EMP confounds some common expectations of the relative dangers of different nuclear weapons. Aside from the displacement of the Earth’s magnetic field (E3), the intensity of the phenomenon does not, as indicated above, scale with warhead yield. A Hiroshima-size blast (14 kilotons, less than 1/20th the K Project yields and 1/100th that of Starfish Prime) will do very nicely. Counter-intuitively, a hydrogen bomb with yields in the megaton range short-circuits EMP by the phenomenon of pre-ionization. The hydrogen bomb’s trigger (an A-bomb) prematurely strips electrons from the atoms of the air, so that the later, larger quantity of electrons shorts out in the atmosphere rather than interacting with the Earth’s magnetic field. H-bombs thus cause less EMP damage than A-bombs.
EMP means that a foe does not need the massive explosive yield of an H-bomb to inflict grave damage. An A-bomb will perform the EMP task with greater effect. North Korea already has an A-bomb, and Iran is getting tantalizingly closer to one.
Altitude is a critical factor in EMP effects—the bomb must go off at the right height to hit the Earth’s magnetic field. Deep space detonations do not cause EMP effects on earth—the gamma ray emissions from the bomb dissipate long before reaching Earth’s magnetic field. And low-altitude nuclear detonations, which generate vast blast, heat, and radiation damage, explode below most of Earth’s magnetic field and hence generate less EMP.
An attacker could detonate an EMP weapon 300 miles over Kansas, and cover a 1,470-mile radius that would encompass the entire lower 48 states. On a smaller scale, even a ground burst weapon’s EMP effects could devastate local electric power in a radius of roughly 6 to 12 miles, potentially hugely effective over a major metropolis. EMP can create imbalances within the grid that cause the system to shut down and inflict severe damage. Because newer infrastructures rely so much on digital technologies, far fewer people are required to run them; thus, in a crisis, there are far fewer workers available to rapidly reconstitute damaged parts of the system. Infrastructures driven by modern silicon computer chips are much more vulnerable to disruption via EMP than are infrastructures built with older-generation electric power technologies.
In 1998, Iran, which lacks strategic bombers and missile subs, test-fired a missile from a floating barge, validating its ability to launch a ballistic missile from a platform less stable than a ground launch (and thus more susceptible to inaccurate guidance). Barges could easily cruise offshore in international waters, i.e., outside the 12-mile limit.[54] Iran would have to launch its missiles a few hundred miles at sea, to limit the chance of detection. Reaching 1,500 miles inside the U.S. homeland would require a missile range of about 2,000 miles. New Iranian models are approaching this range. Such missiles could be launched from either the Atlantic or the Pacific Ocean, or from the Gulf of Mexico.
In 1999, Iran tested an armed ballistic missile in an “EMP mode”: this means that the missile was fired in a steep trajectory whose angle of ascent matched that required for an EMP attack. The missile’s conventional warhead detonated at high altitude. This test validated Iran’s ability to carry out a coastal EMP strike. When newer, longer-range missiles enter service, Iran could target the lower 48 states by detonating an EMP weapon centered over the interior.
Using shorter-range missiles Iran could target selected cities easily from offshore, with lower-level EMP bursts. Ship-launch scenarios were one threat specifically identified by the 1998 Rumsfeld Commission report on growing ballistic missile threats. Not that this threat was new: in his 1949 memoirs Dr. Vannevar Bush, wartime science adviser to Presidents Roosevelt and Truman, warned of the threat posed by “atomic bombs smuggled in by innocent-appearing ships, to be detonated at the chosen moment.” The U.S. successfully launched a Polaris ballistic missile off a commercial ship in 1962.
Infrastructure Vulnerabilities
AMONG THE warnings issued by the congressional EMP panel in 2008, perhaps the strongest concerned the risks of infrastructure interdependency, specifically its tendency to increase the time needed to recover after an EMP attack:
Safeguards against single point failures generally depend on the proper functioning of the rest of the national infrastructure, a plausible assumption for high reliability infrastructure systems when they experience random, uncorrelated single point failures…. Planning for multiple failures, particularly when they are closely correlated in time, is much less common….
No currently available modeling and simulation tools exist that can adequately address the consequences of disruptions and failures occurring simultaneously in different critical infrastructures that are dynamically interdependent.
In other words, if neighboring communities cannot help, recovery time is much longer. “Edge” communities can bring in supplies, give shelter, and send in needed funds, but we cannot predict how much help they will be able to offer. Recovery from Hurricane Katrina included large-scale resettling of displaced residents, with some even choosing to become residents in edge communities that hosted them. A wider circle of destruction would have hindered recovery everywhere.
The second report issued by the EMP panel examined 10 specific infrastructures and detailed their potentially greatest vulnerabilities. It should be noted that one major change in the past half century has increased societal vulnerability: the shift from vacuum tubes to silicon chips inside America’s electrical infrastructures. The latter are less resistant to EMP damage.
Electric power drives virtually all infrastructures in the United States. Backup is provided by generators whose life typically is 72 hours or less, along with batteries with a life of a few hours at most. Even a short blackout can cause losses of between 18 and 60 percent of production in the affected area.
Note that in the past 20 years the margin of redundant capacity for emergency needs has halved, from 20 to 10 percent. Increasing use of wind power, a mode that relies on the vagaries of fickle weather, can place unpredictable demands upon the system, increasing reliability problems. Overseas factories often produce (and customize) high-power transformers that step up and down voltage levels as electric current travels between power generation and customer distribution. But these transformers are not an immediate-term solution; the lead-time to order one is about a year, and there are 2,000 transformers in the U.S. electric grid.
As with computers, digitally controlled power systems can suffer extensive damage if shut down without the proper procedures. Thus the electric grid transmission system that links generators and consumers is, the panel said, “highly vulnerable” to EMP.
Telecommunications networks are another major potential weak spot. Backup power typically lasts 4 to 72 hours. (One significant exception: EMP can’t hurt fiber optics, which lie outside the frequency range EMP effects occupy; but computers, telephones, etc. are electrical, and thus the end points of fiber networks are susceptible.)
Banking and finance networks are highly automated electronic digital systems. These networks are impossible to operate without communications connectivity. In the past three decades, the transaction volumes that these networks carry have jumped by several orders of magnitude. A generation ago, a 10 million–share trading day on the New York Stock Exchange was huge, whereas today trading volume averages several billion shares per day. The public securities markets trade trillions of dollars of securities annually; other specialized financial networks also trade trillions of dollars in value. In all, financial communications networks daily carry several times the amount of data held in the entire print collection of the Library of Congress.
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Some countries claim a 200-mile limit to territorial waters, but such claims are not currently recognized under international law.