[MarkPawelek (OP)]

How much upper atmospheric pollution is likely from a 15 kt atomic bomb?

1. In particular how much black carbon will be released into the upper atmosphere and under what circumstances will it be released?

2. The worst case scenarios all describe a nuclear winter consequent on the after effects of firestorms. Which particular nuclear powers are targeting mass incineration of cities?

3. If a nuclear war was fought but cities were not incinerated, could the same nuclear winter still happen? If so, how?

I must admit to being skeptical over claims that 5 Tg of black carbon will be released into the atmosphere from the detonation of 50 15kt bombs. That's 100,0000 tones of black carbon per 15 kt A-bomb detonation.

Where's the evidence that our governments are planning genocidal wars against civilians in our cities, and that each 15kt bomb will cause a massive fire-storm?

[evan_au]

This may not be such a consideration for those who didn't live through the 1950s and 1960's, but nuclear conflagration was a topic very much on people's minds (and it probably suited the politicians and generals too).

In what must be one of the most apt acronyms ever, the policy where a government based its defence policy on totally destroying an opponent's country was called MAD: "Mutually Assured Destruction". The oxymoronic nature of this policy could be summed up by the overkill: How many times over a country could kill the population of its opponent (in theory).

It is said that "Imitation is the sincerest form of flattery". A policy based on a couple of superpowers facing each other with an arsenal of nuclear weapons becomes unsupportable when the information about how to build atomic weapons is available on the internet, and the raw materials are available in many locations around the world. Many small states and even some terrorist organisations have the ability to build atomic weapons, and becoming a superpower (at least in their own minds) is a big attraction.

Fortunately, the superpowers have realised the damage that this nuclear arms race has already done to their economies and to world politics, and are making progress to reduce their excessive stocks of nuclear weapons.

How much upper atmospheric pollution is likely from a 15 kt atomic bomb?

It totally depends on how it is delivered.

• If it is exploded at ground level, the superheated fireball will carry considerable irradiated material into the upper atmosphere, as well as causing a firestorm at ground level.
  
• If it is exploded at a moderate altitude, it can still cause considerable damage to the city and lots of smoke and CO₂, but not so much of it will reach the upper atmosphere, and it will be less radioactive when it does.
  
• If it is exploded outside the bulk of the atmosphere, it will cause very little pollution; the radioactive mass of the bomb will still mostly fall into the Earth's atmosphere, causing a radioactive marker in the bones of the survivors.

The acronym is still appropriate: anyone wanting to explode a nuclear device inside Earth's (extended) atmosphere is MAD.

[CliffordK]

It would really depend on the parties in the war.

There have been suggestions to use nuclear "bunker busters" against non-nuclear countries such as Iraq.  If such war efforts were contained, then the global fallout of such actions might be minimal. 

Even war with a country such as North Korea would be of limited scope as the country may only have a couple of bombs for deployment. 

A full-on war between the USA and Russia would be a different story as each country may let fly hundreds, or perhaps thousands of nuclear warheadds. 

[evan_au]

15 kilotons is at the low end of nuclear weapons - some of them are in the megaton range.

[alancalverd]

The Hiroshima and Nagasaki bombs were around 15 kt, and there have been plenty of groundbursts since then of up to 50 Mt, all with pretty minimal atmospheric disturbance beyond a few miles. Most of the debris is washed out by local rainfall within hours, but the ease with which we can detect radioactive debris means that the small amount that persists can be tracked for days or weeks.

Other notable firestorms were ignited by conventional bombing of Hamburg, Dresden and Cologne with similar effect.

Apart from nuclear depth charges and very small (kiloton) artillery shells, the main use of nuclear explosives seems to be the pre-emptive destruction of enemy silos or attacks on the civilian population. Since everyone with a silo or other hardened weapon base also has an early warning system, pre-emption seems improbable. The outcome of a nuclear exchange is therefore predictable: a predominantly urban and centralised society such as the UK or Japan cannot survive whereas a decentralised society with a low population density outside of its capital cities (e.g. USA, Russia), can. Which is one reason why British nuclear weapons are a waste of money. The other principal reason is that the UK is unlikely to be attacked by a nation state, which would gain nothing by doing so as the UK does not pose a military or economic threat to any nation state. However people of various superstitions seem to dislike our freedom of thought and action, so a low-yield nuke exploded over sinful Birmingham for the glory of god is always a possibility, and you can't retaliate against a suicidal nutter.