In context it seems clear they intended to short hand the possible effects of possible global dust clouds that are possibly aloft for some time with the term "nuclear winter", itself a name for a possible effect of some number of large ground level nuclear blasts.
Surely it'd be a nuclear winter if the same number hit not-cities.
eg: Castle Bravo .. not a city, but a ground level strike.
> It's unclear how this is related.
From a geophysics PoV meteorite strikes are not unlike ground level nuclear explosions in so far as dust plumes go.
> another asteroid strikes, raises dust plumes and causes volcanic activity for years?
At least that's my recollection from those old old first approximation nuclear winter papers that were largely circles and arrows on the back of envelope guesstimations.
If we're to quibble, I'd be asking about the meteorite strikes causing volcanic activity (or is it the dust plumes that cause that activity?) .. cause that seems tenuous unless it's a direct strike on an unstable part of the Ring of Fire / Yellowstone Caldera.
Whether it's nuclear or meteorites the theory rests not so much on number of ground events as it does on volume (and type) or particles raised up high ... the Iridium K-Pg anomaly layer is global yet postulated to have come from a single (large) strike.
Because cities have more concentrated flammable material than random locations on the earth surface, and will typically be the targets in a nuclear war, and is why most calculations are done with strikes against cities.
The nuclear strikes would create columns of burning material that stretch into the atmosphere.
I responded to a comment using a concept "nuclear winter", in a way not widely used.
It was interesting, because I assumed to commenter meant that "humanity powers through with nuclear power during the long winter", compared to nuclear winter as in "humanity attacks itself because of greed and stupidity", as it is commonly used.
You then interpreted it in the common way, but explaining it using meteor strike dust plumes, which is not how nuclear winter is commonly explained, as the mode is typically burning stacks of flammable material("guesstimated" first by Carl Sagan and his peers). It's been a long time since I researched the very plausible nuclear winter(stockpile in Switzerland is my plan).
Yes, it is also likely that strategic oil fields will be set ablaze by nuclear strikes, another dimension to the nightmare.
I don't know how valid this theory is, it seems plausible. It was just an interesting scenario, with nuclear powering us through a catastrophe, man made or otherwise, and with current leadership the best we can hope for.
Sweden, my native country, had a similar idea(offensive nuclear capabilities combined with SMRs) in the 50s and 60s, but was eventually(probably for good reasons) cancelled and dismantled it's nuclear weapons program and eventually closed it's first and only SMR in operation, Ågestaverket, eventually building a capable but conventional nuclear industry that provided cheap electricity to the country for decades.
A few nuclear plants will do absolutely nothing against a nuclear winter.