If global warming isn't stemmed, "we'll be 8 degrees hotter in 30 or 40 years and basically none of the crops will grow," Turner said during PBS' "Charlie Rose."
"Most of the people will have died and the rest of us will be cannibals," said Turner, 69. "Civilization will have broken down. The few people left will be living in a failed state ... living conditions will be intolerable."
Population control can help combat global warming he said. People should voluntarily pledge to have only one or two children, the founder of CNN in Atlanta said.
"We're too many people; that's why we have global warming," he said.
Commenting on the military, Turner said military budgets should be cut.
"Right now, the U.S. is spending $500 billion a year on the military," he said, "more than all 190 countries in the world put together."
Despite the huge budget, "we can't win in Iraq," he said.
"We're being beaten by insurgents who don't even have any tanks," Turner said.