After the Pulse: Musings about EMP

EMP mechanism

Some of you might remember a short-lived television series called Dark Angel, which aired on the Fox network for two seasons (2000-2002). The series’ backstory included the premise that a terrorist group set off a high-altitude nuclear burst that destroyed most of the United States’ electronic and communications infrastructure, plunging the nation into chaos. Recently, Republican presidential candidate Newt Gingrich has been voicing concerns that one of our enemies – presumably either a terrorist group or a rogue nuclear nation – might attack us in just this fashion and his speculations have raised a flurry of commentary (including this one, I guess). Before diving into the plausibility of such an attack, a bit of review on EMP might be in order, drawing upon an interesting discussion by Harvard Smithsonian Center for Astrophysics astrophysicist Yousaf Butt, who is also a scientific consultant to FAS, and a more technical description is found elsewhere on the FAS website. Going back a few decades, the National Academy of Sciences examined this matter in a 1984 report and came down between these two extremes.

The short version is that a nuclear blast generates a huge amount of radiation, and this radiation can strip electrons from atoms, creating ionization. The ions that are formed interact with the Earth’s magnetic field creating huge electrical currents and generating electromagnetic radiation. This, in turn, can induce electrical currents in conductors – pipes, wires, cables, and the like – and it is these currents that can fry electronic and electrical systems. According to Butt, “The exact value of the induced peak electric field depends upon the bomb yield, its design, and other factors already mentioned above, such as the detonation altitude, local magnetic field strength, and the geographic latitude of the explosion. Higher geomagnetic field strengths and higher latitudes (i.e. farther away from the equator, north or south) will typically create a stronger peak EMP field, other things being equal.” Butt also notes that, for high-energy bursts (100 kT and higher) the EMP will affect everything within the line of sight to the explosion. For a surface burst this would be several miles; a 100 kT explosion at an altitude of 500 km (about 300 miles) would be capable of blanketing the entire United States.

The effects of EMP have been documented – both American and Soviet nuclear weapons tests have knocked out power grids, street lights, and communications facilities hundreds of miles away, and these effects were not unanticipated by nuclear weapons scientists. So the bottom line is that Gingrich’s comments are not without a basis in both science and our experience. The question is that of plausibility rather than possibility, but the plausibility question is an important one. How likely is it that a terrorist group or a rogue nation will set off a 100 kT nuclear weapon at a high altitude over the United States in an effort to wipe out our electronics and plunge our nation into chaos? And to even start to address this we have to unfold this into its component questions:

Are there enemies who would like to see the United States slammed by such a blow? Almost certainly. There is no shortage of terrorist groups that have made no bones about wanting to hurt us as much as possible and who would likely love to strike such a blow against us. And not only terrorist groups – there are also nations (e.g. Iran, North Korea, maybe Venezuela, are a few) who would take some satisfaction in seeing the United States humbled.

If so, do “they” have the capability of making or obtaining a 100 kT nuclear device? Very few nations have the ability to produce their own nuclear weapons of any yield – besides the United States these are Britain, France, Russia, China, India, and Pakistan. Add to that list Israel (whose government has not declared it has nuclear weapons but it seems almost certain to possess) and South Africa (whose government gave up a nuclear weapons capability). North Korea has tested nuclear weapons, but both explosions were very low-yield; it’s not certain that North Korea can yet produce a 100 kT device.

If so, do “they” have the ability to loft it to an altitude of several hundred km over the US? Most of the nuclear powers have developed (or purchased) some ballistic missile capability, although not all of them have yet demonstrated the ability to reach the United States with their weapons. On the other hand, one can speculate endlessly about packing shorter-range missiles onto ships, assembling a weapon and delivery system in a nearer nation, and so forth. However, it seems less likely that a terrorist group will have such a capability.

If so, are “they” likely to use a nuclear weapon in this manner? This is the kicker – any missile launched arrives with a “return address” (its trajectory) that can be traced back to the point of origin. It is almost certain that we will know fairly precisely where a missile originated long before the pulse that would wipe out our electronics, and any nation would have to consider the possibility of nuclear (or non-nuclear) retaliation from ballistic missile submarines and from locations not affected by EMP.  Not only that, but nuclear-armed nations also have to contend with the possibility that nuclear forensics would be able to identify them as the source of fissionable materials should they donate or sell a weapon to a terrorist group. While we cannot rule out blind hatred or stupidity, enlightened self-interest and a strong sense of national preservation would suggest that the nations capable of attacking us would likely refrain.

This leaves terrorist groups, which (as far as we can tell) lack both nuclear weapons and missiles. This lack would seem to make a terrorist high-altitude nuclear attack unlikely. Even if a terrorist group were to develop its own nuclear weapon, going straight to a 100 kT device – about 8 times as powerful as the Hiroshima device and over 100 times as powerful as North Korea’s first attempt – seems as likely as Henry Ford’s first factory turning out a Prius. And even if a terrorist group were to come up with a 100 kT nuclear weapon we have to wonder if they would choose to set it off at high altitude and to forgo the imagery of a nuclear strike in the heart of a large city. All of these factors make me suspect that Gingrich’s scenario, while possible, it not likely very plausible.

If “they” do attack us, what will really happen? So let’s think about a few possibilities. Maybe the members of a terrorist group gets their hands on a nuclear device (any yield), but they set it off as a ground burst because they can’t reach a high altitude. Since EMP effects seem to be pretty much limited to line-of-sight, a single city and some of the suburbs might be knocked out but the entire nation would continue on as normal. But even taking the “Gingrich scenario” – assuming that someone launches a nuclear weapon 500 miles up – would we see the millions dead that Gingrich envisions?  Probably not.

A blast 300 miles up would no more kill people on the surface of the Earth any more than a blast in Washington DC would kill people in New York City. Of course there could be problems – especially if control systems are knocked out in airplanes, hospitals, and other places where even a short loss of “attention” by the electronics can be deadly. But aside from these obvious things it is far more likely that the loss of electronic systems would be a huge (and costly) inconvenience but it is hard to place credence in Gingrich’s projection of millions of lives lost. Our civilization predates the electronic age by centuries – our electronics make our lives more comfortable, more fulfilling, more efficient and so forth. But when the lights went out during the Northeast Blackout of 2003 civilization somehow managed to muddle along without massive loss of life.

Having said all of this it is easy to poo-poo Gingrich as being on a different plane of existence (and not necessarily a higher plane). As the above should make clear, I sincerely doubt that a terrorist group or a rogue nation is going to try to launch an EMP attack against the United States – not because it’s impossible but because it is unlikely. This is where we have to decide how (and whether) to prepare. If the outcome is so horrible that we simply cannot live with the results then we must prepare for this contingency, however unlikely – just as we prepared for both conventional and nuclear war with the Soviet Union. But if the cost of preparation is too high, the likelihood of such an attack is too low, and the possible negative effects are not too horrible then it might be unreasonable to give this matter an inordinate amount of attention.


Dr Y is a certified health physicist, trained in nuclear power plant design and operations, with experience in nuclear power, environmental science, and planning for radiological and nuclear emergencies. He has 30 years of experience in the areas of nuclear and radiation safety.

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