The joys of nuclear war

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The last couple of weeks have changed many things in the world. One of the most distressing changes is that the possibility of nuclear war is once more a reality rather than a thought experiment. Therefore it could be illuminating to explore what such a war would entail.

From time immemorial we have been told that all-out nuclear war means the end of humanity or at least something very close to the end of humanity. There are reasons to believe that this is a slight exaggeration. Nuclear weapons hold lots of destructive power, no doubts about that. But the world is also a large place. Which side of the equation will win out? 

Out with a bang

A nuclear weapon is, at its simplest, nothing but a big bomb. A very big bomb, that can obliterate entire cities. But can it, really?

The only nuclear weapons to actually be used against real targets are the two atom bombs used by the United States against the Japanese cities of Hiroshima and Nagasaki. Both cities are said to have been utterly devastated. In a way they were, but maybe not as devastated as the legends have it.

On 6 August 1945 an American bomber dropped an atom bomb on the city of Hiroshima. The bomb detonated at a height of 580 m. The radius of total destruction, approximately the area where no humans could expect to survive, was 1600 m.

Total human fatalities from the Hiroshima bombing are calculated to between 90 000 and 146 000 (according to Wikipedia). The uncertainties are due to the fact that people continued dying for several months after the actual bombing. Some, no doubt, due to radiation exposure, but most succumbed to “normal” wounds, especially burns from exposure to the nuclear explosion or to the firestorm that swept through most of Hiroshima.

Many people died, of that we can be sure. More interesting is that people actually survived. Hiroshima before the bombing had a population of more than 250 000 (source). That means that something between half and two thirds of the population actually survived. And this is despite the fact that Hiroshima was a densely populated city mostly built from wood.

This brings up the question of resistance to nuclear explosions. Despite being very powerful it is actually possible to withstand their effects. In Hiroshima the survivor who was closest to the actual explosion was 170 m from the point on the ground above which the bomb exploded. He survived because he was in the basement of a concrete building (and lived for another 40 years, so no very serious adverse radioactive effects either).

In fact, many stone and concrete buildings in Hiroshima survived the blast, at least partially. The most famous of these is the former exhibition hall of Hiroshima (pictured above), whose steel dome withstood the explosion, despite being located a mere 150 m from the epicenter. The building lives on in a semi-ruined state, it was totally burnt out after the explosion, and now lives on as the Hiroshima Peace Memorial.

Modern cities are generally not built from wood. Instead most of the houses are made of reinforced concrete, which, as the concrete buildings of Hiroshima show, is very good at withstanding both radiated heat and intense air pressure, the two components of a nuclear explosion. This should limit casualties somewhat. The Hiroshima bombing also took a great human toll because air raid alerts were not sounded. People were going about their morning routines instead of cowering in the bomb shelters. Had they been sheltering underground casualties would likely have been substantially lower.

Back to reality

The sceptic reader might now remark that what was true in 1945 is not necessarily true today. After all, modern nuclear weapons are much more powerful than those dropped on Japan. That is true. But only to a point, due to a quirk of mathematics. The yield of a nuclear weapon is dissipated in all directions, that is, in 3 dimensions. But it will only spread destruction on the surface of Earth, that is, in 2 dimensions. And its radius of destruction will be measured in only 1 dimension.

In practice this means that a 1000 times more powerful nuclear weapon will only have a destruction radius 10 times as large. The Hiroshima bomb had a yield of about 15 kilotons and a total destruction radius of 1.6 km. The most powerful nuclear weapon ever constructed, the Soviet Tsar Bomba, had a yield of almost 60000 kilotons, 4000 times more than the Hiroshima bomb, but a total destruction radius of 25 km, only 16 times the Hiroshima bomb.

A total destruction radius of 25 km is of course a lot of destruction. It will, for example, obliterate all of central Paris and most of its closer suburbs. But despite this being the world’s most powerful hydrogen bomb, it will still leave the outer suburbs largely unharmed and a lot of buildings left standing. And this is Paris, a dense European city. An American sprawl like Los Angeles or Houston would fare even better.

Then there is the question of how many nuclear weapons there actually are. Headline figures often talk about 12 000 nuclear bombs around the world, with the great majority residing with the US or Russia. This, however, masks the fact that there are nuclear bombs and nuclear bombs. What we generally think of when we think of nuclear bombs is the large bombs that are capable of devastating cities, called strategic weapons in the military jargon. But many nuclear bombs, how many is classified, are actually significantly smaller. Called tactical nuclear weapons they are intended for use on military targets on a battlefield and often have a yield even lower than the Hiroshima bomb.

Another way of looking at the destruction capacity is to look at the number of intercontinental missiles able to carry nuclear weapons onto an enemy’s cities. The USA only has one type of these missiles, called Minuteman. Each Minuteman carries one nuclear bomb and the US owns about 400 of them. Russia has more missiles with the capability to carry multiple warheads which makes calculations more difficult. According to Wikipedia Russia has enough missiles to carry between 700 and 1200 nuclear bombs.

Add in a few long-distance cruise missiles and the nuclear powers still do not have capacity to devastate more than maybe 2000 cities worldwide. An “average” hydrogen bomb has a yield of maybe 4000 kilotons, giving it a total destruction area of something like 40 km². 

Measuring population density for cities is tricky since all cities are denser in the center, where nuclear bombs can be expected to hit. A population density of 10 000 people per km² should be a decent guess for the average population density of developed cities. 

Assuming 100% fatalities within the total destruction area and none outside it is very much an oversimplification but survivors within the total destruction area probably even out fatalities outside the area giving it some plausibility. The average strategic nuclear weapon would thus kill 400 000 people. 2000 nuclear weapons would kill 800 million people.

That would be, with some distance, the biggest catastrophe in human history. But only in absolute terms. 800 million deaths still mean that 90% of the world’s population survived. When the Black Death swept over Eurasia in the middle of 14th century only 70% of world population made it out alive (imperfect source, apparently the effects of the mid-14th century bubonic plague pandemic are not very well studied outside of Europe, while well-studied England lost more than 50% of its population this seems exaggerated for the whole world, a death rate of 30% seems more probable). Put in another perspective 800 million is about the number of people the world has added since 2012. Population-wise, a nuclear war could mean that humanity would be thrown back ten years. Hardly the end of mankind.

Winter is coming

Even the most apocalyptic among us realise that nuclear bombs alone will not be the end of humanity or even the end of most humans. Those wishing for a clean end put their hopes in an artificial winter. The theory being that a multitude of atomic bombs going off in multiple places on the Earth’s surface will generate ash and dust that will be elevated into the stratosphere where these particles will block out sunlight leading to significantly lower temperatures on Earth and a devastating nuclear winter.

The problem with this theory is that it is… a theory. There is in fact preciously little evidence speaking for it. There is no doubt that particles in the stratosphere can lower global temperatures. The Mount Pinatubo volcanic eruption in 1991 threw tens of millions of tons of particles and aerosols into the stratosphere which led to a (temporary) global temperature decrease of around 0.4°C.

To put that in perspective, one of the largest forest fires of recent years, the 2017 British Columbia fires, injected hundreds of thousands of tons of particles into the stratosphere. This is relevant because it is not the actual nuclear explosion that generates potentially climate altering particles. Instead it is the hypothetical firestorm that the nuclear explosion triggers that will create copious amounts of soot and particles.

Obviously there are no well-studied examples of big cities burning to the ground. The mass of particles such a fire could be expected to generate is thus unknown. However, it seems plausible that modern cities do not burn more easily than West Canadian forests. And since the British Columbia forest fire mentioned earlier covered 12 000 km², far more than any nuclear weapon can set alight, it is plausible to assume that an individual nuclear bomb can only generate a fraction of the stratospheric particles that the British Columbia forest fires generated. And since the British Columbia fires only generated a hundredth of the stratospheric particles of the Mount Pinatubo eruption it should be very difficult indeed for a nuclear war to cause any significant global climate change.

All theories of nuclear winter are based on the presumption that nuclear bombs will create giant firestorms that in turn will elevate particles and aerosols into the stratospere. Even if there is no hard evidence either for or against firestorms after nuclear bombs what evidence there is implies that fires will be limited. Of the two bombs dropped over Japan in 1945 only the one over Hiroshima resulted in a firestorm. And Hiroshima was mainly built of flammable wood. For a modern steel-and-concrete city the risk of uncontrolled fires should be significantly lower.

A radiant future

Of course nobody really wants a nuclear war. As the old cliché goes, there are no winners in a nuclear war. However, even if you do not win, you can still lose less. In other words, even if nuclear war is a very bad outcome it can still be better than the alternatives. 

Can anything really be worse than 10% of the world’s population dying and the global economy likely ruined for years to come? Well, yes, many things could be worse than that. The entire world turning into Russia for example. Russia has an average life expectancy 8 years lower than Western Europe and a GDP/capita 40% lower than the EU. Compared to the West it lacks both the rule of law and civil liberties. As some Ukrainans have recently discovered, laying down arms and accepting foreign overlordship does not mean your survival is guaranteed. 

But we do not need to find the most dreadful outcomes in order to justify a closer look at nuclear war. Nuclear war, as any vaguely conceivable occurrence, needs to be analyzed and understood, as a matter of principle. Even the unthinkable can and should be thought about. 

It is convenient to equate nuclear war with the end of the world. No further arguments are required after that. But it is also dangerous, because it will lead to faulty decision making. Nuclear war is an appalling alternative. But it is still an alternative and it needs to be regarded as one.