The post discusses nuclear winter briefly, but I'll cover that in more detail here:
The theory of nuclear winter is predicated on a specific chain of events:
* The mass use of nuclear weapons causes massive firestorms in large cities.
* These firestorms pump soot in unprecedented amounts into the stratosphere.
* The stratospheric soot causes massive, persistent climatic cooling.
If any of these claims fail to be true, then the entire thesis breaks down. And there is some reason to doubt all of them, especially the hyperbolic versions of the hypothesis (e.g., "going like 100 years without being able to grow food").
Let me tackle just the last one. Volcanic eruptions are the most effective stratospheric soot pumps we know of: the eruptive columns of even smallish eruptions (like the 2018 summit explosions of Kilauea) routinely reach the stratosphere. In modern history, the most powerful eruption would be the 1815 eruption of Tambora, which is calculated to have erupted about 41 km³ of tephra. The result was a well-documented global cooling (the Year Without a Summer). Now ask yourself how likely it is for even several simultaneous nuclear explosions to inject that into the stratosphere. Now also consider just how much impact the eruption had in history: it doesn't merit a mention in many history books--a far, far cry from "100 years without being able to grow food".
This paper [1] looks at a nuclear war between India and Pakistan, with 100 Hiroshima sized nukes on the most populated urban areas in the country. Taking into account the amount of combustible material in the target areas, they estimate 5 Tg of soot aerosol particles into the upper atmosphere.
They apply climate models to that and get a mean 1.8 C temperature reduction and 8% precipitation reduction for at least 5 years. Using state of the art crop models they estimate the food loss over that time, with the strongest effects in temperate regions of the US, Europe, and China for 10 to 15 years.
It's not an end of humanity scenario, but it seems it would be a lot worse than any past volcanic eruptions. A lot of people would go hungry, and not just in the poorest countries.
This particular scenario seems particularly worrisome because both India and Pakistan depend on Himalayan glaciers for a large part of their fresh water, and climate change is hitting those. India and Pakistan already hate each other, so it is not hard to imagine a fight breaking out over dwindling regional water supplies.
Here's an article about that paper that summarizes it well [2].
To be cynical, we're not far off from a scenario where a 1.8 C temperature reduction would simply mean getting back to normal temperature range to which our agriculture is well suited.
The theory of nuclear winter is predicated on a specific chain of events:
* The mass use of nuclear weapons causes massive firestorms in large cities.
* These firestorms pump soot in unprecedented amounts into the stratosphere.
* The stratospheric soot causes massive, persistent climatic cooling.
If any of these claims fail to be true, then the entire thesis breaks down. And there is some reason to doubt all of them, especially the hyperbolic versions of the hypothesis (e.g., "going like 100 years without being able to grow food").
Let me tackle just the last one. Volcanic eruptions are the most effective stratospheric soot pumps we know of: the eruptive columns of even smallish eruptions (like the 2018 summit explosions of Kilauea) routinely reach the stratosphere. In modern history, the most powerful eruption would be the 1815 eruption of Tambora, which is calculated to have erupted about 41 km³ of tephra. The result was a well-documented global cooling (the Year Without a Summer). Now ask yourself how likely it is for even several simultaneous nuclear explosions to inject that into the stratosphere. Now also consider just how much impact the eruption had in history: it doesn't merit a mention in many history books--a far, far cry from "100 years without being able to grow food".