By Astrid Scholz,

Ulf Sonesson,

and Peter Tyedmers

Go local. Eat organic. Buy fresh. Those food mantras continue to make waves among environmentally conscious consumers. But if the motivation is to truly make our diets more Earth-friendly, then perhaps we need a new mantra: Buy frozen.

Several years ago, the three of us - two ecological economists and one food system researcher - teamed up in an effort to understand how to develop sustainable systems to feed a planet of nine billion by 2050. As the focus of our study, we chose salmon, an important source of protein around the world and a food that is available nearly anywhere at any time, regardless of season or local supply.

We examined the salmon's life cycle: how the fish are caught in the wild, what they're fed when farmed, how they're processed and transported, and how they're consumed.

We found that, when it comes to salmon, the questions of organic versus conventional and wild versus farmed matter less than whether the fish is frozen or fresh. In many cases, fresh salmon has about twice the environmental impact as frozen.

The reason: Most salmon consumers live far from where the fish was caught or farmed, and the majority of salmon fillets they buy are fresh and shipped by air, which is the world's most carbon-intensive form of travel. Flying fillets from Alaska, British Columbia, Norway, Scotland, or Chile so that, 24 hours later, they can be served "fresh" in New York adds an enormous climate burden that swamps the potential benefits of organic farming or sustainable fishing. (Disclosure: A nonprofit subsidiary of Ecotrust, the North Pacific Fisheries Trust, lends money to sustainable fisheries.)

Fresh fish is wonderful and healthful, and if it's driven a reasonable distance to market, its relative environmental impact is low. Fortunately for conscientious diners, when fish is flash-frozen at sea, its taste and quality is practically indistinguishable from fresh. More important, it can be moved thousands of miles by ship, rail, or truck, with a much lower environmental impact than when airfreighted. If seafood-loving Japanese consumers, who get most of their fish via air, were to switch to 75 percent frozen salmon, it would have a greater ecological benefit than if all of Europe and North America ate only locally farmed or caught salmon.

Is the future full of fish sticks? No. But when it comes to eating seafood from halfway around the world, we need to get over our fetish for fresh. With the challenges facing the world's oceans mounting, buying frozen is a powerful choice that concerned eaters everywhere can make.