lunedì 8 settembre 2014

Carbon dioxide from problem to resource

The challenge for the intensification of agricultural production

di Luigi Mariani
The invaluable ecological role of carbon dioxide

Carbon (chemical element of atomic weight 12.01) is a critical component of the living matter and, like all the biogenic elements, undergoes a series of cyclic transformations passing continuously from the mineral to that of living beings and vice versa. The carbon in the organic matter is in average 45% of the dry weight and always comes directly or indirectly from atmospheric carbon dioxide (CO2).
Through the reaction of photosynthesis powered by solar energy, the photoautotroph organisms (green plants, algae and some bacteria) take six molecules of CO2 and six molecules of H2O to synthesize a molecule of glucose (C6H12O6) which in its turn feeds the pathways leading to a long series of organic compounds used by plants and animals (heterotrophic organisms) both for structural purposes and for their metabolism (Enciclopedia Treccani, 1999). The passage of the carbon from the inorganic to the organic world is carried out through the respiration, which is the reverse reaction of photosynthesis.
On the other hand CO2 is the responsible of about the 20% of the greenhouse effect, while 51% of this phenomenon is given by water vapor and 24% by clouds (Lacis al. 2010). By the way, I remember that GE is a fundamental presupposition for life on our planet because the mean global temperature without this beneficial effect would be -20°C against the present +15°C.
In view of the above, the CO2 can be considered the fundamental building block of life on our planet (figure 1) and therefore its demonization carried out since decades by media and the same scientific community (Thompson et al., 2014) is staggering both scientifically and anthropologically. 

Figure 1 – Plants need CO2 (source:

Carbon dioxide and climate

I’m not so worried by the negative effects on climate of the CO2 increase in the terrestrial atmosphere (from 280 ppmv of the 1750 to the 400 ppmv of today) given mainly by human activities like combustion of fossil fuels and emphasized by the enhancement of the ecosystem activity driven by an increase of global temperatures of + 0.78 °C during the period between the 1851÷1900 and the decade 2003÷2012 (IPCC, 2014). In fact the climatic system shows a lot of stabilizing safety valves. If we observe the period from 1958 (figure 2), characterized by a steady growth of CO2 atmospheric levels, global surface temperature showed a decreasing trend until 1976 (-0.2°C on the whole period). Then from 1977 to 1998, the trend reversed with an increase of 0.6°C on the whole period. 

Figure 2 – Diagram showing the HadCRUT4 ( monthly global surface air temperature (blue) and the monthly atmospheric CO2 content (red) according to the Mauna Loa Observatory, Hawaii ( The Mauna Loa data series begins in March 1958, and 1958 has therefore been chosen as starting year for the diagram. The dotted grey line indicates the approximate linear temperature trend, and the boxes in the lower part of the diagram indicate the relation between atmospheric CO2 and global surface air temperature, negative or positive. Last month shown: July 2014. Last diagram update: 28 August 2014 (source: Hole Humlun -

The scientific mainstream attributed this increase to the effect of anthropogenic CO2 amplified by the increase of atmospheric water vapor mainly coming from the ocean evaporation (IPCC, 2014). On the other hand the increase of air temperature would have had to give a further recall of water vapor from oceans (the maximum quantity of water vapor that can be stored in a given air volume doubles for each increase of 10°C of air temperature) which would have had to produce a further increase in air temperature and so on, thus triggering a runaway greenhouse effect. However this very negative scenario did not occurred and after the warmest year (1998) the atmospheric water vapor in excess was simply expelled from the atmosphere as rain, giving way to the stage of stable global temperatures that still today persists.

Agriculture as a government system of the carbon cycle

In any case, even if we consider the atmospheric CO2 increase as a climatically negative factor, a reasonable answer to this phenomenon may be to strengthen the role of the agriculture as a system for the government of the carbon cycle (Burney et al., 2010). In fact, the increase in CO2 compared to pre-industrial phase has so far resulted in an increase of 20-40% of the global agricultural production (Sage and Coleman, 2001; Araus et al., 2003), very beneficial in terms of global food security. Furthermore each year, during the boreal summer, a decrease of about 6 ppmv in CO2 atmospheric concentration is observed (figure 3) as a proof of the effectiveness of vegetation in the regulation of the atmospheric segment of the carbon cycle.

Figure 2 – Monthly atmospheric CO2 behavior 
in the last 5 years 
These facts show that the use of agriculture to stabilize the atmospheric levels of CO2 is a concrete and reliable perspective. In this regard it should be noted that the vegetation absorbs Earth every year about 198 GT of CO2 and about one third of this is already absorbed by plants grown (DeLucia etal., 2014).

Such a perspective can materialize if a substantial increase in crop productivity will be attained and the key techniques to do this are the genetic improvement of crops (GMO included) and the progress of relevant technologies like water management, fertilization, plant protection and irrigation. The substantial increase in crop productivity is crucial in order to:
  • satisfy the future needs of food (in 2050 the global population will reach 9.5 billions)
  • use the remaining product to substitute the hydrocarbons with organic molecules coming from crops in order to feed industrial chains to produce biofuels, plastic and other chemical products essential for human life.

In other words a “green future” in the true sense of the word, and not the one full of solar panels and wind turbines propagandized and financed by a plethora of local and international organizations!
In this context the carbon sequestration into the soil could play a significant but secondary role, because aerobic microbes that work on soil organic matter are not only responsible of the release of CO2 into the atmosphere (Reinau, 1927) but also of the release of macro and micronutrients which are essential for plant nutrition and soil fertility. So the most profitable strategy could be to guarantee a sufficient speed to the carbon cycle into the soil and at the same time to promote cover crops that intercept CO2 emissions and at same time prevent soil erosion and increase rainfall infiltration (Love et al., 2014).

Organic farming and intensification of agriculture

The policy of intensification of agriculture is promoted by the same FAO (2011), conscious of the gradual increase in world population. At the same time organic and biodynamic agricultures can a solution for single farmers that work on niche markets but they are unable to face the global problems of food security. More specifically the recent reviews by De Ponti et al. (2012) and Seufuret et al. (2012) concluded that organic farming yields on average 80% and 75% of the conventional. Moreover more substantial decreases are signaled in intensive agricultural systems (Cavigelli et al., 2008). This gap is structurally related to the obsolete principles of these agricultures and in the future it is set to worsen with the increase of technological performance of agriculture. In fact it can be considered that:
  • organic agriculture is the mere re-proposition of the paradigms of the XVIIIth century agriculture, before the chemical revolution of the XIXth century. This latter had the great merit of providing the scientific basis for the green revolution of the XXth century which defused the Malthusian bomb because in front of a quadrupling of the world population it multiplied for six the production of the main crops.

  • biodynamic farming links the outdated techniques of organic farming with a magical and astrological background that was already criticized by Lucius Moderatus Columella (I th century a.C.) in the eleventh book of his De re rustica and is absolutely incompatible with an approach to agricultural production founded on a scientific background.

Objections against the crop intensification option

A possible objection to the perspective of intensification is that in the future crop productivity could only decline because the upper limit of crop productivity was already reached. About this argument I point out the work of DeLucia et al. (2014) which on the base of a review of the most recent scientific literature state that the highest dry matter production of C4 plants observed thus so far is 100 t/ha of dry matter. Furthermore by means of a simulation approach they highlight that the upper limit of crop productivity is about 200 t / ha per year, a value incredibly high if compared to the 18-20 t/ha of the best varieties of maize grown at mid-latitudes.
These data echo so amazing the thinking of Lucius Moderatus Columella which in the opening words of De re rustica, addressing to Publius Silvino, says to be fiercely opposed to the pessimistic view of many prominent Roman citizens that the earth would have already exhausted its fertility. Just to challenge that belief, the whole treatise of Columella is devoted to describe the techniques needed to ensure high quantity and quality levels in crop production.
The 5-6 t / ha of annual average production of wheat grain in Italy (ISMEA, 2012), well above the average production of the imperial Roman (less than 1 t / ha), show that 2 thousand years ago Columella was right and I think the rightness of the intensification thesis will be stated in the next years, when finally the States and the public opinion will appreciate the strategic value of this option.

Intensification, a great opportunity for expo2015

The intensification of agriculture in order to stabilize the atmospheric levels of CO2 and to obtain more food and more consumer goods for the world people is a relevant opportunity that should be taken by the agricultural system and could be usefully discussed in the context of the EXPO 2015. On the other hand, it is very difficult that arguments like the agriculture intensification by means of relevant technological innovation will have a space in Expo2015, in the light of preliminary choices that highlight the anti-technological drift for this world event. Symbol of this drift was the choice as ambassador of Expo 2015 of Vandana Shiva, which not only is prejudicially against the innovation in agriculture but is also favorable to the return of the traditional agricultural techniques that for centuries ensured a very low production and a substantial food insecurity for the min part of the world people.


Araus et al., 2003. Productivity in prehistoric agriculture: physiological models for the quantification of cereal yields as an alternative to traditional Approaches, Journal of Archaeological Science 30, 681–693

Burney J.A., Davis S.J., Lobell D.B. 2010. Greenhouse gas mitigation by agricultural intensification, Proceedings of the National Academy of Sciences, 107, 12052-12057.

Cavigelli M.A., Teasdale J.R., Conklin A.E., 2008. Long-Term Agronomic Performance of Organic and Conventional Field Crops in the Mid-Atlantic Region, Agronomy Journal, Vol. 100, Issue 3, 785-794.

Delucia E.H., Gomez-Canovas N., Greenberg J.A., Hudiburg T.W. et al., 2014. The theoretical limit to plant productivity, Environ. Sci. Technol., 214, 48, 9471-9477.

De Ponti et al., 2012. The crop yield gap between organic and conventional agriculture. Agricultural systems 108, 1-9.

FAO, 2011. Save and grow, a policymaker's guide to the sustainable intensification of smallholder crop production, FAO, Rome, 102 pp.

IPCC, 2014. AR5, Summary for policymakers (

Lacis A.A., Schmidt G.A., Rind D., Ruedy R.A., 2010. Atmospheric CO2: Principal Control Knob Governing Earth’s, Science 330, 356-359.

Love J., Dillard J., Brock K., Dourte D., Fraisse C., 2012. Agricultural Management Options for Climate Variability and Change: High-Residue Cover Crops, University of Florida Extension,

Reinau, E. Praktischen Kohlensäuredüngung in Gärtnerei und Landwirtschaft. Springer, Berlin 1927.

Sage R.F., Coleman J.R., 2001. Effects of low atmospheric CO2 on plants: more than a thing of the past, TRENDS in Plant Science Vol.6 No.1 January 2001.

Seufert,   V.,   Ramankutty N., Foley J.A., 2012.  Comparing   the   yields   of   organic   and   conventional Agriculture, Nature, 485, 10  May  2012, 229-234.

Thompson T.M., Rausch S., Saari R.K., Selin N.E., 2014. A systems approach to evaluating the air quality co-benefits of US carbon policies, Nature Climate Change, doi:10.1038/nclimate 2342.

Luigi Mariani graduated in Agricultural Sciences in 1981 at the University of Milano. At present he works as independent professional and he is contract professor of Agrometeorology and Crop science at the Università degli Studi di Milano.
Research fields:
Applied climatology
Crop Simulation models
Analysis of land suitability
Weather forecast for agriculture

1 commento:

  1. the atmospheric water vapor in excess was simply expelled from the atmosphere as rain, giving way to the stage of stable global temperatures that still today persists.

    Utterly wrong. The CO2 is still in the atmosphere, as your graph showed.