To feed today's and tomorrow's cities using sustainable food production is an urgent task. With continually-growing world and urban populations, climate change and pressure on natural resources, global food security is paramount. How can we feed more people on limited agricultural land, with limited resources?

How can we best utilise space, light and logistics for an increasingly urban population? What can zero waste and low energy technologies contribute to food production in an urban environment?

These questions are being addressed at the International Conference on Vertical Farming and Urban Agriculture being held today and tomorrow at Nottingham University.

Vertical farming and urban agriculture, if designed and implemented appropriately, could offer sustainable and innovative solutions for improving food security.

Vertical agriculture  on apartment block concept design by Sadie Alsop, Samantha Barclay, David Brook (FloodPlainTower) High-Rise Architecture Studio, University of Nottingham.

Sky Greens vertical farm in Singapore, is one example. This grows vegetables in towers that are up to 9 meters tall and covers 3.65 hectares, and began selling a variety of vegetables commercially in May 2012. Its aim is to increase vegetable production while minimizing use of natural resources (water, electricity, land) and reducing contamination to the environment. It was designed by Jack Ng, for which he was awarded Singapore's Ministry for National Development R&D Merit Award in 2011.

Singapore, a tiny city state, imports most of its food, and the vertical farm is an attempt to become a little more self-sufficient.

Dickson Despommier, author of The Vertical Farm: Feeding the World in the 21st Century, noting that by the year 2050, nearly 80% of the earth's population will reside in urban centers, says that to feed the extra 3 billion mouths that will be around then, an estimated 109 hectares of new land (about 20% more land than is represented by the country of Brazil) will be needed to grow enough food, if traditional farming practices continue as they are practiced today.

At present, throughout the world, over 80% of the land that is suitable for raising crops is in use (sources: FAO and NASA). Historically, some 15% of that has been laid waste by poor management practices. What can be done to avoid this impending disaster? 

He sees the growth of urban farming as exponential. "Local agriculture addresses so many issues", he said.

"The USA has lost most of its forest since the 1620s.  The Colorado river has disappeared and agricultural runoff is poisoning our oceans. It destroys the larval forms of shellfish and fish. Deforestation has removed the carbon sink and accelerated human-cause global warming. "

Cities are responsible for 70% of emissions but occupy 2.3% global land mass. 7 billion people on the planet require the size of the South American continent to feed them, not incl grazing lands. By 2050 we will need an extra area the size of Brazil.  Agriculture requires 70% of our available fresh water.

Today's cities are unsustainable. But then so were many of yesterday's such as Jericho and Babylon –  which collapsed due to environmental pressures. How do we avoid this happening to us?

Can we feed all these people and repair the earth's damaged ecosystem? "We have to," he said.

"The future of agriculture is growing soil-less. Hydroponics, aeroponics and drip irrigation. Everybody is on board for this.

"We do it by applying the indoor growing strategies we already have to growing vertically in cities. It uses 70% less water, allows restoration of damaged ecosytems, remediates greywater. We can use abandoned buildings.

"Each indoor acre is more productive than 10 outdoor acres. If everyone grew 10% of their food it would be equivalent to 340,000 square miles of hardwood forest.

"Cities should make it illegal to not recycle water. Do you know that New York City throws away 1billion gallons a day!" he exclaimed. "And don't throw away the poo! Use it for energy and nutrients in anaerobic digestion."

The sustainable eco-city must use vertical farms, he believes.  The market is forecast to grow to $20bn  by 2020. There are VF market research reports on  marketresearchreports.biz/analysis/195172.

LED growlights are energy efficient and provide the right frequencies of light for plants; the latest from Phillips are twice as efficient as the current ones on the market.

He followed this up with a series of examples:

• John Edel in Chicago has one of the first.
• Gotham Greens in Brooklyn on top of a supermarket chain.
• Future Growing LLC in Florida. The Epcot Centre.
• Jolanda Hardej's Farmed Here.
• Green Spirit Farms in New Buffalo, Michigan.
• Nuveg is a big operation in Japan. Their VF has no windows. You can harvest the plant yourself and buy it in the store.
• PasonaO2 in Tokyo grows food on the outside of the building. People work there and eat the food that is grown.
• Vertical Harvest in Wyoming
• Green Farms, Valparaiso
• Plantagen, Sweden
• Manhattan School for Children, on 93rd and Amsterdam Ave, NYC, is growing food and using the science as a teaching tool.

This is part of a series of articles covering the International Conference on Vertical Farming and Urban Agriculture. They include:

• Urban Agriculture – A Next Big Thing for Cities
• The Nine Challenges to Food Security That Threaten Our Ability to Feed the Cities
• Launch of the international Centre for Urban Agriculture in Nottingham
• How Singapore and Japan are Feeding Cities with Low Carbon Indoor Farms
• China's Indoor Farming Research to Feed Cities Leads the World
• Cityfood: Encouraging Urban Agriculture and Forestry in Developing Countries
• The World's First Commercial Rooftop Aquaponics Farm
• How Cities Will Feed Their Citizens in the Future