So what is the chance of somebody taking out the whole USA economy with a few well-placed EMP nukes? Should I lie awake at night worrying about it? I don't think so.
First you must realize that it takes a megaton bomb for EMP to do anything as serious as blowing streetlight breakers 900 miles away. Electronics inside metal boxes (like a car hood or a computer case) not connected to long outside wires will not be damaged, even at that level of EMP. While EMP is different from lightning, travelling over a long distance through wires attenuates the pulse and slows it down, so that ordinary surge protectors can activate in time. Computers safe from lightning are also safe from megaton EMP more than a couple hundred miles away.
Three countries in the world have megaton nukes at this time: the USA, Russia, and China. England had them at one time, but apparently no longer. China depends on the American economy to provide cash flow into their own; they are not foolish enough to destroy that (and half their own cities in retaliation). Russia does not have that economic dependency, but they proved themselves smart enough not to go beyond saber rattling during the Cold War when they were a superpower; they don't have that status now, and nuking the USA would not return it to them.
North Korea's bombs are in the small kiloton range, about the same size we set off over Japan. Instead of blowing breakers at 900 miles, they'd do little more than set off alarms at 100 miles from ground zero. North Korea may have an insane leader, but they have neither the nukes nor the delivery systems to destroy more than a city or two -- certainly leaving enough American manufacturing and war-making power to reduce the entire Korean peninsula to a green glow. I suspect Kim Jong Il (and anybody who follows him) understands that. That's not the sort of legacy a megalomaniac wants to leave to history.
We officially don't know about the size of India's and Pakistan's bombs, but it's doubtful that their first efforts are much bigger than anybody else's first efforts. Iran (with North Korea's help) might soon have a bomb, but why would the Koreans help them make bigger bombs than the Koreans themselves have? Mahmoud Ahmadinejad may qualify as crazy, but not crazy enough to go after the 800-pound American gorilla when Israel is much closer and looks far more tempting. Besides, Israel has the technology and the motivation to prevent Iran from getting their own nukes.
Israel has more PhDs per capita than any other nation in the world, and while they are not admitting it, they almost certainly have nukes. How many and how big nobody else knows, but they are aimed at Iran and Syria, not the USA.
The Taliban and Al-Qaeda and other certifiable crazies do exist out there, and they might actually get their hands on a small nuclear bomb or two, but everybody -- including other Islamic countries -- is afraid of the militants, so they don't have much liberty to pull that off. Even if they did, and even if they successfully detonated one or more of them high above the USA, they might take out a city or two, but the rest of the country would still be very much functional and the economic devastation described in Forstchen's One Second After would remain fiction. North Korea and Iran and perhaps western Pakistan would still glow in the dark.
Rather than 90% mortality as suggested by Forstchen, a successful EMP
strike against the USA might kill off as many as 5% nationwide. It's not
a pretty picture, but at least it's not as horrible as Forstchen would
have us believe. People living in New York, Washington, and perhaps Los
Angeles are at risk. The rest of us are more likely to die in a car accident.
Science fiction typically imagines a future world that mostly obeys the present known laws of physics, with exceptions made for interstellar travel by some kind of hyper-drive not yet understood, and artificially intelligent robots. A related genre, fantasy, imagines a world in the distant past or future where the laws of physics do not apply -- typically through the use of magic and/or fantastic creatures. In the case of future, the boundary is somewhat nebulous, so you can hardly blame the librarian for tagging some works by an author as sci-fi and others -- often in the same series of sequels -- as fantasy. One look at the cover clearly betrays the fantastic quality of the plot line, and I put it back on the shelf. Any more, if I see both spine stickers next to each other by the same author, I don't even look.
Anyway, I'm working my way through the fiction, which is shelved alphabetically by author. I never heard of William Forstchen, but then there are a lot of new sci-fi authors since I last went through the whole library (several decades ago, different library).
One Second After is mistagged. It's not really set in the future so much as an alternate version of today, with no intended violations of any physics. It imagines what would happen to the USA economy if a terrorist (think: Iran or North Korea) were to detonate three nukes a 100 miles above continental USA. It's not a pretty scene. Unlike typical sci-fi, there are no deus ex machina scientific solutions that overcome the inevitable chaos. Instead, Forstchen kills off 90% of the population from disease and starvation and bullying, basically setting the economy back 500 years. His heroes have better than average survival -- their town lost only 80% -- and there is a lot of "we are Americans" flag waving, but it's still a pretty depressing story.
The problem is, it's not really fiction. That destruction could really happen from EMP (electro-magnetic pulse) delivered by high-altitude nuclear detonation.
The author is no scientist, and I don't think he understands the inverse square law for electromagnetic propagation, but even if EMP only took out half of the country's electronics and power grid, the economy would be devastated. His big preachy sermon is "Why are we not prepared?" I suspect the answer is the same as it was for New Orleans: It hasn't happened before, so nobody has reason to believe the Chicken Little cries. We survived Y2K, didn't we? At least, as Forstchen points out, the risk and the downside of EMP is far greater than so-called Global Warming. He did not say so, but the remedy is also rather less harmful to the economy. But neither one has happened, so we don't know that for sure, do we?
The book gave a web link that does not have any technical data I could find, but Google turned up one useful link in a general search. I'm no expert in radio propagation, and most of the material related to conduction by nearby control cables (not available in an air burst), but the numbers seem to suggest that more than a couple hundred miles away from an air burst would produce "detectable" radiation, but not necessarily crippling currents. They did atmospheric tests during the 50s and 60s, and that half of the world -- notably Hawaii, only 900 miles away and well within line-of-sight -- did not stop functioning (some Honolulu streetlight breakers were blown). One diagram showed a 1.4V/m pulse at 1000 miles; later they reported tests applying 50 kV/m to transistor radios, which knocked out sets with extended antennas, but not the fully enclosed set. That's 2000 times stronger than the pulse of a 1kT air burst 50 miles away, according to the distance diagrams, and 20,000 times stronger than shown for 1000 miles. Obviously there are some non-linearities.
Bottom line: there is a risk of major damage near the blast location,
but probably not enough to wipe out the entire economy.