The reduced fuel combustion combined with a lower fuel load means that Los Alamos predicted that only 3.2 Tg of black carbon would be produced in total following the 100 detonations, vs around 6 Tg for the Rutgers team, a factor of 1.9 difference.
I think the team at Los Alamos would argue 3.2 Tg is an underestimate. From Reisner 2019 (emphasis mine):
While the BC content is significant in the constant fuel simulation, as previously noted, our BC emission factor is high by a factor of 10–100, places our BC profile used in climate simulations in the range of Mills et al. that used a much smaller BC to fuel mass fraction (1.6–2%; Toon, et al., 2007) “Therefore, we demonstrate that the amount of BC used in the Reisner et al. climate simulations is indeed an upper bound.”
So Los Alamos might argue for a difference of a factor of 19 to 190 (instead of 1.9). I have no idea how they got to the above range of 10 to 100, nor whether it is reasobable. However, I think they are working to get better estimates. From Hess 2021:
Jon Reisner gave a seminar at the National Center for Atmospheric Research on 12 November 2019 in which he discussed the need to reduce the uncertainties and appealed to the community for help to do this (Reisner 2019). Work is underway at LANL to upgrade HIGRAD-FIRETEC to run faster, and to include detailed chemical kinetics (the formation of black carbon), probability density functions for the mean temperature and its variation within a grid cell, pyro-cumulus formation and the release of latent heat. Validation tests with other fire models and field data are being carried out, as well as tests on modern building materials to see if they will burn.
The 3.2 Tg figure is their figure for the worst case scenario, based on 1 g/cm2 fuel loading. In their later paper they discuss this may be too high for a 1 g/cm2 scenario, as you say they mention that their soot conversion was set to be high for caution, and they could have it an order of magnitude or so lower, which Rutgers do.
However, this presents a bit of an issue for us in my calculations and factors. I’m comparing headline results there, and the 3.2 is the headline worst case result. It could be that they actually meant that the 100 fires generated just 0.32 Tg of soot total (or less), and we could take that as a fair comparison, but then we have a further issue in that Hiroshima led to an estimated 0.02 TG alone, meaning that seems to raise questions on if they’re calibrated correctly.
Again, you can assume that maybe India/Pakistan just don’t have the fuel to burn, maybe that keeps you that low, but then it’s not a relevant factor of comparison for a full scale exchange on dense cities which do have the fuel. Either way, for the full scale comparison, it returns to firestorms: will they form? Assumptions around fuel loading/combustion feed into that, but that’s the core.
we have a further issue in that Hiroshima led to an estimated 0.02 TG alone, meaning that seems to raise questions on if they’re calibrated correctly.
Would Los Alamos agree that is an issue? From Reisner 2019:
Of the two nuclear bombs detonated in WWII, a firestorm was reported in Hiroshima. The relatively dense wood structures (10-g/cm2 fuel loading) in Hiroshima promoted a long-lived (2 to 3 hr; Rodden et al., 1965) firestorm, but estimated BC production (0.02 Tg) over the entire firestorm and smoldering phases was similar to the estimate (0.037 Tg for one incident) produced by the no-rubble simulation in Reisner et al.
BTW, where did the estimate of 0.02 Tg come from? I did not find it in Rodden 1965 searching for “0.02”, “soot” and “carbon”.
Great post, Mike!
I think the team at Los Alamos would argue 3.2 Tg is an underestimate. From Reisner 2019 (emphasis mine):
So Los Alamos might argue for a difference of a factor of 19 to 190 (instead of 1.9). I have no idea how they got to the above range of 10 to 100, nor whether it is reasobable. However, I think they are working to get better estimates. From Hess 2021:
Quick responses Vasco!
The 3.2 Tg figure is their figure for the worst case scenario, based on 1 g/cm2 fuel loading. In their later paper they discuss this may be too high for a 1 g/cm2 scenario, as you say they mention that their soot conversion was set to be high for caution, and they could have it an order of magnitude or so lower, which Rutgers do.
However, this presents a bit of an issue for us in my calculations and factors. I’m comparing headline results there, and the 3.2 is the headline worst case result. It could be that they actually meant that the 100 fires generated just 0.32 Tg of soot total (or less), and we could take that as a fair comparison, but then we have a further issue in that Hiroshima led to an estimated 0.02 TG alone, meaning that seems to raise questions on if they’re calibrated correctly.
Again, you can assume that maybe India/Pakistan just don’t have the fuel to burn, maybe that keeps you that low, but then it’s not a relevant factor of comparison for a full scale exchange on dense cities which do have the fuel. Either way, for the full scale comparison, it returns to firestorms: will they form? Assumptions around fuel loading/combustion feed into that, but that’s the core.
Thanks for the reply!
Would Los Alamos agree that is an issue? From Reisner 2019:
BTW, where did the estimate of 0.02 Tg come from? I did not find it in Rodden 1965 searching for “0.02”, “soot” and “carbon”.