Conservative estimates say the human population will increase by about 3 billion people by 2050. Using today’s farming practices, a landmass 20 percent bigger than Brazil will be needed to grow enough food to feed them. But we don’t have anything like that available; we’re already using 80 percent of the land suitable for raising crops, according to research from NASA, and something like 15 percent of that has been ruined already by poor management.

Where to go to grow more food? How about up?

That’s the idea behind vertical farms. Picture a giant hothouse, growing everything from fruits and vegetables to grains, even fish, poultry and pork. (So far, cows aren’t under discussion.) A 30-story farm, occupying one city block, could feed 50,00 people. It would have glass walls and solar panels on the roof, and be built to use space efficiently and allow light to reach everywhere. Different floors could be kept under conditions appropriate for different crops. It would use its own byproducts for fuel, eliminating agricultural run-off and untreated waste.

The vertical farm is the brainchild of Columbia University professor Dickson Despommier, who’s been talking about it for years and has a Web site devoted to the concept at www.verticalfarm.com.

Despommier recalls hearing from the California state food advisory board that in 25 to 30 years, the entire Imperial Valley  —  a $65 billion agricul-tural industry  —  will fail. In response to that knowledge, they are outsourcing the job of growing food to Chile, Argentina and Thailand, but the resources there cannot last for-ever either.

Growing crops in the controlled environment offered by a vertical farm could provide numerous benefits, he says. Agriculture would be protected from pests and weather-related disasters, and the natural world would be protected from genetically modified strains accidentally escaping. All crops could grow year-round in an organic environment, without herbicides or fertilizers. People in inner cities would have easy access to fresh produce. Transportation costs would be slashed.

In fact, a vertical farm in an urban center would be the very definition of local food: 60 percent of the earth’s population lives near or in an urban environment, and that number is projected to swell to 80 percent by 2050.

It would be good for the earth, too, according to Despommier. Vast amounts of land currently in agricultural production could be returned to forest, able to sequester great quantities of carbon dioxide. The farmers put out of their traditional work could still farm, but focusing on a new crop  —  they would manage their developing forests and become, in essence, carbon farmers.

The idea has generated much interest, both here and abroad, but so far not the capital needed to build the world’s first vertical farm. Despommier is confident that will change soon. “Ten years from now, there will be vertical farms throughout the world,” he writes. “I guarantee it.”