A recent report from Natural Resources Defense Council and Union of Concerned Scientists, Nathanael Greeneâ€™s Growing Energy: How Biofuels Can Help End Americaâ€™s Oil Dependence (pdf), shows both the excitement of a new technology and how easy it is to overestimate the advantages.
The paper begins by observing that no solutions can be found without reducing demand substantially. Improving efficiency and Smart Growth are necessary to decrease fuels consumption by 2050 to below 2000 levels â€“ Iâ€™d like to read more about how they expect to see this occur, as US population in 2050 is expected to be 40% higher, 420 million people. Biofuels would supply the majority of the remaining fuels, according to this paper.
[Biofuels use plant matter, or waste matter including tires, to make fuels. The US currently consumes oil at the rate of 21 million barrels/day (2.8 gallons per capita), about 70%, 15 million barrels/day, for fuels.] The proposed plan would by 2050 replace a slight majority of the fuels used today from oil with fuels from plant matter.
Currently biofuels are made from waste oils or other waste (usually biodiesel, or diesel from plant matter), or ethanol from sugars. In the US, the sugar of choice is in corn, while in Brazil sugar cane is favored. Cellulosic biomass is all the above ground portion of the plant except for the seeds and fruit. Cellulose is a long chain carbohydrate that helps provide structure for plants. Along with the smaller molecule hemicellulose, found in cell walls, this accounts for 2/3 of plant mass. Lignin, about a quarter of plant mass, helps protect against pathogens because it is difficult to degrade.
The sugars in corn kernels dissolve easily in water, and are easy to ferment. The cellulose can be converted to sugars and then fermented. Lignin cannot be fermented easily, but can be made into synthesis gas, syngas, which can then be converted to fuels or burned to make electric power. There are a variety of possibilities for the products, but fuels should be a sizable portion of the mix, as no other real alternatives to fossil fuels exist (perhaps hydrogen fuel cells in a few decades, but no one knows this), while there are numerous alternatives to electricity. More experience and analysis will show what mix of power, fuels, and animal feed works best.
While carbon is released during the processing, and when the fuel is burned in an engine, carbon is absorbed initially when the plant grows. There is a net loss due to the oil used and greenhouse gases emitted in fertilizers, herbicides, etc., harvesting, and transportation. With the proper selection of crop, minimal use of fertilizers, and so on, and train transportation (lots and lots of train cars), only about 10% as much oil will be needed and greenhouse gas emitted by our current method.
A variety of plants are considered good candidates for this process, notably poplars, willows, and switchgrass. The last has been most studied, and has many attractive qualities. It is found throughout much of the US and is a perennial so no tillage is required and carbon is stored in the soil. As a native, it is resistant to local pests and diseases. It requires less herbicide and fertilizer than many crops, and is good at preventing soil erosion. It makes a good habitat for wildlife, and the twice a year harvesting can be scheduled around hatching times. It may be better to use a variety of crops to make biofuels, but switchgrass is the one now being most intensely studied.
A few numbers: average yield is about 5 dry tons/acre. With or without transgenic breeding, yield can be increased â€“ Greene estimates 12.5 dry tons/acre by 2050 without. Each dry ton of biomass should be able to replace two barrels of oil (it will make more than two barrels of ethanol, but ethanol has smaller molecules and less energy/barrel), and reduce the emissions of greenhouse gases by 1.3 tons. In the beginning, plant waste from wood, corn, etc will supply the biomass, but eventually dedicated cropland must be assigned.
My source in the field tells me this looks to be promising and well thought out. The use of switchgrass and other crops will produce a combination of electric power, fuels, and animal feeds with little oil and much reduced greenhouse gas emissions.
But most of the rest of the report raises questions in my mind, from the small (how do the advantages of using transgenes to produce much larger yields today compare with the perceived disadvantages of using transgenes, and is there too much dancing around to justify transgenes for the bacteria while avoiding them for the switchgrass?) to the large (where does all that land come from?) It is this latter that I want to address.
In the report, the assumption is that only current cropland will be used, some of which now lays fallow or is inefficiently used, and the farmer is expected to benefit, all farmers. This says to me that acreage for food and fiber will compete with acreage for fuel crops, and prices of food and fiber will increase. However, the assumptions about the needs for food and fiber seem to assume no change over 50 years, a poor assumption even with maximum penetration of transgenic crops.
The population of the US will rise 40% by 2050, and the world population will increase by about the same amount, from 6.5 billion today to 9 billion in 2050. Many of these people will want to eat more calories, and more meat, so food needs will approximately double by 2050. Asia will lose the ability to feed itself this decade. The US is likely to be exporting increasing amounts of food and fiber over the next few decades.
Additionally, the ability of the Earth to feed us will deteriorate. In many countries, problems with water, salinity, desertification, and soil loss have already led to significant loss of arable land. In the US, we are increasing soil salinity and using up groundwater. Additionally, climate change will lead to yield drops in most parts of the world now densely populated, for example, a 1 C increase in night temperature will lower rice yield by 10%. Pests able to move into new areas will be an increasing problem; they are currently devastating much of the Alaskan and Canadian spruce and pine forests. Even if precipitation increases, the soil of 2050 is likely to be dryer, and the Breadbasket states may need to add expensive irrigation.
Any plant use for other uses of oil, the 30% that doesnâ€™t go to fuels, would compete with plants used for fuels.
There will necessarily be competition for land. Any widespread shift to biofuels in a world with a growing population will require land conversion. The area not yet farmed will likely have lower productivity than current cropland â€“ this may be less of a problem for growing biofuels than food crops, but it will be a problem.
This does not mean that we should not give over some of our land to be used in this way. But there are many demands on our land and water supply, with too many hands reaching for too few slices of pie, and some of our needs will be shortchanged.
It is a problem that we perhaps should be acknowledging better today so that we can address it today.
I went to the Energy Information Administration to find out what happens to a barrel of oil. Because the products of a barrel of oil take up more volume than the original oil (lots of larger molecules broken down), percentages add to 105%.
There are many ways that petroleum (oil) is used. Oil is refined into useable petroleum products . Most of the petroleum products are used to produce energy. Other products made from petroleum include: ink, crayons, bubble gum, dishwashing liquids, deodorant, eyeglasses, records, tires, ammonia, and heart valves. From a barrel of oil, 47% is refined to gasoline for use in automobiles, 23% is refined to heating oil and diesel fuel, 18% is refined to other products, which includes petrochemical feedstock such as polypropylene, 4% is refined to propane, 10% is refined to jet fuel, and 3% is refined to asphalt.
The Greene paper says that 70% of oil consumed in the US goes to transportation, so substitutes for heating oil, petrochemical feedstock, etc, and propane may lower greenhouse gas emissions, particularly the propane and heating oil. Again, these will compete with biological substitutes for transportation fuels.