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The Aerial Fertilization Effect of Atmospheric CO2 Enrichment: Can We Make a Good Thing Even Better?
Volume 5, Number 25: 19 June 2002

In a fascinating review article, Sage and Coleman (2001) discuss what we know about plant responses to both increases and decreases in the air's CO2 content.  At the most basic of levels - and in the most simple of terms - we can summarize this knowledge by noting that plants photosynthesize at reduced rates and produce less biomass at lower-than-current atmospheric CO2 concentrations, while they photosynthesize at enhanced rates and produce more biomass at higher-than-current atmospheric CO2 concentrations.

At optimal temperatures for C3 photosynthesis, the scientists from the University of Toronto's Department of Botany note that "reducing atmospheric CO2 from the current level to 180 ppm [an approximate 50% reduction] reduces photosynthetic capacity by approximately half," while it "causes biomass to decline by 50%."  Doubling the atmosphere's current CO2 concentration, on the other hand, typically increases photosynthesis and biomass production by 30 to 50%.  In addition, as Sage and Coleman report, "high CO2 concentrations reduce the impact of moderate drought, salinity and temperature stress, and can indirectly reduce low nutrient stress by promoting root growth, nitrogen fixation and mycorrhizal infection," which phenomena boost the basic CO2-induced productivity increase still more, as we have also noted in reviewing the literature on this subject (Idso and Idso, 1994).

All of these observations, of course, are common knowledge among plant biologists; and in the present instance, they but serve as introductory material for Sage and Coleman's provocative new hypothesis, i.e., the idea that modern bioengineering techniques might enable us to make plants even more responsive to increases in the air's CO2 content and thereby, as we have suggested, "make a good thing even better."

Their thinking runs this way.  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, say Sage and Coleman, might not be much above the "critical CO2 threshold at which catastrophic interactions 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 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 what is characteristic of the elevated CO2 conditions of the present.  Hence, the innovative plant scientists conclude that - 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 - there may well be additional and what they call "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 that we cannot allow that to happen.

Dr. Sherwood B. Idso
Dr. Keith E. Idso
Vice President

Idso, K.E. and Idso, S.B.  1994.  Plant responses to atmospheric CO2 enrichment in the face of environmental constraints: a review of the past 10 years' research.  Agricultural and Forest Meteorology 69: 153-203.

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.