Why are Americans so afraid of ISIS when you’re more likely to be crushed by a falling television than killed by terrorists? Why do we fear far-off outbreaks of diseases like Ebola and SARS when climate change threatens to drown parts of the eastern seaboard?

According to Juliette Kayyem, former Assistant Secretary for Intergovernmental Affairs at the Department of Homeland Security and author of the book “Security Mom,” it’s because we fear the unknown.

The root of much of this fear is 9/11 and its aftermath. “We had stratified the world into foreign threats and domestic peace [before 9/11],” Kayyem says, “and it always was ‘over there.’” Today, with the rise of ISIS and lone-wolf domestic terrorists, the modern fight feels much closer to our doorsteps - even if it is very unlikely that we would ever become directly involved.

For a long time, Kayyem says, this same kind of misplaced fear drove our national security agencies. They focused on preventing big, mass casualty terrorist attacks. Then there was a system-wide wake up call in 2005 when Hurricane Katrina devastated New Orleans.

“For people in my field, including counterrorism,” she says “to look at an apparatus of response that could not save an American city from drowning, you realized, ‘Oh my gosh.’ We were too focused on one particular scary thing that was low probability, high consequence. Maybe we should look at an all hazards approach to thinking about our safety and security.”

When it comes to what we should really fear, climate change tops Kayyem’s list. Even in a year when three presidential debates went by with barely a mention of climate change, the national security apparatus is taking notice.

“The movement of people and the fight for resources is why wars are fought, and that’s what we anticipate,” she says. “When someone says climate change is the biggest existential threat, they don’t mean ‘because you’re going to get wet…’ It’s actually about defense and national security.”