Bernie Sanders during the second Democratic debate. Sanders doubles down: 'Climate change is directly related to the rise of global terrorism'

Bernie Sanders stood by his remark from the last Democratic debate in which he called climate change the greatest threat to national security, a day after the deadliest attack on French soil since the end of World War II.

“Absolutely. In fact, climate change is directly related to the rise of global terrorism," he said. "This is what the CIA says," he went on to say, noting a struggle for limited resources like water and land.

During the October debate, Sanders explained it in a different context.

"The scientific community is telling us if we do not address the global crisis of climate change, transform our energy system away from fossil fuel to sustainable energy, the planet that we're going to be leaving our kids and our grandchildren may well not be habitable," he said.

Martin O'Malley has voiced similar concerns about climate change being the underlying cause of unrest in the region.