How many carrots?

One of the tricks you learn, as an academic, for deciding whether to trust the author of a paper you're reading is to check the details. Authors who pay attention to the small details are often more reliable when it comes to believing their conclusions about the main issues.
So it is quite sad to point out a line from Tom Axworthy's op-ed (of advice for Stephane Dion) in the Toronto Star today where he writes about,
"...the monumental cost of importing farm produce from thousands of miles away, rather than supporting local farmers (carrots grown in Millgrove, Ont. and shipped to Toronto create 15 grams of CO2 from transport exhaust; if imported from California, 840 grams, for example.)"
This statement about carrots is clearly missing a context because there is no indication about what mass of carrots is being transported. What was he thinking when he casually quoted a figure of 15 grams of CO2?
This line appears to be taken from this article from the Toronto Star a couple of years ago where it is attributed to Stephen Bentley, a grad student at UBC. It refers to an amount of carrots actually used by the Star to prepare a Christmas meal.
If Mr. Axworthy took even more care with regards to the issue of greenhouse gas emissions, he may have decided to avoid any link with that article because near the end it touts the advantages of eating locally grown food from Ontario greenhouses. The energy required to heat greenhouses far outweighs the transportation costs of food from California!