The dynamics of the standoff between the US and North Korea have shifted dramatically in the past week.

First, the North started with an unexpectedly sharp provocation - launching a missile over the Japanese island of Hokkaido - before following that up with its sixth nuclear test. Also, judging by the size the earthquake detected in the country’s mountainous North on Sunday morning, North Korea may have been telling the truth when it said it conducted what it described as its first hydrogen bomb test.

And while the North bragged about the weapon’s “great destructive power” in a TV broadcast, what caught analysts’ attention was a mention of a different tactic: detonating an H-bomb at high altitude to create an electromagnetic pulse that could knock out parts of the US electrical grid.

Here’s WSJ:

“North Korea’s threats against the U.S. now include a tactic long discussed by some experts: an electromagnetic pulse, or EMP, triggered by a nuclear weapon that would aim to shut down the U.S. electricity grid. North Korea’s state news agency made a rare reference to the tactic in a Sunday morning release in which the country said it was able to load a hydrogen bomb onto a long-range missile. The bomb, North Korea said, ‘is a multifunctional thermonuclear nuke with great destructive power which can be detonated even at high altitudes for super-powerful EMP attack.’”

Unlike a conventional nuke, an EMP blast - think Oceans' 11 - is not directly lethal, and serves mostly to knock out key infrastructure (useful when robbing a casino).

However, it would probably lead to an unknown number of indirect deaths as hospitals and essential infrastructure lose power.

“The idea of an EMP attack is to detonate a nuclear weapon tens or hundreds of miles above the earth with the aim of knocking out power in much of the U.S. Unlike the U.S. atomic bombs dropped over Hiroshima and Nagasaki in 1945, such a weapon wouldn’t directly destroy buildings or kill people. Instead, electromagnetic waves from the nuclear explosion would generate pulses to overwhelm the electric grid and electronic devices in the same way a lightning surge can destroy equipment.”

In the worst possible scenario, regional power grids could be offline for months, potentially costing many deaths as people would eventually start running out of necessities like food and medicine. Lawmakers and the US military have been aware of the EMP threat for many years, according to WSJ. IN a 2008 report commissioned by Congress, the authors warned that an EMP attack would lead to “widespread and long-lasting disruption and damage to the critical infrastructures that underpin the fabric of US society.”

In a report published last month, the Hill noted that the North could choose to carry out an EMP attack on Japan or South Korea as a more politically acceptable act of aggression. Such an attack could help the North accomplish its three most-important political goals, the Hill said.

“North Korea has nuclear-armed missiles and satellites potentially capable of electromagnetic pulse (EMP) attack. EMP is considered by many the most politically acceptable use of a nuclear weapon, because the high-altitude detonation (above 30 kilometers) produces no blast, thermal, or radioactive fallout effects harmful to people. EMP itself is harmless to people, destroying only electronics. But by destroying electric grids and other life-sustaining critical infrastructures, the indirect effects of EMP can kill far more people in the long-run than nuclear blasting a city. In this scenario, North Korea makes an EMP attack on Japan and South Korea to achieve its three most important foreign policy goals: reunification with South Korea, revenge upon Japan for World War II, and recognition of North Korea as a world power.”

Scientists first discovered a hydrogen bomb’s ancillary EMP capabilities after testing one in the Pacific in the early 1960s.

“When the U.S. tested a hydrogen bomb in the Pacific in 1962, it resulted in lights burning out in Honolulu, nearly 1,000 miles from the test site. Naturally occurring electromagnetic events on the sun can also disrupt power systems. A 1989 blackout in Quebec that came days after powerful explosions on the sun expelled a cloud of charged particles that struck earth’s magnetic field.”

Some experts who spoke with WSJ said it would be impossible to guarantee success during an EMP attack, since the weapon would need to detonate with near perfect accuracy.

“Skeptics generally acknowledge that an EMP attack would be possible in theory, but they say the danger is exaggerated because it would be difficult for an enemy such as North Korea to calibrate the attack to deliver maximum damage to the U.S. electrical grid. If it a North Korean bomb exploded away from its target location, it might knock out only a few devices or parts of the grid.”

The North Korea said its hydrogen bomb had explosive power of tens of kilotons to hundreds of kilotons – so of course if it landed to close, or the attack was mishandled in other ways, what was meant to be an EMP attack would result in a nuclear strike. At least one expert said using an EMP attack would make little sense when the North could cause much more destruction with a nuclear ground attack.

“Others say that even if North Korea had the technical capability to deliver a damaging electromagnetic pulse, it wouldn’t make strategic sense to use it because Pyongyang could wreak more destruction with a traditional nuclear attack directed at a large city. A rogue state would prefer a “spectacular and direct ground burst in preference to a unreliable and uncertain EMP strike. A weapon of mass destruction is preferable to a weapon of mass disruption,” wrote physicist Yousaf M. Butt in a 2010 analysis.”

Luckily, if US military authorities truly fear an attack, there are some long-term steps the US could take to minimize the effectiveness of an electromagnetic pulse attack. Defenses could be bolstered inexpensively by designing electrical-grid components to withstand sudden pulses, just as the grid already is protected against lightning strikes. The US could also build backup systems that could step in for the principal electrical grids in an emergency.

If the North’s latest nuclear test, conducted early Sunday, didn’t involve a hydrogen bomb, the weapon used was at least close to it according to US officials. It was the North’s first nuclear test since late last year, and also the first since tensions between Kim Jong Un and President Donald Trump began escalating shortly after his inauguration. China, Japan, South Korea and the US have already condemned the attack, with China and South Korea threatening to work with the Security Council to bring more onerous sanctions against the defiant North.

Meanwhile, President Donald Trump in a series of tweets hinted that he was frustrated with diplomatic measures, which he referred to as “appeasement.” We imagine there are more than a few generals whispering in his ear about the potential success rate of a surgical strike.

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Finally, here is a repost from July 2014, in which hedge fund legend Paul Singer, head of Elliott Management, said that "there is one risk that stands way above the rest in terms of the scope of potential damage adjusted for the likelihood of occurrence" - an electromagnetic pulse (EMP). Three years he may be proven correct.

From: "The "Most Significant Danger" According To Elliott's Paul Singer"