The backyard of Sustainable Cities

Your backyard

HOW BIG IS YOUR backyard? Is it a roof top or patio garden, a patch behind a terrace house, or the proverbial quarter acre in the suburbs. Could your backyard sustain you?

“Are you self-sufficient?” is a question often asked by visitors to Dr Richard Stirzaker’s Canberra backyard at the height of summer. At this time of year his fruit trees are laden and the backyard overflowing with vegetables, leading visitors to wonder about whether he ever visits the shops.

The reality is that Richard’s bountiful backyard falls a long way short of feeding himself for the year, let alone his wife and three kids. In his book, The Scientists Garden Richard calculates that on his 877-square-metre block, the backyard could just grow enough potatoes, fence to fence, to supply enough calories for himself only. Gone would be the fruit trees and vegetables which make the backyard so appealing during summer and provide the necessary variety in our diets.

Sustainable Cities

The notion of sustainable cities requires us to redefine our backyard. For cities are not, and never will be sustainable within their boundaries. Instead the backyard of a sustainable city extends well past what you see from your back door. The challenge is how can we contribute to the stewardship of this extended backyard?

Dome

To understand how big a backyard a sustainable city needs, let’s imagine an air and water-tight dome over our city. Such a dome would be roughly 40 kilometres across to enclose a city the size of Sydney or Melbourne and be home to around four and a half million people.

Our dome needs some farmland to produce our food as even Richards’s bountiful backyard is too small to provide a balanced diet. In fact our current diet requires around 2.8 hectares of farmland per person to grow enough food for the year (pdf). So we need to extend our dome out to 400 kilometres to include this farmland for our 4.5 million people.

But our dome needs to be much bigger to supply the water and fresh air we need. It would balloon to nearly 600 kilometres if we add a catchment area to supply water, and vegetation to absorb the carbon dioxide released by our city and stabilise the atmosphere.

A dome spanning 600 kilometres would be quite an engineering feat. When we tried running one on a small scale in the 1990’s Biosphere 2 project we could not manage it with only eight people in a dome 128 metres across. And our mega dome would become even more unmanageable if we add in space for the treatment of waste, the energy used by the city, resources for commerce, climate regulation, the national parks we like to retreat too, and room for Australia’s diverse plants and animals.

Our imaginary dome highlights the fact that the backyard which sustains you is a lot bigger than what is immediately outside the back door.

Extended backyard

So when you stand in your backyard, be it a roof top or patio garden, a patch behind a terrace house, or the quarter acre in the suburbs, look beyond the boundaries of your own backyard. Look beyond your street, your suburb and your city, for this is where the future of sustainable cities lies.

The need to connect and look after our expanded backyard is not just altruism, but enlightened self-interest: last time I looked there were no new continents to move to, so we better start looking after what we have.

This article first appeared on the ABC website