[I’m publishing this ‘as is’ for comments/corrections. It’s a reference document in progress for how much energy/water/greenhouse gas/landfill might be saved by home food gardening. I’ve been regularly updating the article, the last was to include more embodied water information on 6 December 2007, and new greenhouse emission information added 11 December. -Adam]

How much energy and greenhouse emissions can we save if we grow more home food? How much water? How much waste can we stop going to landfill?

Broadacre industrial agriculture uses 65% of Australia’s water. Our food system (including imports) consumes almost twice as much energy as personal transport, and thanks to soil carbon loss, methane and nitrous oxide emissions, the greenhouse impacts of the food system are disproportionately large. Meanwhile, according to the most recently available figures, most of Victoria’s household wastes going to landfill are organic materials.

Home food production can use existing resources and infrastructure, and use methods which radically reduce resource consumption. This suggests that the potential savings to be made if existing resources and infrastructure are used to increase urban food production are dramatic.

I’ve looked at the Havana example, and various estimates of how much food can be produced in suburban situations and chosen the aspirational targets that by producing the most energy and water intensive portion of our diets at home we can halve our resource use of both energy and water. This is possible because the most energy and water intensive crops — when grown on an industrial scale — are the ones best suited to resource efficient home gardening.

The findings are that the average Victorian household has the potential to reduce landfill waste by around 1.5 tonnes a year by composting, which represents 64% of household total. This resource can be used to enrich urban soils. Further landfill savings would be made ‘upstream’ because there would be less industrial wastes and packaging involved in feeding the household, although no figure has so far been arrived at for this.

Meanwhile, we can drop the total water we use at home in Melbourne by around 100,000 litres with a 10,000 litre rainwater tank, which amounts to 35% of the average household use. Most of the water we use isn’t at home directly, it’s embodied in the food we buy. Through home food gardening we can potentially save a further 410,000 litres of ‘embodied water’. So that’s a potential saving of 510,000 litres per household in total.

Potential energy savings are impressive. Without any authorative Australian studies, I’ve adopted estimates based on a 1993 study of the US food system that around 10 units of fossil fuel energy go into producing every one unit of energy in the food we eat. There’s no evidence to suggest that the Australian system is any better. By these estimates, each individual can save the equivalent of about four barrels of crude oil, or around 1.5 tonnes of carbon dioxide emissions every year by home food gardening. Each household could save about 3.75 tonnes of CO2 annually on average, out of about 20 tonnes per household (about 18%). These CO2-equivalent figures may be conservative estimates, as they do not consider the extra non-CO2 greenhouse emissions associated with agriculture.

For these reasons it seems that home and urban food production will be a major ingredient in peak oil adaptation and climate change mitigation and reduction strategies.

More details and an explanation of these respective figures follows.

Water

Australia is the driest continent on earth, with an increasingly dire outlook due to climate change.

The average Australian household directly uses 285,000 litres of water every year through the tap. [1]

Roof area of average home is 175 square metres in Melbourne.[2] With our rainfall since 1980, that’s on average 156,000 litres available every year.[3] We can’t capture 100% of that rain, but we could easily fill a 10,000 litre tank 10 times over, reducing our overall draw on mains water by over 35%. Combined with water saving gardening techniques, such as water harvesting from paths, mulching, and dripper irrigation, we can drop it even further. A quick review of the scientific literature (eg here, here) suggests that soil water retention can be doubled with mulch alone. The Food Forest in South Australia, using permaculture designed water harvesting and storage techniques (including within the rich soil), uses one tenth to one fifth of the water used by a comparable conventional orchard system.[4]

However we never even see much of the water we use. We have to also consider ‘embodied water’ — the water it took to grow and process the food we buy. In 2004-2005 Australian agriculture used 12,191 GL of water, 65% of our total water use, down from 70% a few years earlier. [5]

Figure 1. Water Consumption in Australia. Source: National Water Commission

In their 2001 study, An input–output analysis of Australian water usage, Manfred Lenzen and Barney Foran applied the methods of embodied energy accounting to do the first embodied water analysis for Australia. “Australia’s annual water use of 22,000 Gl is dissected using input–output techniques, showing that 30% of Australia’s water requirement was devoted to domestic food production and a further 30% to exports, compared with 7% required for direct consumption by households.”

Incidentally, in 2005 Australia exported enough grain — 95% of it wheat — to provide the basic calorific requirements for 40 million people. Wheat is relatively low in terms of it’s irrigation requirements however. [x] So, according to Foran and Lenzen, about half of agricultural water goes to domestic food, half to exports.

If we were to take the 2004-5 figure of water use by Australian agriculture, halve it so that we’re ignoring exports, and then divide the remainder by Australia’s 7.4 million households, it equates to 823,000 litres per year per household. So the potential savings are still huge. Lets say that we produce the most agriculturally water intensive third of our food at home, using tank water and water efficient gardening techniques. (Ie. the kind of thing which we grow best at home: fruit and vegetables. We could roughly halve our embodied water use. That’s a saving of up to 400,000 litres in embodied water per household per year.

For more on the water efficiency of garden agriculture as opposed to industrial agriculture see David Holmgren’s Garden Agriculture: A revolution in efficient water use (PDF).

Landfill and waste

The average Australian household sends 2.4 tonnes of waste to landfill each year. [6]

A 2000 report by the Victoria Auditor-General’s office reported that kitchen waste, greenwaste, paper and cardboard contributed to most of Victorian household waste — 64% in total. See figure 2. These three components are easily used as sheet mulch or composted on site — representing the potential of saving 1.5 tonnes of organic material from going to landfill, and instead using it to enrich our gardens! [7]

Figure 2. Composition of Municipal Landfill Deposits (% tonnages)

Commercial, industrial, building & demolition waste amounts to another 2,790,000 tonnes per year in Victoria (total household waste is 2,133,000). [8] What percentage of this would be saved if we halved our dependence on the industrial food system? Further breakdowns aren’t reported so we can’t be sure. But every saving we make at home may well be matched further up the industrial supply chain.

Energy and greenhouse emissions

To the best of my knowledge, no one has ever done a comprehensive study of the energy which goes into our food system in Australia, but we can look elsewhere for some guides.

According to Worldwatch Institute, nearly 21 percent of fossil fuel used goes into the global food system. [x] Ecologist Folke Gunther’s research suggests that, in Sweden, food is the single biggest energy cost for a household — and the one with by far the biggest potential for decreasing energy use, as illustrated in the following graph. [9]

Figure 3. A rough breakdown of the energy use of a family of four in Sweden. The single largest energy user is the food system which is where the largest potential for increased energy efficiency (grey part of the bars) to be found.

Is the same true for Australia? Former Deputy Prime Minister John Anderson certainly thinks so, based on his recent comment that, “We’re pouring as much oil into refrigerators as we are into our cars”. of a similar scenario here in Australia. [10]

To figure out if he’s correct lets consider David Pimental’s 1994 study into the US food system. Pimentel traced all the fossil fuel inputs into the food chain and found that it takes around 10 calories of fossil fuel energy to deliver every calorie of food to the shop. He didn’t even consider in his calculations the transportation back to homes, and home refrigeration, preparation and cooking. [11]

Say you have a roughly average Australian intake of 13,500 kilojoules a day. If we assume that our food system now is about as energy intensive as the US food system was back in 1994, the food system consumes equivalent of 8 barrels of oil to feed you every year. [13]

So how does that compare to car travel? In the year ended 31 October 2004, Australia’s 10.7 million registered passenger vehicles travelled an estimated 148 billion km, each averaging 13,900 km per year. [14] The average fuel use was about 11.5 litres per 100 kilometres, so each car used about 1600 litres. [15] There’s about one car for every two Australians, so we each on average use about 800 litres worth of petrol each year on car travel — about 26 million BTUs of energy. Eight barrels of oil — how much energy we each consume indirectly through our food — contain 46 million BTUs of energy. So John Anderson was right — we really do put more fuel into our refridgerators than into our cars — almost twice!

This also squares with the Australian Conservation Foundation’s Consuming Australia study which found that food consumption is responsible for 28% of the average Australians’ greenhouse gas pollution, whereas personal and public transport accounts for 10.5%. Note that a great deal of personal transport and home energy is related to food procurement, storage and preparation.

How much food can we grow?

John Jeavons the guru of biointensive gardening and his followers shows how we can grow the complete diet for a human on less than 4000 square feet of land, or 1/10th of an acre, including growing material set aside for compost. David Holmgren has pointed out that suburbia is a similar population density as high intensity Asian self sufficient cultures.

However it’s more realistic for most of us to be aiming to provide about half of our diet by weight, focusing on fresh greens, vegetables and fruit. The average house block size is something in the ballpark of 2/10th of an acre (although new blocks average less, especially in Melbourne where they are down to about 0.14 acres on average, whereas houses are growing to about 250 m2 or 0.6 of an acre [x]). But on average each household has access to about 1/10th of an acre of potential food producing area. So enough to feed a single person. But since we’re focusing on nutrition rather than energy crops, we can actually grow a larger percentage of a person’s diet by weight, since it is the energy crops which tend to be more demanding of space. My experience suggests that on a decent sized suburban block we can expect to produce all of our fresh vegetables for a family of four, perhaps 10 percent of our carbohydrates via potatoes and jerusalem artichokes, and a good deal of our fruit — especially if we both eat more seasonally and home preserve.  (From a barely head-height untended, unwatered quince tree in an abandoned neighbours yard in one of Australia’s worst ever drought years, I bottled over 10kg of preserved fruit earlier in the year).

The fresh foods are actually those which involve the most energy in transport, because they’re more easily crushed and spoiled, so must be stacked more sparsely, moved more quickly and kept refrigerated — and these are exactly the things we can easily grow at home. Of course freshly picked organic vegetables are much healthier, so much so that you need to eat less of them.

So really it’s the most fossil fuel intensive half of our diet which we can grow. But to be conservative, lets say that we reduce the energy costs in the food we eat by just 50% with intensive home food gardening. Shopping local, attending farmers markets, buying local organic produce and unprocessed foods could all help drop the remaining 50% significantly.

But just considering the home gardening component, every household on a suburban block could save the equivalent of 4 barrels of crude oil, or around 1.5 tonnes of carbon dioxide emissions.[16]

Home gardening inputs

It may seem a simplification to assume that home food gardening consumes no fossil energy. And of course it is one, given that almost everything we do within an industrial society directly or indirectly consumes some fuel. However, if you save seed with friends, build composts from on-site or locally harvested materials, practice water conservation, there’s no particular need for high energy inputs. The biggest energy costs are the embodied energy in the infrastructure of tanks and hoses. In a future version I hope to consider this.

References

[1] Calculation is based on 7.4 million households (in 2001) using 2,108GL / year
Sources:
http://www.water.gov.au/WaterUse/Waterusedbytheeconomy/index.aspx?Menu=Level1_4_2
http://www.abs.gov.au/ausstats/abs@.nsf/ProductsbyTopic/0AAC8BFAE9DD3241CA2568A90013942A?OpenDocument

[2] http://www.enviro-friendly.com/tank-water-savings.shtml

[3] ibid

[4] http://holmgren.eatthesuburbs.org/DLFiles/PDFs/WaterJournalOpWeb.pdf

[5] http://www.water.gov.au/WaterUse/Waterusedbytheeconomy/index.aspx?Menu=Level1_4_2

[6] Calculation is based on the number of Victorian households in 2001 (886,000)
Source: http://www.greenhouse.vic.gov.au/CA256F310024B628/0/A55E3A4F916BE3D2CA256F620014A6A1/$File/YQA+-+Households.pdf

The total amount of solid landfill waste per year in Victoria is:
Household: 2,133,000 tonnes
Commercial, industrial, building & demolition: 2,790,000 tonnes
Source: http://www.environment.gov.au/soe/2006/publications/report/human-settlements-2.html#table7

[7] http://www.audit.vic.gov.au/old/par65/ags6504.htm

[8] http://www.environment.gov.au/soe/2006/publications/report/human-settlements-2.html#table7

[9] http://www.feasta.org/documents/feastareview/guenther.htm

[10] http://www.eatthesuburbs.org/2007/09/john-anderson-on-food-shocks-oil-dependency-and-drought/

[11] http://dieoff.org/page69.htm

[13] 1 barrel(42 gallons) of crude oil = 5,800,000 Btu
Source: http://www.eia.doe.gov/kids/energyfacts/science/energy_calculator.html

[14] http://www.abs.gov.au/ausstats/abs@.nsf/productsbytitle/18830D3F1604281FCA25723600056557?opendocument

[15] http://www.ptua.org.au/myths/efficient.shtml

[16] Assuming that the greenhouse gas intensity of the fossil fuel inputs into agriculture are about the same as crude oil — about 384kg CO2 per barrel. <http://tothetarsands.ca/wp-content/uploads/2007/09/kealans-greenhouse-gas-research.doc>
The truth is we can save more greenhouse gas emissions by reducing our dependence on soil destroying agriculture — and focusing on soil building home gardening. Methane loss and nitrous oxide from agriculture are major contributors to climate change, and this has not been considered in these calculations yet. Recent research suggests that industrial agriculture and chemical nitrogren fertilizers contribute far more to climate change that was previously thought. <http://www.rsc.org/chemistryworld/News/2007/September/21090701.asp> Rebuilding the humus content of soils is actually a major carbon sink, so we have the potential to have a positive impact on carbon levels.