Study: Environmental benefit of biofuels is overestimated

Two scientists are challenging the currently accepted norms of biofuel production. A commentary published recently in GCB Bioenergy
reveals that calculations of greenhouse gas (GHGs) emissions from
bioenergy production are neglecting crucial information that has led to
the overestimation of the benefits of biofuels compared to fossil fuels.

   

The
critique extends to the Life Cycle Analysis models of bioenergy
production. Life Cycle Analysis (LCA) is a technique used to measure and
compile all factors relating to the production, usage, and disposal of a
fuel or product. The authors conclude that LCAs are overestimating the
positive aspects of biofuel use versus fossil fuel use by omitting the
emission of CO₂ by vehicles that use ethanol and biodiesel even when
there is no valid justification.

   

Proponents
of bioenergy argue that analyses should always ignore this CO₂ because
plants grown for biofuel absorb and therefore offset the same amount of
carbon that is emitted by refining and combusting the fuel. The
commentary critiques this method by arguing that doing so double counts
the carbon absorbed by plants when the bioenergy crops are grown on land
already used for crop production or already growing other plants
because the bioenergy does not necessarily result in additional carbon
absorption. Biofuels can only reduce greenhouse gases if they result in
additional plant growth, or if they in effect generate additional
useable biomass by capturing waste material that would otherwise
decompose anyway.

   

The
overestimation of bioenergy LCAs becomes increasingly magnified when
the omission of CO₂ is combined with the underestimation of nitrogen
emissions from fertilizer application.

According
to lead author Dr. Keith Smith, from the University of Edinburgh,
“Emissions of N₂O from the soil make a large contribution to the global
warming associated with crop production because each kilogram of N₂O
emitted to the atmosphere has about the same effect as 300kg of CO₂.” He
notes that several current LCAs underestimate the percentage of
nitrogen fertilizer application that is actually emitted to the
atmosphere as a GHG. The authors claim that the observed increase in
atmospheric N₂O shows that this percentage is in reality nearly double
the values used in the LCAs, which greatly changes their outcome.

   

Since
results of the LCAs have been widely utilized, Searchinger and Smith
conclude that the overall development and research of alternative fuels
has been heading in the wrong direction. “The best opportunity to make
beneficial biofuels is to use waste material or to focus on relatively
wet but highly degraded land,” notes Dr. Smith. If bioenergy crops are
produced on degraded land, less GHGs will be emitted and more will be
stored. There are additional benefits: this method will not compete with
crop production for food, textiles, and other products.

GCB Bioenergy

Source: Wiley-Blackwell