Reply: In theory, yes, and EMP or High-Altitude EMP (HEMP) has been part of U.S. and Russian nuclear strike planning for decades. Some also believe China might also use it in a war. But in recent years some people have warned about scenarios ranging from DPRK, Iran, or terrorist organizations using EMP against the United States or its allies to disrupt critical electronic infrastructure. An EMP Commission has even been established by Congress in 2001.

HEMP threat scenarios depend on several factors, such as delivery vehicle, nuclear yield, and motivation. It would probably require detonation of a large thermonuclear warhead very high above Kansas to cause country-wide disruption in the United States. Neither “rogue states” nor terrorist organizations have such capabilities or seem likely to get the in the foreseeable future. But smaller less optimal scenarios could also cause local disruptive effects, if carried out effectively. See here for recent assessment.

As always in these matters, it is always possible to construct frightening worst-case scenarios. It is much harder to assess how realistic the threat is and what to do about it. The debate has become highly politicized, and some warn that while EMP in principle is serious the capability is being simplified and the threat overblown. See for example the assessment by Stephen Younger, the former director of the Defense Threat Reduction Agency, in his book The Bomb:

“Since an electromagnetic pulse (EMP) is generated in the upper atmosphere and projected downward, the affected area is quite large, potentially encompassing an entire country. However, the consequences of such an attack are limited to electronics (people and structures are not affected), and there is considerable debate within the scientific community about the sensitivity of electronics to a given type of pulse. Contrary to media reports, it is not true that an EMP attack from a typical strategic weapon would completely shut down the electronics within a country. First, the effect is statistical in nature – some systems will not notice the pulse at all while identical counterparts will be affected. Second, the most likely effect from an EMP attack is “upset” rather than destruction, that is, a temporary scrambling of the memory of a computer or the frequency of a communication device, something that is easily corrected by rebooting or resetting the device. (Upset can, however, have catastrophic consequences if the computer is the flight controller of an aircraft or another time-critical system.) Third, the EMP output from a typical device is degraded by several design issues so that few, if any, weapons currently deployed in military stockpiles will produce the maximum possible effect. Of all the nuclear effects, EMP seems the most prone to misunderstanding and misinterpretation.”

My recommendation is to keep a cool head, be skeptical of worst-case scenarios, and as questions. HK