What if... everyone bought locally?

I'm continuing the food theme for this latest post. Maybe it's my love of eating; or maybe it's because the more I read into it, the more fascinating the carbon economics of food seem to be. This time round it's the local food movement. We should all buy locally, right? Well, what would happen if we did?

You're probably familiar with the concept of food miles - the distance our food travels before it reaches our supermarket shelves. Transporting goods causes greenhouse gas emissions. Reduce your food miles, the theory goes, and reduce emissions from your food. And when 14% of global emissions come from agriculture, there's big savings to be made!

If you've read any of my previous posts, you'll know that things in the world of emissions are never as simple as they first appear. Take the case of Young's, who got in trouble a few years back when it was revealed their locally sourced Scottish prawns where flown to Thailand for shelling before returning to the UK to be sold in our supermarkets. Customers thinking they were buying local produce were unsuspectingly buying a product with 12,000 embedded food miles!

Luckily studies have shown that it's not food miles that count - the methods used to grow your food are much more important. It's helpful here to have a look at a few case studies. Consider the tomato. A 2008 DEFRA study found that tomatoes grown in the UK were responsible for three to four times more emissions than those imported from Spain, even when the additional food miles were taken into account. This is because UK tomatoes tend to be grown in gas heated greenhouses. A similar study by New Zealand researchers found British lamb was four times more energy intensive than New Zealand lamb, even allowing for transport to the UK - due mainly to the use of larger quantities of fertilisers by UK farmers.

He may look tasty. But if he's from the UK, his carbon emissions may be bigger than you think

All the evidence seems to say that, if you're looking to reduce emissions from food, you need to look at the entire lifecycle of the foods you eat. If you do that, as these American researchers did, you'll find that food miles account for only about 11% of emissions from our food. Even more scarily, a study by the University of California looked at what would happen if everyone in their local area of Santa Barbara County bought locally. Amazingly they found it would reduce emissions from food by less than 1%!

So there you have it. If we all ate locally, the impact on food emissions might be as low as one percent!

Tesco now put carbon footprints on products to help consumers make informed choices

So what should you buy? Well in his excellent book How bad are bananas? author Mike Berners-Lee says you can't go wrong with a banana. Good advice if you ask me. Imagine the detrimental impacts to countries like Ecuador - where 61% of the agriculturalGDP comes from banana exports - if we all stopped eating bananas. When you start looking at situations like this, you can see the issue of buying locally extends far beyond just carbon emissions.

If you want more about food miles, the ever brilliant Freakonomics team have produced this excellent podcast. In it they speak to the authors of the Santa Barbara county study.