ghost a·cres (noun): The amount of land needed by a nation to produce the equivalent amount of food it procures by trade and sea.
Closely related to the concept of "food miles," ghost acres was coined by scientist, geographer, and ecologist Georg Borgstrom in his 1965 book The Hungry Planet.
Anthropologist John H. Bodley explained the meaning of the term in his 2007 book Anthropology and Contemporary Human Problems:
In 1965, food scientist Georg Borgstrom introduced the concept of ghost acres, referring to the fact that trade and fishing were ways of gaining extraterritorial acres. Ghost acres were calculated as the amount of land a given country would need to put in production to gain an equivalent amount of animal protein equivalent to its net food imports and fishery production. Ghost acres have also been called "phantom carrying capacity." According to this reckoning many nations had already far exceeded the carrying capacity of their farmlands -- at least given their culturally prescribed food patterns -- and had become precariously dependent on uncertain international markets and frail marine resources. At that time Borgstrom calculated that Japan's ghost acres exceeded its agricultural acreage by more than six times and the United Kingdom's effective acres were nearly tripled by ghost acres."
"The problem with subsisting on ghost acres," Bodley explained, "is that global fisheries are now heavily over-exploited and in danger of collapse. By 2003, seven of the top-ten species, constituting 30 percent of global wild fisheries, were considerd to be fully exploited and in danger of collapse."
Hat tip to The Ethicurean for bringing this interesting concept to our attention.