Bioenergy has hidden costs

There always seems to be a hidden cost. It seems that we can never win.

Biofuels are no exception.

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It seems that the latest discussions around energy focus on the idea of using biofuels as a solution. It sounds good - using biomass to replace fossil fuels. And the solution generally offered in this region is to switch from natural gas to wood as a source of heat.

However, biofuels are not always an environmentally friendly solution.

At a simplistic level, it might seem to be the case. Burning a tree creates carbon dioxide and water vapour - the very same compounds needed to make more trees. All you need to do is throw in some sunlight. But the rate of tree growth is not commensurate with the rate of carbon dioxide production.

Indeed, it can take 60 years for a tree to reach maturity in the north and only a few hours to burn it. This means that the carbon dioxide released by combusting a tree will reside in the atmosphere for the next 60 years. The trees that get burnt next year will add their carbon dioxide for the following 60 years. And so on.

Wood burning might sound like a good plan. Certainly it will avoid the carbon tax that our government has imposed on natural gas. But it will not address the central issue that there is too much carbon dioxide in the atmosphere.

But, critics argue, increased carbon dioxide will result in increased tree growth. More carbon dioxide means more wood.

If carbon dioxide was the limiting reagent in the reaction, then this would be correct. However, a tree's growth is not limited by carbon dioxide. In fact, the growth rate of a tree has little to do with the carbon dioxide content of the atmosphere and a lot to do with the availability of nutrients in the soil. Without fertilization, trees are not going to grow any faster.

There is a caveat to that statement. A slight increase in the length of the growing season as it gets warmer won't change the rate of growth but the total amount of wood generated annually will increase slightly. Unfortunately, even an increase in the growing season of 10 per cent will only shorten the time to maturity by maybe six years from 60 to 54. Not enough to make a difference.

It is the nutrient requirements that make biofuels unattractive as a source of carbon for running the economy. Period.

Not just trees but the various proposals that exist for using other agricultural crops, such as switchgrass or canola. Aside from removing valuable arable land from the production of food crops and limiting biodiversity, the requirement for fertilizers ultimately limits the effectiveness of using plants as fuel.

Most studies have centered on corn as it is presently being used to make ethanol. An acre of good farmland, under good weather conditions and rainfall levels, will generate about 135 bushels of corn. But, for the sake of argument, let's say that we use genetically modified corn and we can get that yield to 150 bushels.

This is enough corn to generate 1,500 litres of ethanol or about 40 per cent of the average annual consumption for a car in North America.

To generate that corn, you would need 550 kilograms of high-grade fertilizer, 70 kilograms of agricultural limestone, 125 kilograms of magnesium sulfate, 15 kilograms of powdered sulfur, and seven kilograms of iron sulfate.

There are even a few more inputs but they don't amount to a kilogram of material. And this is not counting the 4,000 tonnes of water required. After all, we are assuming adequate rainfall.

All of these fertilizers - nutrients - are either mined or manufactured and need to be moved from source to field, requiring transportation which burns fuel. Further, the ammonia content of the high-grade fertilizer is presently synthesized using the excess hydrogen generated at refineries.

In essence, fertilizer requires fossil fuels to make.

Where is the advantage in all of this?

Many people have argued that we can grow fuel crops without these inputs. Unfortunately, the minerals and nutrients must come from somewhere. Stripping them out of the ground only leaves the ground unable to support further crops.

This is what happens in the Amazon where the soil reclaimed from the forests is nutrient poor and will only yield a couple of years of growth before it is abandoned for new fields. Many areas of the world suffer poor growing conditions because of nutrient depletion. It is not a sustainable system.

Switching to bio-fuels might sound environmentally friendly, but when you examine the hidden costs things don't look quite as good. The solution isn't a different source of carbon-based compounds, but a change in the way that we use and think about energy.

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