1. “the impact of secondary ignitions, such as gas line breaks, are not considered … For example, evidence of secondary ignitions in the Hiroshima conflagration ensuing the nuclear bombing … led to unique conditions that resulted in significantly enhanced fire behavior.” They ignored processes that took place in Hiroshima, preventing their simulation from producing as big fires.
2. In contrast to the Hiroshima fire, Reisner et al. simulated a line fire, similar to most forest fires that start at a single point. Hiroshima mass fires started from many ignition points distributed over the zone of the thermal pulse and pressure wave. Such mass fires are much more intense than line fires.
3. Reisner et al. assume a wind profile with 6–8 m/s winds in the boundary layer, which they call “very calm,” but which are significantly above the threshold of 3.6 m/s for a firestorm.
4. They used “a section of suburban Atlanta, GA were chosen for use as a ‘generic suburb’ for the study.” This is clearly not representative of dense cities in India and Pakistan, and therefore would not have the correct fuel loading. They did this because they do not have data for India and Pakistan cities. They claim, without support, that buildings there are primarily concrete and not wood. However, even for concrete buildings, it is the contents that burn and provide the fuel load. We are actually doing inventories of actual buildings to get this right.
5. “A dry atmosphere was utilized, and pyro-cumulus impacts or precipitation from pyro-cumulonimbus were not considered.” Thus they eliminate a major source of buoyancy that would loft the soot, and latent heat of condensation.
6. Their simulations of fire were only run for 40 minutes, and they did not actually model firestorms.
In summary, Reisner et al. (2018) modeled the wrong type of fire (they should have modeled a mass fire), in an area with lower fuel loading than we considered (a suburb not a city), they omitted factors known to be important to smoke lofting (latent heat release), they used too high wind speeds, and they didn’t model the full duration of the event.
I read their reasoning is that any nuclear weapon will create a firestorm. So the size of the weapon is almost irrelevant. It is true that a smaller weapon created the Hiroshima firestorm. Therefore they argue that even a Pakistan-India conflict would generate enough firestorms and generate enough aerosols to disrupt agriculture and kill billions.
I do not believe modern cities would firestorm as easily as Hiroshima which had mostly wooden structures. Most concrete structures would collapse and smother material inside them extinguishing fires created from the initial flash. To get Tokyo to firestorm a special weapon was created and used under ideal conditions.
The Dresden firestorm was also engineered and consisted of two waves of airplanes. The first dropped blockbuster bombs to open up the concrete structures to expose the flammable materials inside. The second wave dropped incendiary bombs to ignite the exposed materials.
However, let’s assume that every nuclear weapon creates a firestorm. Also I will assume the fires cannot be put out due to the fallout dangers after a nuclear attack which suppress firefighting.
I also trust their atmospheric modeling and famine simulations for different levels of soot in the stratosphere which are here:
The model focuses on soot, black carbon, which is lifted into the stratosphere with the pyro-cumulonimbus cloud that forms with a firestorm. They argue the black carbon does not rainout but instead absorbs sunlight and is lifted even higher into the stratosphere where it persists for years.
Soot will auto-ignite at the temperatures required to generate firestorms. Above 500C with oxygen present it will turn into carbon dioxide. They also argue that cities have more plastics that generate soot and even that the asphalt will burn. All the plastics are petroleum products which at high enough temperatures and in the presence of oxygen, like in a firestorm will turn into water vapor and carbon dioxide.
I suspect the pyro-cumulonimbus clouds are mostly water vapor and a mixture of other aerosols which are less efficient at absorbing sunlight. There should be enough water vapor that condenses around any black carbon at those altitudes.
A forest fire, like in Australia, that created the pyro-cumulonimbus clouds they reference was created in dry conditions with extremely dry eucalyptus trees. It did not boil lakes, rivers or the standing water left in destroyed urban infrastructure. Cities are relatively wet, fire-sprinklers are everywhere.
Here’s the analysis:
The problems with Reisner et al. (2018):
1. “the impact of secondary ignitions, such as gas line breaks, are not considered … For example, evidence of secondary ignitions in the Hiroshima conflagration ensuing the nuclear bombing … led to unique conditions that resulted in significantly enhanced fire behavior.” They ignored processes that took place in Hiroshima, preventing their simulation from producing as big fires.
2. In contrast to the Hiroshima fire, Reisner et al. simulated a line fire, similar to most forest fires that start at a single point. Hiroshima mass fires started from many ignition points distributed over the zone of the thermal pulse and pressure wave. Such mass fires are much more intense than line fires.
3. Reisner et al. assume a wind profile with 6–8 m/s winds in the boundary layer, which they call “very calm,” but which are significantly above the threshold of 3.6 m/s for a firestorm.
4. They used “a section of suburban Atlanta, GA were chosen for use as a ‘generic suburb’ for the study.” This is clearly not representative of dense cities in India and Pakistan, and therefore would not have the correct fuel loading. They did this because they do not have data for India and Pakistan cities. They claim, without support, that buildings there are primarily concrete and not wood. However, even for concrete buildings, it is the contents that burn and provide the fuel load. We are actually doing inventories of actual buildings to get this right.
5. “A dry atmosphere was utilized, and pyro-cumulus impacts or precipitation from pyro-cumulonimbus were not considered.” Thus they eliminate a major source of buoyancy that would loft the soot, and latent heat of condensation.
6. Their simulations of fire were only run for 40 minutes, and they did not actually model firestorms.
In summary, Reisner et al. (2018) modeled
the wrong type of fire (they should have modeled a mass fire),
in an area with lower fuel loading than we considered (a suburb not a city),
they omitted factors known to be important to smoke lofting (latent heat release),
they used too high wind speeds, and
they didn’t model the full duration of the event.
http://climate.envsci.rutgers.edu/robock/talks/NuclearWinter109Lamont.pptx
I read their reasoning is that any nuclear weapon will create a firestorm. So the size of the weapon is almost irrelevant. It is true that a smaller weapon created the Hiroshima firestorm. Therefore they argue that even a Pakistan-India conflict would generate enough firestorms and generate enough aerosols to disrupt agriculture and kill billions.
I do not believe modern cities would firestorm as easily as Hiroshima which had mostly wooden structures. Most concrete structures would collapse and smother material inside them extinguishing fires created from the initial flash. To get Tokyo to firestorm a special weapon was created and used under ideal conditions.
https://m.youtube.com/watch?v=uPteVZyF4U0
The Dresden firestorm was also engineered and consisted of two waves of airplanes. The first dropped blockbuster bombs to open up the concrete structures to expose the flammable materials inside. The second wave dropped incendiary bombs to ignite the exposed materials.
However, let’s assume that every nuclear weapon creates a firestorm. Also I will assume the fires cannot be put out due to the fallout dangers after a nuclear attack which suppress firefighting.
I also trust their atmospheric modeling and famine simulations for different levels of soot in the stratosphere which are here:
https://www.nature.com/articles/s43016-022-00573-0
The model focuses on soot, black carbon, which is lifted into the stratosphere with the pyro-cumulonimbus cloud that forms with a firestorm. They argue the black carbon does not rainout but instead absorbs sunlight and is lifted even higher into the stratosphere where it persists for years.
Soot will auto-ignite at the temperatures required to generate firestorms. Above 500C with oxygen present it will turn into carbon dioxide. They also argue that cities have more plastics that generate soot and even that the asphalt will burn. All the plastics are petroleum products which at high enough temperatures and in the presence of oxygen, like in a firestorm will turn into water vapor and carbon dioxide.
I suspect the pyro-cumulonimbus clouds are mostly water vapor and a mixture of other aerosols which are less efficient at absorbing sunlight. There should be enough water vapor that condenses around any black carbon at those altitudes.
A forest fire, like in Australia, that created the pyro-cumulonimbus clouds they reference was created in dry conditions with extremely dry eucalyptus trees. It did not boil lakes, rivers or the standing water left in destroyed urban infrastructure. Cities are relatively wet, fire-sprinklers are everywhere.