I agree the footprint is tiny. But the amount of farmland is vast. At the equivalent of 150 acres it pencils out to about 5000 vertical farms to equal the farmland of New Jersey. 50,000 to equal the farmland of New York State and 850,000 to equal that of Texas. [1] For comparison, New York City has approximately 1,000,000 buildings and structures [2].
Just running back of envelope calculations using cropland instead of farmland:
20 million people in NYC Metropolitan Statistical Area [wikipedia]
324 million people in the US [wikipedia]
406 million acres of crop land in US [3]
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25 million acres of cropland for NYC MSA [per capita basis]
That's about 165,000 high tech farms at 1:150 acres. At 70,000 square feet per farm it's 11.5 billion square feet. For comparison, there are 2 billion combined total square feet of office space in the major US markets[4]. Converting all of it to vertical farming would be equivalent to the per capita cropland for the NYC MSA if my calculation is high by more than 500% and if pastureland (another 30 million acre equivalents [3]) aren't part of the picture.[5]
More locally converting all Manhattan's 500 million square feet of office space [4] to vertical farming could provide about 5% of the cropland equivalent for the New York City MSA. Or roughly half the 945,000,000 square feet of vertical farms to provide Manhattan's population of 1.6 million people with a per capita cropland equivalent.
[5]: For equity, cropland does include a lot of cotton even if it's not that much relative to pastureland. On the other hand, major food crops like corn and soy and citrus don't provide the same vertical density as leafy greens.
While I agree that the world's appetite for leafy greens will not be sated by growing them in warehouses, the debate over whether worldwide food production can ever migrate to this type of system should probably be framed in terms of something like protein or calories produced per acre. What this movement is really about (it seems to me) is figuring out a way to feed the developing world in a way that does not involve converting tons of new rainforest to farmland or inundating additional watersheds.
Just running back of envelope calculations using cropland instead of farmland:
That's about 165,000 high tech farms at 1:150 acres. At 70,000 square feet per farm it's 11.5 billion square feet. For comparison, there are 2 billion combined total square feet of office space in the major US markets[4]. Converting all of it to vertical farming would be equivalent to the per capita cropland for the NYC MSA if my calculation is high by more than 500% and if pastureland (another 30 million acre equivalents [3]) aren't part of the picture.[5]More locally converting all Manhattan's 500 million square feet of office space [4] to vertical farming could provide about 5% of the cropland equivalent for the New York City MSA. Or roughly half the 945,000,000 square feet of vertical farms to provide Manhattan's population of 1.6 million people with a per capita cropland equivalent.
[1]: http://www.stuffaboutstates.com/agriculture/farm_by_total_ac...
[2]: http://www.nyc.gov/html/sirr/downloads/pdf/final_report/Ch4_...
[3]: http://www.ers.usda.gov/about-ers/strengthening-statistics-t...
[4]: http://www.colliers.com/-/media/files/marketresearch/uniteds...
[5]: For equity, cropland does include a lot of cotton even if it's not that much relative to pastureland. On the other hand, major food crops like corn and soy and citrus don't provide the same vertical density as leafy greens.