Corn ethanol and Water in the US Part 4 - by Robb

Efficiency and emissions in personal transport in the US

In the US, petroleum is primarily used in the transportation sector, 14 million barrels per day of the 20.6 mb/day consumed in 2006. In 2005 average fuel economy for all passenger cars was 22.9mpg, up from the 1990 average of 20.3mpg, for other 2-axle 4 tire vehicles, SUV’s, light trucks, vans and the like it was 16.2mpg, up from the 1990 average of 16.1mpg! 15 years of virtually no progress.

If we use a figure of 20mpg, roughly midway between the two figures above, for all light vehicles and the average distance travelled by the typical household of 24,800 miles multiplied by 104,700,000 households, we can calculate the average fuel used to be 1,240 gallons/household with a total for all households of 129,828 million gallons which breaks down to 3,091 million barrels of transportation fuel/year or 8.5 million barrels/day. (Rutledge 2006)

A standard of 40 mpg, easily achieved with current technology, would half that figure to 4.25 million barrels/day. That would be a reduction of GHG emissions of 50% from this sector which accounts for 20% of US GHG emissions, a total US GHG emissions reduction of 10%.

Ethanol, Energy, and Emissions

Corn grain ethanol only reduces GHG’s by 12% compared to gasoline with a meager 25% net energy gain, one of the lowest ratios of all biofuels. (Food and Water Watch 2007) In addition, ethanol has a more negative effect on air, water and soil quality compared to biodiesel. A study based on the 2005 crop from two institutions based in the heart of the corn belt, University of Minnesota and St. Olaf College, determined:

“In 2005, 14.3% of the US corn harvest was processed to produce 1.48x1010 liters of ethanol energetically equivalent to 1.72% of US gasoline usage...... Devoting all 2005 US corn and soybean production to ethanol and biodiesel would have offset 12% and 6% of US gasoline and diesel demand, respectively. However, because of the fossil energy required to produce ethanol and biodiesel, this change would provide a net energy gain equivalent to just 2.4% and 2.9% of US gasoline and diesel consumption, respectively.”

So referring back to the gasoline use figures mentioned earlier, and applying the 12% offset
.12 offset x 129,828,000,000 gallons = 15,579,360,000 gallons x .024 net energy gain = 373,905,000 gallons x .12 emissions reduction = 44,869,000 gallons

So for giving up the entire 2005 crop to ethanol the emissions from just 44,869,000 gallons of gasoline would have been offset, .035% of total usage in the sector which is responsible for 20% of overall GHG emissions resulting in a total reduction of .7%

There is much dissension on this issue. A 1995 USDA study found corn ethanol to have a net energy value 3X that found by ethanol dissenter, David Pimentel, and also compared many other studies. Results for net energy values of corn ethanol ranged from a low of -33,517 btu/gal (Pimentel) up to a high of +25,653 btu/gal.

The Pew Center on Global Climate Change estimates corn ethanol reduces emissions 20 to 30% compared to gasoline. If the more optimistic figure were used in the formula, using the same net energy gain, emissions reductions comparable to cutting 112,172,000 gallons of gasoline would result. This is .086% of total usage which would result in an overall US GHG reduction of 1.72% This is still a very small improvement in the GHG emissions situation in the US compared to improvements to be gained from higher fuel efficiency standards.