Dear Stan.
I think there are issues with this analysis. As it stands, it presents a model of nuclear winter if firestorms are unlikely in a future large scale nuclear conflict. That would be an optimistic take, and does not seem to be supported by the evidence:
In my post on the subject that you referenced, I discuss how there are serious issues with coming to a highly confident conclusion in relation to nuclear winter. There are only limited studies, which come at the issue from different angles, but to broadly summarize:
Rutgers are highly concerned about the threat of nuclear winter via soot lofting in firestorms. They look at fission and fusion weaponry.
Los Alamos find that firestorms are highly unlikely to form under nuclear detonations, even at very high fuel loads, and so lofting is negligible. They only look at fission scale weaponry.
Lawrence Livermore did not comment on the probability of firestorms forming, just that if they did form there is a significant probability that soot would be lofted. They only look at fission scale weaponry.
Comparing the estimates, the main cause of the differences in soot injection are if firestorms will form. Conditional on firestorms forming, my read of the literature is that at least significant lofting is likely to occur—this isn’t just from Rutgers.
We know that firestorms from nuclear weaponry are possible, we have seen one in Hiroshima and it had a plume that reached stratospheric levels (the anvil shaped cloud photograph is it reaching and breaching the stratospheric barrier). Los Alamos cannot replicate this in their model, even at high fuel loads they get nothing like our observations of the event. This failure to replicate observations makes me very cautious to weigh their results heavily versus the other two studies, as you implicitly do via a mean soot injection of 0.7 Tg following 100 detonations, which is a heavy skew towards “no firestorms”.
Fusion (Thermonuclear) weaponry is often at least an order of magnitude larger than the atomic bomb dropped on Hiroshima. This may well raise the probability of firestorms, although this is not easy to determine definitively. It is however another issue when projecting a study on the likelihood of firestorms under atomic bombs onto thermonuclear weaponry.
Not all detonations will cause firestorms—Nagasaki did not due to the location of the blast and local conditions, and this is likely to be true of a future war even with thermonuclear weaponry. However, given projected lofting if they do occur (which is only modeled in Rutgers and Lawrence Livermore as a full firestorm only forms in their models) you only need maybe 100 or so firestorms to cause a serious nuclear winter. This may not be a high bar to reach with so many weapons in play.
As a result, blending together the Los Alamos model with that of Rutgers doesn’t really work as a baseline, they’re based on a very different binary concerning firestorms and lofting and you exclude other relevant analysis, like that of Lawrence Livermore. Instead, you really need to come up with a distribution of firestorm risk—however you choose to do so—and use that to weight the expected soot injection. I would assume such analysis would seriously raise the projected soot that is injected and subsequent cooling versus your assumptions.
In addition, there are points to raise on the distribution of detonations—which seems very skewed towards the lower end for a future nuclear conflict between great powers with thousands of weapons in play and strong game theoretic reasons to “use or lose” much of their arsenals. However, we commented on that in your previous post, and as you say it matters less for your model than the sensitivity of soot lofted per detonation, which seems to be the main contention.
Hi Stan + others.
Around one year after my post on the issue, another study was flagged to me: “Latent Heating Is Required for Firestorm Plumes to Reach the Stratosphere” (https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022JD036667). The study raises another very important firestorm dynamic, that a dry firestorm plume has significantly less lofting versus a wet one due to the latent heat released as water moves from vapor to liquid—which is the primary process for generating large lofting storm cells. However, if significant moisture can be assumed in the plume (and this seems likely due to the conditions at its inception) lofting is therefore much higher and a nuclear winter more likely.
The Los Alamos analysis only assesses a dry plume—and this may be why they found so little risk of a nuclear winter—and in the words of the authors: “Our findings indicate that dry simulations should not be used to investigate firestorm plume lofting and cast doubt on the applicability of past research (e.g., Reisner et al., 2018) that neglected latent heating”.
This has pushed me further towards being concerned about nuclear winter as an issue, and should also be considered in the context of other analysis that relies upon the Reisner et al studies originating at Los Alamos (at least until they can add these dynamics to their models). I think this might have relevance for your assessments, and the article here in general.