Nuclear weapons are not as destructive as you think

As usual, this is a crosspost from Naval Gazing.  The original has links and a couple of photos.  It’s definitely inspired by the recent thread here, but cleaned up and all in one place.

How destructive are nuclear weapons really? This is a question that seems to be asked far less often than it should be, and is rarely discussed in a non-alarmist way. Often, overheated and frankly ludicrous claims from anti-nuclear activists are taken seriously, even though we’ve had very strong evidence against them for at least 30 years. None of this is to say that nuclear war wouldn’t be a big deal, or a terrible humanitarian catastrophe, but it wouldn’t be enough to wipe out civilization, much less the human race or all life on Earth.

We should probably start with a look at the state of the global stockpile, because it’s fallen dramatically in the last 30 years. After peaking at around 70,000 warheads in the mid-80s, it’s fallen to only 12,700 according to the Federation of American Scientists. The majority of these are in the reserve stockpiles of the United States and Russia, which are there in case the current arms-control regime fails, and would take time to deploy. Denying the other side this time is undoubtedly a major objective of both nation’s nuclear forces, so in practice, we should instead look at deployed warheads. Arms-control treaties limit both nations to 1,550 deployed warheads, although FAS estimates 1,588 for Russia and 1,644 for the US, probably due to slight differences in definitions. Worth adding to this are the Chinese (380 warheads), the French (280) and British (120), for a global total that we can round to 4,000 warheads for simplicity. Some of these won’t work, or will get shot down, but we can assume that other nations and the surviving stockpile weapons will bring the total back up. Note that this is a worst-case all-out nuclear war, and there are potential off-ramps short of it even if there was, say, a tactical nuclear exchange in Eastern Europe, although they aren’t certain.

The obvious next question is what each of those bombs can do, which in turn requires us to remember that not all nukes are the same. The biggest-ever American nuclear test, Castle Bravo, was a thousand times more powerful than Little Boy, the bomb dropped on Hiroshima. To put it in other terms, the ratio between these two is approximately the same as the ratio between Little Boy and MOAB, the most powerful conventional bomb in the American arsenal today. Or between MOAB and an 8″ artillery shell. Many of the scarier numbers come from unreasonably large bombs, the vast majority of which have been retired. In practice, most strategic nuclear warheads today are in the 300-500 kT range, with tactical weapons being smaller. If we take the American W88 (455 kT) as representative of this range, if slightly on the larger end, my handy nuclear bomb slide rule1 gives severe damage to typical buildings (5 psi overpressure) out to about 3.3 miles and light damage like broken windows (1 psi) out to about 10 miles. Even 1st-degree burns are unlikely past 8.5 miles or so, and to get slightly sick from radiation would require being within 1.7 miles. For a civilian target, the most important number here is the 5 psi radius, which we can approximate as “destroyed”, and all but the smallest cities are more than 7 miles across. If you want to see how this would look in your city (or somewhere you don’t like very much), Nukemap is an excellent tool, although it defaults to shooting at the center of cities, which is flashy, but not how targeting actually works (see below).

To put this another way, each bomb can destroy an area of 34.2 square miles, and the maximum total area destroyed by our nuclear apocalypse is about 137,000 square miles, approximately the size of Montana, Bangladesh or Greece.

But of course the bombs won’t be spread out evenly in a manner calculated to maximize the total area covered by a 5 psi radius, which brings us to the matter of targeting. Obviously, the actual plans are highly classified, but there’s enough in the public domain to let us make some informed guesses. Broadly speaking, we can expect nuclear weapons to be aimed at one of three types of targets: strategic (nuclear) targets, conventional military forces, and industrial/infrastructure targets. Notably absent is a direct interest in killing the opposing population, although people tend to live near infrastructure, so it is going to happen. Obviously, the highest priority is to try to take out the enemy’s nuclear weapons and command and control systems, just in case you catch them napping and can avoid getting nuked yourself. But most of these targets are in remote areas, so a lot of warheads are going to fall where there aren’t many people. ICBM silos are of particular note here, with the US having 150 and the Russians about 170. Each might well get two warheads, given that they’re high-priority and well-hardened. That in turn will meant that these are ground bursts, which changes the damage profile (much worse to be right at ground zero, but 5 psi radius falls to 2.1 miles with the W88), but also causes vastly more fallout. In total, it’s probably a reasonable estimate that a quarter of the global stockpile is going towards such targets.

That leaves 3,000 warheads for the global military-industrial complex, which is a surprisingly small number when you consider the scale of the problem. Possible targets include bases for armies, air forces and navies, factories, oil refineries, ports, railroad marshaling yards, communications hubs, airfields, power plants, and even major bridges. To put this into perspective, there are currently about 1,200 international airports and 732 oil refineries worldwide. Allocating a single warhead to each of these would leave only a thousand or so for every single other target on the planet. Some targets are quite difficult to destroy, which will mean they will need surface bursts, and possibly more than one given the limited radius over which said bursts are effective against hardened targets. Railway marshaling yards are a notorious example of this. Even a major city is unlikely to get more than a handful of warheads, which will be carefully placed to do maximum damage to as many targets as possible, but as these targets don’t actually include the local population, the majority will survive. For instance, priority targets in New York City are likely to include Bayonne/Port Elizabeth and Red Hook in Brooklyn instead of Manhattan, as Moscow cares more about New York as a place where armies can sail for Europe than as a place where investment bankers live.

Which brings us to what happens after the war. Even though most of the population, even in quite large urban areas, is still alive, won’t they all be killed by fallout and nuclear winter? Fortunately for mankind, this is an area where the public perception bears no resemblance to reality. Fallout is the term for various radioactive particles that return to the surface after a blast, and can be divided into two types. Early fallout comes within 24 hours and is downwind of the blast, while late fallout is worldwide and very dispersed. Airbursts produce only late fallout, and in practical terms, this will have surprisingly little effect. The total yield of our 4,000 weapon war is going to be on the order of 1,800 MT, only 4.25 times the yield of atmospheric nuclear testing worldwide, which even at peak seems to have produced doses of maybe half of natural background radiation. Even if we assume that our war will product 10 times as much late fallout as the tests (due to shorter timescale and the fact that operational warheads may be dirtier than test ones), the peak exposures are approximately the same as those for aircrew today.

Early fallout is a much bigger concern, particularly if you live downwind from a missile silo. But even here, the risk is often oversold. Calculations here are horrendously complex, but looking through Effects of Nuclear Weapons, it appears that you’d probably be sick but survive 140 miles downrange of our W88 surface burst, provided you took no protective measures at all.2 Even simple protective measures (staying indoors, preferably in a basement or interior room) and evacuation after a few days would be enough to minimize ill effects as little as 70 miles downwind.

Which brings us to nuclear winter, and in no area is there more disconnect between public perception and reality. The basic idea, that fires resulting from a nuclear war would loft huge amounts of soot into the stratosphere, cooling the planet by 20°C or more and killing crops, came from some extremely simplified models in the 1980s. It was quickly seized by a group of anti-nuclear scientists, most prominently Carl Sagan, who continued to push it even as better models showed that soot production would be lower and the effects of the soot had been overestimated. The real test came in 1991, when Sagan predicted that Saddam setting fire to Kuwait’s oil wells could seriously alter global climate, on par with the eruption of Krakatoa. Instead, the soot didn’t reach the stratosphere, and was scavenged by rain in a few days. Some have attempted to salvage the theory, but none seem to have really dealt with the problem since. In reality, even a nuclear war 30 years ago would have produced at most a nuclear autumn, and that was with an order of magnitude more weapons than we have today.

The basic conclusion of all of this is simple. Nuclear war is definitely not an existential threat to humanity, much less to all life on the planet. Most people even in major urban areas would survive the initial attack, along with a surprising amount of infrastructure. This isn’t to minimize the effects, as it would be a humanitarian catastrophe unprecedented in human history, as the global economy breaks down and regions are pushed back on their own resources. This could easily kill more people than the war itself, particularly in densely-populated areas, but I would expect things to stabilize at a technology level of maybe the late 19th/early 20th century and start back up.

Again, nuclear war is bad, and we should be very careful not to have one, but it is not as bad as it is often made out to be. Some of this is because the threat has routinely been exaggerated by anti-nuclear groups, and some of it is the result of arms control efforts over the past half-century, which have significantly reduced the potential human toll of a nuclear war.3

1 Yes, I have an original version from 1977 which I used for these calculations, so results from other sources may vary slightly. All numbers are for airburst, which is the most effective option if you want to damage a city. ⇑

2 Dose of about 250 rem from 9 hrs to infinity. This is worked out of Chapter 9, mostly using Table 9.93 and Figure 9.20. The unit dose rate of 100 rad/hr is for 1 hr after the explosion, and has decayed significantly in the 9 hours it took to reach the analysis point. ⇑

3 Thanks to John Schilling for his commentary on this post, including several examples.

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Marquis Motsinger