A couple of points about you column :“What’s up with compostable plastics?”.
Dow sold its have of the joint venture to Cargill several years ago. Cargill-Dow is now a wholly owned subsidiary of Cargill called "Nature Works LLC. They have a large production facility in Blair Nebraska that uses corn starch is fermented to produce lactic acid and that is polymerized to produce PLA. Nature Works has been developing processes to use cellulosic feedstocks (e.g. corn stover) to produce PLA but they haven’t commercialized the technology yet. PLA is used is to make plastic cups, food containers, and some clothing.
There is significant differences in opinion on the amount of fossil energy required to PLA. Small changes in some factors shift the calculations significantly. For instance, you reference a 2006 report for the Life Cycle Analysis. Corn yield per acre has increased substantially since then, which decreases the fossil energy needed to produce PLA, other biobased plastics and biofuels. One of the best sites for up to date information on Life Cycle Analysis is Argonne National Laboratory’s GREET site: http://www.transportation.anl.gov/modeling_simulation/GREET. (Disclosure: I work in Argonne’s biofuels program).
You are correct that non-biodegradable plastics may provide significant benefits for controlling GHG emissions. In a landfill, biodegradable materials produce methane. Methane has over 20 times the GHG impact than CO2 so its release from a landfill has a much strong impact that. Watson and El-Ashry just published an opinion in the Wall Street Journal (http://online.wsj.com/article/SB10001424052748704039704574616130812043404.html) discussing the impact of methane release