It also works the other way. A nuclear war between two countries nowhere near the US and that doesn't draw in any other nuclear powers could still have pretty annoying effects in the US.
Here's a paper [1] and an article [2] based on that paper that looked at what a limited nuclear war between India and Pakistan could do to the rest of the world.
The scenario they look it is each firing 100 nukes the size of the bomb used at Hiroshima at the other, aimed at major population centers.
Here's the abstract from the paper:
> A limited nuclear war between India and Pakistan could ignite fires large enough to emit more than 5 Tg of soot into the stratosphere. Climate model simulations have shown severe resulting climate perturbations with declines in global mean temperature by 1.8 °C and precipitation by 8%, for at least 5 y. Here we evaluate impacts for the global food system. Six harmonized state-of-the-art crop models show that global caloric production from maize, wheat, rice, and soybean falls by 13 (±1)%, 11 (±8)%, 3 (±5)%, and 17 (±2)% over 5 y. Total single-year losses of 12 (±4)% quadruple the largest observed historical anomaly and exceed impacts caused by historic droughts and volcanic eruptions. Colder temperatures drive losses more than changes in precipitation and solar radiation, leading to strongest impacts in temperate regions poleward of 30°N, including the United States, Europe, and China for 10 to 15 y. Integrated food trade network analyses show that domestic reserves and global trade can largely buffer the production anomaly in the first year. Persistent multiyear losses, however, would constrain domestic food availability and propagate to the Global South, especially to food-insecure countries. By year 5, maize and wheat availability would decrease by 13% globally and by more than 20% in 71 countries with a cumulative population of 1.3 billion people. In view of increasing instability in South Asia, this study shows that a regional conflict using <1% of the worldwide nuclear arsenal could have adverse consequences for global food security unmatched in modern history.
BTW, both India and Pakistan rely on the glaciers in the Himalayas for freshwater. The glaciers in effect act as a natural reservoir system.
Something like 70% of Pakistan depends on that system, and a similar percent for northern India. Overall in Southeast Asia about 1.9 billion people depend on those glaciers.
As global warming reduces those glaciers it is not a stretch to imagine disputes over allocation of the remaining water getting heated enough for war to break out. I've read that if we let it get to 3℃ above pre-industrial levels we lose about 75% of those glaciers.
This is Trump. He's not going to war with Russia but if he gets out of the wrong side of his bed and reads the wrong social media post he might have to get talked out of nuking Portland
... but with China instead. The trouble with this guy is, you can't be sure if what he spouts from his mouth is him being actually serious, him just parroting whatever the last person to talk to him said (seems to be a common trope regarding anything Ukraine) or if he's just out of his mind and gone off script, off rails. And on top of that you got stuff like the sinking of the "Venezuelan drug boats" that would be seen as and dealt with as a declaration of war if the aggressor weren't the USA.
All it takes for stuff to go Seriously Damn Wrong is one person on the other side taking his verbal diarrhoea seriously and literally and acting accordingly.
Well, anybody have any modern simulation models for fallout distribution after a nuclear war between the USA and Russia?