Populations are growing and cities are booming – but could we soon see skyscrapers turned into centers for crop production? From Chicago warehouses to the south pole growth chamber in Antarctica, the concept of growing food indoors is catching on. Plant scientist Dr Erik Murchie, from the University of Nottingham, reveals how agriculture could be turned on its head.

  • What is vertical farming?

It’s vertical because you are trying to grow more crops on a smaller land area and this usually means going upwards into buildings. It normally means that, instead of having a single layer of crops over a large land area, you have stacks of crops going upwards. It’s also associated with city farming and urban farming.

Why do we need it?

It is the need to increase crop yield without increasing the land area for crops. If we can move some of that away from the countryside into the city, and get some of that food production close to the high concentrations of population, then we can make a real impact. People want to do it as well – it puts the food supply in the control of people living in the cities.

How high are we talking – skyscrapers?

The beauty of vertical farming is that you can go as high as you want – if you have a system that works efficiently. The only risk with that is getting things that plants need like water and nutrients up there. And you need a way of getting your product out efficiently.

Can we grow all crops like this?

Wheat, maize and rice – these things that provide the bulk of our calories- will be very difficult to grow on a vertical farm because you need to accumulate a massive biomass for those crops – you might expect typically anything between 5 and 12 tons per hectare of grain from something like wheat, but to do that you have to accumulate upwards of 20 tons per hectare of dry weight of plant. So, it’s the weight of the plant. The crops that are likely to be grown are high-value nutritious crops – like tomatoes, lettuces, green crops.

What’s holding us back?

Energy will be the great limiting factor for this. Plants need a lot of light for photosynthesis. There’s a couple of examples in the US of warehouses being converted into stacks of plants. They use LED lights which are cool, efficient lights you can put close to the plants. They are very efficient at making plants grow and you can control plant growth very well, but again you need energy to do that.

How do you see this developing?

What will drive it is technology – the technology to have new buildings, or convert old buildings, where you can have high concentrations of plants; where you can get enough light in there for the plants to grow, and have the recycling of water and nutrients.

You don’t need soil for this, you can do it hydroponically. It’s good to keep soil out of it, then you can keep it clean and control the nutrient cycling and water cycling very efficiently. There is plenty of opportunity for biological control of pests and diseases.

  • Interesting travel fact: urban heat island effect

According to Jane McGrath, if you don’t like hot weather, get out of the city. If you turn on the local weather report, you’ll probably notice an interesting trend. Temperatures are often a few degrees higher in cities than they are in their surrounding country areas. This temperature difference is the result of a phenomenon called the urban heat island effect.

This effect makes cities into islands of heat. According to the U.S. Environmental Protection Agency, temperatures in U.S. cities can get as much as 10 degrees Fahrenheit higher than their surrounding country areas. Normally the temperature difference is not quite that large, but even a few degrees can make a huge difference.  Because of the higher temperatures, the demand for air conditioning in the summer leads to increases in greenhouse gas emissions from power plants that provide that extra energy. On the other hand, higher temperatures in cities mean less need for heating in the winter.

Perhaps the worst result of the heat island effect is the number of heat-related deaths. Although storms caused by global warming get the most media attention, the National Oceanic and Atmospheric Administration reports that heat is usually more deadly. In the U.S., heat typically kills more people each year than tornadoes, hurricanes, floods and lightning put together.

To understand the urban heat island effect, we first need to understand a few simple rules of physics. Most importantly, we should understand that objects can absorb and reflect light. Darker colored objects are excellent absorbers of light. In fact, black surfaces absorb almost all light. On the other hand, lighter colored surfaces do not absorb much light at all; they reflect almost all of it.

So, what does the absorption of light have to do with heat? When an object absorbs light, it converts that light to heat. So, because black objects absorb more light, they also hold more heat. That’s why wearing a black shirt on a hot, sunny day will only make you hotter. The black shirt absorbs light and makes you hot. Wearing a white shirt, on the other hand, will help reflect the sunlight and keep you cooler.

When we build and expand cities, we tend to build buildings with dark surfaces and lay down black asphalt roads. The buildings and the roads absorb a lot of light and hold a lot of heat, warming the city. Because of this, the temperature difference between cities and rural areas is highest a few hours after sunset. Cities hold on to more heat for a longer period of time than rural areas do.

But that’s not the only thing that causes the urban heat island effect. Scientists believe that plants play a large part in keeping an area cool through a process called evaporative cooling. Evaporation is when liquid turns into gas. Plants take in water through their roots and depend on it to live. But after the plant is finished with the water, dry air absorbs it by turning it into water vapor (gas). So, because of this, the air loses heat and becomes cooler. We experience the same type of thing when we sweat – when air hits your sweaty skin, it absorbs the moisture and cools you down. Because of city buildings, the city loses the evaporative cooling advantages of vegetation. Other factors also contribute to the effect. For instance, cars and air conditioners, which are everywhere in urban areas, convert energy to heat and release this heat into the air.

“Luckily, since we know what causes the urban heat island effect, we can control it. Because the dark surfaces of urban structures heat the area, the logical solution is to reverse this trend. Urban planners may do this by painting structures white, or other light colors. This basic technique does a lot to help reduce the urban heat island effect.

However, some people don’t like the idea of an all-white city. ‘High-reflectivity coating’ is an alternative and it can be done in non-white colors. These kinds of coatings reflect invisible radiation without reflecting all light. So, they keep an object cool without losing its dark color.  Some high-reflectivity coatings can also be applied to asphalt on roads.”