What's the surprising way to cut your diet's carbon footprint?

Food accounts for a quarter of greenhouse gas emissions. Many aspects of food production and distribution contribute to this figure. But with 83 percent of us living in urban areas in the UK, there’s a growing movement to reduce the distance food travels before it reaches our plates.

Next to offices, vertical farms are taking root, with the potential to cut energy use and food miles. Beneath our feet, salad leaves are growing in disused tunnels. Above us, living walls and rooftop gardens are being planted to grow crops.

Many of these developments require cutting-edge technology that promises to be more widely available in the future. But some offer opportunities to reduce your carbon footprint now.

Urban farms, tunnels, rooftops and walls are all being utilised to grow food.

Buying food from futuristic urban farms

High-density indoor agriculture producing fresh food, sometimes in the heart of the city, is a growing business. Developments could give even the most inner-city dwellers the opportunity to buy locally grown produce. Vertical farming techniques are used, with plants being grown in towers of stacked trays. The global vertical farming market is projected to be worth about £5.1 billion by 2023.

This isn’t farming as we know it. Crops are planted hydroponically, in water and minerals instead of soil, using sand, gravel or soft mesh. They grow under LED lights, and the controlled light and temperature make the farming more energy efficient while the high-density planting and faster growth cycle mean high yields.

One of London's first urban farms is Growing Underground. Their herbs and micro greens grow in disused air-raid tunnels 33 metres below ground in Clapham, using hydroponics. Being in the heart of the city means they can supply local restaurants without clocking up food miles. They say their farming method has the added benefit that it uses 70 percent less water than conventional farming.

“Our motivation is to solve problems of food security issues, including shortage of water and land-based resources such as soil, mass distribution of produce and climate change. It's becoming more and more challenging to grow food and we have to, as a society, develop alternative growing methods”, says Olivia O'Brien, Business Development Director at Growing Underground.

Growing Underground grows herbs and micro greens in tunnels underneath Clapham.

Food producer GrowUp opened a miniature vertical farm in a disused shipping container in 2013, in a bid to make food more local and sustainable. Situated on a roof in Hackney, they grew salad and herbs using a combination of aquaculture and hydroponics. Inside the container were tanks of fish, whose poo made nutrient-rich water to feed the plants.

Kate Hofman, co-founder of GrowUp, says “Our aim is to make sustainable food production commercial. We wanted to make use of available waste resources in cities, in terms of heat and energy.” The box is now closed, and GrowUp are working on a larger high-density vertical farm. They acknowledge the future of urban farming will be challenging though. “Land and energy prices are high in the UK, and food prices are low”, says Kate.

Rivers and harbours provide another opportunity. A floating dairy farm has opened in Rotterdam harbour, with the aim of helping to feed the city more sustainably. The 32 cows are able to wander onto a neighbouring field and the stability of the farm is designed to ensure they don't get seasick. It generates all its own electricity from floating solar panels and provides fresh water through a rainwater collection and purification system. The cows are fed with grass from playing fields and golf courses in the city, along with waste food such as potato scraps, bran and brewers' grains. Their manure is used to create a natural fertiliser.

It could be some time before you're stocking your cupboards with food grown within walking distance of your city home, but the technology is developing fast. You can even buy a kit to grow food hydroponically in your own home, and the plants grow about 30 percent faster than they do in soil.

How could new tech help you grow your own food?

Could this be the future of growing food in cities? A design think tank at The London School of Architecture includes ideas for growing food in the dark central cores of residential buildings as well as on rooftops in a conceptual proposal.

The greening of rooftops, walls and even the insides of our homes is gathering pace. A desire to utilise previously underused spaces, combined with developments in technology, mean even those of us with no garden can grow our own veg in new ways. Plus the increased greenery attracts more wildlife and can reduce rainfall run-off.

'Gardening Will Save The World', the Ikea garden designed by Tom Dixon at Chelsea Flower Show, demonstrated how technology can tranform the productivity of small urban gardens. By planting vertically in two layers, they created extra growing space. Plants on the top layer grew in soil, but the bottom layer was fed hydroponically, with only water and minerals, and mushrooms grew in soil created by a 3D printer.

Rooftop vegetable gardens are increasingly productive. The RHS gives advice on the restrictions on what type of rooves can be planted. For inspiration, look no further than the roof of a bank in London's Strand, where 400 metres of gardens are home to 15,000 fruits, vegetables, herbs and flowering plants. Different areas of the roof have their own micro-climate, and fruit, kitchen and herb gardens are located where they will grow best. Purple sprouting broccoli, green beans, cucumber, strawberries and even wasabi are grown. The plants attract pollinators, so it’s great for the bees too.

A farm on the roof of Mercaro Metropolitano’s planned new market in Ilford will convert its own organic waste into energy, heating and compost for the farm via an anaerobic digester.

For the majority of us, the most achievable form of vertical gardening is the living wall. The RHS website tells us that ‘many types of plants will tolerate the high life in a green wall, including herbs and fruit’. Green walls grown using hydroponics are included in a number of new buildings. But a more affordable option is the wall-mounted allotment, which can be bought off the shelf. Veg (including roots), salads and small fruits grow in compost in troughs, often irrigated by an inbuilt system. They require less watering, are less prone to slugs and are easier to weed than conventional allotments.

What's next for growing food in the cities?

Are these the shops of the future? Towers of trays growing food without soil under LED lights, and rotating in line with the growth cycle to deliver produce to the shop floor just when it's ripe in 'living supermarkets' – part of a conceptual proposal from a design think tank at The London School of Architecture.

Architects are considering how to integrate farming into residential areas of a city. A design think tank at The London School of Architecture proposes incorporating urban farming into city housing estates and blocks. They have produced a conceptual proposal that includes a small hydroponic farm in the dark central core of a large residential block. But the real prize, they say, is in using a range of farming techniques, including aquaponics, hydroponics, soil-based farming and trellising, to produce food in every available space of living areas. This could even include living supermarkets, with towering paternosters rotating at the same rate as the plant's growing cycle to deliver produce to the consumer on the shop floor just when it comes into season.

In Singapore, another conceptual proposal from Spark architects for urban housing combines high-density apartments with a commercial vegetable farm. ‘HomeFarm’ is primarily for retirement homes, but the proposal is also to provide employment in the farm for some residents. Vertical growing gives the properties a garden environment too.

It's clear we have only just scratched the surface of urban farming in terms of its potential and scope. As the global population approaches 8 billion, sustainable farming innovation is moving on fast.

Vertical planting and a vegetable farm are integral to 'Homefarm ', a conceptual proposal for a development in Singapore in which residents will grow their own food on their city doorstep, by Spark architects.