Reply #25: Hmmm. A metastudy that modifies the assumptions of the research it analyzes...

[GliderGuider]

Their main objection to Pimentel and Patzek is that they discount the value of DDG. So they have an input to their methodology that allows them to replace P&P's assumptions with their own. And it's even worse than that: "We used EBAMM to (i) add coproduct credit where needed, (ii) apply a consistent system boundary by adding missing parameters (e.g., effluent processing energy) and dropping extraneous ones (e.g., laborer food energy), (iii) account for different energy types, and (iv) calculate policy-relevant metrics (19)"

Hmmm. It kind of sounds like they modified a lot of parameters to suit their own judgment. As they note, the results are very sensitive to considerations of system boundaries. By altering them they have significantly reduced the value of their own result. They also give the game away when they say in the longer paper, "A more appropriate set of metrics would a) be closely correlated with key policy outcomes, ..."

The study also says, "The impact of a switch from gasoline to ethanol has an ambiguous effect on GHG emissions, with the reported values ranging from a 20% increase to a decrease of 32% ... However, current data suggest that only cellulosic ethanol offers large reductions in GHG emissions." Not terribly hopeful, is it? Especially since there is no commercial cellulosic ethanol process available for systems analysis.

Then we get to Fig. 1(A). What's this? The graph would look significantly different if hey had used absolute instead of relative MJ on the X axis. This is a standard statistical trick to sway the innumerate. Given that ethanol has an energy content of about 20 MJ/litre, the range shown (excluding that speculative outlier for cellulosic) is from about 16 to 25 MJ. Not that much of a range, especially given those system boundary issues and the fact that bogus technologies like tar sands synthetic crude would show about three times that. Their placement for cellulosic ethanol is, as far as I can tell, nothing but a a SWAG. They seem to imply that cellulosic ethanol will require virtually no external energy inputs, which doesn't pass my sniff test.

This "science" shows distressing signs of having been worked backwards from a predetermined, desired outcome. I have absolutely no confidence, based on this paper, that the studies they like (aka not Pimentel) correctly set the system boundaries. I also have no confidence in their treatment of the original studies' metrics. However, given the essentially insignificant disagreement (at least in functional real-world terms) between P&P and the others, it's not worth arguing over. In this study the GHG advantage of ethanol is insignificant to negative, the net energy return is likewise insignificant, and the sustainability of the process isn't even discussed.

Plant based ethanol is great for drinking, but the last place we should be trying to put it is in the fuel tanks of vehicles.