Hi Mike, thanks for taking the time to respond to another of my posts.
I think we might broadly agree on the main takeaway here, which is something like people should not assume that nuclear winter is proven—there are important uncertainties.
The rest is wrangling over details, which is important work but not essential reading for most people.
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.
Yes, I agree that the crux is whether firestorms will form. The difficulty is that we can only rely on very limited observations from Hiroshima and Nagasaki, plus modeling by various teams that may have political agendas.
I considered not modeling the detonation-soot relationship as a distribution, because the most important distinction is binary—would a modern-day countervalue nuclear exchange trigger firestorms? Unfortunately I could not figure out a way of converting the evidence base into a fair weighting of ‘yes’ vs. ‘no’, and the distributional approach I take is inevitably highly subjective.
Another approach I could have taken is modeling as a distribution the answer to the question “how specific do conditions have to be for firestorms to form?”. We know that a firestorm did form in a dense, wooden city hit by a small fission weapon in summer, with low winds. Firestorms are possible, but it is unclear how likely they are.
These charts are made up. The lower chart is an approximation of what my approach implies about firestorm conditions: most likely, firestorms are possible but relatively rare.
Los Alamos and Rutgers are not very helpful in forming this distribution: Los Alamos claim that firestorms are not possible anywhere. Rutgers claims that they are possible in dense cities under specific atmospheric conditions (and perhaps elsewhere). This gives us little to go on.
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.
Agreed. My understanding is that fusion weapons are not qualitatively different in any important way other than power.
Yet there is a lot of uncertainty—it has been proposed that large blast waves could smother much of the flammable materials with concrete rubble in modern cities. The height at which weapons are detonated also alters the effects of radiative heat vs blast, etc.
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.
Semi agree. Rutgers model the effects of a 100+ detonation conflict between India and Pakistan:
They find 1-2 degree cooling over cropland at the peak of the catastrophe. This would be unprecedented and really bad, but not serious compared to the nuclear winter we have in our imagination: I estimate about 100x less bad than the doomsday scenario with 10+ degrees cooling.
They are modeling 100 small fission weapons, so it would be worse with large weapons, or more detonations. But not as much worse as you might think: the 51st detonation is maybe 2-5x less damaging than the 5th.
Furthermore, they are assuming that each side targets for maximum firestorm damage. They assume that fuel loading is proportional to population density, and India & Pakistan have some of the world’s densest cities. So this is almost the worst damage you could do with 100 detonations.
Although 100 detonations sounds very small, this idealized conflict would be tapping into most of the firestorm potential of two countries in which 20% of the world’s population live—much more than live in the US and Russia.
It’s possible that 100 firestorms could trigger measurable cooling, but the conditions would have to be quite specific. 1000 firestorms seems much less likely still.
Conclusion
In the post I suggest that nuclear winter proponents may be guilty of inflating cooling effects by compounding a series of small exaggerations. I may be guilty of the same thing in the opposite direction!
I don’t see my model as a major step forward for the field of nuclear winter. It borrows results from proper climate models. But it is bolder than many other models, extending to annual risk and expected damage. And, unlike the papers which explore only the worst-case, it accounts for important factors like countervalue/force targeting and the number of detonations. I find that nuclear autumn is at least as great a threat as nuclear winter, with important implications for resilience-building.
The main thing I would like people to take away is that we remain uncertain what would be more damaging about a nuclear conflict: the direct destruction, or its climate-cooling effects.
[Update: the tool does capture diminishing marginal cost-effectiveness—see reply]
Cool tool!
I’d be interested to see how it performs if each project has diminishing marginal cost-effectiveness—presumably there would be a lot more diversification. As it stands, it seems better suited to individual decision-making.