Greendex Calculator nonsense

I just came across National Geographic's Greendex Calculator, and was about to take the survey, but when I saw the first question, I didn't bother:

1. How often, if at all, do you consume each of the following types of food and beverages?
a) Imported foods
b) Locally grown foods (e.g. from your province/state or region)

How can they be so ignorant?

As The Economist wrote in 2006:

...it turns out that the apparently straightforward approach of minimising the “food miles” associated with your weekly groceries does not, in fact, always result in the smallest possible environmental impact.

The article also notes, "There is a strand of protectionism and anti-globalisation in much local-food advocacy...." Maybe the National Geographic has an anti-globalisation agenda?

And in 2011, Steve Sexton wrote at Freakonomics that in a locavore system, farmed acreage, fertilizer use, fuel use, and chemical demand would all actually increase:

The land-use changes and increases in demand for carbon-intensive inputs would have profound impacts on the carbon footprint of our food, destroy habitat and worsen environmental pollution.

It’s not even clear local production reduces carbon emissions from transportation. The Harvard economist Ed Glaeser estimates that carbon emissions from transportation don’t decline in a locavore future because local farms reduce population density as potential homes are displaced by community gardens. Less-dense cities mean more driving and more carbon emissions. Transportation only accounts for 11 percent of the carbon embodied in food anyway, according to a 2008 study by researchers at Carnegie Mellon; 83 percent comes from production.

It's not just the economists who argue this. Sarah DeWeerdt of the Worldwatch Institute wrote in 2009:

[A] broader, more comprehensive picture of all the tradeoffs in the food system requires tracking greenhouse gas emissions through all phases of a food's production, transport, and consumption. And life-cycle analysis (LCA), a research method that provides precisely this "cradle-to-grave" perspective, reveals that food miles represent a relatively small slice of the greenhouse-gas pie.

In a paper published last year, Christopher Weber and H. Scott Matthews, of Carnegie Mellon University, wove together data from a variety of U.S. government sources into a comprehensive life-cycle analysis of the average American diet. According to their calculations, final delivery from producer or processor to the point of retail sale accounts for only 4 percent of the U.S. food system's greenhouse gas emissions. Final delivery accounts for only about a quarter of the total miles, and 40 percent of the transport-related emissions, in the food supply chain as a whole. That's because there are also "upstream" miles and emissions associated with things like transport of fertilizer, pesticides, and animal feed. Overall, transport accounts for about 11 percent of the food system's emissions.

By contrast, Weber and Matthews found, agricultural production accounts for the bulk of the food system's greenhouse gas emissions: 83 percent of emissions occur before food even leaves the farm gate. A recent life-cycle analysis of the U.K. food system, by Tara Garnett, yielded similar results. In her study, transport accounted for about a tenth of the food system's greenhouse gas emissions, and agricultural production accounted for half. Garnett says the same general patterns likely also hold for Europe as a whole.