Most of America’s baby greens are grown in irrigated fields in the Salinas Valley, in California. During the winter months, some production moves to similar fields in Arizona or goes even farther south, into Mexico. If you look at the shelves of baby greens in a store, you may find plastic clamshells holding five ounces of greens for $3.99 (organicgirl, from Salinas), or for $3.29 (Earthbound Farm, from near Salinas), or for $2.99 (Fresh Attitude, from Quebec and Florida). Harwood’s magic number of eight dollars a pound would be on the cheap side today. Four dollars for five ounces comes to about thirteen dollars a pound.

AeroFarms supplies greens to the dining rooms at the Times, Goldman Sachs, and several other corporate accounts in New York. At the moment, the greens can be purchased retail only at two ShopRite supermarkets, one on Springfield Avenue in Newark and the other on Broad Street in Bloomfield. The AeroFarms clamshell package (clear plastic, No. 1 recyclable) appears to be the same size as its competition’s but it holds slightly less—4.5 ounces instead of five. It is priced at the highest end, at $3.99. The company plans to have its greens on the shelves soon at Whole Foods stores and Kings, also in the local area. Greens that come from California ride in trucks for days. The driving time from AeroFarms’ farm to the Newark ShopRite is about eleven minutes.

All of this makes sense. People will pay a premium for fresh produce and herbs, particularly if growing them close to consumption means that you can optimize for deliciousness rather than for transport-durability and long shelf life. I expect vertical farming to work well in this niche.

But the rest of it -- feeding all of New York City using just the space available in NYC, "Feeding the World in the 21st Century", "what might come of it when we’re nine billion humans on a baking, thirsting globe?" -- that's nonsense. For staple crops that provide most of the calories in a vegetarian diet, there is no net economic or environmental benefit to vertical farming. And there are good reasons to suspect that there will never be such benefits even as the technology evolves.

It's the vertical stacking of greenhouses that doesn't make sense outside of a high-priced freshness niche, and that's because of the requirement for artificial lighting. Artificial lighting is a very expensive way to drive photosynthesis compared to natural sunlight, and remains more expensive even with optimistic assumptions about future LED efficiency and falling costs for clean electricity. The energy requirements to grow e.g. soybeans in a vertical farm inside the NYC city limits wipe out all the environmental benefits of "locavorism," compared to just transporting them from the Midwest like usual. And New York has one of the cleaner electricity mixes in the US. It's worse if you use a fossil-heavy mix to power the lights.

I could see large scale use of greenhouses in the future, particularly things like this: http://www.sundropfarms.com/

Greenhouses and perhaps soil-free growing may be great ways to produce food in places that face extreme weather or lack soil or natural precipitation. But one level construction only, illuminated by natural sunlight. You can ship a ton of dried beans or wheat across oceans for significantly less energy than it takes to grow the same calories locally via artificial illumination.