; Myneni et al., 1997).
Other studies have produced still other evidence for the worldwide increase in vegetative productivity that is implied by the preceding evidence to have occurred since the inception of the Industrial Revolution. Joos and Bruno (1998), for example, used ice core data and direct observations of atmospheric CO2 and 13C to reconstruct the histories of terrestrial and oceanic uptake of anthropogenic carbon over the past two centuries. In doing so, they discovered the biosphere typically acted as a source of CO2 during the 19th century and the first decades of the 20th century, but that it subsequently "turned into a sink."
Hard on the heels of this development, Luz et al. (1999) used a series of empirically-derived mathematical relationships to develop a model of the isotopic composition of oxygen trapped in air bubbles in a Greenland ice core to estimate global biospheric productivity over the past 82,000 years. Their work suggested that productivity at 18,000, 26,000, 37,000, 56,000 and 82,000 years before present was, respectively, 89%, 91%, 87%, 97% and 91% of what it is "currently," at a gas age of 150 years, when the atmospheric CO2 concentration was approximately 280 ppm.
These results imply that biospheric productivity is currently at its highest point of the past 82,000 years, as is the atmosphere's CO2 concentration. Hence, assuming the air's CO2 content is the primary determinant of biospheric productivity, and based on the authors' mean results for the five periods they investigated, we calculate that the 73-ppm increase (from 207 to 280 ppm) in the air's CO2 concentration between "then" and "now" produced a 9.9% increase (from a then/now productivity ratio change of 0.91 to 1.00) in planet-wide biospheric productivity. Further assuming a linear relationship between these two parameters, we calculate that a 300 ppm increase in atmospheric CO2 concentration would produce an approximate 40% increase in biospheric productivity, which is essentially the mean value of the CO2-growth response that has been derived from the thousands of studies that have evaluated this phenomenon for hundreds of earth's plants.
Is this a great coincidence? Or is it a great vindication? … a vindication of what we have been saying for so many years now, i.e., that atmospheric CO2 fuels the biosphere, and that adding it to the air increases the productivity of the total assemblage of life on earth? Others may try to explain away this striking comparison and its logical implications or simply ignore them. We, however, accept them for what they are: indisputable facts of observation and deduction.
In closing, we report the results of the study of Alexandrov and Oikawa (2002), who constructed a model of biospheric productivity based on empirical observations. Applied to the period 1980-90, it suggests that the total terrestrial carbon sink induced by the aerial fertilization effect of the contemporaneous increase in the air's CO2 content was approximately 1.3 Pg C yr-1, which result compares well with estimates of up to 1.1 Pg C yr-1 derived from independent empirical observations of same-period anthropogenic CO2 emissions, changes in land use, CO2 uptake by the world's oceans, and increases in the air's CO2 concentration.
As for the future, Sage and Coleman (2001) suggest that things could improve in still other ways. During the peak of the last ice age and throughout the bulk of all prior ice ages of the past two million years, atmospheric CO2 concentrations have tended to hover at approximately 180 ppm. This value, according to Sage and Coleman, might not be much above the critical CO2 threshold at which serious negative effects on plant growth occur. Hence, they reasonably speculate that plants of the late Pleistocene "might have been adapted to lower CO2 concentrations than currently exist."
In light of the short period of evolutionary time (a mere 15,000 years) since these low-CO2 conditions predominated, the two scientists advance the logical thought that "many if not most plants might still be adapted to CO2 levels much lower than those that exist today," even though thousands of experiments have demonstrated that earth's vegetation responds in dramatic positive fashion to atmospheric CO2 enrichment far above current CO2 concentrations. Hence, as good as things currently are, and as significantly better as they are expected to become as the air's CO2 content continues to rise, they conclude there may well be "substantial room for natural selection and bioengineering to remove the constraints [of low CO2 adaptation], thereby creating novel genotypes able to exploit high CO2 conditions to best advantage."
How important are these ideas? Sage and Coleman state that the low CO2 levels of the past "could have had significant consequences for much of the earth's biota." In fact, they suggest that the origin of agriculture itself "might have been impeded by reduced ecosystem productivity during low CO2 episodes of the late Pleistocene." Since that time, however, the increase in the air's CO2 content has essentially doubled the biological prowess of the planet's vegetation; and projected increases in the air's CO2 content could readily lead to a tripling of the paltry productivity of earth's ice-age past. On top of these phenomenal benefits, Sage and Coleman suggest there may be still other opportunities to improve plant performance even more, by using modern bioengineering techniques to overcome genetic constraints linked to adaptations to low levels of CO2 that may persist in many of earth's plants. Indeed, they note that for agriculture, "this could be a major opportunity to improve crop productivity and the efficiency of fertilizer and water use."
Truly, we are living in an age of unparalleled biological promise, which to a person of the distant past - or even some of us - would appear to be almost beyond belief. The fullness of that promise, however, has yet to be achieved; and how effectively we exploit the opportunities to do so, say Sage and Coleman, "will depend on our ability to conduct the basic research [needed] to identify the genes controlling acclimation and adaptation to CO2 variation."
This effort, together with the public education effort required to stem the tide of irrational pessimism promulgated by climate alarmists intent on living in the past, must be strongly supported if we are to successfully meet the challenges that confront us. Without the dual benefits of the aerial fertilization effect of atmospheric CO2 enrichment and the development of plant genotypes that can take full advantage of this phenomenon, we are almost certainly assured of being unable to feed the burgeoning human population of the planet but a few short decades from now. Morality clearly dictates we cannot allow that to happen.
Alexandrov, G. and Oikawa, T. 2002. TsuBiMo: a biosphere model of the CO2-fertilization effect. Climate Research 19: 265-270.
Bacastow, R.B., Keeling, C.D. and Whorf, T.P. 1985. Seasonal amplitude increase in atmospheric CO2 concentration at Mauna Loa, Hawaii, 1959-1982. Journal of Geophysical Research 90: 10,529-10,540.
Cleveland, W.S., Frenny, A.E. and Graedel, T.E. 1983. The seasonal component of atmospheric CO2: Information from new approaches to the decomposition of seasonal time-series. Journal of Geophysical Research 88: 10,934-10,940.
Enting, I.G. 1987. The interannual variation of carbon dioxide concentration at Mauna Loa. Journal of Geophysical Research 92: 5497-5504.
Galloway, J.N., Schlesinger, W.H., Levy II, H., Michaels, A. and Schnoor, J.L. 1995. Nitrogen fixation: Anthropogenic enhancement -- environmental response. Global Biogeochemical Cycles 9: 235-252.
Hudson, R.J.M., Gherini, S.A. and Goldstein, R.A. 1994. Modeling the global carbon cycle: Nitrogen fertilization of the terrestrial biosphere and the "missing" CO2 sink. Global Biogeochemical Cycles 8: 307-333.
Idso, C.D. 2001. Earth's rising atmospheric CO2 concentration: Impacts on the biosphere. Energy & Environment 12: 287-310.
Idso, S.B. 1986. Industrial age leading to the greening of the Earth? Nature 320: 22.
Idso, S.B. 1995. CO2 and the Biosphere: The Incredible Legacy of the Industrial Revolution. Special Publication. Department of Soil, Water and Climate, University of Minnesota, St. Paul, MN.
Joos, F. and Bruno, M. 1998. Long-term variability of the terrestrial and oceanic carbon sinks and the budgets of the carbon isotopes 13C and 14C. Global Biogeochemical Cycles 12: 277-295.
Keeling, C.D., Chin, J.F.S. and Whorf, T.P. 1996. Increased activity of northern hemispheric vegetation inferred from atmospheric CO2 measurements. Nature 382: 146-149.
Kohlmaier, G.H., Sire, E.O., Janecek, A., Keeling, C.D., Piper, S.C. and Revelle, R. 1989. Modeling the seasonal contribution of a CO2-fertilization effect of the terrestrial vegetation to the amplitude increase in atmospheric CO2 at Mauna Loa Observatory. Tellus Series B 41: 487-510.
Luz, B., Barkan, E., Bender, M.L., Thiemens, M.H. and Boering, K.A. 1999. Triple-isotope composition of atmospheric oxygen as a tracer of biospheric productivity. Nature 400: 547-550.
Myneni, R.B., Keeling, C.D., Tucker, C.J., Asrar, G. and Nemani, R.R. 1997. Increased plant growth in the northern high latitudes from 1981 to 1991. Nature 386: 698-702.
Pearman, G.I. and Hyson, P. 1981. The annual variation of atmospheric CO2 concentration observed in the northern hemisphere. Journal of Geophysical Research 86: 9839-9843.
Sage, R.F. and Coleman, J.R. 2001. Effects of low atmospheric CO2 on plants: more than a thing of the past. TRENDS in Plant Science 6: 18-24.
Schindler, D.W. and Bayley, S.E. 1993. The biosphere as an increasing sink for atmospheric carbon: Estimates from increased nitrogen deposition. Global Biogeochemical Cycles 7: 717-734.
Wittwer, S.H. 1995. Food, Climate, and Carbon Dioxide: The Global Environment and World Food Production. Lewis Publishers, Boca Raton, FL.