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FOOD SUPPLY
/ENERGY CONTENT
source: www.gnn.tv/headlines/1913/
Why_Our_Food_is_So_Dependent
_on_Oil
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One indicator of the unsustainability of the contemporary food system is the ratio of energy outputs – the energy content of a food product (calories) – to the energy inputs… - the latter is all the energy consumed in producing, processing, packaging and distributing that product. The energy ratio (energy out/energy in) in agriculture has decreased from being close to 100 for traditional pre-industrial societies to less than 1 in most cases in the present food system, as energy inputs, mainly in the form of fossil fuels, have gradually increased;
- however, transport energy consumption is also significant, and if included in these ratios would mean that the ratio would decrease further. For example, when iceberg lettuce is imported to the UK from the USA by plane, the energy ratio is only 0.00786. In other words 127 calories of energy (aviation fuel) are needed to transport 1 calorie of lettuce across the Atlantic. If the energy consumed during lettuce cultivation, packaging, refrigeration, distribution in the UK and shopping by car was included, the energy needed would be even higher. Similarly, 97 calories of transport energy are needed to import 1 calorie of asparagus by plane from Chile, and 66 units of energy are consumed when flying 1 unit of carrot energy from South Africa;
- in the UK the food supply chain is the largest energy user. Food travels further than any other product – 129 km compared to the average product travel of 94 km. Food production and distribution contributes up to 22% of the UK’s total greenhouse emissions.
The organic system is more energy efficient to the farm gate, but not when it goes global…- a study comparing organic and conventional livestock, dairy, vegetable and arable systems in the UK found that, with average yields, the energy saving with organic production ranged from 0.14 MJ/kg to 1.79 MJ/kg, with the average being 0.68 MJ/kg or 42%. The improved energy efficiency in organic systems is largely due to lower (or zero) fertiliser and pesticide inputs, which account for 50% of the energy input in conventional potato and winter wheat production and up to 80% of the energy consumed in some vegetable crops; (1)
- in conventional upland livestock production, the largest energy input is again indirect in the form of concentrated and cereal feeds. When reared organically, a greater proportion of the feed for dairy cattle, beef and hill sheep is derived from grass. In the case of milk production, it has been found that organic systems are almost 5 times more energy efficient on a per animal basis and 3.5 times more energy efficient in terms of unit output (the energy required to produce a litre of milk);
- so far so good – but once passed the farm-gate, things begin to go wrong. Britain imports over 3/4 of its organic produce, and despite consumer demand, only 2% of its land is organically farmed. As the market has grown it has been met by imports. A study looking at the energy consumption and carbon dioxide emissions when importing organic food products to the UK by plane found that carbon dioxide emissions range from 1.6 kg to 10.7 kg. Air transport of food is the worst environmental option but road transport, especially unnecessary journeys, is also bad. For example 5kg of Sicilian potatoes travelling 2,448 miles emits 771 grams of carbon dioxide.
(1) One measure of the energy efficiency of food production that allows a comparison between different farming practices is the energy consumed per unit output, often expressed as the energy consumed per tonne of food produced (MJ/tonne) or the energy consumed per kilogram of food (MJ/kg).
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