Trial column: Is local food really better?

On Sunday I trailed the idea of writing a sustainability fact check column, and this is the pilot.  The topic is one of the many that Erin was kind enough to suggest, though I’m avoiding directly crediting her in the piece because I’ll be embellishing the query enough that to do so would be to put words in her mouth.


Fact check: is local food really better?

Dear Eldan,

A few years ago, the Economist ran a hit piece claiming that the local food movement is worse than useless because local food contributes more to greenhouse gas emissions than standard grocery store fare does.  This sounds crazy to me, and I realize that they have their own pro-globalization bias, but they quote a lot of Very Serious Sources and they seem to have done their research.  Could it be true that I’m harming the climate more by shopping at my local farmers’ market than the supermarket?

Yours,

Astro T. Earther

Reusable Bag

photo by Liz Throop

Well Astro, the press just loves stories about how wrong those silly treehuggers are, and this one’s a perfect example.  Like a lot of them, it has plenty of true facts in it, but it ends up making 2 plus 2 equal 5.

This particular story was especially ambitious, because it tried to do the same for Fairtrade products and organic farming, but if I don’t focus I’ll end up writing a book that no-one has time to read, so I’ll only look at the claim they made that local food is no better than what’s been trucked in.  The claim they’re really making is that whatever harm is reduced by not shipping the food so far is outweighed by inefficiencies of the trendy small-scale food system.  Let’s unpack that a little:

One of the arguments for buying local is that typical supermarket food travels shockingly large distances from farm to table.  According to the Leopold Center for Sustainable Agriculture, the average vegetable travels 1,518 miles by truck before we get to eat it.  That study was done for Iowa, close to the center of the U.S. and surrounded by miles of farmland, so it might even be worse if you live at one of the edges of the country like me here in Seattle.  I couldn’t find an estimate for how far the average vegetable sold at a farmers’ market traveled, but that doesn’t matter because we can do better: you can find out exactly how far your produce came by asking the individual traders.  I buy most of mine from three suppliers: one proudly advertises that it’s 22½ miles from the market, one is 142 miles away, and one’s 180 miles away.  That means that my average farmers’ market vegetable has traveled less than a tenth of the distance that its supermarket equivalent.  Sounds impressive, eh?

When I think of the tomato that’s traveled 1,500 miles I think of an individual heroic fruit that’s outdone the Proclaimers in its single-minded dedication to get to me.  But our transport system is more efficient than it looks, mainly because we can pack so much into one truck.  Much as it pains the environmentalist in me to admit this, it’s really impressive.  According to that same Leopold Center report, a typical long-haul truck emits 1 pound of CO2 per 3,000 pound-miles of food transported.  In other words, hauling the average pound of food 1,500 miles only causes half a pound of CO2 emissions.  To put this in perspective, that’s the equivalent of burning 6½ tablespoons of gasoline.  When you think about how many pounds of food each person eats in a year, it still adds up, but it’s not the biggest factor.

As just one example, if the local produce is grown in a greenhouse then a surprising amount of energy will have been used to heat that greenhouse.  A typical greenhouse produces 1¾-2½ pounds of tomatoes per square foot per year, and uses about 54 Kilowatt-hours of heating energy per square foot per year – in other words it uses about 22-31 KWh per pound of tomatoes grown.  At the average carbon intensity for electricity in the U.S., that translates to 29-42 pounds of CO2 emissions to grow one pound of tomatoes; about 70 times as big a deal as the shipping.

So on the face of it, The Economist had a point.  The environmental impact of food miles is often overstated.  But if we leave it at that, we miss some really crucial things.

So far, I’ve compared a relatively clean example of long-haul food—the efficiently loaded truck—with one of the most energy-intensive kinds of local food.  But reality has an awkward habit of being a bit more complicated than that.

What if the long-haul food were fish from Tsukiji in Tokyo?  I’ve seen sushi bars proudly advertising specials from there, because it is by all accounts the mother of all fish markets.  I live in one of closest points to Tokyo in the lower 48, and it’s still 5,000 miles away, so more than 3 times the average distance I assumed before.  Then there’s the need to refrigerate the fish, which consumes energy along the way, though I haven’t been able to find out exactly how much.  Then there’s need to air freight it if it’s going to be fresh when it gets here, and that causes around 6 times the emissions per pound-mile.  Suddenly it’s at least 18 times as bad as the domestic tomato, and that’s for something that can be caught locally within sight of where I’m sitting right now.  So the more perishable and delicate the food, the more food miles do matter.

Foraged & Found Edibles -- Lobster Mushrooms Macro

photo by Brian Glanz

On the other hand, when I described the greenhouse burning energy to grow tomatoes because it’s either in the wrong place or out of season, I was implicitly assuming that was the only way crops could be grown locally.  When crops are naturally in season where you are, they don’t need heating, artificial light or long-haul shipping.  If you’re not sure what’s in season when, you can always ask the farmer.  At least you can at the market, which is one of the harder-to-quantify advantages that a local food system has over a typical supermarket.

Complaints about supposed inefficiencies of the small-scale, local food system also assume that industrial food production actually works as efficiently as it could in theory.  In real life that tends not to happen for all kinds of reasons.  Farm subsidies distort markets for produce, fertile farmland close to cities gets paved over because there’s more money in development, and the effort to have everything available out of season means that 37% of retail store tomatoes are greenhouse grown anyway.

There are all kinds of other advantages to a varied local food system.  That wasn’t what you asked about, so I won’t go into detail, but if you’d like to learn more here are some good starting points:

After all that, what have we learned?  Well, food miles alone are a much less big deal than they sound like they should be, and local food can cause surprisingly large amounts of emissions.  On the other hand, the more perishable the food, the worse the impacts from transporting it, and food that’s in season locally is far less environmentally damaging than food out of season, wherever it came from.


Alright, there’s a first column.  Having just written it, I can’t really judge if it makes a decent read or will put you to sleep – please let me know what you think.  I’m also not sure if the conceit of the letter is the right way to structure it – I could always just introduce the claim I’m going to check by saying why I think it’s interesting, like Ben Goldacre tends to.

Here’s what I learned from writing it:

  • This took much longer than writing a typical blog post.  On the one hand, I’ll have to make the process more efficient if I do this regularly.  On the other, that’s actually kind of reassuring because it tells me that I’m not just restating the obvious and might be able to add something.  I was a bit nervous about that before I started because all the sources themselves are publicly available data.
  • I ended up using less than half of the outline I originally wrote for the post, because it’s already on the long side (almost 1200 words).  With practice I’m sure I’ll get better at writing outlines at the right level of detail.
  • I did most of the research with only the outline written so I could do the writing without interruptions.  That was definitely the wrong approach, because as I wrote I realised I’d need different references, and some of the research I did was for points that never made it into the post.
  • Finding the images took a surprising amount of time, though that’s mainly because looking through other peoples’ photos on Flickr is so much fun.  A little self-discipline will go a long way with that.
  • I can watch that Bruce Lee clip at least 20 times without getting tired of it.

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