Getting the Data
A major task in calculating food miles was identifying information sources and pulling data from them.
Import Sources
There are various sources of import statistics, and it took us some effort to find the best. Statistics are available from Statistics Canada, but you have to pay. Our provincial Ministry of Agriculture produced some statistics on food imports to Vancouver Island, but they were so aggregated as to be unusable. (All vegetables, for instance, were reduced to a single line item.)
In the end, though, we found a very valuable (and free) source: the Government of Canada's Strategis website. The site features detailed data on Canadian (and US) trade, which you can filter by product as well as import location, destination in Canada, year, and other parameters.
The import/export data system takes a bit of getting used to, but once you get the hang of it it's highly configurable.
After selecting "Total Imports" into "British Columbia" over the "Latest 5 Years" from "ALL COUNTRIES (Detailed)", we generated reports by individual commodity types matching our list of locally produced products. Products in this system are listed by Harmonized System (HS) code. (An HS code is an international method of classifying products for trading purposes.) HS codes have varying numbers of digits, with more digits indicating a higher level of specificity. For example, 07 is edible vegetables and certain tubers; 0703 is onions, shallots, garlic, leeks, and chives; and 070320 is garlic, fresh or chilled.
We used a combination of four- and six-digit HS codes, depending on what most closely matched our locally produced product. In some cases, we needed to combine several HS codes into one, where the HS code system was more specific than we needed. A sample search for HS code 070200, Tomatoes fresh and chilled, looked like this:
By following a link, we got data broken down by US state instead of the aggregated US data.
The Strategis website offers an option for downloading data as a spreadsheet. It was labour-intensive to do these searches for each of our products and then compile the results, but in the end we had a comprehensive picture of international imports.
The main shortcoming was that the trade data don't include inter-provincial trade. We haven't yet located a good (and free!) data source on inter-provincial food trade. Tips? Email us!
It's also worth noting that products imported into British Columbia don't always stay here. BC is a common import gateway to other provinces, so the "imported to BC" data include some products that actually end up in Alberta, the Yukon, or elsewhere.
Despite these shortcomings, the Strategis data provide a highly detailed and accurate basis for assessing "food miles".
Import Distances
For each of the US states and countries identified as import sources in the import research, we needed to find import distances.
Of course, any particular commodity might come through a variety of routes by different modes. We decided to make some basic assumptions:
- Products from Mexico and the US come primarily by surface (trucking).
- Products from other countries come primarily by sea (shipping).
For marine distances, we were at first happy to locate a US government publication, Distances Between Ports. Listing distances between various world ports, this seemed to be our answer. But things are never quite so simple! Looking up the Port of Vancouver, we found distances from only a few other ports. It turns out that, to use the distance tables, you need to know what "juncture points" (e.g., the Panama Canal) a particular route will pass through, then calculate each leg of the journey separately.
So, lacking good information on such routings, we kept looking. Our best source in the end was a port distance calculator on a commercial website called Maritime Chain. There, they have done the work for us--calculated the distance from some 314 world ports to the Port of Vancouver, including the distinct route legs. Cross-checking the data with the Distance Between Ports data confirmed the accuracy of the Maritime Chain data.
Marine distances are typically given in nautical miles, while what we needed was kilometres. The Distances Between Ports publication contained a conversion formula from nautical to statute miles ("To convert Nautical miles to Statute miles, multiply Nautical miles by 1.15"), so with that we could easily do the miles to km conversion.
For road distances in North America, we used road atlases that included distance tables.
GHG Emissions
These were the easiest data to compile, though they were not so readily available as you might think. After looking around a bit, we found relevant statistics on an Environment Canada website--specifically, a report called Environment Canada Factsheet 3 - Transportation: 1990-1999 . The data were given in grams per tonne-kilometer--that is, grams of GHGs that will be emitted for every kilometre that a tonne of freight is transported.
This represents domestic Canadian use. It would be preferable to have international data, particularly for marine transport, but we haven't located reliable international data as yet.