Photo: Elizabeth Thomsen via Flickr.

Increasingly, consumers are trying to reduce the environmental impacts of the foods they eat. But it’s not so easy to know what to do, in part because of the bewildering array of food choices the market offers, but also because it’s hard to know what food choices carry the biggest impact.

This nifty study tries to clear away some of the murk by tackling a fairly straightforward question: If you care about the climate, which is more important, what kind of food you eat, or where that food is grown?

To summarize the findings: All else being equal, locally grown food is friendlier to the climate than food grown half a continent away. But if you’re looking for a single food choice that will help curb your climate impact, your best bet is to stay away from cows!

food CO2 intensityTake a look, for example, at this chart of GHG emissions per calorie for different kinds of foods. Red meat (the dark blue bar) has far and away the biggest climate impact. Nothing else comes close. Dairy products (the light blue bar) are next. In comparison, the climate impacts of grains and vegetable oils are pretty modest.

So based on this chart, it seems that the easiest, most climate-friendly food choice you can make is to cut red meat out of your diet. Just about any other way of getting calories is better for the atmosphere. And if you can shift from dairy to something else, all the better.

In a nifty bit of analytical work, the authors compared the GHG impacts of food choices with the impacts of “food miles” — i.e., the distance that food travels from farm field to plate. Based on U.S. data, they estimate that food travels about 1,019 miles, on average, to get from the farm to the grocery aisle. But surprisingly, the climate impact of that journey is pretty minimal: Delivering food “from the farm or production facility to the retail store” — the most common definition of food miles — represented only 4 percent of total food-related GHG emissions.

That’s not to say that eating local isn’t important. But given the outsized climate impacts of beef, it does suggest that subtle shifts in food choices can have a bigger climate benefit than major shifts towards a local diet. In fact, the authors calculate that shifting just 12 percent of your meat and dairy calories to veggie-based foods has the same climate benefit as going 100 percent local for all food purchases.

Still, going veggie and local is better than doing just one or the other. Which is all the more reason why a locally-grown tomato is a wonder of the sustainable world.