Razed cities. Loss of life. Contaminated fishing stocks. Crippled satellite networks.

Should the nuclear crisis between the United States and North Korea escalate beyond hurling test missiles and insults like "madman" and "dotard," the list of possible effects is a long and frightening one.

Whether North Korea were to simply test a nuclear warhead or aim one at a target like the U.S. territory of Guam — as North Korean leader Kim Jong-un has threatened — there would be consequences for both people and the environment.

It's impossible to predict precisely the effects of a North Korean nuclear blast because so much depends on the type, size and method and elevation of the detonation, says Danny Lam, a Calgary-based defence analyst with a PhD in political science and an M.Sc. in civil and environmental engineering.

But using as a guide the size of the nuclear test North Korea conducted Sept. 3 — estimated at 250 kilotonnes — some idea of the scope of the damage can be estimated.

"These are not toys," says Lam, who recently testified before the House of Commons defence committee convened to discuss North Korean aggression. "These are big massive weapons that generate massive effects. These are big city busters."

North Korean Foreign Minister Ri Yong Ho has said the country will perform an atmospheric test of a hydrogen bomb over the Pacific Ocean, after claiming a successful underground test of a hydrogen bomb in early September. Hydrogen bombs have a far larger yield than traditional weapons.

But it's not known if the nation has the technology to make a bomb small enough to fit on a missile. Its missile testing in the Pacific has sent unarmed missiles into the Earth's atmosphere, but some seemed to have a range that could reach the West Coast of the U.S.

Nuclear fallout zone

North Korean leader Kim Jong-un has pledged to continue his weapons program, sending a message to the UN that he will explode an a hydrogen bomb somewhere in the Pacific. (KCNA/Reuters) Should Kim make good on his threat to target Guam with a nuclear bomb the size of the Sept. 3 test, it would generate a fireball covering an area of 1.6 square kilometres and result in close to 100 per cent loss of life within six square kilometres, Lam says. Most residential buildings within 26 square kilometres would collapse, and prevailing winds would carry residual radioactive material about 270 kilometres northeast of the island.

In the 1950s, a series of nuclear tests in Bikini Atoll, part of the Pacific's Marshall Islands, were much bigger than North Korea's most recent test. But they rendered the whole area unlivable due to contaminated soil and water that made farming and fishing dangerous. Eventually all residents had to be relocated and they have not returned.

For context, it's important to know that the world has already seen testing of nuclear weapons far bigger than what North Korea is known to have, says Lam, and it hasn't caused widespread radiation sickness or environmental devastation beyond the blast area.

"If they launched the warhead, we can safely say that it be real bad for any persons nearby … but it is probably not a big deal in terms of radiation release except for the local area."

An atmospheric nuclear test would be far more dangerous than detonations in controlled underground environments, because of the force of the blast and unrestrained release of radioactive materials that could spread out over large areas. Such a launch would potentially endanger aircraft and ships because it's highly unlikely the North would give prior warnings or send naval vessels to the area to control sea traffic.

Lee Choon Geun, a missile expert from South Korea's Science and Technology Policy Institute, says missile tests can easily go wrong, and the consequences of failure could be terrifying if the missile is armed with a nuclear weapon.

If a misfire comes close to Japan, that could trigger retaliation from Washington, he told Reuters.

Electromagnetic pulse

Much more threatening to the broader world is the potential damage from an electromagnetic pulse (EMP) triggered by an atmospheric nuclear blast, says Peter Vincent Pry, executive director of the Task Force on National and Homeland Security in the U.S.

EMP is a burst of electromagnetic energy that destroys or damages satellite networks.

If North Korea was to detonate a certain kind of EMP-emitting bomb at high altitude, the low-earth orbit satellites would be destroyed or damaged, says Pry. "And they are vital to our ability to defend South Korea; they're vital to our economy."

"Even the GPS systems in automobiles, airplanes depend on these satellites. Our communications, both commercial and military, depend on these satellites," says Pry, who has served on several congressional committees on EMP and other aspects of defense.

That means, not only would your cellphone network be down at home, military who normally perform high-tech targeted missions wouldn't have the satellite data they rely upon to do so.

Without those space systems, the U.S. and its allies would move backward to an industrial-era military forced to counter threats like those from North Korea the old-fashioned way — through sheer numbers. "We'd be worse off, because we don't train for that kind of war and they do."

There's a reason that the comprehensive nuclear-test ban treaty forbids this kind of high atmosphere tests, says Lam.

"We haven't had this type of horror really since [the Second World War] and we'd much prefer we never see it again."