This month, all staff and students at Rockefeller University received an email that extolled the virtues of locally grown food and urged us to eat it. We were told that locally grown food is healthier, tastier, and better for the earth. Although these statements are common assumptions, the last is hot air at best and has the potential to do real harm, while the first is not supported by evidence (and as for taste, there’s no accounting for it). A clearheaded analysis of the data shows that importing fruits, vegetables, and meats greatly reduces carbon emissions.

Let’s start by looking at why we grow food where we do. It all comes down to economics: we grow fruits and vegetables and raise animals where there is a comparative advantage to do so. While in the past, agriculture dominated the planet, immense technological leaps have meant that the land and labor devoted to agriculture (at least in the developed world) have diminished. When there are dozens of other productive uses for this land—from housing to factories to power generation—we only grow where it is economically advantageous. At the same time, the myriad greater opportunities open to mankind have led to a great exodus from the countryside, which for most of history has been a place of stale destitution, rather than the verdant Eden that some would like us to think. In the developed world today, people farm only where it is profitable.

To be sure, this picture is distorted by various agricultural subsidies; however, while deleterious in and of themselves (a topic for another column), subsidies affect only the staples markets, mostly grain, sugar, and cotton. The reason, then, that we grow corn in Kansas, grapes in Chile, and lamb in New Zealand, is an immense productivity advantage. Due to economies of scale, productivity necessarily implies greater energy efficiency and less environmental damage. Indeed, the less land we use for agriculture, the better off the earth is. We need fewer tractors to bring in the harvest and fewer road-miles to collect the crops and offer them to consumers. Furthermore, too much agriculture takes place in marginal lands such as the high plains in the US, the river valleys of Australia, and the Sahel throughout Africa. (Incidentally, this is why organic farming practices, if adopted on a large scale, would be extremely harmful to the earth—yields are far lower than in conventional farming, necessitating the use of far greater quantities of land). There is no reason efficient agriculture should be any less healthy than growing crops locally, since the more energy that is available to plants and animals, the more they can produce the nutrients and flavors we desire.

But how is it that importing lamb from New Zealand is good for the environment when it must be shipped halfway across the planet? The answer is that shipping is far more efficient than most people realize. If you put a large container ship in the ocean and give it a strong push, it needs extremely little fuel to get even halfway around the earth. In terms of ton miles per gallon, a container ship is eight times more efficient than a truck and two and a half times more efficient than rail (itself a marvel of efficiency).

The low cost of shipping reflects its efficiency. Additionally, the US has by far the best rail freight system in the world, further reducing shipping costs (and overall carbon emissions). Not only is it cheaper for a person in London to eat lamb imported from New Zealand than lamb raised anywhere in the UK, but the imported lamb generates far fewer carbon emissions than the locally raised lamb. England is a singularly bad place to farm with its cloudy, rainy, climate, whereas New Zealand is ideal for sheep. The sea transport is, of course, extremely efficient.

The false assumption that shipping generates excessive carbon emissions shows the woeful lack of scientific rigor underlying the green task force’s recommendation. Numerous studies on this very issue have been conducted. The conclusions are startling: on the east coast of the US, the carbon emissions are lower for importing French wine than Californian wine. They only become equal somewhere in Ohio.

Consider the suggestion to shop at farmers’ markets. This suggestion is one that has been subjected to scrutiny and is found wanting. Grocery stores are marvels of efficiency—they use large trucks (more efficient per unit weight) to collect both imported and locally grown food. They store it in large quantities that allow immense economies of scale. If people have to drive to the grocery store, it’s frequently not very far at all. Contrast this with farmers’ markets: farmers drive less efficient vehicles to many different places to sell their wares. An even less efficient system would be to buy food by driving to the farms directly, or to have the farmer deliver it. I suspect that ordering from Fresh Direct is the least carbon-intensive form of food purchasing possible.

Shipping and rail freight are not the enemies of the environment. The enemy is inefficient agriculture delivered by inefficient means. The complexities of this case only demonstrate further why carbon must be priced. Simple-minded application of “go-green” ideology results in practices that are damaging to the planet—from local food to many types of organic crops. At a scientific research institute, we deserve better, more thoughtful recommendations from our environmentally conscious peers.

For more statistics check out Stephen Budiansky’s New York Times Op-Ed