Farming under London

In developed countries,  4 out 5 people live in cities, and the whole world is following suit. Population growth, climate change, and resource availability is continuously putting strains on cities. Meanwhile, they also produce 75% of global emissions, largely through its buildings, from building them to heating them. The UK is aiming to be carbon neutral by 2050 though, and to achieve that, we’ve taken a look at some clever engineering solutions. So let’s dig a little deeper in the topic of wasted space, and wasted heat, at a very unusual farm that Adam Murphy’s been visiting...

Adam - 33 meters below the streets of London, in a disused air raid shelter from World War II, is something you might not expect. A pretty large garden! Here, a company called Growing Underground are making use of all the wasted heat and all of the wasted space that a city the size of London will generate. And they're using it to grow tons of greenery that can feed the people on the streets above. Down in the tunnels, I spoke with grower, Greg Crawford about the work they do down there.

Greg - We've got about 14 different varieties at the moment. So pea shoots, red cabbage, micro watercress, coriander, red mustards, broccoli. So you know, we're growing crops down here and 33 meters above us there's people sitting at a table eating our produce. So plants need light water and nutrient -

Adam - Seems like they're all missing down here!

Greg - Well we have LED lighting, we have an irrigation water system with all the nutrients they need. So we're using a growing medium that's made out of recycled carpet. So at the carpet factory, there's always off-cuts and these get re-mixed together and created into half square metre mats. And we grow in that. So it holds the water quite well and it's a material that would otherwise be sent to landfill. So we're re-using it.

Adam - This approach not only uses this space that would otherwise stay derelict, it makes use of the heat given off by cities and can grow all year round un-affected by the seasons deep beneath the earth. And that's not the only reason you might do something like this.

Greg - We use way less water than conventional agriculture. So you don't get the water runoff you do in a field. And we can recycle the water over and over again and keep it clean. Add nutrients and the water will irrigate the bench, go down underneath and be reused the next day.

Adam - But this is just one company, one instance. Can we make use of a city's waste resources on a large scale? Well once we had come out of the tunnels, I sat down and spoke with Ruchi Choudhary, an expert in architectural engineering about the waste made by cities and what we can do about it.

Ruchi - Well, cities naturally have significant amount of resources because wherever there is some amount of consumption, there's a degree of waste. And the kind of waste we are addressing here is either waste in terms of space, physical space, or resources such as energy, water, energy in the form of heat, heat that we consume. But a lot of it also gets wasted because of the process itself. The ground beneath the cities, it's overheating, it's overheating because there's a lot of infrastructure within ground that releases heat. For example, the biggest would be metro tunnels or heated spaces below ground, any kind of heat sources below ground. So if you keep dumping heat into the ground, over time the climate of the underground rises, which can cause problems for groundwater management and sustainability of underground structures. So one way to alleviate this problem is you can actually use that heat for buildings above ground. So growing on the ground is a very good example of using waste or derelict spaces across cities. Other examples could be using, for example, such farms in environments that have excess of heat and excess of CO2. So the most likely example that springs to mind is hospital buildings or schools because these are environments which have a lot of waste heat and they also have a lot of waste CO2, and you can harness them usefully towards what plants need to grow.

Adam - What does a city of the future look like then?

Ruchi - The thing is that right now we have the mandate to move our cities into zero carbon environments. So that means that a lot needs to be changed, a lot needs to be changed in terms of how we operate buildings, how we make buildings, how transport works. And that shift needs to happen now, not gradually but fast. So we should expect some dramatic changes with respect to how we operate buildings, how we commute, how we use or consume cities.