Angst over a potential electromagnetic pulse attack bubbles up every few months, and it’s easy to understand why. The EMP impact envisioned by people who have studied it closely would be downright apocalyptic: a decimated US power grid, and up to 90 percent of Americans dead within a year. It doesn’t help, either, that North Korea recently invoked the specter of an EMP attack, and seems increasingly like it would have the wherewithal to pull one off.

In broad strokes, if you explode a nuclear weapon at high altitude, it generates an electromagnetic pulse, which in turn can disrupt electronics ranging from cars, to street lights, to the US power grid itself. By what degree depends on whom you ask.

Scary stuff, especially that 90 percent number, which was first offered by representative Roscoe Bartlett in a 2008 Congressional hearing, and backed by a physicist—and leading voice in the EMP issue—named William Graham. But Bartlett himself sourced the figure from a work of science fiction, William R. Fostchen’s One Second After. And while an EMP surge, be it from a hydrogen bomb detonated high above North America or powerful solar storm, would surely impact daily life, the extent of the possible repercussions remains uncertain. At least where North Korea is concerned, that lack of an assured outcome should help ease—if not totally erase—EMP concerns.

Blackout or Bust

It’s important to note early that the EMP threat has become an unlikely live wire. Its most extreme proponents genuinely fear near-total annihilation; its vocal detractors dismiss the threat as science fiction.

In between, though, lie some important subtleties. Crucially, you won’t find much disagreement on the very basic science. In fact, both the US and Russia have proven this out in practice. In 1962, the US conducted a nuclear test known as Starfish Prime, in which it detonated a 1.4 megaton nuclear warhead 240 miles above the Pacific. The resulting EMP knocked out hundreds of street lights, and some telephone communications, 900 miles away in Hawaii. Russian tests at around the same time, over Kazakhstan, reportedly resulted in an EMP that took out a 300-mile communication line, among other assorted impacts. Evidence persists beyond those specific corollaries as well.

“You don’t need to do high-altitude nuclear tests to know the EMP threat is real,” says Dr. Peter Pry, who served on the Congressional EMP Commission and has published several books about its potential impacts. Pry points to data gleaned from underground nuclear tests and EMP simulators, all of which, he says, indicate the strong potential for devastation.

“I’m sure you’ve had the experience of driving a car down the road, listening to the radio, and then you’ve driven under a high power line, and suddenly your radio doesn’t work. You come out the other side and it works again. What’s happened is you’ve passed through an electromagnetic field that upset your radio,” says Pry. “I don’t think you have to be Albert Einstein to realize that if that electromagnetic field were, say, a billion times more powerful, that your radio would not just be upset but it would be destroyed, the electronics in your car destroyed. Imagine that now not being a localized phenomenon, but extended to the whole North American continent.”

'I don’t know how the proponents of EMP get such huge results. I just don’t follow their logic.' Philip Coyle, Center for Arms Control and Non-Proliferation

The commission Pry served on—tasked with investigating the threat—laid out that case in a 200-plus page 2008 report, and Pry himself speaks passionately on the topic. But EMP skeptics still abound, particularly in the North Korean context. And the EMP Commission shut down on September 30, after the Department of Defense and Department of Homeland Security didn't seek funds from Congress to continue its operation.

“The fact that North Korea has tested a larger yield nuclear weapon than before is of concern because of the yield of the nuclear weapon, not because of EMP,” says Philip Coyle, a senior science fellow at the Center for Arms Control and Non-Proliferation, who served as the Assistant Secretary of Defense and Director of Operational Test and Evaluation at the Pentagon, and spent decades studying nuclear weapons at Lawrence Livermore National Laboratory.