[LINK] Nuclear winter: a reminder

by Stuart_Armstrong1 min read19th Mar 201249 comments


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Just a reminder that some of the old threats are still around (and hence that AI is not only something that can go hideously badly, but also some thing that could help us with the other existential risks as well):


EDIT: as should have been made clear in that post (but wasn't!), the existential risks doesn't come from the full fledged nuclear winter directly, but from the collapse of human society and fragmentation of the species into small, vulnerable subgroups, with no guarantee that they'd survive or ever climb back to a technological society.

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The authors of the cited paper claim that conditional on nuclear winter, the risk of human population going to zero from the direct climate effects is very low, noting that human ancestors survived supervolcanoes and past ice ages. This could interact with other things though (Industrial Revolution was a fluke, synthetic bio organisms finish us off, asteroids hit while civilization is down, etc), and there is model uncertainty regarding the nuclear winter magnitude and distribution.

The claim that nuclear winter is an existential risk needs additional justification.

It seems almost certain that nuclear winter is not an existential risk in and of itself but it could precipitate a civilizational collapse from which it's impossible to recover (e.g. because we've already depleted too much of the low hanging natural resource supply). This seems quite unlikely, maybe the chance conditional on nuclear winter is between 1 and 10 percent. Given that governments already consider nuclear war to be a national security threat and that the probability seems much lower than x-risk due to future technologies it seems best to focus on other things. Even if nothing direct can be done about x-risk from future technologies, movement building seems better than nuclear risk reduction.

Also, while civilization is on the ropes, humanity could be taken out by a large asteroid, supervolcano, or other natural disaster.

I am a NW skeptic.

I'm a NW empiricist...

BTW on topic of radioactive contamination: in the event of any major disruption of society, most of the nuclear power plants can be expected to melt down, and their spent fuel pools can be expected to run dry. A spent fuel pool of a single reactor, that is maintained the way the reactors are ("i'll take the trash out tomorrow, honey!" approach), can release up to 10 Chernobyls of cs-137 or so (depending to the amount of fuel stored. Ten or more cores can be stored) . Even 1 Chernobyl corresponds to awful lot of nukes. Other fun fact is that the nuclear fuel uses zirconium cladding, which, if overheated, 'burns' even in absence of external oxygen, reacting with the uranium dioxide. When Chernobyl is discussed, it is commonly emphasised how unsafe was the design with combustible carbon inside the reactor. The combustible materials are a major deficiency, yes, and has likely helped the radioactive plume reach high altitudes, but all reactors have fuel that can and will burn if overheated via the decay heat. In the re-racked fuel pools that can result in combustion of even very old fuel after the fresh spent fuel ignites itself. the fuel pools of old reactors typically contain more spent fuel as per original design - once again the 'i'll just cram down trash and put this little bit on top' approach to trash we all know from our daily life.

Other interesting fact: It is a common assertion that fusion bombs are cleaner per yield, often asserted as dramatically so. Not very much in practice. Most of the 'fusion' bombs make half of their yield by fissioning the U-238 casing on the ultra fast fusion neutrons. Those neutrons do fission U-238, producing the fission products. In the testing, the substitute casing can be used; for example the Tzar Bomba had ~60 megaton yield, very clean, with afaik lead casing, but would have had 120 megaton yield, or more, with U238 casing, half of it from fission. So the contamination from nuclear testing is not directly comparable to that of nuclear war.

in the event of any major disruption of society, most of the nuclear power plants can be expected to melt down

Source? I'm given to understand that they have a lot of fail safes. Wouldn't they all just turn off? Also, it seems like the disruption would have to be extremely sudden for even that to happen. Otherwise, they'd just turn the power plant off.

Even 1 Chernobyl corresponds to awful lot of nukes.

It may correspond to an awful lot of nukes in terms of fallout, but it corresponds to exactly zero in terms of sending dust into the air and messing with the climate.

1: One does not simply turn the reactor all the way off (picture of Aragorn, err, Boromir, or who ever). There's the decay heat, several megawatts of it even after months of shutdown (google decay heat), that can't be turned off, and virtually all reactors require intervention to keep that cooled. Likewise for spent fuel pools, that boil itself out over course of a week or two. That's what happened in Fukushima - the reactors did shut down correctly but all powered decay heat removal systems failed when tsunami water flooded the basements (in which they kept the switchgear and emergency generators). The spent fuel pools were an immense problem and at least one - in the reactor building #4 where reactor was not loaded with fuel - did boil off to the point of partially uncovering the fuel, at which point they got the concrete pump to pump water in. That's Japanese, a nation of 127 millions, responding in the tsunami that killed about 16 000 people and displaced perhaps a million (excluding those displaced due to reactor). The spent fuel pool was allowed to boil itself off to the level of fuel.

AP1000 is advanced safe reactor design. It raised the no-intervention time to the whooping 72... hours.



Major safety systems are passive; they require no operator action for 72 hours after an acci-dent, and maintain core and containment cooling for a protracted time without ac power.

Which is typical hard to parse statement which translates to: after 72 hours, the cooling water reserve evaporates off, and you get yourself regular meltdown like in any other design. The protracted time without water is 72 hours. The operator action is getting a lot of water on top of 10 story building somehow. Note that most reactors in use require AC power, that's why it is so awesome AP-1000 doesn't need AC power. Also, note risk estimates at one in 10 millions years. WTF are they even doing at NRC, some sort of circle of self delusion wrt what sort of stuff happens in 10 millions years. Mankind survival is unlikely to have that sort of reliability, and that's counting the recoveries from stone age.

2: Mostly yes, i'm only speaking of radioactive pollution there.

(picture of Aragorn)

Boromir. Goodness, what are they teaching in schools these days?

Ahh, right. lol.

One does not simply turn the reactor all the way off

Perhaps not, but I'd expect you'd flip a switch, and then the automated systems would shut it off, or something to that effect.

Which is typical hard to parse statement which translates to: after 72 hours, the cooling water reserve evaporates off, and you get yourself regular meltdown like in any other design.

So, set it to shut down automatically after 36 hours without operator action, and it will be fine.

can release up to 10 Chernobyls of cs-137 or so

Why didn't they have that problem at Three Mile Island?

Perhaps not, but I'd expect you'd flip a switch, and then the automated systems would shut it off, or something to that effect.

You expect wrong. Nature isn't rubber padded, and technology isn't friendly magic. You flip switch, control rods go in, the chain reaction stops, the decay heat continues.

So, set it to shut down automatically after 36 hours without operator action, and it will be fine.

It is 72 hours after the full shutdown, that it melts itself down. edit: or to be pedantic, gets outside design parameters; the melt may take another couple days.

Why didn't they have that problem at Three Mile Island?

Because the spent fuel pool didn't boil itself dry. They had a core meltdown, luckily they had full external power and could keep circulating the coolant.

The Fukushima is the TMI without external power: same reactor types, 3 out of 3 melting. The Tokio being evacuated is Fukushima the other time of the year when wind is blowing inland. Ain't a safety feature of the reactor design that it failed in the season when wind is mostly blowing to ocean. At least they did consider evacuation.

I wonder about the effect of a bomb (nuclear or otherwise) hitting or detonating at the worst possible distance from a nuclear power plant might be? I'm imagining if it was powerful enough it'd pull a lot of that radioactive material up and out...

In general, if a bomb is powerful enough to result in a major radiation release from a nuclear power plant, then it would probably do more damage if used on a major population center. There are measures you can take to prevent people from getting too irradiated by a dirty bomb, from evacuation to simply staying indoors and wearing a face mask to reduce particulate inhalation. Straightforward explosions, in contrast, do not offer quite as many second chances.

(BTW, on the subject of surviving a nuclear blast: duck and cover. It works. There were some crazy-badass scientific investigations into the effects of nuclear weapons, back in the days when we would actually set off a nuclear bomb in the desert somewhere to get experimental data, and the results were clear: in a fairly large range of radii around a nuclear bomb, you can increase your chance of survival a lot if you can just get a wall between yourself and the flash, and a table or something over you to protect you from falling debris. At the time they were also very concerned about buildings collapsing, but they discovered that some simple changes to typical construction methods could make buildings much more durable, and those have been mandatory in most places ever since.)

good to know:)

AFAIK, they have popped about 1000 atom bombs so far. Do we see any really bad consequences?

But from 10 to 100 times more in a shorter time interval, there would be a Nuclear Winter?

I doubt it.

[-][anonymous]10y 4

From the article:

It’s important to understand that nuclear winter would not be a direct consequences of the nuclear explosions, but of the burning of our cities in the wake of the war (given enough heat, even roads and pavements will burn), generating clouds of very black smoke that rise into the stratosphere

AFAIK, they have popped about 1000 atom bombs so far. Do we see any really bad consequences?

Take that one out of context a sec... ;)

Never take it out of context.

you doubt that 10 to 100 times more over a 1000..10000 times shorter interval - ~ 100 000 larger intensity than 'no really bad consequences' - can cause nuclear winter?

How so? If you doubt that kind of stuff because 5 orders of magnitude are never enough to get from 'not really bad consequences' to 'really bad consequences', then i don't know what you wouldn't doubt.

As I've said. All the atom bombs we have, have combined less energy than a big wildfire. So the energy is not a problem.

Then, the amount of "black smoke", which would those bombs emits, compared to a volcano is small. There is nowhere one ton of a black smoke emitting plastics per person alive, not to mention that everything will not be burned.

I don't see where they are getting their numbers. One of those scenarist was Carl Sagan. He made quite a panic when Saddam Hussein ignited those Kuwait oil pumps. He was wrong.

Look it now either from the energy point of view, either from the soot lifting point of view - it is not such a big event in the geological terms at all.

Billion of people may die, maybe more, maybe less. An unspeakable evil, it would be, yes.

But a nuclear winter from an event comparable with no such a big wildfire? One million square kilometers of the Australian bush burnt. One trillion square meters. One kilogram of grass and wood per square meter burnt. One million J of energy released. This is a very conservative calculation, but it gives you 10 times more energy than the combined nuclear stock pile would. And the biggest wild fire covered 5 times more land. So, maybe 50 times more energy released - caused no nuclear winter.

Every year we have enough wildfires to release more energy than there is in those bombs.

You have to put everything in a perspective.

I don't see the total arsenal yield figure, but i have total yield from testing:


which is slightly above 500 megatons

For the wildfire:

10^12 m^2 * 10^6 j/m^2 = 10^18 j

1 megaton of TNT = 4 * 10^15 joules. Thousand megatons = 4 10^18 joules. 500 megatons = 2 10^18 joules , 2x your fire already. Multiply by your 10..100 (the arsenal vs testing quoted from yourself), you get 20 .. 200x the wildfire, that's just the yield, not the fires in cities.

And while we are on energy calculating, why not calculate how much solar energy Earth receives in a day and say how many zillion times its more than energy of bombs combined, lol.

Note: you just might by dumb luck be factually correct, but your argument is motivated cognition. Nukes are scary, and hence very motivational. Goes both ways.

You are saying, that the total energy amount of all the nuclear weapons is 4*10^18 J. Not 40 times less as I have said.

Even in that case, the wildfire which has covered 5 million square kilometers and consumed 1 kg of dry grass and wood was a bigger event. Especially since I gave 10 times smaller energy per kilogram of wood or dry grass as it is. It's 10^7 J/kg not 10^6 as I have calculated. Not to mention, 1 kg per square meter is a very low number.

But it matters only a little. This calculation is not very exact, but quite enough to see the main point.

I still don't see the main point. Wildfires don't put stuff into stratosphere very well, its not very concentrated, and it ignores burnable stuff in the cities.

For the calculations, just do them carefully one time ok? I don't know full yield, the 1000mt is just example. Your own estimate for yield of arsenal, vs yield of testing, was arsenal = 10..100x the testing. You need to pick your numbers, and stick to them all the way through without fitting them after you arrive at something you don't like. That is just math. If you can't do that why you think your opinion on nuke war results is at all coupled to the actual results in any way?

Very clear numbers:

5 million square kilometers of bush burnt. That's 5*10^12 m2. Every year you can expect at least 1 kg of wood growth per square meter. That's 10^7 J accumulated per year on every square meter. But let say, it is all that it's there.

This gives you 5*10^19 J released by the biggest Australian bush fire. Many times more than your estimation for the atom bombs aggregate energy release.

Pure and simple, do you object this numbers?

you picked one set of numbers, calculated something, then didn't like it, changed from 1 to 10 megajoules per square metre, that's not how you do it if you are thinking straight.

Regarding 'my estimate', once again: 500 megatons is total testing, 10 ... 100x the figure you picked, total 5000 .. 50 000 megaton , the 1 megaton of tnt is 4E15 j , times 5E3 = 2E19 , times 5E4 , 2E20 .

Top it off by the smoke not going into stratosphere from a bush fire because there's too little intensity, it doesn't even burn all at once, so there's nothing whatsoever even comparable about those numbers in the first place?

What part do you not understand about "you have been conclusively demonstrated that you are not thinking straight about existential risks" ? People have two reactions to existential risks: be sure that it exists, be sure that it does not, proceed to not thinking straight one way or another. Sagan demonstrably screwed up with oil well fires, yes. You are demonstrably screwing up right now. Nobody's safe from it. I'm only reasonably sure i'm not screwing up because i haven't been called on bad math, and haven't got very strong belief about nuke winter.

Americans have 10000 atomic weapons currently. Russians also. Others are negligible in this sense.

Say that the average bomb has 1 MT. This means 8*10^19 J of energy. What is a big overestimation, but for the sake of the discussion, would you accept this number first?

I don't accept the idea that the climate effect of the fire is in any way comparable to nukes in the first place, because fire doesn't get smoke high up in the atmosphere. I think its a very screwed up assumption. I've only been criticizing the numbers because the point is that people don't think straight about existential risks. Humans don't think about risks, they evaluate risks rapidly with some feeling & particular really simple strategy that they picked up, then rationalize verbosely.

I don't accept the idea that the climate effect of the fire is in any way comparable to nukes

But you admit, that the energy stored in the nuclear arsenal is hardly as big as the energy released by a really big forest fire?

I don't have a good estimate of energy stored in the nuclear aresnal, and I care about this assertion just about as much as I care about comparison between energy of nuclear arsenal and energy of sunlight that hits the earth in a day.

But yes, I would say it is somewhere within similar order of magnitude, for the yield vs forest fire, ignoring the combustion of items in the cities.

BTW, nukes are incendiary weapons, there's not enough appreciation of this basic fact by public. Don't imagine your house being blown away, imagine all interior catching on fire first, then being blown off. Ditto for all asphalt.

But yes, I would say it is somewhere within similar order of magnitude

I am glad. It is important to understand this fact. I haven't seen it mentioned yet, anywhere.

People should update, not follow Carl Sagan blindly. He had "good intentions" when (probably) misinformed the world.

Important for what exactly? Why is it more important than 'total yield << sunlight in a day' fact? edit: Because forest fires and nukes are both nasty?

Be cause most would say something like "there is a balance in Sun's shinning, but atom bombs are highly concentrated events".

It is important to see, that their energy, as destructive as it is, is not THAT great, at all.

It is not healthy to live with wrong assumptions. Earth is a robust planet, not as delicate as usually heard from certain circles.

Still remember Sagan, the Pope, journalists, some friends of mine even - how they spelled doom in the case of the Kuwait oil fires.

As I said - the Earth is a robust planet and we are robust animals.

Seriously man, there's a giant ton of really wrong stuff out there. People starting idiotic wars, and so on and so forth. Daylight savings time wasting the energy (fun thing to calculate: find estimation of the energy wasted by daylight savings time, compare to all nukes in the world). The extremely ineffective allocation of taxes. The wasting of immense money making, and maintaining, those nukes.

Want to campaign against scaremongering? There is a lot of that going on as well. Consider the man-lifetimes wasted waiting in airports, and money spent on anti-terrorism, vs the risk allegedly prevented, and compare that to how many lives the money could have saved in the healthcare. Easy stuff that you (and anyone with any math skills) can actually prove wrong beyond all doubt without being a climatologist or something, and then actual human lives may get saved! You'll be saving expected human lives. That matters, man.

Now, you have some crusade against the notion of nuke winter, against which BTW you don't actually have any solid argument of any kind, nor means of having one, due to lack of expertise in climatology. And what exactly for? Okay you just might correct the 'public misunderstanding' of the nukes energy vs forest fires, the misunderstanding that public probably doesn't even think about ever. What's next? Which exactly actions should the public update on? Where's the payoff of any kind? Sleeping more soundly at night? Thank you very much, if the profoundly irrational public is now comparing the forest fires to nuke war, and is less afraid of nuke war, that will totally make me feel safer.

Ohh you just are against it because it is wrong? Well, there's a lot of stuff that is way more wrong with large negative consequences to the wrongness. And guess what, I don't even really care if the nuke winter is certain, or most likely. All I care for, is that there's chance it can happen. (And for the Sagan, he shouldn't have gone around telling stuff about the oil wells, what ever, the dude's dead, want to pick on someone, choose someone alive, like, hmm, Michio Kaku or Dawkins or something). And even if I had a proof that nuke winter is impossible, which I don't, I would definitely keep it to myself because public is stupid and irrational, and selective explaining (without correcting all other wrong things first) would most certainly not be a good thing.