We've reported before about the benefits of local food, but the BBC has a good article about how "Local food is usually more 'green' than organic food", meaning that the pollution caused by transportation outweighs the pollution of pesticides & fertilizers used to grow most produce.
"The authors calculated that if all foods were sourced from within 20km of where they were consumed, environmental and congestion costs would fall from more than £2.3bn to under £230m - an "environmental saving" of £2.1bn annually. They pointed out that organic methods can also make an important contribution. If all farms in the UK were to turn organic, then the country would save £1.1bn of environmental costs each year. Consumers can save a further £100m in environmental costs, the authors claim, if they cycle, walk or catch the bus to the shops rather than drive."
Cascadia Scorecard takes the analysis further by mentioning the distinction between personal health and global sustainability, reminding us that organic food is healthier (due to the fewer pesticides and such), even if nonlocal organics are more energy-intensive than local nonorganics. Ideally you'd have both, but the studies referred to by the BBC do something very valuable--they put price tags on the unsustainable practices, which helps governments and companies see where the biggest problems are and what the cost of negligence is.