This is interesting. Although eating locally is still a very important part of making a difference, this study showed that transportation of food actually only accounts for around 11% of the GHG emissions of our food. The actual growing and processing causes way more. Of course buying locally is still one way of knowing just what is going into the process of your food.
Here is the Seventh Generation article: http://www.seventhgeneration.com/learn/news/guide-low-carbon-eating#
Here is a NY Times article focusing mainly on the study by Tropicana: http://www.nytimes.com/2009/01/22/business/22pepsi.html?_r=1
I like the list that Sev Gen gives to help you make better decisions. This also goes along with the Forum about the impact of beef.
So what do you think, should type of food and packaging definitely go first in our purchase decision? Over local origins? Or are these decisions one in the same (local means less packaging and better processing)?