Just as solar flares or coronal mass ejections could wipe out power grids, so could a sudden burst of electromagnetic radiation. The science is the same, but security experts say the cause is more likely to come from a more sinister source, such as the detonation of a nuclear weapon. An EMP blast — whether from a weapon or solar activity — could destroy our entire electronic, transportation and communications infrastructure in less than a second. If such a blast occurred over the United States, 90 percent of all Americans could be dead within a year, according to the Congressional EMP Commission.
The proximity of an EMP attack to the planet’s surface would affect the severity of its effects. This map illustrates how the United States would be affected by an EMP attack based on burst altitude.