The threat of nuclear war, mostly background noise for the past 25 years, is alarming. But given the uniqueness of North Korea’s position in the world, it’s worth wondering how concerned we should actually be.

To answer that question, we need to first identify the “we” we’re talking about. If that “we” includes South Koreans, the answer is: Quite a bit.

The South Korea problem

The North Korean capital, Pyongyang, is about 120 miles from the South Korean capital, Seoul, home to 10 million people. That’s within easy striking range of North Korea’s existing arsenal of missiles, which is a key reason that the United States recently began deploying a Terminal High-Altitude Area Defense system, or THAAD, in South Korea, aimed at intercepting an incoming attack. Whether those missiles could carry an atomic or hydrogen bomb is another question, one we’ll get to in a moment.

Of course, the proximity of North and South Korea means that there is a large risk from conventional weapons, as well. There are artillery already at the North Korean border that could strike Seoul, although it’s not clear how much damage would result.

The threat of a missile hitting the U.S.

If the “we” is the “we” most likely to read this article — residents of the United States — the calculus is a bit different.

Excluding American forces in South Korea (about 25,000 of them), the greatest threat faced by the United States is of nuclear-tipped intercontinental ballistic missiles (ICBMs). Raising three questions: Does it have nuclear weapons? Are those weapons small enough to fit on a missile? And does North Korea have a missile that could reach the United States?

The answer to the first question is yes, the North Koreans have repeatedly tested some form of nuclear device. In September, North Korea tested a bomb with an estimated yield of 10 to 20 kilotons — about the yield of the bomb that struck Hiroshima during World War II. That can do a lot of damage, but it pales in comparison with the sort of warhead currently in U.S. or Russian arsenals.

At the time of that test, the North Koreans also claimed to have developed a weapon small enough to fit onto a missile, though this can be hard to verify. In February, the country released a photo showing a relatively small bomb that expert analysis figured might yield 20 kilotons and could be small enough to fit on a missile — if the photo actually depicted a working device.

The broader question, and the most easily verified, is whether any North Korean missiles could reach the United States. North Korea unquestionably has missiles capable of traveling long distances, and in February 2016, it launched a satellite into space. (That satellite wasn’t deployed properly and soon began to tumble uncontrollably in orbit, suggesting that North Korea’s capabilities were not yet refined.)

To strike the United States, though, the country would need a missile that could travel for thousands of miles, requiring a very specific type of missile.

The Federation of American Scientists catalogues the missiles that North Korea has in its arsenal and those it hopes to add. To strike Alaska, it would need a long-range ICBM that could travel 7,000 kilometers, or about 4,300 miles. To hit the continental United States, it would need a full-range ICBM, which can range from 8,000 to 12,000 kilometers, or 5,000 to about 7,500 miles. The missiles that are under development in North Korea are of the Taepodong-2 variety. If launched from the Sohae launching station in the northwest corner of the country, nearly all of the United States would conceivably be within range, with the exception of southern Florida.

On Saturday, North Korea announced that it had tested a rocket engine of “historic significance” — perhaps a liquid-fueled rocket that could serve as the second-stage of a full-range ICBM.

But there’s no indication at this point that North Korea has such a device prepared — much less a missile that could reliably deliver a nuclear weapon at that distance with accuracy. While North Korean leader Kim Jong Un said last year that his regime had “entered the final stage of preparation for the test launch of an intercontinental ballistic missile,” there are a lot of parts that need to work together flawlessly to be effective: the stages of the missile, the bomb itself.

That said, during World War II, the Japanese launched balloon-based bombs that they hoped would reach the U.S. mainland. Some did, killing six people in Oregon. Point being that even if there are low odds of a lot of things working perfectly, sometimes they can. In 2015, Adm. Bill Gortney told reporters that it was not likely that North Korea could strike the United States but that it was “prudent” to assume that it might be able to.

What to do if an attack is imminent

At the height of the Cold War, the U.S. Civil Defense Administration released a film encouraging young people to learn to “duck and cover” in the event of a Soviet attack on the United States.

As Cold War tensions eased, the animation was cited as a naive response to the threat of a nuclear attack, as though ducking under your desk at school would provide any significant protection from a nearby nuclear attack.

The government’s current recommendations for how to respond, though, aren’t much more sophisticated.

At Ready.gov, the federal emergency-preparedness website, there’s a page dedicated to the threat of nuclear attack. It recommends preparations that can be taken ahead of a possible attack — including storing up supplies or building a bomb shelter. For those who may not be particularly handy, you can also buy a bomb shelter on Amazon.

If an attack is imminent, the government recommends going to an existing bomb shelter, if possible. During the Cold War, facilities that could serve effectively as protection against the explosion’s blast wave were identified and, in some places, marked with special signage. One New Yorker recently began flagging such sites on a Google Map, showing where shelters still exist within the city.

Can’t find such a facility during an attack? The government created this illustration showing the relative safety of different places in different types of buildings.

(Ready.gov)

Try not to be on the first story of a wood-frame house.

Of course, these tips matter only if you’re far enough away from the center of the explosion that the most severe damage would result from a building collapse. If you’re close to the center of the blast, there’s not a lot that can be done. There are other problems, too, of course. Radiation. Heat. An electromagnetic pulse that would knock out electronic devices.

So what happens if you’re in, say, Manhattan, and a nuclear device were detonated overhead — causing much more damage than a bomb at ground level, where more energy would be absorbed by nearby structures and the ground underneath? The Bulletin of the Atomic Scientists walked through that scenario in 2015, including such evocative phrases as “hurricane of fire.” The physical effects are one thing. Scientists are also modeling a strike focusing on how those nearby would react — the social effects.

Again, though, the odds that such a scenario would result from a lucky strike by Kim are low. It would require a combination of a multistage missile, a miniaturized and working nuclear bomb, and proper calculations to target a particular place and detonate at the proper altitude. (That malfunctioning satellite suggests that these calculations are trickier than they may seem.) And that’s just one missile.