I watched the episode on food from the infotainment series Ecopolis. It featured a remarkably dim "scientist" Daniel Kammen, as an expert on energy and emissions issues choosing among various proposed schemes for feeding the population of an imagined future city of 18 million. The base assumption was that trucking in enough food to feed everyone would result in a lot of carbon emissions. None of the proposed schemes considered the possibility of transportation systems that do not have such emissions. Instead they focused on exceedingly improbable ideas such as rebuilding the whole city to support urban high rise agriculture without soil. Their example was lettuce grown with its bare roots being sprayed periodically with a nutrient bath.

OK, its just entertainment and politics rather than any sort of serious presentation and discussion, but it was so ignorant that the socially destructive consequences are serious. People who have no real information believe this crap.

One of the ideas for reducing emissions associated with food production involved the old myths of ruminant emissions of methane. After repeating a lot of bogus figures about methane and ruminants the systems proposed were garden variety anaerobic digesters of dairy manure slurries. With animated diagrams the basic function of such systems was explained: the slurry is inoculated with bacteria that will digest the solids and emit methane.

What is not made clear is that any organic matter will serve as feedstock for the bacteria. There's nothing special about manure in this regard. If the forage that had been fed to the dairy cattle was fed directly into the digesters the results would be much the same.

Once it becomes clear that it is bacterial digestion of organic matter in an oxygen free environment that produces methane - rather than something peculiar about ruminants - and that the results would be the same if there were no ruminants, the supposed savings from such systems evaporate. This is just another biofuels scheme like ethanol production that justifies itself by not looking at the whole system and doing good, green accounting.

All of the organic matter produced on the planet is part of a cycle in which carbon is drawn down from the atmosphere and then returned as microbes break the organic matter down into minerals and gases again. It will either go back into the air as carbon dioxide or methane depending on which microbes eat it. Aerobic bacteria - oxygen breathers - make CO2 and anaerobic bacteria make methane.

In practice some of each is always made since the oxygen available to bacteria is soon exhausted. Those who manage compost piles go to extraordinary lengths to aerate their piles so that oxygen breathing bacteria can thrive. They use huge machines to churn the piles, systems of pipes to inject air into them, and on a smaller scale they just poke holes in the piles or turn them by hand with pitchforks and rakes.

There are hot spots of methane production - point sources such as swamps, landfills, rice paddies and manure lagoons - but even if all of the organic matter was spread out evenly of the surface the amount of methane produced would be much the same, though harder to measure since there would be no point sources. It is by ignoring those non-point sources - because they are hard to measure - that focus is directed at irrelevancies. It's like looking for your lost keys at night under a street lamp. It isn't that the keys are likely to be there, it just that it's easier to see.

We need to look at non-organic sources of methane and carbon dioxide to find the extra emissions that worry us. The organic sources would exist - did exist - even when there were no humans or ruminants on the planet. The obvious big source is the mining of fossil fuels, but mining the soil to grow crops is also a big emitter.

The Ecopolis can be better understood as a confined animal feeding operation - a feedlot, a chicken factory, a CAFO. The difference is that the animals are human, but just like any animal factory the food is shipped in and wastes are shipped out. Rather than having smoke belching machines running around doing such work it is better to have electric motors driving conveyor belts or even robotic vehicles and carts. The materials could be delivered to the factory outskirts by large, efficient mass transportation methods such as trains and ships, and then distributed within the factory by efficient electric powered systems, including the plumbing systems to move liquids. The wastes are removed in a similar fashion, and provide a much better opportunity for emissions control. Send the human wastes to anaerobic digesters and derive some useful gases from them while managing a problem stream of materials that must be dealt with one way or another.

Once we grasp the nature of cities as CAFOs the problem set is clarified. Should we tear them down and return humans to their natural environments - free range humans? Or is that impossible and not ultimately an improvement from an energy and emissions perspective anyway? I find it unlikely, so the focus should be on running efficient factories. The food and wastes issues that need improvement for such factories are within its confines. It's a distribution problem. The production of food and the disposal of wastes are peripheral problems. It isn't that they are irrelevant, it's that they are external. Get the distribution issues within cities managed. The production issues are large scale and far more complex since they are planetary in scope rather than urban.