- Caused by nuclear detonation at high altitude or
- Caused by Coronal Mass Ejection from the Sun
- Result may be the destruction of most modern electronics and the electrical and communications grid.
- A Coronal Mass Ejection has happened in the past (Carrington Event, SEP 1-2, 1859), and is almost certain to happen again at some point.
A recent (NOV 2018) U.S. Air Force study reports the following:
- 99 nuclear reactors would likely melt down without electricity to cool them.
- 4.1 million would be displaced from areas around the nuclear plants as the radioactive cloud spread.
- Military and commercial jets, such as those built by Airbus, could be degraded. “Alarmingly, aircraft designed to carry large numbers of people and sizable cargo are allowed to operate without certainty about their level of resilience.”
- Bases would be cut off, making defense and counter-attacks impossible.
- Civil unrest would start in “hours.”
- Power and GPS could go dark. “An EMP would cause instantaneous and simultaneous loss of many technologies reliant on electrical power and computer circuit boards, such as cell phones and GPS devices.”
- “Failures may include long-term loss of electrical power (due to loss of emergency generators), sewage, fresh water, banking, landlines, cellular service, vehicles.”
- 18 months or more are required to replace key elements of the electric grid that would be damaged or knocked out.
“While it is focused on the devastating impact an EMP hit would have on the military, it appears to support a congressional warning that up to 90 percent of the population on the East Coast would die in a year of an attack that would dismantle or interfere with electricity, transportation, food processing, and healthcare.”
Summary: There are some scenarios that have two key factors:
1) They are relatively high probability given a long enough time frame.
2) They have the potential to end civilization as we know it.
EMP, whether natural or man-made, is just such a scenario.