“On the surface of the Earth the EMP effects are limited to a few radius of the blast for several reason. First there is lots of atmosphere at the surface so free high energy photons (gamma rays) and the high energy electrons they generate are quickly absorbed by collisions with atmospheric molecules. Second surface blasts are not focused and directed along the Earths magnetic field lines. Eargo because of 1 and 2 and the line of sight thing the EMP affects are limited with surface blasts.”
So, a high altitude EMP would also attenuated by the atmosphere once it starts to reach lower altitudes. Oh, wait, that doesn’t allow the theory we’re all going to die from EMP. Hmmm, we’ll need a better explanation.
The Earths atmosphere density increases at altitude decreases. For example 5 miles up you would quickly die from lack of oxygen. Not that there is not plenty of oxygen 5 miles up, simply that the air is so thin you can’t breathe enough of it to keep you alive. This is not complicated stuff. Also remember that the inverse square law does not apply since the “pulse” is following magnetic field lines and not a normal straight line path. Think about it and you will get the concept in time.