Carbon saved by buying local rather than imported food
In the UK, 95% of all our fruit and half of all vegetables are imported, so our food travels a long way before it gets anywhere near our plates. Food transported by boat, air and road travels around 30 billion km each year,
and in doing so is responsible for 19 million tons of CO2, equivalent to the annual output of two coal-fired power stations. Food transport also costs over £9 billion a year, due to congestion (£5 billion), accidents (£2 billion), greenhouse gas emissions, air pollution, noise, and infrastructure (£2 billion).
Although air freight makes up the smallest proportion of food miles, the largest being transport by road, it is the highest emitter of CO2 per tonne of food, and responsible for 11% of emissions. It is also the fastest growing - air miles increased by 31% in 2006 compared with the previous year, and has grown by 379% since 1992.
It's become quite normal to expect supermarkets to be stocked with out-of-season, as well as exotic, produce all year round, and in being able to buy things like green beans in December, we have lost our sense of the seasons. An analysis of 20 common foods was found to have travelled over 100,000 miles
to get to our shelves. Not only does this produce vast quantities of greenhouse gases, the longer an item is in storage or travelling, the lower its nutritional content as nutrients diminish naturally with time. Eating locally grown food is therefore better for us.
Calculating carbon saved by eating local:
Comparison of carbon emissions for different freight methods per tonne kilometre
Short haul air freight emissions are 1580 g CO2 per tonne kilometre
Long haul air freight emissions are 570 g CO2 per tonne kilometre
Medium truck is 85 g CO2 per tonne kilometre
Bulk ship is 10 g CO2 per tonne kilometre.
Assuming that a typical plate of food contains ingredients that are half imported, and half produced in the UK. Produce such as mange tout, green beans and mushrooms commonly come from places like Kenya, Peru and Zambia.
Averaging the distances of these long haul destinations comes to 9408 km.
Long haul air freight emissions are 570 g CO2 per tonne kilometre so total emissions:
0.57 kg CO2 per tonne km x 9408 km = 5363 kg per tonne or 5363 g per kg.
If we assume the food has another 300km to travel once it gets to the UK, to/from the packing facility, regional distribution centre and supermarket, then emissions due to road transport are:
0.085 kg CO2 per tonne km x 300 km = 25.5 kg per tonne or 25.5 g per kg.
Therefore total emissions due to air freight = 5363 g + 25.5 g = 5388.5 g per kg or 5.4 kg CO2 per kg imported produce.
If we assume that UK grown food has also travelled 300km from the local producer, to the regional distribution centre and then supermarket, then the local food is responsible for another 25.5 g CO2 per kg, so total emissions of plate = 5388.5 + 25.5 = 5417 g CO2 per kg. If a portion of food is measured as 80g, then whole plate will contain approx 250g.
Therefore emissions for one plate of food = 5417 / 4 = 1354 g per plate.
Compared with a plate that is completely locally sourced = 25.5 x 2 = 51 g CO2 per kg or 12.75 per 250 g portion.
Emissions saved by eating local = 1354 - 12.75 = 1341.25 g or 1.34 kg per meal.
