How does this square with the global effects of large volcanic eruptions? The largest eruption in the 20th century exceeded the yield of the combined Soviet and US nuclear arsenals at their Cold War peak by an order of magnitude, yet the global effects were mild.

Interesting trivia: the largest volcanic explosion of the 20th century is a volcano in the US that most people have never heard of, Novarupta in 1912.

Volcanic eruption energy is partitioned between thermal and mechanical energy. The mechanical energy is distributed between translation (ejecta) and vibrational (tremors). These proportions vary significantly between volcanoes and eruptions. So, perhaps little of the energy is imparted to bring cooling aerosols and particles into the high atmosphere.

A limited nuclear exchange between RF/USA could extend to all large munitions stores, rocket stores, and petrochemical stores. All stores of nuclear launchers, warheads, and supplies intended for strategic war could be targeted.

Imagine all significant above-ground petroleum storage in RF/USA - large petroleum producers - is ignited. All counterforce sorties against targets near wooded areas will result in large forest fires.

"Imagine all significant above-ground petroleum storage in RF/USA - large petroleum producers - is ignited."

During the First Gulf War, the uncontrolled oil fires in Kuwait were burning at a rate equivalent to 30% of all US consumption. Nothing remotely resembling a climate apocalypse occurred; major volcanic eruptions have far greater effects. Empirically, it seems highly improbable that repeating that experiment on modestly larger scale will unleash a global apocalypse. It isn't a convincing argument based on the evidence.

The above-ground petroleum storage facilities only hold days worth of oil that we are going to burn anyway.

When modeling was done for the Kuwait oil fires, there were two opposing expectations. One was that the fires would cause a kind of "year without a summer" similar to the Tambora eruption in 1815. The other was that the smoke would affect local weather conditions and be rained out within a week. In retrospect, we know that the latter proved most accurate.

But from what I understand, the crucial difference between the two models was how high the smoke would go, and as such the gap between the two models is actually a lot closer than the outcomes would imply. Had the conditions (weather, geography, etc) been ripe for more "self-lofting" of particulates, far more of them may have made it as far as the stratosphere, at which point they would stay in the atmosphere for far longer and would spread much further, without any weather patterns at that altitude to accelerate their return to the surface.

Wouldn't we be burning that oil anyways? I'm sure it burns less 'clean' in a particulate sense, but orders of magnitude worse?

Seems from the petroleum front it's likely to actually reduce particulate matter over the course of months due to the lack of human industrial activity on the planet.

For particulate emissions I would imagine uncontrolled burning in the atmosphere is orders of magnitude worse than the very carefully controlled combustion in an engine with catalytic converters and particle screens. In the US anyway.

https://en.wikipedia.org/wiki/Novarupta link for the lazy

Hmm, I imagine nuclear winter scenarios widely depend on how much is actually deployed.

In one article in the New York Times from the 1980s (http://www.nytimes.com/1984/12/14/opinion/in-the-nation-tamb...) the estimate used for exploding half of the world's nuclear arsenals is equivalent to 6,500 megatons of TNT.

Mount Tambora, in contrast, a much more powerful explosion than any 20th century eruption, is widely quoted from various sources as being equivalent to 800 megatons of TNT (example: https://books.google.com/books?id=NuFfCgAAQBAJ&pg=PA15&lpg=P...). And Mount Tambora definitely had climate effects (https://en.wikipedia.org/wiki/Year_Without_a_Summer).

Climate cause and effect is difficult to nail down, but it seems with that much firepower back then a "nuclear winter" scenario was much more plausible. We have dismantled a lot of the nuclear arsenal since the 1980s these days -- estimates I see of current firepower vary by quite a bit, but I'm not even sure there's 6,500 megatons of nuclear weapon firepower in service globally anymore.

volcanic winter caused by the 1815 eruption https://en.m.wikipedia.org/wiki/Year_Without_a_Summer

Well, to be fair, Novarupta is on the Alaskan Penninsula, away from anything possibly resembling a major population center - and even Alaska itself wasn't a State when this Volcano erupted in 1912.

Volcanic eruptions have caused global mini-ice ages, widespread famine, and revolutions before.

How could this possibly be true given the fact that there have been >1,000 nuclear tests performed, including devices with orders of magnitude higher yield than in Hiroshima?

Most tests have been performed underground. And for an above-ground test to cause anything close to a nuclear winter, you need a lot more material than the bomb itself and the soil beneath it. Tons and tons of debris would need to be shot up into the atmosphere.

So, the theory of nuclear winter depends on bombs detonating over cities and forests, causing massive amounts of debris, and also inducing firestorms that would act as chimneys for even more smoke and particles to be funneled up into the troposphere and stratosphere.

Because those were most all carefully controlled to prevent such damage. Top of the list: those that were above ground were tested above empty terrain. The bomb doesn't create most of the ash. The burning city under the bomb is where the bulk of sun-blocking ash comes from. No city, no ash, no nuclear winter issues.

I would expect that some of the predicted effects of a "nuclear winter" would start to appear after a series of forest fires--albeit smaller in scope and intensity--but AFAIK this is not the case. What gives?

They aren't usually big enough to get the particulates high enough. But big events can do it:

https://en.wikipedia.org/wiki/Year_Without_a_Summer

Most forest fires don't create strong enough firestorms (if they do at all) to funnel material high enough to have an effect -- most of the ash falls back down in a matter of weeks (even sooner if it gets rained out of the atmosphere). I'd compare nuclear blast firestorms with volcanic eruptions -- we do have a record of eruptions funneling material high enough into the troposphere and stratosphere to have a noticeable, longer-term effect on the climate (over the subsequent months and years).

There have been "volcanic winter" events. Or at least, reduced insolation for a year or more.

> Nuclear winter is not a discredited myth.

It has been discredited. Even Sagan admitted as much. The idea that all humanity/life would end has been discredited.

Billions would surely die, but millions of humans would survive.