This post picks up a thread based on comments that Prof. Robert Brown and Prof. Bruce Dale made on my "Don't pitch low-carbon fuel ..." post. Both Robert and Bruce take strong exception to my analysis. They invoke the commonly made assumption that substituting a biofuel for a fossil fuel reduces net CO2 emissions because biofuel use recycles carbon while fossil fuel use does not.
|This widely used view of the biofuel lifecycle does not tell |
the whole story. [Image credit: www.EthanolRFA.org]
Their argument is based on the following logic:
(1) Fossil fuels send old carbon on a one-way trip to the atmosphere, thereby increasing the amount of CO2 in the atmosphere.
(2) Biofuels use carbon recently taken from the air that is then released back to the air, resulting in no net change in the amount of CO2 in the atmosphere.
(3) Therefore, substituting a biofuel for a fossil fuel reduces the rate of CO2 buildup in the atmosphere.
Although this basic analysis neglects processing emissions, we can leave those aside for the purpose of this discussion. They are not what's at the heart of the disagreement, and in any case processing emissions do get tracked by lifecycle models, e.g., as used in the RFS and LCFS.