Hi Ulrik, good to hear from you again!
We do not know what will happen if a nuclear weapon is again detonated offensively, other than that the world would be forever changed. This is a fear shared by pretty much everyone who deals with nuclear weaponry (including recent speeches at EAG London—such as John Gower, who we met before), and even without immediate retaliation the expected probability of a large scale future exchange would rise hugely in such a world. That’s what I meant about the “all bets are off” line.
Certainly, many countries would seek to acquire weapons under this scenario (especially if the use was against a non nuclear power, which breaks a further taboo), and even if there are no further detonations in 30 days, the chances of a full scale exchange in such a world may rise by an order of magnitude.
I’m not sure that second projection is correct, and I put the mean projected additional detonations at higher levels. However, even if it is an accurate projection, I think the core point of the article holds: An offensive detonation significantly raises the probability of large exchanges, and there is a baseline risk of such an exchange today anyway → Large exchanges with thermonuclear weaponry risk nuclear winters → this is worth considering in our calculus around the expected impacts of nuclear warfare.
I feel there are a few things here:
Los Alamos claims that they are being pessimistic, but then end up with very low soot conditions compared to observations.
They claim that firestorms are difficult to form with 15kt weapons. If their logic holds this may be accurate, due to the circle of blast damage nearly overlapping with the circle of fire damage (see the map above), but that wouldn’t be the case as weapons get larger (see the 100kt + weapon circles). This makes their conclusion less relevant for larger exchanges.
Their claimed soot lofting in the 72.6 g/cm2 scenaro is still very low. They claim the fire is in the “firestorm regime”, but it again doesn’t seem to meet observations (of lofting post Hiroshima for example, with the photo above). This also contradicts other modeling as well as the few observations we have of firestorms: both Rutgers and Lawrence Livermore model that soot would be far more effectively lofted than their model.
My point from the article is that:
There is uncertainty, BUT:
Some of the Los Alamos critiques may not apply at larger weapon sizes and larger exchanges.
Los Alamos’ modeling may or may not be correct, we have credible reasons to be concerned about soot lofting from multiple other sources (both observations and models), and there are questions on some of their key model outputs.
If Los Alamos is correct in all of their modeling, and it all holds for larger exchanges, then there would likely be no climate shock. If any of the points raised above hold, there is a threat, even without the most pessimistic of Rutger’s projections.
Therefore: nuclear winter is a threat.