Typical office light is only about one percent as intense as the full sunlight needed to grow crops, Bugbee notes.
"People get confused about the amount of light needed to get plant yield versus the amount of light needed to keep people happy and productive and healthy," he said. "They are roughly a hundred-fold different."
Despommier counters that architects are already designing buildings to harvest the maximum amount of natural light.
What's more, by incorporating new energy sources such as hydrothermal and wind power, these buildings don't necessarily have to look like typical skyscrapers.
Another consideration is creating a vertical farm design that would be economically viable.
Despommier said he is particularly intrigued by Eco-Laboratory, created by Seattle, Washington-based architectural firm Weber Thompson.
Other proposed buildings, which can be solely farms or mixes of farms and houses, would reach up to 60 stories high.
But the Eco-Lab complex would be just 12 stories tall and would mix residences with gardens that produce food for the local neighborhood.
"This was [an] attempt at something that seemed viable to a developer," said project designer Myer Harrell.
Residents might tend the crops and own equity in their production, or they might assign the work to outside agricultural firms and later purchase the crops at a local market.
Selling the housing at market rate and proceeds from the farmers' market could generate significant funds.
For example, Harrell said, sales of tomatoes and lettuces grown in the high-rise's hydroponic gardens could total about a million U.S. dollars a year, based on revenue minus the base production costs.
The market viability of Eco-Lab, Harrell noted, distinguishes it from taller vertical farm proposals.
"Those [designs] have merit, but it would be difficult for us to see this idea jump to a larger scale right away," he said.
Harrell believes breaking ground on Eco-Laboratory or a similar scaled-down building could be feasible within the next few years. Even the burst housing bubble and global recession, he noted, may work to the concept's advantage, as people become more interested in self-sufficiency such as growing their own food.
(Related video: "Urban Farming Blooms in London".)
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The need for vertical farms is most urgent in Southeast Asian countries, Columbia University's Despommier said. Many of those places have seen increasing crop failures due to extreme weather and disease amid surging population growth.
(Related: "Food of the Future to Be More Diverse?")
Indoor farming eliminates vagaries of the weather, he said. And even if disease destroys a harvest, the next crop can be planted immediately.
Bugbee, the vertical farming critic, has another solution to feed Earth's swelling population: Eat less meat. This would free up land currently grazed by livestock to be sown with food crops.
"That," he said, "is a rock-solid principle if you are looking for a way to be environmentally responsible."
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