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If all the world's know nuclear cache were to be placed in a single location and detonated, how would it effect the opposite side of the world?

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    $\begingroup$ I like the answers this question has gotten, but I did want to make a comment because this is tagged with reality-check. Setting off that many nuclear weapons with enough simultaneity could be quite difficult. Its surprisingly difficult to get a nuke to explode with full force. The first nuke may disrupt the trigger mechanisms for the other nukes, causing them to not explode, or to "fizzle," where they explode a little, but well under their rated power. $\endgroup$ – Cort Ammon - Reinstate Monica Jul 10 '16 at 17:45
  • $\begingroup$ Hey cort. In the story it isn't necessary that they all go off at full force, only that they go off. $\endgroup$ – Terry Jul 11 '16 at 7:17
  • $\begingroup$ Well, the issue could vary the yield from the 5000MT of the theoretical entire stockpile all the way down to 0.01MT if the smallest nuke disrupted the entire stack before they went off. One is on the order of supervolcanos, as Neil pointed out. The latter was the perceived yield of a North Korean underground test, as measured by seismographs. The only people who noticed those effects were those with sensitive instruments designed to pick such effects up. $\endgroup$ – Cort Ammon - Reinstate Monica Jul 11 '16 at 17:04
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    $\begingroup$ I couldn't agree more with Cort's comment. Nuclear weapons are highly technical pieces of technology and have built in safe-guards. If anything is wrong or "off" with a nuke, chances are its a large (expensive/radioactive) paperweight. You would be looking at a massive pile of "duds" almost immediately after that first nuke went off. $\endgroup$ – bluerojo Jul 11 '16 at 17:21
  • $\begingroup$ Thanks for your comments, they are really helpful with my story. $\endgroup$ – Terry Jul 11 '16 at 17:23
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It may be informative to compare total energy levels with a potential asteroid strike. It is made a more reasonable comparison in the question by concentrating the blast at a single place. There is a table of asteroid sizes and expected kinetic energy on Wikipedia which can be used for a rough comparison. For instance a 50 megatons (MT) bomb - the largest yield ever tested - is similar in principle to a ~140 metre diameter asteroid impact, which might causes a 2km diameter crater. The consequences are severe locally, and probably felt globally in some minor, but the Earth has suffered thousands of such events, and maybe one or two during human pre-history and dawn of civilisation.

Scaling up, we need an estimate for total energy yield of all nuclear weapons. I found an estimates of 5,000 MT. In terms of raw energy, this is roughly equivalent to the impact from a 500m diameter asteroid.

A 500 metre asteroid impact event would cause a crater between 6 and 10km across where it struck, and an estimate of frequency might be one per 150,000 years. This is relatively frequent, and not related to massive extinction events.

Another natural event at a similar scale is a supervolcano eruption. Depending on which estimates you calculate from, the most massive eruptions (Toba, Yellowstone) are expected to yield something around 1000-2000MT, so in the same order of magnitude. These occur on similar timescales, and it is thought that one event (Toba) is responsible for a detectable blip in human pre-history where population was reduced and this has still left a mark on our genome.

So there are likely to be a range of unpleasant effects associated with the explosion and its aftermath. Locally, the area will be devastated for many kilometres form the centre. Ground bursts will pulverise and excavate many cubic kilometres of rock, and the dust from this is likely to affect the atmosphere and thus climate for a few years. This is not the same as the "nuclear winter" scenario, which is predicted from global firestorms when the arsenal is distributed across major cities.

The precise impact of the explosion is hard to evaluate, because details matter, such as actual nature of what gets into the atmosphere. Long-term climate effects require fine dust to get very high in the atmosphere so that its effects will be felt for many years. I would guess we are talking about a "mini ice age" style of event - something that would cause a lot of hardship, but not directly eradicate people. Crops will fail, and starvation would be problem, but this is not going to be a big extinction event, just a nasty decade or two.

Of course then there is the radiation. This is conjecture so far (I need to research it): Locally there is a huge impact, the area around the detonation site would cause mammals and birds to get sick and die for weeks afterwards. Spread out over the world, the background radiation level would spike. Some areas would receive high, potentially deadly amounts of fallout in first few weeks, mostly close to the original point, but the spread will depend on weather and prevailing wind. The peak will be short-lived though, and resolve to a higher than normal background count - not dramatic, but health-affecting for many creatures for several years after the event. Long-lived creatures that survived the famine years would take a further blow to their life expectancy.

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  • $\begingroup$ Give a look at what fukushima seems to be releasing and how far that has spread to give an idea of how radiation would spread. Otherwise best answer so far $\endgroup$ – Twelfth Jul 10 '16 at 17:09
  • $\begingroup$ Whether and how much radiation is an issue depends upon too many factors to really say with any certainty. One issue is whether they truly detonate or whether they fizzle. Bigger detonations (with the same fissionables), yields lower radiation. Air detonations are better than ground ones, etc. Location matters too. We really couldn't say what the radiation would do without those details. $\endgroup$ – Jim2B Jul 11 '16 at 6:50
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Effects of detonating the Earth's nuclear stockpile

According to research performed at the time, during an all-out nuclear war in which the former USSR elected to maximize loss of life by spreading its warheads out among US population centers (this would be the worst case scenario), the US casualties were expected to amount to about 132 million people (almost 50% of the US population at the time).

Any other scenario yields significantly lower casualties, for instance, approximately 52 million or 16% of the population were anticipated if the USSR had targeted military capabilities. If those warheads were concentrated into a single site, especially one not close to population centers, you could expect the casualties to be significantly lower than 16% of the population.

Effects at the antipodal nodes of the explosion

I do not believe the opposite side the Earth would experience the shock concentration that we can see at the antipodal nodes of the Caloris Planitia on Mercury, but don't really have any references to back up that feeling (or counter it).

Aha, I found some actual references for my opinion.

It looks like the Caloris Planitia impact was approximately >200x the Chicxulub impact. From the Atomic Rockets: Boom Table,

So the energy delivered by a complete detonation of the world's nuclear inventory (assuming no fratricide and fizzles) is in the same order of magnitude as the Caloris Planitia impact.

Mercury is substantially smaller than the Earth so I suspect that this will reduce the consequences of the detonation but I don't know the physical relationship (is it a volume relationship, a surface area relationship, or something else?).

I still don't think it would cause chaotic terrain at antipodal node, however, it would certain be plausible for this to happen if you want it for a story.

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