The global production of biofuel, an energy source harnessed from different types of agricultural crops, has nearly quadrupled from 17 thousand million liters in 2000 (Balat 2007) to 65 thousand million liters in 2008 (Biofuels Platform 2010). Many governments around the world are aiming to transfer much of their dependence on fossil fuels over to the more renewable biofuel in the hopes that CO2 emissions from fossil fuels may be reduced. However, the crops that are necessary for the production of biofuel require inorganic phosphorous fertilizer, which is also necessary for global food production and has a limited supply here on Earth. Today, global biofuel production utilizes about 2% of inorganic phosphorus fertilizer production. As governments aim for even higher productions of biofuel than ever before, Hein et al. (2012) aim to answer the question of whether the mitigation of CO2 emissions should be chosen at the expense of depleting Earth’s precious phosphorus supply. The depletion of the phosphorus supply for biofuel production will negatively affect future food supply by raising food prices and exhausting the necessary phosphorus fertilizers for food crops. With more informed knowledge about how phosphorus is mined, used in agriculture, and ways in which it can be recycled, more efficient ways to combat the depletion of global phosphorus reserves can be developed. —Shelby Long
Hein, L., Leemans, R., 2012. The Impact of First-Generation Biofuels on the Depletion
of the Global Phosphorus Reserve. AMBIO 41(4), 341–349.
Hein et al. examined the current uses of phosphorus fertilizers in the production of biofuel using statistics from FAOSTAT, crop data, and fertilizer data from the International Fertilizer Industry Association. They analyzed how the amount of phosphorus depletion compares to the avoided CO2 emissions from fossil fuels in order to determine whether the shift in energy supply towards biofuel is ultimately more favorable. They focused on the seven main crops used for biofuel production—sugarcane, corn, rapeseed, soybean, wheat, sugarbeat, and palmoil (Balat and Balat 2009). The production of biofuel also results in co-products, such as corn gluten feed, rape meal, soy meal palm kernel. Many of these co-products are used for animal feed or other economically-valuable purposes. In order to determine the amount of phosphorus that is used in biofuel production Hein et al. adjusted for the share of phosphorus that contributed to the production of co-products as opposed to the biofuel. They calculated the proportion of phosphorus used in biofuel production by dividing the value of biofuel production by the value of the total production. They then calculated how much phosphorus is required to produce 1 gigajoule (GJ) of biofuel energy and how much CO2emissions could be avoided per GJ of biofuel energy. Hein et al. compared these amounts to the level of CO2 that is acceptable to emit while still maintaining a less than 2˚, 3˚, and 4˚C increase in global temperatures. They also took into account that the exact size of the global phosphorus reserve is uncertain, so they used a low and high estimate of 16 thousand million ton (Jasinski 2010) and 65 thousand million ton rock phosphate (Jasinski 2011). Hein et al. then compared the amount of phosphorus required to produce 1 GJ of biofuel energy to the high and low estimated values of the global phosphorus reserve.
Using the calculated values of phosphorus amounts used to produce 1 GJ of biofuel energy and amounts of avoided CO2 emissions per GJ due to biofuel production, Hein et al. were able to compare the effects of biofuel versus fossil fuel production. They took into account the high and low estimates of the global phosphorus reserve when comparing the avoided CO2 emissions to the amount of phosphorus reserve depletion during biofuel production. Hein et al. found that in each case, except for the scenario with the 2˚C temperature change threshold in conjunction with the high reserve estimate (65 thousand million ton rock phosphate), the phosphorus depletion exceeds the CO2emissions avoided. In the 2˚C exception, sugarcane was the only crop out of the seven taken into consideration that exhibited phosphorus depletion, positively outweighing the level of climate change mitigation. These results are important in forming future policy on energy production because they illustrate the wide range of factors that must be taken into account when evaluating the pros and cons of various energy sources. Climate change mitigation is not the sole factor when determining levels of biofuel production because phosphorus reserve depletion can be similarly devastating to life on Earth.
Phosphorus is lost through erosion in agricultural fields, inadequate storage and transport, and most especially during refining steps where much of the biofuel production waste becomes liquid that is difficult and expensive to recycle. As governments continue to set even higher target levels for biofuel production, we must take into account the tradeoffs taking place between the exhaustion of precious and limited phosphorus reserves and climate change mitigation. In order to prevent the future threats against food security, policy must be enacted to increase the efficient use of phosphorus (Ometto et al. 2009). Although exact values of phosphorus reserve size and acceptable temperature increases are uncertain, it is clear through the research of Hein et al. that in most cases the depletion of the global phosphorus reserve does not positively outweigh the resulting climate change mitigation.
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