“Redemption of the Beast” (part 2)
The Miracle of Photosynthesis
A study of the effects of CO2 enrichment on trees in a controlled environment was published in 1985 and its findings were consistent with earlier experiments.
“Seedlings of two tree species from the Atlantic lowlands of Costa Rica, Ochroma la-gopus Swartz, a fast growing pioneer species, and Pentaclethra macroloba (Willd.) Kuntze, a slower-growing climax species, were grown under enriched atmospheric CO2 in controlled environment chambers. Carbon dioxide concentrations were maintained at 350 and 675 [ppm] . . . Total biomass of both species increased significantly in the elevated CO2 treatment; the increase in biomass was greatest for the pioneer species, O. lagopus. Both species had greater leaf areas and specific leaf weights with increased atmospheric CO2. . . Stomatal conductances of both species decreased with CO2-enrichment resulting in significant increases in water use efficiency.” [see: Oberbauer, Steven F., Boyd R. Strain & Ned Fetcher (1985) Effect of CO2-enrichment on seedling physiology and growth of two tropical tree species: Physiologia Plantarum, vol. 65, Issue 4 (Dec.) pp. 352-356.]
In a report appearing in 1987, coauthored by none other than Roger Revelle, to whom Al Gore attributes his interest in climate change (as described in An Inconvenient Truth) there was an acknowledgement of the positive side of carbon dioxide effects:
“A large number of CO2 stimulation experiments with selected plant communities in controlled or semi controlled environments suggest that the annual production and biomass accumulation is increased at elevated CO2 concentrations . . . If CO2 stimulation of net primary production is a real effect in natural ecosystems as well, the dynamics of the presented models suggest that there may be an increase in standing biomass as well as in litter and humus carbon . . .” [see: Kohlmaier, Gundolf H; Bröhl, Horst; Siré, Ernst Olof; Plöchl, Matthias; & Revelle, Roger (1987) Modelling stimulation of plants and ecosystem response to present levels of excess atmospheric CO2: Tellus, Vol. 39B, pp. 155 – 170]
The term ‘net primary production’ refers to the fundamental processes driving the activity of the biosphere. One of the textbooks to which I referred in the early days of my studies into global change was The Economy of Nature: A Textbook in Basic Ecology by Robert E. Ricklefs, [2nd ed. 1983, Chiron Press, Inc.] The author presents a succinct and clear explanation of primary production:
“Organisms need energy to move, grow, and maintain the functions of their bodies. Energy to support these activities enters the ecosystem as light, which plants convert to chemical energy during photosynthesis. The rate at which plants assimilate the energy of sunlight is called primary productivity. It is important to realize that primary production underlies the entire trophic structure of the community. The energy made available by photosynthesis drives the machinery of the ecosystem. The flux of energy through populations of herbivores, carnivores, and detritus feeders, and the biological cycling of nutrients through the ecosystem are ultimately tied to the primary productivity of plants.” P. 124
In other words, the health of the whole system depends upon the health of the plant kingdom, and the health of the plant kingdom is substantially enhanced with an increased supply of carbon dioxide.
“The energy made available by photosynthesis drives the machinery of the ecosystem.”
And what drives photosynthesis? CARBON DIOXIDE + LIGHT. With an input of light energy plants perform a miracle of transformation, converting the incoming light energy into chemical energy and in the process combining carbon dioxide with water to form organic compounds out of two inorganic compounds. These organic compounds take the form of a simple glucose sugar that can store energy for later release as it is needed by living things.
The chemical equation for this remarkable process is:
6CO2 + 6H2O ⇒ ⇒ C6H12O6 + 6O2
This equation tells us that 6 molecules of carbon dioxide added to 6 molecules of water yields one molecule of glucose sugar plus 6 molecules of oxygen. This glucose is the fuel that drives biological processes in almost all living things from bacteria to humans. Living organisms employ glucose for the synthesis of various polymers such as starch, cellulose and glycogen. These polymers serve several functions that are indispensable for biological processes such as energy storage and the creation of structural components out of which organisms are built.
The authors discuss the role of changing atmospheric moisture content in relation to photosynthesis and rates of transpiration:
“Because photosynthesis requires gas exchange across the surface of the leaf, productivity also parallels the rate of transpiration of water from the leaf surface. As the moisture content of soil decreases, plants have greater difficulty removing water from the soil and leaves must close their stomata to reduce water loss. When soil moisture is reduced to the wilting point, leaves are effectively shut off from the surrounding air and photosynthesis slows to a standstill. Rate of photosynthesis is, therefore, closely tied to the plant’s ability to tolerate water loss, to the availability of moisture in the soil, and to the influence of air temperature and solar radiation on rate of evaporation. Humid environments favor high rates of photosynthesis by reducing transpiration from leaves.” pp. 132 – 133
Stomata are pores in the leaves of plants through which carbon dioxide is taken in and water vapor is released. Transpiration is the conveyance of water up from the roots throughout the structure of the plant and its ultimate evaporation from the aerial portions such as the stems, flowers and leaves. Of the total amount of water drawn in by the plant roots as much as 98 or 99%, even more, is lost to the atmosphere through transpiration. It has been found that the size of stomatal apertures is directly related to the amount of carbon dioxide in the atmosphere. When the stomatal apertures contract, less water is lost through transpiration. This fact has interesting implications with regards to the use of “stomatal density” as a tool for the purpose of determining paleoatmospheric CO2 concentrations. Because many fossil leaves have preserved their stomatal size and density, it allows them to be used as an accurate and effective proxy measure of ancient atmospheric carbon dioxide concentrations, one perhaps more accurate than entrained air bubbles extracted from glacial ice. That, however, is a topic for another discussion. For now all I will mention is that there is, in some cases, a considerable divergence between CO2 concentrations in air bubbles trapped in glacial ice and that which is indicated by fossilized leaves of the same time period.
Carbon Dioxide and Agriculture
In another study published in 1989, three horticultural researchers conducted tests to determine the combined effects of carbon dioxide enrichment and dehydration-induced stress on winter wheat. The authors describe their protocol and the results:
“Seedlings (one per pot) were grown in growth chambers maintained at 350 (ambient) or 700 [ppm] . . . and subjected to three levels of soil moisture (well-watered, medium stress, and severe stress). . . The ratio of dry wt. to leaf area . . . and water use efficiency were significantly higher in plants grown under CO2 enrichment.”
In other words, the bulk mass of the wheat plants was greater in the CO2 enriched environment, as well as their ability to withstand the stress of water deprivation, as would occur in the real world during times of drought. [See: Schonfeld, Manette; Richard C. Johnson & Davis M. Ferris (1989) Development of Winter Wheat under Increased Atmospheric CO2 and Water Limitation at Tillering: Crop Science, vol. 29, no. 4, pp. 1083-1086]
A commissioned review was published in the peer reviewed journal Plant, Cell and Environment in 1991, authored by D.W. Lawlor and A.C. Mitchell with the Institute of Arable Crops Research, Biochemistry and Physiology Department. The Institute of Arable Crops Research, now known as Rothamsted Experimental Station, in Harpenden, England was founded in 1843 and has been doing continuous agricultural research since that time. The article was effects of increasing CO2 on crop photosynthesis and productivity: a review of field studies.” The research reported in this paper was part of the increasing effort to understand the effects of carbon dioxide enrichment on the field environment as compared with the more controlled environment of the laboratory or greenhouse. Lawlor and Mitchell report that: “Only a small proportion of elevated CO2 studies on crops have taken place in the field. They generally confirm results obtained in controlled environments: CO2 increases photosynthesis, dry matter production and yield, substantially in C3 species . . . and greatly improves water-use efficiency in all plants.” They mention several earlier reviews such as the one by Kimball discussed above and point out that these reviews “of experiments done under a wide range of conditions, show that doubling of atmospheric CO2 concentrations from ca. 330 to 650 cm3 CO2 m−3 (330 to 650 ppm) increases the productivity of a large number of C3 crop plants on average by 33%.” They follow that remark with a prescient observation: “Given the increasing ambient CO2 concentrations over the last ca. 250 years, an increase in the productivity of vegetation, either natural or agricultural, would be expected.” [See: Lawlor, D.W. & Mitchell, A. C. (1991) The effects of increasing CO2 on crop photosynthesis and productivity: a review of field studies: Plant, Cell and Environment, Vol. 14, pp. 807 – 818]
Another interesting report appeared in 1993 authored by H. H. Rogers with the National Soil Dynamics Laboratory and R. C. Dahlman with the Environmental Sciences Research Division, U.S. Department of Energy. In regards to the increasing amounts of atmospheric carbon dioxide the authors state that: “The fixation and release of this compound by plants is a two-way bridge linking the atmosphere and biosphere. Regardless of whether there are accompanying climate shifts, as have been predicted, CO2 increases will directly affect growing plants. Not only is CO2 essential for plant life but it also enhances growth and yield. Thus CO2 is of pivotal significance to both natural and plant communities and agro-ecosystems.” [see: Rogers, H. H. & R. C. Dahlman (1993) Crop responses to CO2 enrichment: Vegetatio, vols. 104/105, pp. 117-131.]
To restate the observation of Rogers and Dahlman: “Not only is CO2 essential for plant life but it also enhances growth and yield.”
Botanists have known this for at least a century. It is the consistent and relentless message of many hundreds of tests, experiments, studies and observations going back as much as two centuries. It is the 800 pound gorilla in the room that proponents of anthropogenically induced catastrophic greenhouse warming refuse to admit or to talk about. Rogers and Dahlman continue:
“What physical climates will prevail and what interactions will occur in a future world are not known. What we can be sure of, however, is that as CO2 levels climb higher and higher, the growth of vegetation will be stimulated, some plant species more than others. Most experimental probings have revealed two main responses: (1) increased rates of photosynthesis, i.e. carbon fixation, and (2) enhanced water use efficiency. The proper function of these two vital plant processes can spell the difference between feast and famine. So the potential of elevated CO2 to positively impact plants – our primary producers of food and fiber – is great. Virtually all works to date have shown enhanced crop growth, the alleviation of some stresses, and substantial boosts of yields.”
This statement bears repeating: “The potential of elevated CO2 to positively impact plants . . . is great.” Here in the work of these scientists is demonstrated the remarkable relationship between the plant kingdom and carbon dioxide, showing enhanced crop growth, stress reduction and substantial boosts of yields. In any kind of economic or cost/benefit analysis of the effects of the continued introduction of carbon dioxide from fossil fuel consumption on the global climate and environment these factors absolutely must not be neglected. I will say again, in any discussion relating to carbon dioxide or climate change this aspect of the matter should not be ignored, yet somehow, belaboring a point, it is conveniently and entirely disregarded.
One is motivated to ask: Who are the real “denialists” in this debate, to use the term typically hurled at anyone who questions the so-called consensus regarding climate change.
Note, also, that here are a pair of scientists who are experts in the effects of CO2 and they, like many others, are expressing uncertainty with regards to the supposed settled conclusion that the increase in atmospheric carbon dioxide is going to trigger a global warming catastrophe. It would behoove us to examine in more detail the process by which carbon dioxide is presumed to lead to a substantial increase in the global average temperature. And that I will do in another place. Here we are focusing on the relationship between carbon dioxide and the world of vegetation, and by implication, the biosphere.
The graph below, from the work of Rogers and Dahlman (1993) shows the effect of rising CO2 levels on the efficiency with which corn, soybeans and sweetgum trees use water in the course of transpiration. The x-axis ranges from 300 parts-per-million up to 900 parts-per-million of atmospheric CO2, or about 2.26 times greater than the present atmospheric concentration. The y-axis shows the milligrams of carbon dioxide fixed per gram of water as the concentration of CO2 rises. The higher the amount of carbon “fixed,” the greater is the efficiency with which plants use water, the other indispensable element for biological processes. This increased WUE, or water use efficiency, has extremely important implications.
Figure 3. The caption to this graph that appeared in the original article reads as follows: “Typical gains of water use efficiency. . . Many experiments suggest that WUE may increase by as much as 100% as CO concentration doubles.”
Let us recall the comment by Bruce Kimball quoted above from Carbon Dioxide and Agricultural Yield: An Assemblage and Analysis of 430 Prior Observations. Pointing out that most of the 430 observations were performed on plants in greenhouses or growth chambers he concedes that “Open fields might respond less than greenhouses or growth chambers to increased CO2.” By 1993 the question of CO2 effect on open fields had been answered, for in that year the same Roger C. Dahlman, who was at that time with the U.S. Department of Energy – Office of Science, Biological and Environmental Research, reported on a decade long series of tests on field environments with controlled CO2 enrichment on vegetation. [see: Dahlman, Roger C. (1993) CO2 and Plants: revisited: Vegetatio, vol. 104/105, pp. 339 – 355] Dahlman reported that:
“The decade-long USA research program on the direct results of CO2 enrichment on vegetation has achieved important milestones and has produced a number of interesting and exciting findings. Research beginning in 1980 focused on field experiments to determine whether phenomena observed in the laboratory indeed occurred in natural environments. The answer is yes . . . Nearly all experiments demonstrate that plants exhibit positive gain when grown at elevated CO2 . . . Most crop responses range from 30 to 50% increase in yield . . . Huge growth responses (100 to nearly 300% relative to controls) are reported from several tree experiments.”
These are truly extraordinary results. Think for a moment about the implications of these findings: crops responding with a 30 to 50 percent increase in yield, and an almost unbelievable growth response from several tree species of 100 to 300 percent occurring as a result of CO2 enrichment. Dahlman goes on to say that:
“The global rise of atmospheric CO2 is well-established from numerous measurements beginning in the mid-1950s . . . A great many studies have confirmed that plants will respond to this increase, and it is important to obtain a good measure of the myriad of responses in order to understand implications for food and fiber productions systems… Moreover, there is a growing recognition that increasing atmospheric CO2 represents a resource to be tapped by the earth’s mantle of vegetation.”
Describing CO2 as “a resource to be tapped by the earth’s mantle of vegetation” is certainly not in accord with the viewpoint of global warming advocates who now regularly refer to carbon dioxide as a “pollutant,” and have even managed to pressure the EPA into declaring it a pollutant as well. Though a ludicrous designation, it is important to realize that such a declaration confers upon the EPA – a thoroughly politicized bureaucracy – considerable power over the private sector and the economy.
The author continues with his analysis of the increasing amount of data culled from field studies in addition to more controlled experiments in the laboratory:
“Some of the most significant accomplishments of the past decade derive from field experiments, which have demonstrated that field observation of the effects of CO2 on plant growth and physiology is consistent with findings from laboratory studies. Carbon dioxide-induced increases in photosynthesis, and the growth and yield responses are of the same sign and magnitude for both laboratory and field experiments. In some case field responses may even exceed those from the laboratory such as the striking increase of root growth and production associated with some field studies.” P. 345
So not only do the positive field results equal those of the laboratory and controlled environment, in some cases they actually exceed it! The increased growth in root mass confers upon the plants enhanced ability to withstand a variety of catastrophes from flood to fire, and also allows the plant to draw deeper into the soil for water and nutrients during times of rain deficit or stress.
“Experiments on the interaction of CO2 with other factors continue to produce interesting and exciting results. With some experiments the effect of elevated CO2 tends to alleviate stress, and in other cases the combined effects of CO2 and other factors are additive, such as temperature enhancement of the response to CO2 . . . One striking set of experiments illustrates the combined effect of increased CO2 and temperature on growth. Plants with C3 type metabolisms typically show a 30 to 40 % growth response at doubled CO2 concentrations.” However when the plants were grown at doubled CO2 concentrations AND higher temperatures “the CO2-induced growth response was doubled to 60 to 80 % more than the controls. The final result is a substantial gain in productivity for the combined increase of CO2 and temperature.” P. 346
So whatever other effects may be attributed to increasing amounts of carbon dioxide and temperature, as far as plants are concerned they create a “substantial gain in productivity,” almost unbelievably up to 80% in some cases when accompanied by a modest rise in temperature of perhaps a degree or two. C3 plants, by the way, are the most common type of plants, comprising up to about 85% of all plants. They include all tree species, both evergreen and deciduous; many cereal grains such as rye, oats, wheat, barley, and rice; beans, potatoes, grapes, oranges and lemons, carrots, peaches, apples, pears, mango, coffee, peanuts and other nuts, spinach; many species of flowers and grasses and the list goes on. The subscript 3 refers to the type of photosynthetic pathway by which the carbon dioxide molecule is introduced into the plant.
The authors reconfirm the effect of elevated CO2 concentrations with respect to water use efficiency:
“Plants grown at elevated CO2 often reduce conductance of water vapor. Field experiments continue to show this effect for a wide variety of plant types, including herbaceous and woody species . . . Lowered conductance translates into increased WUE, (water use efficiency) which appears to be a ubiquitous response of vascular plants. Mounting experimental evidence is confirming that CO2 enrichment improves plant water use efficiency.”
To once again belabor a point: Improved water use efficiency has important implications. It means that in times of drought plants that have otherwise been thriving in a carbon dioxide rich environment are also more able to withstand the effects of water deprivation. In regards to this effect Norman J. Rosenberg, a Professor of Agricultural Meteorology with the Center for Agricultural Meteorology and Climatology, University of Nebraska, pointed out that “This predicted effect on water use efficiency may be of particular importance in the semi-arid and arid regions where limitations in natural rainfall limit current agricultural productivity.”[See: Rosenberg, Norman J. (1981) The increasing CO2 concentration in the atmosphere and its implication on agricultural productivity: Climatic Change, Vol. 3, pp. 265-279]
In other words, it is entirely possible that, to express this idea is less prosaic terms, with a carbon dioxide-enriched environment Earth’s deserts might begin to bloom.
In 1993 a six member team drawn from The Ecosystems Center, Marine Biological Laboratory, Woods Hole, Massachusetts and the Complex Systems Research Center, Institute for the Study of Earth, Oceans and Space at the University of New Hampshire, published the results of their estimate of global patterns of net primary production and soil nitrogen cycling under current environmental conditions. In their study they employed a process-based ecosystem simulation model that referenced information on climate, soils, land elevation, vegetation type and availability of water. This terrestrial ecosystem model (TEM) was applied to vegetation spatially referenced to a grid of 0.5 degrees latitude by 0.5 degrees longitude. These grid cells were programmed with appropriate regional climatic and hydrological data and vegetation parameters.
As do the majority of researchers into the role of carbon dioxide and climate change since the early 1990s, the authors first cite the IPCC projections of temperature rise over the next century. Remarking that climate changes of the magnitude predicted by IPCC models are certain to have an effect on net primary production (NPP) of the world’s land ecosystems, that is, the ability of land plants to capture carbon each year through the process of photosynthesis, the authors emphasize that NPP “is of fundamental importance to humans because the largest portion of our food supply is from productivity of plant life on land, as is wood for construction and fuel.” [See: Melillo, Jerry M. et al. (1993) Global climate change and terrestrial net primary production: Nature, vol. 363, May 20, pp. 234 – 240]
In considering the factors that can limit net primary production, the authors point out that:
“In many northern and temperate ecosystems, NPP is known to be limited by the availability of inorganic nitrogen in the soil. . . Under contemporary climate conditions in dry regions, TEM (Terrestrial Ecosystem Model) generally predicts that water availability limits productivity more than nitrogen availability. With a doubling of atmospheric CO2 TEM predicts that the water-use efficiency of vegetation increases in these regions; that is, there will be an increase in production per amount of water used. These predictions are consistent with research findings that increases in water-use efficiency with elevated CO2 are generally greatest in water-stressed systems.”
In other words, carbon dioxide confers upon plants in arid climates a means of conserving water use, and, as the amount of carbon dioxide in the air increases, so does the ability of the plant to thrive in a water deficient environment. Carbon dioxide acts as a sort of safety valve for plants, in that its power to improve water use efficiency becomes stronger as water supply diminishes. This increased water use efficiency is brought about because the stomatal apertures of the affected plants decrease in size and density, limiting the amount of water lost from the plant through transpiration.
There are other benefits that accompany this physiological change in the plants. In 1978 a varied group of experts was assembled by the U.S. Department of Energy to review “what is known and not known about the response of plants to CO2 enrichment.” The report produced by this group, called the Quail Roost Study, made 10 recommendations for research. One conclusion of the study was that little to no field data existed by which to determine the consequences outside of controlled laboratory or greenhouse conditions. Field experimentation was highly recommended. Subsequently this deficiency was partially rectified by the work discussed above from Dahlman, “CO2 and Plants: Revisited.” This report served to encourage several other research projects.
One of these subsequent studies was the most comprehensive up to that date on the effects of increasing carbon dioxide on plants. It was sponsored by the American Association for the Advancement of Science (AAAS) who convened a series of panels in the late 1970s and early 1980s to make recommendations to the Department of Energy (DOE) for a wide-ranging research program to further understand the consequences of rising atmospheric CO2. Especially urged by the AAAS, following the recommendations of the Quail Roost Study, was research into the effects on plants with respect to such things as photosynthetic responses, nitrogen fixation, transpiration, reproductive biology, water use efficiency, microbial activity and biochemistry. As a result of this lobbying an international conference was convened in 1982 with the objective of investigating ‘Rising Atmospheric Carbon Dioxide and Plant Productivity’. While there were many findings and new insights gained from the work of this conference a number of them were particularly useful in understanding the benefits of increased carbon dioxide to the planetary biosphere, and this led to further studies.
Evidence for the beneficial role of carbon dioxide was supported and confirmed by a follow-up report appearing in 1985 that was also conducted by the Department of Energy. The full report consisted of seven scientific reviews of various aspects of CO2, climate change and biospheric responses. Results relative to plant, vegetation and crop responses were presented in a 286 page report entitled “Direct Effects of Increasing Carbon Dioxide on Vegetation” edited by botanists Boyd R. Strain and Jennifer D. Cure. This particular work was fully peer reviewed by the Committee on Climate of the American Association for the Advancement of Science, whose chairman at the time was none other than the aforementioned Roger Revelle, mentor to Al Gore, who, in writing a forward to the volume praised its careful and thorough review of the relevant research up to that date. He also stressed the uncertainty and the embryonic state of knowledge regarding the effects of rising CO2 concentrations on other environmental aspects, especially atmospheric effects, and, by implication, the climate.
In the preface to this volume the program manager, Roger C. Dahlman again, elaborates upon the role of CO2 in the biosphere.
“Carbon dioxide enhancement of plant growth is one important direct effect of rising atmospheric CO2. Through photosynthesis, plants produce food and fiber from light and carbon assimilated as CO2 and for the foundation of the Earth’s life support system. Rising atmospheric CO2 is thus an essential input to the food producing process, and effects of CO2 enrichment described in this document have far-reaching implications for agricultural and ecological productivity. . . Enhanced plant growth and yield from more CO2 is now widely recognized in different scientific and public sectors as an important element of the CO2 problem.”
Dahlman goes on to say that:
“Although it is not currently possible to accurately state magnitudes of many effects of CO2 enrichment, there are strong indications from the work that has been done for this SOA (State of the Art) volume that rising atmospheric CO2 represents a resource for agriculture and food production rather than a conventional air pollutant. There are potentially beneficial consequences for crop productivity . . .”
How far we have come since 1985 in our revisionist science where the EPA, responding to political pressure, has now redefined carbon dioxide as a pollutant! No more talk about carbon dioxide as a resource for agriculture and food production, nor talk about potentially beneficial consequences allowed! Carbon dioxide has been dishonestly transformed from a life-giving trace gas into a demonic poison that is going to provoke global catastrophe. Hundreds of millions of dollars have gone into promoting anti-carbon dioxide propaganda and a manufactured consensus on climate change and millions of people have fallen for it. Could there be any mechanism of social control more effective than that of exploiting carbon dioxide, a gas that every living thing produces through respiration? In other words, the implication of this politically contrived model of global warming is that you are guilty simply by virtue of breathing, and, being part of the problem, must, therefore, subject all of your activities to regulatory control! If you think I exaggerate you haven’t been paying attention to the relentless direction of environmental policy since certain factions realized the advantages to be gained from demonizing carbon dioxide. Some of this I have addressed here: “Who are the Real Deniers?” article
I mentioned earlier an experiment by Sherwood Idso that was particularly compelling and worthy of consideration. In July of 1987 Professor Idso undertook a study of orange trees grown in a carbon dioxide enriched environment. He began by planting 30 cm tall (12”) sour orange tree seedlings in open-top containers with clear plastic walls and carefully monitored all variables for consistency except for the concentration of carbon dioxide. In this experiment air was fed in through tubes at the bottom and allowed to exit through openings in the top. The trees were planted in pairs, one receiving the ambient CO2 and the other enriched 300 ppm above ambient concentration.
The results shown in the next image speak for themselves. The orange tree on the right was grown in the CO2 enriched enclosure. In remarking upon these results Idso says: “The net result of these differences in physiological response has been dramatic. After two full years of growth, an assessment of the volumes of the trees’ trunks and branches revealed that the CO2-enriched trees contained 2.8 times more above-ground sequestered carbon than did the ambient-treatment trees. Six months later a similar assessment of below-ground growth revealed that the CO2-enriched trees also contained 2.8 times more root-sequestered carbon than did the trees grown in ambient air. [see: Idso, Sherwood B. (1991) The Aerial Fertilization Effect of CO2 and Its Implications for Global Carbon Cycling and Maximum Greenhouse Warming: Bulletin of the American Meteorological Society, vol. 72, no. 7 (July) pp. 962 – 965]
Figure 4. The original caption reads: At the conclusion of two full years of growth under ambient and CO2 enriched conditions, when this photo was taken, the CO2-enriched trees on the right were 2.8 times larger. In terms of both above- and below- ground biomass than the ambient trees on the left.
What we see happening, in effect, is the tree consuming the carbon dioxide from the atmosphere and transmuting it into organic, living substance out of which it creates itself as a mature plant.
A 1991 study by plant physiologist Bert G. Drake and ecologist Paul Leadley reviewed 7 experiments on canopy photosynthesis that had been conducted up to that time. A plant canopy is the assemblage of leaves by which the plant is able to intercept sunlight in order to uses its energy in the assimilation of carbon dioxide. [see: Drake, B. G. & P.W. Leadley (1991) Canopy photosynthesis of crops and native plant communities exposed to long-term elevated CO2: Plant, Cell and Environment, vol. 14, pp. 853 – 860]
The review examined two studies of canopy photosynthesis in soybeans; one study of rice; one study of ryegrass; a study of meadow fescue and red clover; a study of Arctic tussock tundra; and a study of a salt marsh. In all 7 experiments by separate teams closed chambers were constructed in which temperature, humidity and carbon dioxide concentration were controlled. The authors begin by asking a critical question: “Will rising atmospheric CO2 increase ecosystem carbon assimilations?” They then comment that while biomass production typically increased in plants with greater CO2 availability when compared with those grown in ambient CO2, in some experiments there was a gradual decline in photosynthetic capacity after long-term exposure. This led to the assumption that nutrient availability was the critical factor that would lead to reduced photosynthetic capacity. But, the authors of this review point out, the data was drawn from plants grown in controlled environments or greenhouses, and that many of the experiments were performed on annual plants with low carbon storage capacity. To rectify this bias the authors turned to studies that had been performed “on swards or small sections of the whole ecosystem exposed to long-term elevated CO2 treatment.” The crux of Drake and Leadley’s review of these experiments were succinctly expressed in the abstract to their paper:
Abstract: “There have been seven studies of canopy photosynthesis of plants grown in elevated atmospheric CO2: three of seed crops, two of forage crops and two of native plant ecosystems. Growth in elevated CO2 increased canopy photosynthesis in all cases.”
Specifically, the authors explain that:
“The studies of canopy photosynthesis reviewed in this paper indicate that elevated atmospheric CO2 increases CO2 assimilation by 25—50%. This appears to be slightly higher than anticipated from laboratory studies. There is no evidence to support the notion that the effects of rising CO2 would not be sustained.”
In 1993 Bruce Kimball, Sherwood Idso along with colleagues J. R. Mauney and F. S. Nakayama updated their researches and reported their findings in an article in Vegetatio entitled “Effects of increasing atmospheric CO2 on vegetation.” At the very outset they state that “The increasing atmospheric CO2 concentration probably will have significant direct effects on vegetation whether the predicted changes in climate occur or not.” Paraphrasing: Whether the climate changes due to the increasing CO2 or not, the effect on plants is still expected to occur. As to the nature of these “direct effects” Kimball et al. explain that “The main purpose of this paper is to describe these direct effects of increased CO2 on plants and also to discuss some interactions between CO2 and climate variables that are likely to have important consequences for the growth of vegetation. . .” The first graph in their paper shows how net photosynthesis is increased by an increase in CO2. They comment that “Of crucial importance is whether the actual growth of plants will be similarly increased, because there are numerous intermediate steps before the carbohydrates produced in the leaves are transformed into root, stem, flower, fruit, seed, or additional leaf tissue. For the most part, the answer appears to be ‘yes, growth and yield are also increased’. Figure 2 in their paper shows the results of several years of experiments conducted by the authors using open-top carbon dioxide enrichment chambers on seed cotton. The results of their experiments were that “In spite of the year to year variability and the influence of other treatments, CO2 obviously stimulated cotton yields, amounting to a 64% increase at 650 µL/L (650 ppm) averaging over all the data. Thus, cotton is highly responsive to additional CO2, but what about other species of vegetation.” [see: Kimball, B. A. et al. (1993) Effects of increasing atmospheric CO2 on vegetation: Vegetatio, vol. 104/105, pp. 65 – 75]
The following photo from their article shows the authors CO2 enrichment chambers at the USDA Agricultural Research Service, US Water Conservation Laboratory at Phoenix, Arizona. Photo taken June 9, 1987 by Bruce Kimball.
A 64% increase in cotton yield for the same amount of land is remarkable and has important implications for future conservation measures. So, what about other species of vegetation? The authors of this paper refer back to Kimball’s 1983 study from which I quoted earlier.
“Kimball assembled and analyzed much of the existing data available in the literature in 1983 about the yield or growth response of 37 species of plants to CO2 amounting to 430 prior observations. The average response was a yield increase of about 33%. . . Cure (1985) assembled the available data about the carbon exchange rate (net photosynthesis), biomass accumulation, yield, and other physiological parameters of 10 major crops – wheat, barley, rice, corn, sorghum, soybean, alfalfa, cotton, potato, and sweet potato . . .the results of her analysis were close to the 33% reported by Kimball.”
Kimball, Idso and their co-authors mention a review by L. H. Allen Jr. in 1991 in which he “tabulated the response of C3 soybean to elevated CO2. He concluded that a doubling of CO2 concentration causes photosynthesis to increase about 50%, biomass accumulation to increase about 40%, and marketable seed yields to increase about 30%.”
The authors also confirm that if temperature does increase it will have the corresponding effect on plant growth of amplifying the effect of carbon dioxide, pointing out that if temperatures do continue to mildly increase (which is not a certainty) then
“. . . the growth stimulation may be closer to 56%, rather than the mean 32% presented earlier. Therefore, a present-day cool climate like that of Canada, Northern Europe, or the Soviet Union conceivably could get a triple benefit from the predicted CO2 increase and global warming . . . (1) The increase in air temperature raises crop temperature closer to optimum and growing seasons may be longer. (2) The crop grows faster because of stimulation due to CO2. (3) And it grows faster yet because of the interaction between CO2 and temperature.”
In their concluding remarks the authors reconfirm that “There appears to be a strong positive interaction between CO2 concentration and temperature, which would greatly increase the CO2 growth stimulation under some conditions. . . The growth response to elevated CO2 is large, even under water-stress conditions . . . Plants growing in nutrient-poor soil also respond to elevated CO2 . . .”
So, to the extent that temperature does rise even more carbon dioxide will be converted to biomass through photosynthetic uptake, thus reducing the amount in the atmosphere in the process.
The realization that increasing biomass would consume ever greater amounts of anthropogenically sourced CO2 was apparent by 2005. The work of a 19 person team published that year looked at the potential role of carbon dioxide fertilization in the biosphere. Richard J. Norby, with the Environmental Sciences Division, Oak Ridge National Laboratory, and the 18 others report that:
“Climate change predictions derived from coupled carbon-climate models are highly dependent on assumptions about feedbacks between the biosphere and atmosphere. One critical feedback occurs if C uptake by the biosphere increases in response to the fossil-fuel driven increase in atmospheric [CO2] (‘carbon fertilization’), thereby slowing the rate of increase in atmospheric [CO2]. . . Exchanges between the terrestrial biosphere and atmosphere are represented in models using empirical and theoretical expressions of net primary productivity (NPP), the net fixation of C by green plants into organic matter, or the difference between photosynthesis and plant respiration. Because the photosynthetic uptake of carbon that drives NPP is not saturated at current atmospheric concentrations, NPP should increase as fossil fuel combustion adds to the atmospheric [CO2] . . . Our analysis indicates a 23% increase in forest NPP as atmospheric [CO2] increases to 550 ppm over the next few decades. . . The effect of CO2 fertilization on forest NPP is now firmly established, at least for young stands in the temperate zone. Recent observations of older and larger deciduous trees in a mature Swiss forest demonstrated that physiological responses were similar to those of younger trees, thereby increasing our confidence that our results are generally relevant.” Norby, Richard J. et al. (2005) Forest response to elevated CO2 is conserved across a broad range of productivity: Proceedings of the National Academy of Sciences, Vol. 102, no. 50 (Dec. 13.) pp. 18052 – 18056
I will return again to this theme of positive feedbacks between carbon dioxide availability and biomass. While it is likely that at some point plants will become acclimatized to higher concentrations of atmospheric CO2, this study and others demonstrate that trees continued to take up carbon dioxide well into their mature stages. This fact has important implications for any estimate of future atmospheric carbon dioxide concentrations.
Figure 5 Sherwood Idso showing a succession of pine trees of the same age and grown under identical conditions except for the addition of greater concentrations of carbon dioxide. The tree on the left is grown under ambient concentrations and the trees to the right with enrichment above ambient as shown. Source: Moore, Patrick (2016) The Positive Impact of Human CO2 Emissions on the survival of life on Earth: Frontier Centre for Public Policy.