"Carbon-Low" Fuels Compared. (May 16, 2009)

At the end of April the California Air Resources Board (CARB) set out a low-carbon fuel standard to enforce greater use of fuels to reduce greenhouse emissions, compared with petrol.

And CARB is damning of the use of ethanol derived from maize "because diverting corn into ethanol production increases deforestation and the clearing of grasslands". In fact overall it's about 5-6% worse than burning pure petroleum-derived petrol.

Not surprisingly the Renewable Fuels Association is taking issue not only with the CARB assessment but also with a regulation drafted by the US' Environmental Protection agency last year which came to  a similar conclusion.

On the other hand Princeton University's Timothy Searchinger, who initially trained as a lawyer, but now works primarily on interdisciplinary environmental issues related to agriculture, says that the so-called benefit is based on "an accounting error. They treat the land as free". With that sort of assessment in mind California's new low-carbon fuel standard will require a 10% reduction in greenhouse gas emissions from the average litre of transportation fuel by 2020. In fact CARB has used a model developed at Indiana's Purdue University that estimated that corn-based ethanol produces slightly greater greenhouse emissions than does petrol. According to the model about 30% of those emissions occurring as farmers clear land for crops.

It's reported in  Science that the data assembled by the US' EPA suggests that "an even larger area of the world's forest and grassland being converted into food and ethanol production, but ethanol receives a better overall grade [on the assumption] that current ethanol refineries are more efficient".

The matter is assuming truculent political overtones. According to  Science, US Senators from a dozen farm-states want EPA to halt any effort to calculate the greenhouse effects of land-use change caused by biofuels. "It defies common sense that EPA would publish a proposed rulemaking with harmful conclusions for biofuels based on incomplete science and inaccurate assumptions," Senator Charles Grassley (R–IA) said in March but CARB is not having it: ""We feel that our recommended value [for greenhouse emissions from land-use change] is very reasonable," but has agreed to "a full review of the issue in January 2011, 1 year before the regulation takes effect."

Below we reproduce a chart from Science which is adapted from CARB.