Apocalyptic A to Z: Electromagnetic Pulse

When we think of the fall of civilization, we tend to think of meteors, nuclear weapons, plagues, or the Second Coming. There are other nasty ways we can lose all we hold dear. One of these is an electromagnetic pulse (EMP).

An EMP is a sudden, massive discharge of electromagnetic energy. "Massive" is a relative term, of course, and switching on any electrical equipment like a car ignition is a type of EMP. A more powerful EMP comes with lightning, with a relatively limited area of effect, or something with a more global effect, such as a solar flare.

When we really have to worry is when an electromagnetic pulse is both powerful and spread over a large area. A massive solar flare could burn out all electrical equipment in the globe, and a nuclear strike can do the same over a large area. This U.S. Army graphic shows the effect of a 400 km high altitude burst EMP: gamma rays hit the atmosphere between 20-40 km altitude, ejecting electrons which are then deflected sideways by the earth's magnetic field. This makes the electrons radiate EMP over a massive area. Because of the curvature of earth's magnetic field over the USA, the maximum EMP occurs south of the detonation.

Thus we see that a nuclear strike can disable the power grid and burn out all electrical equipment. Goodbye 21st century! It wouldn't take too many of these to put civilization out of commission. There can also be additional damage from knock-on effects such as fires caused by sparks and heat from the equipment, and injury to people handling the equipment.

Luckily, the principles of mutually-assured destruction have kept any nation from launching a nuclear strike, and scientists say the chance of a massive solar flare are low.