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As you know, it takes more than planting trees to grow a forest.

If you let it grow back on its own, the forest will re-create itself. If you want proof of concept, look at the Northeastern U.S., which used to be farm land, but is now a haven for wildlife thanks to benign neglect.

Eliminate the herbicides and pesticides and other pressures and nature will return. Remember the Grapes of Wrath? Six-hundred-foot dust clouds blew the topsoil off our heartland, but instead of turning into a desert, the buffalo and antelope are back as is the tall grass prairie.

Another great example is the demilitarized zone between North and South Korea. No one has lived there since 1952 — it's verdant, and the tigers are back.

If we allowed the hardwood forests to grow back in Ohio, Indiana, Illinois and Iowa, they would suck up 4 percent of the CO2 we produce.

How far along are you in this process?

I've been to Dubai, Paris, Argentina and am about to go to Korea. In Dubai, I met with developers of the eco-city Masdar, and while there's a lot of interest, no one has committed yet.

The city of Incheon in South Korea, their largest port, is also creating an eco-city, and they are much more serious about vertical farming. Our proposal is about to go before the city council and the mayor.

Developers in Las Vegas, San Francisco and Nashville have expressed interest, along with many others.

Meanwhile, we have an exhibit going up at the Chicago Museum of Science and Industry — it opens on June 10. They've identified 10 innovators, of which the vertical farm is one.

The World Science Festival will be held in New York City at the end of May, where I'm also participating in two big events. One of them is "Future Cities" — the way they'll look in the future.

Holland and China have established a joint venture to establish urban agriculture. Michael Braungart (McDonough Braungart Design Chemistry) and I were the only outsiders invited to the launch meeting.

The technology is all there. NASA wants to grow food on Mars, so they've been experimenting with how to do it. They have big greenhouses growing wheat, for example.

Let's take the example of New York. The first thing you have to do is get the liquid waste, right?

That's the easy part. NYC treats 1.4 billion gallons of wastewater a day in 14 treatment plants — all the bath water, sink water, human feces and urine — and then ships it to Ward's Island for desludging.

Desludgers are giant centrifuges that act like a cream separator at a dairy farm — all the particulates are thrown against a wall of a turning drum, like a dryer. They scrape that stuff off, dry it up, which heats it and kills the pathogens. Then they tamp it into pallets and sell it to farmers as fertilizer. They chlorinate the water, send it back to the treatment plant where it's dumped into the Hudson River.

Talk about retro thinking! Use that much water once and then throw it away? If Los Angeles continues to do that they will run dry.

Isn't it better to use the water again to grow crops and dry the sludge and then burn it? The technical aspects of high tech incinerators have been solved; there's a plant in New Jersey that traps 99.99 percent of all emissions. Germany requires sewage to be incinerated in downtown business districts — the buildings are gorgeous, you'd never know it's an incinerator.

In terms of the energy required to power the plant, it would depend on the kind of renewable energy most appropriate for the site. In New York, it could be a challenge to use solar because of the number of sunny days, but they have plenty of tidal power. In Iceland, it's obviously geothermal.

How do biofuels fit in?

Biofuel crops could be grown in a vertical farm, but I think they're terribly inefficient — a waste of space and a poor use of land. And do we want to convert wheat farms into switchgrass farms?

There are other, smarter ways to solve our problems. Let's go straight to a hydrogen economy. It's easy to split off water from hydrogen because all the major power plants do that now anyway. All you have to do is collect it instead of venting it into the atmosphere as we do now.

We could collect it and allow it to combine with oxygen inside a car engine to make water, and the combination of the two would make energy.

Or imagine that every gas station has its own vertical farm. They could raise sugar beets — genetically modified sugarcane — which could produce 10 times as much sugar per beet.

What's your estimated cost to build vertical farms and what revenues do you expect to generate?

To produce a prototype would cost $10 to $20 million, while a full blown vertical farm could cost as much as $200 to $300 million.

The amount of revenue it generates depends on food prices. Michael Pollan, a professor at the University of California, Berkeley, estimates that for every calorie of food, we burn 10 calories of oil!

That means a head of lettuce that costs $1.49 a head has 75 cents of oil in it. If I don't have to transport it, store it or even wrap it in cellophane, I can sell it for half price and still make a lot of money.

It also depends on the kind of crops you grow. If you grow the most expensive crops you'll make the most profit, but then you're building a gourmet farm, not a farm to feed people.

If the U.S. took $2 billion of the $100 billion Farm Bill to construct vertical farms, it wouldn't have to worry about supporting the agricultural economy anymore.

China and India are desperate for an agricultural solution — they're throwing huge amounts of money down the black hole of pesticides and herbicides and fertilizers. In these situations, the question isn't the amount of money we can make, it's about literally being able to supply healthy food for citizens.

On the other hand, if Whole Foods wants a vertical farm on top of its building, we'll have to look hard at what it would cost.

How realistic is it that you'll actually get this off the ground?

Do we know how to do it? Absolutely. Are we going to do it? Absolutely. There will be a vertical farm within the next four years.

It might be a five-story demonstration project that can supply food for say four good sized restaurants and maybe a school and a hospital. When the scale-up issues are worked out we'll be able to ramp up to supply whole communities.

I'd like to use World Bank funding to build the first vertical farms in Africa, in places like Darfur or Chad. It saves the land and saves them from having to use human feces as fertilizer (which spreads infections). The plants will filter dirty water and make clean water.

Let's give people the food they need at a price they can afford and everyone gets healthy, and that includes wildlife and nature.

Interviewer Rona Fried is editor and publisher of Progressive Investor, and president of SustainableBusiness.com, which provides global news and networking services for green businesses.