Former U.S. secretary of State George P. Shultz believes it's crucial to fight global warming to protect national security.
Global warming is created by burning fossil fuel, he says, and payments for foreign oil sometimes wind up financing terrorism.
And Shultz, who's also a former Treasury secretary, thinks the nation suffers an "economic vulnerability" because of its oil addiction.
"While we have benefited from low-priced energy," he says, "we've also suffered from periodic spikes in the price of oil. Usually recessions go along with it."
Moreover, continues the man who set up the Environmental Protection Agency four decades ago, "There's a climate problem connected with the burning of fossil fuels.... The basic facts are pretty clear."