So you're grocery shopping in Halifax, waffling between buying fresh Atlantic salmon or frozen Alaskan sockeye. You choose the fresh filets because buying local adds up to a bigger environmental and sustainable bang for your buck, right?
Well, maybe not.
Embracing the local food philosophy - a guilt-reduction approach adopted by many environmentally confused but well-meaning shoppers - is not always as Earth-friendly as it seems, according to new results emerging from a global, three-year study on the life cycle of salmon production. In fact, buying imported fish that "swim" frozen into local ports via environmentally economical cargo ships can have a bigger impact on reducing the carbon impact of your meal - and global climate change - than choosing organic or local stock.
While the study focuses on salmon, "a global super commodity" available almost universally in any season thanks to commercial-farming operations, its authors say their findings are applicable to other major food commodities. Their findings challenge a body of food activism that has grown up around notions that buying close to home is the most environmentally ideal, a philosophy that is under increasing pressure from critics.
"We have this prioritization, this fetish of fresh," said Peter Tyedmers, an ecological economist at Dalhousie University's School of Resource and Environmental Studies, who helped author the study. "We're making a lot of poor assumptions around why we pursue local," he said, adding: "If we want to prioritize local economies, that's a great thing. But let's understand that it comes at a cost."
To decode when local is truly best, consumers need to take a few steps backwards along the food chain, focusing not on where their food was produced, but how. In the case of farmed salmon - carnivorous fish that live on pellets made from other fish - that means awakening to the intense environmental drain caused by making those pellets, which are culpable for around 90 per cent of the total greenhouse-gas emissions the fish generate up to the point of harvest.
Fresh is a big problem over long distance. If it's fresh, it's being air-freighted. And air freight comes at a huge environmental impact.
The environmental weight of the inputs salmon require is similar to those in other types of conventional farming, a factor that allows researchers to generalize some of their findings to other consumer products.
"Intensive livestock production, whether it be salmon or milk, is predicated on concentrated feeds ... that are global commodities," Prof. Tyedmers said. "Your milk may be from down the block. But what fed the cow? Usually people are completely overlooking what the milk was built on," he said.
Prof. Tyedmers and his colleagues at the Swedish Institute for Food and Biotechnology, and Ecotrust, an Oregon-based environment research organization, examined data from salmon-farming operations in Norway, the world's biggest salmon producer, Chile, Scotland and British Columbia over the course of their study. Their aim: to quantify the carbon footprint of man-made salmon farm systems.
Aside from feed, the researchers found that modes of catching and preserving salmon mattered more on the environmental balance sheet than whether they were grown on organic feed, which doesn't have as much environmental impact in salmon as in other forms of agriculture because in salmon the creation of organic feed pellets requires higher amounts of energy.
When weighing fresh versus frozen, Prof. Tyedmers said considering the salmon's mode of transport is critical.
"Fresh is a big problem over long distance. If it's fresh, it's being air-freighted," he said, adding: "And air freight comes at a huge environmental impact.
"If you're choosing salmon that has been frozen at sea, it probably came to you at a very low-scale environmental impact," he said.
In spite of his research, Prof. Tyedmers said he doesn't view the local-food movement as invalid.
