About the most the Iranians could accomplish with an EMP detonation would be to set off every car and burglar alarm in Europe simultaneously.
To start with, EMP has to be high altitude, because its effects are in a downward cone, like an upside down funnel. It is also dependent on the size of the detonation.
The classical example is of an EMP burst over Kansas, having to be between 1-3 Megatons, at near orbit altitude, to affect most of the continental US. The Iranians nuclear weapons capability is about 25 Kilotons, which would have to be detonated at a much lower altitude, and would create an electrical overcharge in about half the state.
In other words, why waste it on EMP, when if they allowed it to hit the ground, it would be far more destructive?
Their other problem are targets. To start with there, Iran is ringed on three sides with 300 or so PAC-3 anti-missile missiles. They have a very high “overkill” (missile and warhead failure rate), and then their missiles would have to contend with this layered anti-missile defenses.
The US aircraft carrier fleets are designed to be very resistant to nuclear attack, both in taking out enemy missiles, and having hardened electronics. Plus our ship Captains are a testy bunch when irritated, and will retaliate with enough destructive force to wipe out a continent.
The US has also calculated that somebody might put a few missiles on a cargo ship an try and sneak them up to one of our coasts, so we not only have anti-missile defenses, but our Coast Guard regularly stops ships hundreds of miles at sea to make sure they have no nuclear cargoes.
In the last few years, it was alleged that the North Koreans were trying to smuggle nuclear materials to Iran, and two of their ships were “lost at sea” in the process. We have no sense of humor about these things.
EMP would require either a large number of smaller nukes (as someone said, going off at some altitude) in proximity to various sites, or a couple really enormous bombs — and why oh why was it so simple to get everyone (except China and France) to stop atmospheric testing? ;’) And France did it in a remote spot in the Pacific. Thanks LucyT.
So many ways to plot against us.