Biodiesel Resource

Biodiesel has a Closed Carbon Cycle; Therefore it does not Contribute to Global Climate Change

• In the natural carbon cycle, there are two main processes that occur: photosynthesis and metabolism.
• During photosynthesis, plants use carbon dioxide and produce oxygen
• During metabolism, oxygen is used and carbon dioxide is a product

Humans impact this natural carbon cycle during the combustion of any type of fossil fuel, which may include oil, coal, or natural gas. Fossil Fuels were formed very long ago from plant or animal remains that were buried, compressed, and transformed into oil, coal, or natural gas. The carbon in fossil fuels is "fixed" in place and is essentially locked out of the natural carbon cycle. Humans intervene by burning the fossil fuels. During combustion, the hydrocarbon fossil fuels react with oxygen to form carbon dioxide and water molecules, which are released into the atmosphere.

The question becomes: What effect does this extra carbon dioxide have? There is considerable debate about the consequences the greenhouse gas effect may or may not have. The widely accepted fact is that human activities have changed the chemical composition of our global atmosphere through the buildup of greenhouse gases. The main greenhouse gases (GHGs) of concern are carbon dioxide (CO2), nitrous oxide, and methane. Like glass on a greenhouse, these gases have heat-trapping capabilities. Carbon dioxide in particular has risen in our atmosphere since we began burning fossil fuels for energy.

Although global climate change is a hotly debated science, evidence shows an extremely strong correlation between increased carbon dioxide concentrations in our atmosphere and increased global temperature. Since the beginning of the industrial revolution, carbon dioxide concentrations have risen 30-35%. The Intergovernmental Panel on Climate Change (IPCC) reported in 2001 that carbon dioxide concentrations have increased from approximately 280 parts per million by volume (ppmv) in pre-industrial times to 367 ppmv in 1999. The IPCC also stated that “this concentration has not been exceeded during the past 420,000 years, and likely not during the past 20 million years. The rate of increase over the past century is unprecedented.” The IPCC has zero doubt that the “the present atmospheric CO2 increase is caused by anthropogenic emissions of CO2.” Anthropogenic emissions are those caused by human activity.

In 2003, petroleum emissions amounted to 2,500 million metric tons of CO2. Although coal produces the most CO2 per unit of energy gained, petroleum is currently producing the most CO2 emissions because of consumption increases. In 1999, the transportation sector overtook the industrial sector as the largest source of atmospheric energy-related CO2. Between 1990 and 2002, on-highway vehicle miles traveled increased by 32 percent and between 1990 and 2003, transportation CO2 grew by 19%.

Greenhouse gas emissions per unit of GDP did decline by 21.3 percent and CO2 emissions per unit of GDP declined by almost 19% in the same time frame of 1990-2002. A major reason for the decline in greenhouse gas emissions is improvement in vehicle technologies. Engineers are designing more efficient, cleaner vehicles. However, the percentage of vehicle miles traveled has increased dramatically, and mobility and convenience are important American values. As a result, the overall CO2 emitted has increased. Transportation related carbon dioxide is one of the predominant sources of energy-related U.S. greenhouse gas emissions. This becomes even more apparent when energy-related CO2 emissions are represented graphically:

Greenhouse gas emissions allocated to economic sectors in teragrams of carbon dioxide equivalent

In general, biodiesel decreases carbon dioxide and methane emissions. In theory any fuel produced entirely from biomass can have a closed carbon cycle since all of the carbon within the fuel came from the plants it was made from, and the carbon in the plants came from the atmosphere. As Figure 7 shows, when plants grow they take CO₂ from the air to make the stems, roots, leaves, and seeds. Oil from the seeds is converted to biodiesel, which when burned produces CO₂ and other emissions, which returns to the atmosphere. This cycle does not add to the net CO₂ concentration in the air because the next, for example, soybean crop will reuse the CO₂ in order to grow. Since fossil fuels are normally still used to produce biodiesel, the recycling of CO₂ with biodiesel is not 100%, but substituting biodiesel for petroleum diesel reduces life-cycle CO₂ emissions by 78%. A 20% biodiesel, 80% petroleum blend reduces CO₂ by almost 16%. The percentages may seem low but they equate to huge numbers! In contrast, petrodiesel requires 100% new CO₂ to make and emits another 100% more when used. The petrodiesel life cycle emits 178% more CO₂ than biodiesel.