Seattle ? Forget the debate over farmed vs. wild salmon. Never mind the issue of food miles.

The most important thing to know about that salmon on your plate is whether it’s fresh or was frozen out at sea — the latter being better for the global environment, according to a new study conducted by researchers from Sweden, Canada and an environmental think tank in Portland, Ore.

“Popular thinking about how to improve food systems for the better often misses the point,” the researchers said in a news release.

The three-year study looked at salmon in the global sense, calculating its carbon footprint. That’s a different approach from other research telling us what fish to eat. You might see stickers on grocery-store fish saying it’s sustainably caught, for example, but that’s more a matter of whether a fishery is well-managed and whether other species are accidentally caught at the same time.

“These are all very important issues, but they tend to be focused just on what’s going on in the water,” said Astrid Scholz, the study’s co-author. “They’re missing some of the main drivers for environmental change globally.”

A big one is transportation, she said.

“Fresh fish come on an airplane. That’s the only way it can get to you,” she said. And that flight has a high cost, in terms of greenhouse gases. If the fish was frozen, it could instead be transported around the globe on container ship, which uses far less energy, the research showed. In environmental terms, fresh fish is roughly twice as bad as frozen, according to the research.

It counters the notion that buying “local” food is best for the environment.