A new idea for allowing NYC residents to grow produce locally (h/t Robin
MaroneyMoroney/WSJ Informed Reader):
High-rise city farms could allow city dwellers to eat local produce as the population of the countryside dwindles, reports U.S. News & World Report. Columbia University parasitology professor Dickson Despommier, came up with the concept with his students while investigating ways to make third-world agriculture less prone to the parasites that can enter the food chain when human waste is used as fertilizer. His “vertical farm” would work around the year without pollutants or parasites. He estimates 150 farms, 30-stories each, could feed all of New York City. It would water the plants with some of the 1.4 billion gallons of water that New Yorkers pour down the drain. The plants would be grown without soil, suspended in water or a nutrient-packed solution. Lots of windows and solar panels would bring in light. Fish would be kept in tanks and poultry in small pens. Several New York companies, including International Business Machines Corp., have shown interest in building a vertical farm, said Mr. Despommier, who predicts one will be in business in 10 years.
A 30-story building means steel-and-concrete construction, especially if each floor will be loaded up with plants and elaborate irrigation systems. Around here, that kind of building costs $300+ per square foot, without the fancy finish-out. Equivalent high-rises in NYC go for $1,000+ per square foot. That would be the market price -- or opportunity cost -- of one square foot of this "urban farmland."
Let's see. There are 43,560 square feet in an acre. That means this "urban farmland" would cost between $13 million and $43 million per acre. I don't know exactly how productive this super-duper advanced hydroponics system would be, but I doubt it's 4,000-14,000 times as productive as $3,000/acre farmland in Indiana. That locally-grown broccoli had better taste really, really good.
Update: There's a lively discussion of vertical farming over at Slashdot. Some people actually think this will make sense for New York when gas gets real expensive.
I'm always surprised that people don't have a better sense of relative magnitudes. If you assume that an acre of hydroponic "land" can support 10 people per year (a generous estimate), then 8,000 acres could support 80,000 people per year -- or 1% of New York City's population.
8,000 acres is roughly 348 million square feet, which, coincidentally, is almost exactly the size of Manhattan's entire inventory of office space. So to meet just 1% of NYC's annual food needs, you would have to find space in NYC to duplicate one of the planet's great concentrations of skyscrapers.
Out in the heartland, where space isn't as valuable, they're more likely to measure land in square miles than square feet. 8,000 acres there isn't 348 million square feet; it is just 12.5 square miles -- a tiny corner of an average county.
I'm apparently too pessimistic, though. The vertical farm people claim you can feed 50,000 people per year with just 13 million square feet of floor space. This extrapolates to 21 million square feet for 80,000 people. As best I can tell, they get there by assuming that hydroponic techniques will yield 10 to 100 times as much as dirt farming. (Someone should tell the farmers.)
Fine. So we really need just 21 million square feet to feed 1% of NYC's population for one year. No sweat. That's just eight Empire State Buildings. And, for another 792 Empire State Buildings, we could feed the other 99% as well.