Could a single nuclear EMP kill 90% of Americans within one year?

Question

From the latest doomsday scenario:

At a U.S. House of Representatives hearing on October 12th, experts warned that the greatest existential threat to the country may come from the detonation of a nuclear EMP bomb. It could kill as many as 90 percent of all Americans within a year.

What would an EMP attack actually do? It could involve the detonation of a hydrogen bomb delivered by missile or even satellites at a high altitude of 30-400 km, creating an electromagnetic pulse that would knock out the electrical grid. But not only that - all electrical devices in the range of the blast could be fried. No lights, no computers, no phones, no internet, not even cars would work. The lack of refrigeration is likely to spoil food, causing mass starvation. Add to that lack of clean water, no air traffic control or any financial transactions taking place and you have widespread devastation in the U.S.

The casualties incurred would not be from the explosion, as it can happen too high for its nuclear effects to be felt strongly on the ground. But the loss of life-sustaining infrastructure could bring slow but sure disaster.

This kind of doomsday prediction comes courtesy of two members of the former congressional EMP commission - Dr. William R. Graham and Dr. Peter Vincent Pry. Dr. Graham is a physicist who was a science advisor to President Reagan and administrated NASA. Dr. Pry is a former CIA officer responsible for analyzing Soviet and Russian nuclear strategy, who has served on numerous congressional boards related to security.

Are nuclear/EMP experts in agreement that a single nuclear EMP can destroy the electronics of a whole country? What are the conditions for such an event, given that enough nuclear tests have been performed in the atmosphere in the past, yet disruption/destruction of electronics was never that large? Ok, some are mentioned in the snippet. Is that all it would take? Wikipedia does mention a HEMP being more destructive, but without citations or much detail.

The info/claims have also been reported in more mainstream media, but with less detail.

Answer 1

That number was mentioned in the statement of Dr William R Graham and Dr Peter Vincent Pry, chairman and chief of staff of the Commission to Assess the Threat to the United States from EMP attack.

The statement quotes an article by ambassador Henry Cooper, former Director of the U.S. Strategic Defense Initiative:

The result could be to shut down the U.S. electric power grid for an indefinite period, leading to the death within a year of up to 90 percent of all Americans—as the EMP Commission testified over eight years ago.

With the following note below the line:

Ambassador Henry F. Cooper, “Whistling Past The Graveyard…” High Frontier (September 20, 2016) highfrontier.org/sept-20-2016-whistling-past-the-graveyard/ See also: highfrontier.org/category/fobs. On up to 90% U.S. fatalities from an EMP attack, during a congressional hearing, Rep. Roscoe Bartlett asked me if such high fatalities could result, and I responded: “We don’t have experience with losing the infrastructure in a country with 300 million people, most of whom don’t live in a way that provides for their own food and other needs. We can go back to an era when people did live like that. That would be—10 percent would be 30 million people, and that is probably the range where we could survive as a basically rural economy.” U.S. House of Representatives, Hearing, “Threat Posed By Electromagnetic Pulse (EMP) Attack” Committee on Armed Services (Washington, D.C.: July 10, 2008), p. 9.

Here is the full statement for the record. The 2008 EMP commission report does not give any casualty estimates.

In conclusion that 90% estimate is highly speculative estimate given by Dr Henry Cooper. While he is certainly a credible individual, it appears this is just a "gut" estimate that is not backed by any serious studies.