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I'm writing a story where a total nuclear WWIII occurs in the early 21st century. in a matter of minutes all of the world's nuclear powers unleashed their entire arsenals on each other in an event known as the Second Wave. Although it caused an unbelievable amount of damage in the short term (crop failure, a nuclear winter, annihilating our biggest cities, etc.), the biggest impact of it all came far after the end of the war.

After the initial nuclear blasts scattered fallout into our atmosphere, much of it fell on top of our ice caps as snow in the nuclear winter that followed. Over the course of the next 50 years, the radiation it created heated up the snow and ice; destabilizing the ice caps and accelerating sea level rise to levels that (at our current rate) we thought we wouldn't see until a few hundred years from now (most of the Earth's original coastlines are submerged, the Midwest is severely flooded by the expanded Mississippi River, the entire Florida peninsula is completely gone from the map, etc.).

Could a scenario like this really occur, and if so, how much damage could an event like this actually cause?

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    $\begingroup$ You have things backwards. Nuclear winter would drop temperatures. $\endgroup$ – GrandmasterB Jul 11 '16 at 18:50
  • $\begingroup$ Some nukes could blow up at the poles due to faulty guidance maybe? $\endgroup$ – AndreiROM Jul 11 '16 at 18:57
  • $\begingroup$ I don't know if nuclear fallout produces thermal heat. If it did, I don't think you could have radioactive snow and icebergs...and nuclear winter. I think it is the actual initial blast etc that produces the heat that could vaporise ice. $\endgroup$ – EveryBitHelps Jul 11 '16 at 18:59
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    $\begingroup$ No. Hard numbers aside, any heat produced by radioactive fallout spread over a large area is minuscule compared to threat that same amount of radiation would have to living beings. Enough fallout to produce any significant heat, would kill all life (even viruses) pretty quickly. Worse, the nuclear winter effect is many orders of magnitude greater than any heating effect, thus you'd cause an Ice Age long before you could melt any ice. $\endgroup$ – RBarryYoung Jul 11 '16 at 20:23
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    $\begingroup$ I think you severely overestimate the radioactivity of nuclear fallout, and even more severely underestimate the energy required to melt ice. There is very little danger from the thermal effects of all the radioactive material we have available (mind you, a block of plutonium will burn you, but so will a wood fire). Don't forget that with all the radioactive matter on the whole planet, about 50 TW of heat is released (about fifth of the current estimated energy use of all of humanity). Compare to solar influx at 173 000 TW. $\endgroup$ – Luaan Jul 12 '16 at 8:09
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No. There's nothing like enough energy in nuclear fallout to melt the ice caps.

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    $\begingroup$ In addition with enough ash thrown up into the air (and other factors) from the nuclear explosions and aftermath we would likely see global temperatures fall during the initial nuclear winter. So we'd probably see the inverse of what the asker is supposing. $\endgroup$ – Ranger Jul 11 '16 at 19:20
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    $\begingroup$ For that matter, you could probably pop out all the warheads ever made and drop them on the polar ice caps, and still not have any appreciable effect. Thousands of pounds of radioactive material are no match for millions of cubic miles of ice. $\endgroup$ – HopelessN00b Jul 11 '16 at 19:45
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No.

as Mike Scott already answered there's simply not enough energy in the nuclear materials in the fallout to make a dent in the temperature or entire ice masses.

It would be hard to provide numbers even if the number of warheads and amount of nuclear materials weren't classified, since it's very hard to predict how much of which radioactive isotope would end up where.

But to make a rough guess, let's start with the percentage of ice on the planet surface, thanks to NASA:

Global sea-ice coverage averages approximately 25 million km2, the area of the North American continent, whereas ice sheets and glaciers cover approximately 15 million km2, roughly 10% of the Earth's land surface area.

And the total volume of ice on the location that would cause the highest sea level rise:

The Antarctic Ice Sheet contains 30 million cubic kilometers (7.2 million cubic miles) of ice.

That's a lot of ice, especially if only 10% of the fallout lands on it (we're being generous here, or some missile command decided to target Antarctica instead of cities). Unfortunately, there are quite a few nuclear weapons in the world, about 15,000 between the US and Russia.

So the fallout of each nuclear weapon would need to melt 20,000 cubic kilometers of ice to melt all of Antarctica. Converting to mass, it's slightly less than $ 20,000 km^{3} * 1,000,000,000 (km^{3} -> m^{3}) * 1,000 kg/m^{3} = 20 * 10^{15} kg $.

That's 20 Quadrillion kilograms of ice.

At this point I could guesstimate the energy needed to melt that mass of ice and probably express it in megatons of TNT. My feeling is that even if most of the warheads were detonated right on Antarctica and magically converted into heat aimed at the ice, that still would barely scratch the surface.

But the question is not about the nuclear explosions, but about the heat from radioactive decay released by the fallout. The pre-detonation contents of the nuclear weapons is likely just as radioactive as the fallout. And those warheads seem to be just fine inside their silos and nuclear subs.

So if the nuclear warheads are not melting their casings, do you think they can melt 20 Quadrillion kilos of ice (that's twenty Million Billion kilos) each?

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    $\begingroup$ To melt 20e15 kg of ice (ignoring the energy to get it to 0 celcius) requires 6.671e21 joules of energy. That requires about 30,000 Tsar Bombas, or 1.6 million megatons of explosion worth of energy. One number I found for the total yield of the world's nuclear stockpiles said there were 64,000 megatons of nuclear weapons in existence (though there's no way to know how accurate that is). So like you said, not enough to even scratch the surface. $\endgroup$ – Rob Watts Jul 11 '16 at 20:22
  • $\begingroup$ @RobWatts Thanks for the assist! I stopped when I realized the temperature below zero of all that ice deep down is hard to find. $\endgroup$ – Cyrus Jul 11 '16 at 20:29
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    $\begingroup$ @Cyrus, you can mostly ignore the temperature of the ice: the heat capacity of ~2 J/gK is dwarfed by the 333 J/gK enthalpy of fusion. Raising the temperature from -150C to the melting point will only double the amount of energy needed to melt it. $\endgroup$ – Mark Jul 11 '16 at 21:07
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There is a concept of a "Nuclear Summer" (also here). Wiki says that it is far less scientifically supported than nuclear winter, however.

Some content from one of the sources (pdf link) reads as follows:

Nuclear winter might give way to a nuclear summer. The high temperatures of the nuclear fireballs could destroy the ozone gas of the middle stratosphere. The result would be an increase in ultraviolet radiation on the surface of the earth, affecting both plant and animal life.

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    $\begingroup$ This still wouldn't increase temperatures, however. It would simply make the sunlight more dangerous. $\endgroup$ – user2979044 Jul 12 '16 at 9:30
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Actually if there was an all out nuclear war the amount of radiation released would raise global ocean temperatures that will eventually lead to the melting of all ice on earth

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    $\begingroup$ Welcome to Worldbuilding! Currently, you've just stated the answer without any explanation - would you be able to explain how you get to this answer by editing it? Thanks $\endgroup$ – Mithrandir24601 May 26 '17 at 19:40
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    $\begingroup$ Hi Mike. We prefer answers that go into some depth. When answering an older question, you have every chance to make an answer as great as it can be, because you have no significant time pressure (known as the "fastest gun in the west" effect, though it's less of a problem on our site than some of our sister sites in the network). Especially if your answer goes against at least two highly voted answers, you should take the time to really explain why it does. Ideally, show us the math that led you to this conclusion! It's not unheard of for a late answer to turn the table on a question. $\endgroup$ – a CVn May 26 '17 at 20:59
  • $\begingroup$ Please show your math, because I think that's completely wrong. This also contradicts the high-voted answers. See what Cyrus wrote — is the math wrong? How do you get a different result? $\endgroup$ – JDługosz May 27 '17 at 7:01
  • $\begingroup$ And, welcome to Worldbuilding! $\endgroup$ – JDługosz May 27 '17 at 7:04

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