What do vertical farms, green roofs, soft cars, breathing walls, and Dongtan, China, have in common? They were all subjects of discussion at Friday’s Future Cities event in New York City, part of the four-day 2008 World Science Festival.

To a packed house, Columbia University microbiologist Dickson Despommier described his vision for feeding the planet’s burgeoning, and increasingly urban, population. The vertical farm takes agriculture and stacks it into the tiers of a modern skyscraper. Instead of stopping at the corner pizzeria for dinner, Despommier suggested, you could pluck a nice head of lettuce, maybe some corn, and some tomatoes for a big salad, all in your own building, on the way to your apartment. You can’t get fresher or more local than that.

According to Despommier, the farms will be “grown organically: no herbicides, pesticides, or fertilizers.” (Of course, being indoor, there won’t be many insects to spray for.) The farms will also require much less irrigation since all water can be re-circulated, and they’ll curb the growing pressure to turn forest into farmland.

The vertical farm sounds (and looks) pretty amazing, and certainly Despommier deserves much credit for thinking boldly … but I was left with several questions.

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How, for instance, do the crops on a completely bug-free indoor farm get pollinated? Would this system only work for a few fruits and vegetables, or also grains? (It’s one thing to imagine urbanites planting some veggies on a veranda, but very much another to contemplate how this would work with things like wheat, rice, sugar, and corn.) The much larger question, of course, is yield. How many of these high-rise farms would it take to put even a minor dent in global food consumption?

That said, I enjoyed Despommier’s spirited talk enormously.

Here’s a short list of the other participants in last night’s panel, if you’d like to read more about them:

Blaine Brownell is an architect with expertise in how revolutionary eco-materials have the potential to facilitate sustainable building and design. He is a visiting professor in sustainability at the University of Michigan as well as founder and director of the design/materials research firm Transstudio.

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Majora Carter is a leading environmentalist whose rallying cry is “Green the Ghetto.” A 2005 MacArthur fellow, she is the founder of Sustainable South Bronx, a community-based organization that is spearheading efforts to revitalize disadvantaged neighborhoods in New York City and beyond.

Dickson Despommier is a pioneering researcher in the development of urban vertical farm skyscrapers for food production. He is a professor of public health and microbiology in environmental health sciences at Columbia University’s Mailman School of Public Health.

Peter Head is an expert on the sustainable development of cities and the project leader for China’s first eco-city, Dongtan. An award-winning structural engineer, he is the director of Global Planning at Arup, the worldwide engineering, design, and consulting firm. Head was recently named one of “50 global green heroes who could save the planet” by The Guardian.

Walter Isaacson is the president and CEO of the Aspen Institute. He has been the chair and CEO of CNN and the editor of Time magazine. He is the author of Einstein: His Life and Universe, as well as biographies of Benjamin Franklin and Henry Kissinger.

Mitchell Joachim is an architect and urban designer as well as a partner in Terreform, a New York-based organization for philanthropic architecture and ecological design. His design of a compact, stackable “city car,” developed with the MIT Smart Cities Group, was a 2007 Time Magazine Invention of the Year.