How many megatons would it take to bring on nuclear winter?

[farmerben]

As I understand it; the secondary firestorm consuming cities and vegetation provide the aerosol particles that lead to nuclear winter.  The mushroom cloud helps loft particles into the stratosphere.  So where and when they hit may be more important than the bomb yield.  How wet the forests are matters a great deal.   The northern hemisphere tends to be wet almost everywhere in late winter early spring.  Many people believe that if the USA and Russia had an exchange they would target each others capability, requiring a scale enough to cause a nuclear winter.  What do you think?   Is there a scenario where nuclear winter is minimal?

[DDE]

9 minutes ago, farmerben said:

As I understand it; the secondary firestorm consuming cities and vegetation provide the aerosol particles that lead to nuclear winter. 

That's the theory, but there's vigorous disagreement that there would be a firestorm afterwards. Knocked-over buildings and trees don't burn, they smolder, which doesn't result in sufficient updraft for stratospheric injection (which is independent of the mushroom cloud).

So it's difficult to gauge something that doesn't even uncontroversially exist.

[kerbiloid]

Not aerosol, but soot particles, i.e. elementary carbon.

But the firestorm causes intensive oxidizing and thus produces more gaseous carbon oxides and less soot.
While the smouldering produces a lot of soot, but weaker vertical flow, so most of the soot stays below the tropopause and falls down in weeks.

The nuclear winter theory presumes that the burning is as sooty as the smouldering, and as intensively flowing up as the firestorm, i.e. it's based on two excluding processes, as the smouldering happens where the burning is weak and slow, and the carbon compounds lack oxygen, while the firestorm sucks the air from around into the fire, and intensively burns the soot into CO/CO2.

They were predicting that the Gulf War would result into at least local nuclear winter, but even when many oil rigs had been burnt by the strikes or intentionally by the retiring army, it just resulted into several weeks of cloudy weather.

The mushroom clouds are produced by any source of heat. They are just toroidal clouds of hot air, less dense than the surrounding air, raising up and sucking dust from below.
Their height is defined only by the heat per time production (height ~ heat power^0.25, iirc, or so), thus low-yield explosions don't reach the troposphere, and the particles stay below and fall down.

***

In case of the USA it's probably more important that its agriculture is mostly based on forced irrigation, thus powerplants, thus nuke plants and big dambs, which are not numerous, and their destruction may cause the collapse of the agriculture due to both lack of energy for the pumps, loss of the biggest water reservoirs, and radioactive fallout contamination of big rivers.

As the current US population is based on the current technological capability, this would significantly decrease the food production, limit the ability to support the non-productive jobs in the cities, and cause mass exodus from starving cities to the private farm lands.

Also, while the Soviet/Russian silos are mostly placed in wet forests and desert regions, a lot of American ones are placed right between the crops in the agricultural states.

Thus, I find it possible that in case of it, the US would occupy the territory up to the Panama channel (and a no-man territory at its opposite coast), with corresponding casualties of local population, to turn the tropic forests into plowlands.

The same of China.

Edited June 3 by kerbiloid

[farmerben]

42 minutes ago, kerbiloid said:

 

In case of the USA it's probably more important that its agriculture is mostly based on forced irrigation, thus powerplants, thus nuke plants and big dambs, which are not numerous, and their destruction may cause the collapse of the agriculture due to both lack of energy for the pumps, loss of the biggest water reservoirs, and radioactive fallout contamination of big rivers.

 

Midwestern grain does not require irrigation.  There is enough in storage to feed to humans instead of livestock for over a year, assuming everybody like corn pone.  You could easily get a wheat crop instead of corn if the temps were 10 degrees lower.

[JoeSchmuckatelli]

8 hours ago, farmerben said:

secondary firestorm consuming cities

Based on wooden cities of Nagasaki and Hiroshima. 

 

8 hours ago, farmerben said:

Is there a scenario where nuclear winter is minimal?

Almost all of them. 

 

In fact, the scenario where nuclear winter happens is almost impossible. 

[magnemoe]

9 hours ago, DDE said:

That's the theory, but there's vigorous disagreement that there would be a firestorm afterwards. Knocked-over buildings and trees don't burn, they smolder, which doesn't result in sufficient updraft for stratospheric injection (which is independent of the mushroom cloud).

So it's difficult to gauge something that doesn't even uncontroversially exist.

This, best parallel is volcanoes and the year without summer, but it required an high number of cubic kilometers of rock into the stratosphere. This is hard to do starting fires. 
 

[JoeSchmuckatelli]

1 hour ago, magnemoe said:

This, best parallel is volcanoes and the year without summer, but it required an high number of cubic kilometers of rock into the stratosphere. This is hard to do starting fires. 
 

True - to add to this; when Mt St Helen's went off there were two, brief local effects. 

1. Daytime temps under the ash cloud were up to 8 degrees cooler during the day. 

2. Night temperatures under the ash cloud were 10-12 degrees warmer. 

Third - the unexpected result was how temporary the effect - and that there was almost no global cooling.  This is attributed to the lack of sulpur in the ash.  Aerosol sulpur is linked to the Icelandic volcanoes that caused the year without summer. 

 

The bigger crop risk that no one is talking about is the fact that most crops are engineered to die.  Monsanto, et.al. like their profits - so you cannot get a second year of crops from the presently planted seeds.  Only organic crops might be available for follow on years. 

Thus when the Nuke war happens - the logistics will be cut off and then the human tragedy will cascade. 

[darthgently]

10 hours ago, JoeSchmuckatelli said:

The bigger crop risk that no one is talking about is the fact that most crops are engineered to die.  Monsanto, et.al. like their profits - so you cannot get a second year of crops from the presently planted seeds.  Only organic crops might be available for follow on years. 

Support your heirloom variety maintainers and growers!  Seeds keep for decades (centuries?) if stored properly.  Properly can be as simple as a sealed 5 gallon bucket with the oxygen displaced by nitrogen kept in a cool and dry place. 

There are for-profit and  nonprofit outfits one can get heirloom seeds from,  I'll try to get some links.  DM if interested

Ppl who try to patent existing, or slightly modified, life forms are merely annoying.  But when they set out to make the naturally reproductive lines fade away, it is pure malicious idiocy and an attack on everyone and on everything it means to be alive on earth.  Seed banks on the Moon and Mars are probably a good idea.  Not just ag varieties, but all kinds of plants and microbes too.

This is one I've bought from and would recommend

https://seedsavers.org

Edited June 4 by darthgently