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What is the Contribution of Fossil Fuels to Feeding Humanity?

Analyses of policies related to fossil fuel usage usually focus on the negative impacts from that usage, while generally ignoring the positive aspects, such as their contribution to global food production and, through that, the alleviation of hunger which, it should be noted, is the first step to maintaining a healthy and productive population. However, fossil fuels are critical for food production worldwide, contributing via a number of pathways. First, they serve as raw materials for the production of fertilizers and pesticides, without which yields would be substantially lower. Second, they provide most of the energy needed to move agricultural inputs (including water) and agricultural outputs to and from farms, markets and consumers. Third, fossil fuels also provide the energy for running farm machinery. Fourth, they have helped increase atmospheric carbon dioxide concentration, which increases the rate of photosynthesis and water use efficiency in crops (and other vegetation). Fifth, much of the decrease in post-harvest losses, from farm to eventual consumption, also depends on fossil fuel powered technologies (e.g., refrigeration, storage in plastic products, and more rapid delivery systems).

This review reports on two studies which together can be used to provide a notion of the lower bound contribution of fossil fuels to global food production. Both address nitrogen fertilizers and pesticides, that is, they address only the first of the five pathways sketched out above by which fossil fuels enhance food supplies. Consequently, considering only this pathway would likely understate the contribution of fossil fuels to global food production.

Contribution of Nitrogen Fertilizers to Global Food Production:
Nitrogen, the fourth most abundant element in the human body, is critical for life on earth. It is an essential component of amino acids, proteins, RNA and DNA. Without it, plants would not grow and there would be no food.

It is also the most abundant gas in the atmosphere. However, plants are generally unable to directly use the nitrogen in the air for their growth. For that, nitrogen has to be "fixed" in the soil (or other growth medium) via either natural processes (e.g., through the action of various soil or aquatic bacteria) or synthetic processes. Generally, natural processes are unable to fix nitrogen in the amounts needed to feed humanity. This is why synthetic processes have to be used to fix nitrogen in the form of fertilizers which can then be used to grow crops.

Synthetic fixation of nitrogen is accomplished via the Haber-Bosch process. In this process, invented in 1908, hydrogen is first produced from natural gas, and then reacted with nitrogen from the air under very high temperature and pressure in the presence of a catalyst (generally iron). Because the hydrogen is derived from natural gas, and the need for high temperatures and pressures, the entire process is very energy-intensive.

Erisman et al. (2008) estimate that in the 100 years since the invention of the Haber-Bosch process, that even as the global population has increased, the percentage of global food production dependent on nitrogen from the Haber-Bosch process has also grown. By 2008, they estimate, it was responsible for 48 percent of global food production (see Figure 1 below). Thus, as they note, "the lives of around half of humanity are made possible by Haber-Bosch nitrogen." Their estimate, which is generally consistent with earlier estimates from Smil and Stewart et al. (2005), assumes that in the absence of the Haber-Bosch process, other substitute technologies would have boosted productivity by 20% between 1950 and 2000.


Figure 1: The percentage of the world's population estimated to be fed through the Haber-Bosch process, 1908 to 2008 (indicated by the short dashed line, right axis). Trends in human population and nitrogen use throughout the twentieth century are also shown. The total world population is shown by the solid gray line (left axis). The estimate of the number of people that could be sustained without nitrogen from the Haber-Bosch process is shown by the long brown dashed line. The average fertilizer use per hectare of agricultural land (blue symbols) and per capita meat production (green symbols) is also shown. Source: Erisman et al. (2008).

Figure 1 shows that in the absence of the Haber-Bosch process, the world would have had enough food to feed only 3.5 billion people (out of a world population of 6.7 billion) in 2008. It would be even fewer if there were no fossil fuels. This is because regardless of which substitute technologies are used they would more likely than not rely on energy to one degree or another -- as no substance can be extracted, moved, processed and distributed without an investment of energy. And in today's world, energy is synonymous with fossil fuels for practical purposes. Currently, 81% of the world's energy consumption is derived from fossil fuels (6% from nuclear). Consequently, the 48% estimate derived by Erisman et al. (2008) as the contribution of the Haber-Bosch process to world food production is a lower-bound estimate.

Contribution of Pesticides to Global Food Production:
Used data from 19 regions around the world for the period 2001-03, Oerke (2006) estimated losses in five major food crops from the full gamut of pests: pathogens (fungi, chromista, bacteria), viruses, animal pests, and weeds. In the absence of pesticides, those pest-induced losses amounted to 50-77 percent of the world's wheat, rice, corn, potatoes and soybean crop. Fortunately, pesticides have reduced these losses to 26-40 percent. But most pesticides are made from feedstock derived from petroleum, another fossil fuel. [Oerke also estimated loses for cotton, but that is not a major food crop, so will not be discussed further here.]

If one assumes that the mid-point of the above ranges for actual and potential losses due to pests applies to global food production, then in the absence of any pesticides, yields would be 46% lower. However, one ought to expect that in the absence of fossil fuels, substitute pesticides would be employed. In the following, it is assumed that in the absence of fossil fuels, actual yields would be 10% lower, although it might be lower still. But 10% will serve the purpose of developing a lower-bound estimate of the contribution of fossil fuels to food production.

A Lower-Bound Estimate of the Contribution of Fossil Fuels to Global Food Production
Combining the lower bound estimates of the contribution of fossil fuels to food production, via nitrogenous fertilizer and pesticidess indicates that because of fossil fuels, food production has increased by at least 114%. That is, in their absence, food production would be at least 53% lower. And the corollary to this is that, in the absence of fossil fuels, the world would need at least 114% more cropland, but conversion of habitat to cropland is generally regarded to be the primary threat to ecosystems and biodiversity worldwide (Wilcove et al., 1998; Millennium Ecosystem Assessment, 2005).

Additional References
Erisman, J.W., Sutton, M.A., Galloway, J., Klimont, Z. and Winiwarte, W. 2008. How a century of ammonia synthesis changed the world. Nature Geoscience 1: 636-639.

Fogel, R.W. 1995. The Contribution of Improved Nutrition to the Decline of Mortality Rates in Europe and America. In: Simon, J.L. Ed. The State of Humanity. Cambridge, MA, Blackwell, 61-71.

Millennium Ecosystem Assessment [MEA]. 2005. Synthesis Report. Washington, DC, Island Press.

Oerke, E.-C. 2006. Centenary Review: Crop Losses to Pests. Journal of Agricultural Science 144: 31-43.

Stewart, W.M., Dibb, D.W., Johnston, A.E. and Smyth, T.J. 2005. The Contribution of Commercial Fertilizer Nutrients to Food Production. Agronomy Journal 97: 1-6.

Wilcove, D.S., Rothstein, D., Dubow, J., Phillips, A. and Losos, E. 1998. Quantifying threats to imperiled species in the United States. BioScience 48: 607-615.

Archived 7 December 2011