Biocarburants : calculons les faits

Les biocarburants sont favorables à l'environnement puisque, théoriquement, ils recyclent le carbone de l'atmosphère et qu'ils peuvent facilement être utilisés dans les véhicules. Par contre, l'auteur, Tim Moerman, constate que malgré ces avantages les problèmes qui sont rattachés aux biocarburants sont nombreux.

Si l'on tient compte du montant de pétrole utilisé aujourd'hui, une quantité énorme de terrain de ferme serait nécessaire pour produire l'équivalent en biocarburant. Malgré le fait que des terrains moins fertiles peuvent être ensemencés pour générer des produits agricoles capables d'être utilisés comme biocarburant, plusieurs terres devraient être conservées pour la production de la nourriture. En préservant une portion importante des terrains, la production massive de nourriture ne fait qu'alimenter les riches en laissant les pauvres sans nourriture.

De plus, une production intensive de plantes transformables en biocarburant épuiserait rapidement la terre de ses nutriments. Une demande croissante d'énergie provoquera donc une réduction de la fertilité de la terre.

L'auteur offre une solution : un changement de comportement et de conditions de vie de la part des pays les plus riches du monde.

Biofuels: 
Doing the Math 

Tim Moerman, MCIP
Urban Planner
Moncton, New Brunswick
June 2007

s alternatives to petroleum, biofuels such as ethanol and biodiesel have two major advantages.  Firstly, they are theoretically carbon-neutral, in that they recycle carbon dioxide already in the atmosphere rather than adding to it from fossil fuel deposits.  Secondly, they can be used to run our existing motor vehicle fleet and infrastructure.  This makes them extremely attractive to a society that wants to keep enjoying the mobility of personal automobiles without (further) disrupting the global climate.

Unfortunately, these qualitative advantages are overshadowed by enormous problems, which become obvious once we actually do the math and look at biofuels from a quantitative standpoint.

A barrel of oil contains 6100 megajoules of energy.  Today, the world uses about 30 billion barrels of petroleum and natural gas liquids each year.  Roughly half of that,1 or 91.5 trillion megajoules' worth, is used for transport fuels.


A barrel of oil contains 6100 megajoules of energy.
(photo: Engi
nes of Our Ingenuity)

There have been a number of studies on how much total biofuel (including byproducts) can be produced per hectare.  These range from 57,650 MJ/ha2 to 108,800 MJ/ha.3  This works out to between 850 million and 1.6 billion hectares of land required to produce the gross equivalent of the oil we use today for transportation.4

There are between 1.5 billion5 and 2.4 billion hectares6 of arable land on Earth.  So, it would take the equivalent of between 35% and 107% of all the potential farmland on the planet to produce enough biofuels to replace today's transport oil consumption.

Today, even with unprecedented farm productivity, plus the ability to store and transport food over long periods and distances, 800 million people worldwide are still chronically malnourished.  Futhermore, today's productivity is itself dependent on enormous fossil fuel inputs, the main limiting factor being the artificial nitrogen fertilizers made from natural gas.  Research by Wolf (2003) suggests that without these nitrogen inputs, per-hectare farm yields would drop by between one-third and one-half.7  Since natural gas is itself being depleted, we can look forward to a day when we need a lot more farmland -- between half again and twice as much-to sustain today's farm yields.


Today's productivity is itself dependent on enormous fossil fuel inputs. 
(photo: Dexter's Farm)

It has been suggested that biofuel produced from cellulosic plants such as switchgrass could make use of marginal grasslands, leaving the more fertile farmland for food production.  And there is, in fact, a lot of grassland on Earth-some 3.5 billion hectares of it.8  But there are still several problems with this approach.  First, as mentioned above, we'll need all our farmland and then some to produce food.  The "and then some" is going to have to come out of our grasslands.  The reason humans domesticated meat animals in the first place is that they can produce food from otherwise marginal land.  A cow basically takes a plant that humans can't eat (grass) and turns it, albeit very inefficiently, into something we can (meat and milk).  We are likely to need our grasslands to raise cattle the old-fashioned way.

Secondly, it would be painfully naive to assume that the best land will be saved for food production.  Will farmers use their most productive land to grow food for poor people when they could use it to produce luxury goods for the rich?  It's hardly as if they do today.  Currently the market devotes a huge part of the world grain crop not to feeding hungry people, but to fattening up cattle to produce meat for wealthier markets.  A more ominous example is the recent (very small) increase in ethanol production in the United States, whose effect on corn prices in turn helped drive a 400% increase in the price of tortillas in Mexico.9

The third problem is that even if we stick to growing switchgrass on marginal land, the large-scale growth and removal of plant matter may quickly deplete the soil's nutrients.  The graveyard of history is full of civilizations that collapsed because-even with farming practices that were in many ways more sustainable than today's-they over-exploited and destroyed their farmland.


Will farmers use their most productive land to grow food for poor people when they could use it to produce luxury goods for the rich?
(Photo: Tim Moerman)

And, as bad as the numbers are for biofuels today, they are likely to get worse.  The world's population, having already overshot its sustainable carrying capacity, is still growing.  The International Energy Agency projects a 50% increase in global energy demand by 2030.10  Climate change, combined with the already-advanced depletion and erosion of our existing farmland, and exacerbated by the depletion of the natural gas we currently use to make artificial fertilizers, are likely to reduce our ability to grow crops in the future.  Many of our alternate food supplies, such as ocean fisheries, have been completely decimated.  In other words, we face a future of more mouths to feed, higher demand, declining supply of critical resources, and reduced flexibility.  To devote our fertile land to producing motor fuels, while blindly assuming that the food situation will somehow work itself out, is to flirt with genocide.

What is to be done?

The situation is grim but not hopeless.  Today's consumption of energy and resources is so badly managed (or not managed at all, this being the defining trait of a pure market economy) that there are enormous opportunities for improved efficiency.  These will require substantial lifestyle changes on the part of the world's wealthy nations.

Unfortunately, the current vogue for biofuels is driven by people's desire to believe that they don't have to modify their behaviour-that they can have their cake, eat it, and burn it in the gas tank.  Dispelling this foolish and dangerous notion must be our first priority.

[1] U.S. Energy Information Administration, International Energy Annual 2003.  May-July 2005.
[2] Patzek, 2004.  “Thermodynamics of the Corn-Ethanol Biofuel Cycle.”  Critical Reviews in Plant Sciences 23(6), pp.519-567.  2004.
[3] Figure for cellulosic (switchgrass) ethanol production from Farrell, Alex et. al. “Energy Balance Analysis Meta Model (EBAMM) Release 1.0.”  December 26, 2005.
[4] What’s worse, the per-hectare biofuel yields cited above are gross yields, not net yields.  In other words, we must subtract the energy used in growing, harvesting and processing the biofuel crops, as well as the energy contained in the fossil fuels that made the pesticides and fertilizers.  When those numbers are taken into account, the net energy yield for grain-based biofuels generally ranges from negative (i.e., it takes more energy to produce the ethanol than you get in usable fuel, making it pointless from an energy capture standpoint) to very, very low.
[5] Nonhebel, Sanderine.  “Renewable Energy and Food Supply: Will There Be Enough Land?”  Renewable and Sustainable Energy Reviews 9, pp. 191-201.  2005.
[6] Wolf, J. et. al.  “Exploratory study on the land area required for global food supply and the potential global production of bioenergy.”  Agricultural Systems 76, pp. 841-861.  2003.
[7] “The crop rotations with leguminous crops in the LEI [i.e., without artificial nitrogen fertilizers] system resulted in a modeled nitrogen supply from mainly biological N fixation of 90 kg N ha_1 year_1.  This N supply was only 35–50% of that for a crop in the HEI system and hence, yields were proportionally lower.” Wolf et.al. 2003.
[8] Identified as pasture in Nonhebel 2005.
[9] “Mexicans Stage Tortilla Protest.” BBC World News, February 1, 2007.  http://news.bbc.co.uk/2/hi/americas/6319093.stm
[10] “World Energy Outlook 2006.” International Energy Agency.  2006.  http://www.worldenergyoutlook.org/summaries2006/English.pdf