Green food:

So even though a meat-free world sounds good on paper, it is likely that a utopian future will still have some animal products in it. And we are talking meat, not just milk and eggs...

Under this scenario, the goal will have to be producing the most meat at the lowest environmental cost. That means fewer free-range cattle and sheep grazing in bucolic pastures and more animals, especially chickens, packed into feedlots or high-density enclosures. "If you're going to keep some livestock systems, I think the ones you'll want to keep are the intensive ones," says Walter Falcon, an agricultural economist at Stanford University in California.

That's because pasture grazing is inherently inefficient. Animals burn large amounts of energy roaming about the landscape feeding on relatively indigestible grasses. They grow more slowly than feedlot animals and, as a result, emit more methane over their lifetime. A beef cow in a US pasture, for example, emits 50 kilograms of methane per year, compared with just 26 kilograms in a feedlot, according to Livestock's Long Shadow.