Greening planet

how CO2 benefits plants and ecosystems
By Dr J Floor Anthoni (2010)
(This chapter is best navigated by opening links in a new tab of your browser)
Without any doubt, the rising levels of CO2 in air have benefited plant life, and thus animal life and people. This chapter studies the ecology of carbon and plants, and where carbon is located in the world's ecosystems. In order to understand scientific studies of CO2-enriched plant growth, one must also know their limitations. Finally some examples are given of the evidence provided by hundreds of studies.
A short introduction to this chapter
The ecology of carbon: how it is formed and how it is transported. How ice ages create a poor unproductive world and warm interglacials the opposite.
A refresher of some basic plant ecology: where the carbon is found; the main ecosystems of the world with their carbon stores above and under ground; the basic plant types and their reactions to increased carbondioxide concentrations.
Before their results can be evaluated, it is important to understand the various kinds of scientific experiment and their limitations.
The data from scientific experiments, illustrating improvements in plant growth.
With satellites the areas covered by ecosystems can be measured and also their leaf densities as chlorophyll concentrations.
Various loose notes.
related chapters
Related chapters on this web site
  • Soil: an extensive section about soil and plant life. Must-study.
  • abundance of the elements for life: in the universe, our solar system and on Earth in soil and sea.
  • periodic table of elements: the properties of the elements of life and a short course in chemistry
  • sea water: the elements in sea water and what they mean to life.
  • external links
  • a web site devoted to the study of the effect of CO2 on plant life, complete with extensive scientific data of many plant species. The evidence is overwhelming: more CO2 means more life. This web site is highly recommended for further studies.
  • tables of photosynthesis and bulk growth for many species, kept uptodate.
  •  An excellent article about that miracle greenhouse gas CO2, by Paul Driessen, Aug 2013. Summing it all up. Recommended reading.
  • Back to climate index and introduction

    Begin your study of planet and sea at the Seafriends home page or our sitemap.

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    -- Seafriends home -- climate index -- global issues -- Rev:20100620,20171129,

    The huge propaganda aimed at making carbondioxide the main villain of global warming, threatening humanity's future and prosperity, is now believed by a majority of people. Carbondioxide is now pollution, on a par with oil slicks and industrial poisons. But nothing could be further from the truth, as CO2 is the life-bearing gas on which all life depends. How could society deceive itself to such extent?
    The benefits from CO2 are not even mentioned in the IPCC assessment reports. In this polarised world of warmists and skeptics, warmists sometimes acknowledge that "CO2 may have some effect on plant growth, but never long-lasting." Yet scientific experiments, now on-going for over two decades, tell a different story: all plants react very favourably to CO2-fertilisation, and some more so than others.

    In this chapter we will put some misunderstandings to rest, beginning by reviewing the ecology of carbon and how it recycles. Then we'll study where the carbon is found in ecosystems and how these ecosystems acquired it. Before reviewing some important findings, we'll review how scientific experiments are done and learn about their limitations.

    On the Seafriends website we have quite extensively documented the geology, ecology and biology of soil and the world's ecosystems (see soil) in order to foster a thorough understanding necessary for combating soil loss (in quality and quantity), the world's foremost ecological problem. This educational resource now also serves to understand an important side of 'global warming'.

    We are happy and fortunate that somewhere else exists a web site specialising in the science of CO2 fertilisation, complete with extensive data for many plant species. It is also scientifically independent and objective. So please continue your studies at

    Carbon ecology
    Carbondioxide is food for plants, like nothing else. While making live tissues through photosynthesis, they combine carbondioxide with water, simplistically as::
    6CO2 + 6H2O + Light => C6H12O6 (Glucose) + 6O2
    or more simply
    CO2 + H2O => CH2O + O2
    For making more complicated biochemical substances like proteins, also minerals are required like nitrogen (N), potassium (K), sulfur (S) and some twenty more. See the elements of life. But CO2 and water remain the most important ones. Of these two, water is the most abundant substance whereas CO2 the least abundant, by far. For instance, in the air around us, only one in 3000 molecules is CO2, and plants must be able to catch these, in competition with all other plants on Earth. No surprise then that CO2 is highly in demand, and higher concentrations of it promote plant growth like nothing else.

    plants living in a dearth of carbondioxideTo understand that plants live in a world where CO2 is scarce, these two diagrams provide an ecological explanation. The green S-curve is how a population grows in relation to its resources like food. First (on left), their world is unexploited and food is plentiful. so the population grows explosively (exponentially) until mid-way growth slows down as food becomes more scarce. As the population grows further, growth slows to a trickle until it stops for lack of food. If such a population is a warm-blooded species, the maximum population cannot reach the top of the curve because such species require much food to survive. However, cold-blooded species can survive better in the almost fully exploited world, and 'cold-blooded' species that do not even move, like plants, can survive and still grow in the grey band of an almost fully exploited resource.
    Remember that CO2 is the only resource in the world that is evenly spread and can be accessed anywhere to the same extent. So it is also the only 'global' resource that is competed for by each and every plant on Earth.

    The red graph shows growth rate (horizontal) as a function of the use of the resource (vertical). One can see that in the grey band, the growth rate is severely limited by the scarcity of the resource. Move the black arrow slightly down, and a large increase in growth rate follows. This is again depicted in the diagram shown here.
    rapid growth for an increase in CO2The green curve in this diagram is in fact the same red curve of previous diagram, but now rotated such that the resource is now horizontal and growth vertical. It is expected that a relatively small increase in the concentration of CO2 in air, results in an enthusiastic response in growth rate. But experiments show varying results, even though all are positive. Why?
    Firstly, each species responds differently to CO2 and their condition also depends heavily on other factors like temperature, moisture, competition for space, root competition, nutrients and quality of the soil. So it is practically impossible to mimic the natural situation in experiments.

    The amount of fossil fuel burnt by humans has been increasing exponentially, which means that annual emissions have been growing, and 57% of that is consistently retained in air.

    Does sequestration by plants keep up with human emissions?
    Natural carbon sinks over 50 yearswe've seen overwhelming evidence that plants sequester only 43% of human emissions, which was confirmed by a recent study of Ballantyne et al [1] who plotted the missing CO2 against total emissions. Their diagram shows CO2 emissions in red and plant sequestrations in black. Although plants capture only about half of increased emissions, they are doing so ever more progressively. Indeed, in the past 50 years, their uptake has even doubled rather than levelled off as was feared by warmists.

    [1] Ballantyne A P et al (2012): Increase in net carbon dioxide uptake by land and oceans during the past 50 years, Nature 488, 70-72.

    the carbon pipeThe Carbon Pipe concept
    We've shown before that the idea of carbon reservoirs is perhaps inaccurate, and that carbon flows more like inside a pipe, where the flow is determined by pressure (concentration in air). One cannot talk about carbondioxide without looking at the full picture with all its pathways, and much of this remains unknown. Plants absorb the CO2 breathed out by animals (not much) and from decomposition (much). Most of this interchange happens nearby, in fact on the roots of land plants, and likewise for plankton. Thus carbondioxide cycles fastest outside the atmosphere.
    The imaginary carbon pipe also connects the land with the sea in such a way that during warm interglacials, carbon travels from sea to land and during the cold ice ages in the opposite direction.

    land vegetation in ice ages and warm interglacials
    In the discourse about CO2, never forget these two images, showing world vegetation during an ice age (right) and warm interglacial (left). The difference is ENORMOUS. The world as we know it today, is rich with vegetation and life, and its soils are also rich in carbon. All that carbon came from the sea, through the imaginary carbon pipe discussed above.

    Thus the main movement of carbondioxide happens as follows:

    global warming => oceans expel CO2 => higher CO2 in air => CO2 absorbed by plants and soil
    and the man-made CO2 is just part of this very large shift in fertility. Let's just hope that it continues for a few more millennia, rather than reversing into the next ice age. The first thing to notice could well be a lowering of the CO2 concentration in the atmosphere. From there on, the world rapidly descends back into poverty and cold. In an ice age, life is brutal and short.

    Plant ecology
    The world is large and has many climate zones, each with its own type of vegetation and type of soil. In order to understand where land plants will sequester the additional anthropogenic carbondioxide, one must understand some basic plant ecology.
    Where is the carbon found?
    carbon in the biosphereThe diagram shows where the carbon is found on land. If we take one metre squared, then the air above it contains a mass of 10,000kg = 10 tonnes. CO2 makes up 3kg = 1kg Carbon. Above the soil stand forests 15kgC, grass 3kgC and their grazers 0.05kgC. The predators make up an even smaller carbon weight. Under the surface extends the soil, of which only the top soil is rich in carbon. 10cm topsoil weighs about 200kg and the microfauna alone weighs 10kgC, very much more than the grazers above it. In addition to this there are roots, leaf litter and humus which could weigh as much as the vegetation above.
    carbon_pools_biosphereThis rather complicated diagram brings together the main types of world vegetation (colours), their extents (vertical scale), their biomass above and under the ground (left columns; soil leftmost; canopy rightmost), and their productivities (righthand column). The quantities are expressed in petagram PgC which is identical to gigaton GtC. It can be seen that some ecosystems store more carbon underground than above (tundra, taiga, grassland), whereas others store more above than below (conifers, humid broad-leaved forests). Amazingly, their productivities are roughly equal once temperature suffices (tundra is too cold). The humid broad-leaved forest is the tropical rainforest, which eclipses all others.

    soil_and_ecosystem_gradientsFinally, to show where the world's ecosystems are found, together with their soils, this diagram brings together the climate variables of temperature, rainfall and potential evapotranspiration. Starting from the left in the Arctic, the tundra's growth is severely hindered by permafrost. But as one goes southward, the temperature (red curve) rises quickly to allow for productivity in the taiga boreal forests. It crosses the rainfall curve (blue) where soils are deepest and agricultural productivity highest. This is also the most sustainable area on the planet. But from here on, rainfall quickly becomes insufficient for evapotranspiration, resulting first in dry grasslands (steppe) and then the desert. In desert soils, rainfall is even insufficient to wash out calcium compounds and other salts, which results in strata ('horizons') of salts, limestone and gypsum.
    One can see that the soil depth keeps up with productivity until it becomes thickest in the black cernozem, before thinning out through the steppe grasslands towards the desert. One can also see the ground water table dipping accordingly. It must be noted that the most productive ecosystems are found where evapotranspiration equals rainfall, a relatively small band across the planet. Not surprisingly, these areas are heavily farmed. It can be expected that these areas benefit most from CO2 fertilisation.
    C3 and C4 plants
    Not all plants react equally to enriched CO2. The old plants which stem from the age of dinosaurs (cycads, ferns, horse-tails) evolved in an age rich in CO2, and they are now severely stunted in their growth rates. Not surprisingly, they react most enthusiastically.

    Later came the conifers, now found naturally in the very cold regions of the boreal forests. They too react well.

    Then came the leafy trees, shrubs and weeds with their wide leaves optimised for photosynthesis, together with their ability to drop leaves in response to frost or drought. All of these are powered by the C3 photosynthesis, which consists of three biochemical steps. They too react well.

    Then arrived the most recent grasses (maize, sorghum, sugarcane, bamboo) powered by a new method of photosynthesis, the C4 process which happens in 4 steps, and which is able to capture CO2 more efficiently. They are about twice as efficient in converting sunlight, while needing four times less water. Photosynthesis in C3 plants converts 0.1-0.4 g CO2 with 1 kg water, whereas C4 plants convert 0.4-0.8 gram. However, a higher temperature is also needed. Thus C4 plants are found mainly in warm areas, even though plant breeding has extended their temperature range. Not surprisingly, they do not react as well, because they are already better than others at capturing CO2.

    To complete the list, there are also plants powered by the Crassulean Acid Metabolism CAM photosynthesis (cacti, succulents, agaves, lilies, bromeliads, orchids, euphorbia, geraniums) which enables them to store CO2 at night for delayed photosynthesis by day. In this manner they can close their water pores during the day, while opening up at night. Such plants grow rather slowly but resist dry climates.
    During the night, CO2 is absorbed and converted into chemical storage as oxaloacetic acid and then as malate. During the day, these compounds are converted and normal C3 photosynthesis takes place, with the plant's leaf pores closed to prevent unnecessary evaporation. They use a minimum of water.

    Read more in soil/fertility.

    Scientific experiments
    "Watching grass grow" is an expression of impatience with a slow but steady process. Plant growth is indeed very slow, which means that plants cannot react immediately to an increased supply of CO2. They need to grow more leaves and roots, process more water such that next year they can do the same and perhaps a little more. But in doing so, they also produce more leaf litter, insects and other animals that eat their leaves, and all this must be recycled by the soil, which needs more bacterial activity, and so on. Thus keeping up with an ever increasing flow of CO2 is hampered by delays. It is therefore important to recognise how scientists do their CO2-enrichment experiments. 

    But before we do so, a general comment of disenchantment. All these experiments look only at INCREASED carbondioxide levels, and NONE have looked at DECREASED levels, which is entirely unscientific. Thus ALL carbondioxide enrichment experiments so far are POLITICALLY or INDUSTRIALLY driven. Real science would have studied the whole gamut (reach) of CO2.

    We can now split plant growth experiments into separate categories:

    citrus growth over 17 yearsThis graph shows the results of one of the few experiments carried out over a long time period, with sour orange trees at ambient CO2 and enriched by +300ppm. The trees growing in nearly twice the concentration, consistently outperform the controls at ambient CO2 by almost 100%, particularly towards the end of the series. The graph does little justice to the visual side of the experiment, because if one increases its wood consistently twice each year, the difference with their controls becomes very large over time. Location: Maricopa, Arizona.
    Paradoxically, the authors state that "Carbon dioxide fertilization increases plant water use efficiency, which may help explain why the desert ecosystems responded more dramatically than other ecosystems."

    The plant growth experiments unanimously agree that:

    As CO2 is linked to temperature, this could lead to the following advantages:
    Stressed plants benefit more from CO2Whereas plants cultivated in optimum conditions benefit substantially from elevated levels of CO2 (blue curve), an overwhelming number of studies have shown that stressed plants which are limited in one or more resources (water, temperature, nutrients, light, herbicides, etc), benefit even more so (red curve). Their growth rates indeed double for a doubling in CO2. Reader please note that this is paradoxical because CO2 effects on growth do not simply follow Liebig’s law of the minimum (Walter Larcher), and that these studies confirm our exponential growth paradigm above. What this means, is that elevated levels of CO2 have proved to be extremely beneficial for the world. "Increasing atmospheric CO2 is an unmixed blessing – it will bring currently unproductive land into use and bring greater yield from existing land without additional fertilizer use. This is a wonderful benefit in being able to feed an increasing world population."

    [1] CO2 Enrichment and Plant Nutrition.

    There has been and still remains, a great reluctance on the part of many climatologists and ecologists, and especially environmentalists, to accept the concept that the rising level of atmospheric CO2 could be more beneficial than harmful for plant growth, food production, and the overall biosphere…Yet the scientific evidence is overwhelming. - Sylvan Wittwer

    From various sources we have selected the growth responses of the most important plant species, all in terms of biomass. These results give a good idea of what to expect from certain ecosystems, and what carbondioxide fertilisation means for food.

    ancient species
    Sago Palm Cycas revoluta
    Water Fern Azolla pinnata
    Fern, Tropical Pyrrosia piloselloides
    +300ppm enriched
    +90% at +600ppm
    conifer species 
    European larch Larix decidua 
    Douglas Fir Pseudotsuga menziesii
    Spruce various Picea spp
    Pine various Pinus spp
    +300ppm enriched
    +22 to +38%
    no reaction to higher CO2
    P.eldarica +150%; P.mercus +200%
    broadleaf tree species (C3)
    Various Acacia spp
    Aspen Populus spp
    Beech Fagus spp
    Birch Betula spp
    Gum trees Eucalyptus spp
    Ash species Fraxinus spp
    Tropical Savanna Tree Kielmeyera coriacea
    Maple various Acer spp
    Oak various Quercus spp
    +300ppm enriched
    +71 to +100%
    +29 to 58%
    +24 to +88%
    +15 to 34%
    +46 to 130%
    +13 to 33%
    +30 to +95%
    +38 to 110%
    American beech responds better
    large variation between species
    grain species (C3)
    Oats Avene spp
    Barley Hordeum vulgare
    Rice Oryza sativa
    Common Wheat Triticum aestivum
    +300ppm enriched
    +23 to +33%
    +141% at +600ppm. Most important food crop
    reacts little to higher CO2
    C4 grasses species
    various permanent grassland species
    Johnsongrass Sorghum halepense
    Sugarcane Saccharum officinarum
    Corn Zea mays
    +300ppm enriched
    +20 to +65%
    0 to +13%
    reacts poorly
    33% at +600ppm
    fruit species
    orange trees Citrus spp
    Grapevine, Common Vitis vinifera
    Olive Tree Olea europaea
    Peach Tree Prunus persica
    +300ppm enriched
    +30 to +60%
    vegetable (leaf) species
    Peanut Arachis hypogaea
    Various beans Phaseolus spp
    Mustard, oilseed, broccoli Brassica spp
    Cucumber cucumis spp
    Soybean Glycine max
    Garden Lettuce Lactuca sativa 
    Cultivated Tobacco Nicotiana tabacum
    Tomato Solanum lycopersicum
    +300ppm enriched
    +50 to 70%
    +28 to 56%
    do not respond to higher CO2
    do not respond to higher CO2
    +61% at +900ppm
    +115% at +900ppm
    +53% at +600ppm!
    root crop species
    Carrot Daucus carota
    Cassava Manihot spp
    Sweet Potato Ipomoea batatas
    Potato, White Solanum tuberosum
    +300ppm enriched
    +148% at +600ppm!!
    +71% at +900ppm

    desert species
    various Agave spp
    +300ppm enriched
    +30 to +35%

    Most annual 'weeds' react vigorously, up to +460%. Weeds are species that grow fast, reproduce profusely but live short lives.
    Most human food crops react very positively, a huge benefit for growing populations.
    Water Fern Azolla pinnata +54%. Reacts vigorously to higher concentrations. Azolla is an important fertiliser of rice paddies.
    White Clover Trifolium repens +65%. An important fertiliser of grasslands.
    Water Hyacinth, Common Eichhornia crassipes +50%. A pest growing in waterways.
    Wild Spikenard Hyptis suaveolens +1700%. The winner? Pignut or bushmint, a tropical noxious plant with antibacterial properties.
    In glasshouses, flowers are grown in very high CO2 concentrations of +900ppm, with medium response. for more data and details

    Satellite observations of plant growth
    plant_growth_satelliteIt is still a bit early to detect plant growth from satellite observations, but here is an early result. The colour scale was chosen such that yellow means no additional growth, whereas green to purple signify an increase in growth. As can be expected, the very cold and very dry areas did not respond and the tropical forests reacted most (the authors warn that extra rain could have caused this). Leaving those two areas aside, it looks like half of the green world has increased productivity by 1% per year. Would this mean 40% in 40 years or 40 GtC? That would be close to the missing CO2 of 60GtC. The future will tell.

    Various notes
    Finally various notes as a 'rats and mice' selection.

    From the literature
    Hundreds of studies and extensive research conclusively show the link between CO2 levels and plant growth. Using a conservative estimate for the range of the recent atmosphere, for every 10 ppm (parts per million) that CO2 increases, plant growth increases roughly 1%. This varies from species to species and with other conditions/nutrients needed for growth.  With CO2 levels rising from 280 ppm to 390 ppm (+110 ppm) since the Industrial Revolution, this equates to an 11% increase in plant growth.

    [Note. Since the beginning of the Green Revolution (1960), CO2 increased by 60ppm, accounting for 6% increase in plant growth and crop productivity. It could well be that new crops, more fertilisation and more irrigation did little compared to the concurrent increase in CO2]

    The carbon:nitrogen ratio of leaves of plants is usually increased under CO2 enrichment. Plants may acclimate to elevated CO2 by requiring less rubisco and photo-synthetic apparatus, which would lead to lower nitrogen contents. The overall change in C:N ratios is governed both by increases in structural and non-structural carbohydrates, and by decreases in protein content. However, seed nitrogen content is little affected (Allen et al., 1988).

    Water-use efficiency (WUE) (ratio of CO2 uptake to evapotranspiration) will increase under higher CO2 conditions. This increase is caused more by increased photosynthesis than it is by a reduction of water loss through partially closed stomata. Thus, more biomass can be produced per unit of water used, although a crop would still require almost as much water from sowing to final harvest. If temperatures rise, however, the increased WUE caused by the CO2 fertilization effect could be diminished or negated, unless planting dates can be changed to more favourable seasons.

    The direct effect of increasing temperatures across the range of 28 to 35°C appears to increase transpiration rate about 4 to 5% per °C, based on both experimental and modelling studies (Allen, 1991). This is in close agreement with the rise in saturation vapour pressure of about 6% per °C. Allen et al. (1985)

    Cow-madness in New Zealand
    New Zealand has an unusually large agricultural sector with pastoral (grass) farming. Since the global warming scare, it was discovered that cows belch (burp, exhale) methane while chewing their cud, and that since methane is a "twenty times more potent greenhouse gas", this must be combated and compensated for in New Zealand's carbon footprint.

    NIWA (National Institute for Water and Atmosphere) explains it as follows [1]: Why is farming not carbon-neutral or carbon-negative? After all, cows eat grass made from CO2, defecate some of it, and produce milk and meat which is exported. They are thus a sink for CO2 and agriculture should be carbon-negative.
    Not so, because while digesting grass, cows produce some methane (CH4), and although this was made from CO2, a cow produces enough of this gas to power a car for 4km every day! Since methane is a 21 times more potent greenhouse gas (false), our cows and sheep are the source of 47% of all NZ's greenhouse gas emissions (also false).
    Methane acts as a blanket in the atmosphere, absorbing infrared rays as they radiate off the earth and bouncing some of them back down to re-heat it. In that way it traps heat like all greenhouse gases, but methane is more efficient than CO2 at absorbing infrared rays. On top of that, it spends an average of nine years in the atmosphere before it is oxidised back into CO2.

    See how deep the global warming madness has rooted itself? These are the words of scientists, intent on wreaking the NZ economy for no benefit whatsoever. Guess what our children are learning at school? When will common sense begin?

    [1] Water & Atmosphere, July 2010. "Why isn't grass in, methane out, carbon neutral?"


    For extensive documentation of scientific articles and experimental data, please refer to the excellent and objective web site