Even a slow rise in water levels would be disasterous. Untold amounts of land would become unusable, and there would be serious overcrowding in surviving cities.
taltamir, while I agree with you that ManSh00ter is underestimating the power of EMP's, I think that you are not taking into account the incredible unlikeliness of such an attack.
You could, theorectically, wipe out the entire country with one nuke, but it has to be high enough above the planet that it is all but impossible for a terrorist group or rouge country to acheive. They just don't have the tech to get a sufficently large nuke higher than the ISS.
They could do it with multiple nukes+missiles, which wouldn't need as powerful missiles, like the OP, but that is still very unlikely. They would need to get their hands on multiple nukes, which would be quite difficult. IMO, if someone did manage to get that many nukes, I think they would do like ManSh00ter said, and use them on a number of important cities, rather than mess around with an EMP
You also have to take into account the relative intelligence of wouldbe terrorists and/or rouge nations. They don't exactly have a bunch of MIT graduates with Nobel prizes in Nuclear physics. It's very unlikely they'll have anyone who could make the calculations of angle of launch, optimal height of detonation, etc, assuming they even know that nukes can be used as an EMP.
IMO, the only threat we face from an EMP attack is if a country that has the technical know-how (Russia, probably China, etc) decides to launch an attack, and uses one as a pre-emptive strike. Although, I would think that if they were to do that, they would be more likely to just nuke the s*** out of the US, and not bother with the EMP.
This is just a little nit-picky thing, but there are not ground level nuclear explosions (at least not on purpose) For optimal damage, a nuke needs to be detonated above the target, not when it hits the street below. A detonation at ground level wastes a large part of the destruction force. A large part of it gets absorbed by the ground below, and another large part is reflected off the ground into the air, neither of which does much good if you're trying to destroy a city.
ManSh00ter, I think that you are wrong computers+cars being largely immune to the effects of an EMP. Computers have a large amount of wire in them. The motors inside (like the cooling fan, etc) are basiclly just a bunch of coiled wire, and each motor easily has a couple feet of wire in it, more than enough to feel the effects of an EMP.
Cars, particularly the newer ones with built in computers, also have large amounts of wiring. Older cars, and possibly some newer ones that don't rely as heavily on computers probably would still work, however, you might not be able to get gas for them. Many of the pumps used for gas have integrated computers, so they might not work, either.
While I agree that EMP's are greatly exagerated by the media, games, fiction, etc, I don't think they should completely disregarded as a "useless side effect, either.