This was written by Stuart, and is probably the best explanation of Nuclear Winter I've found...
Desert Fox wrote:I remeber throughout the years hearing about nuclear winter and then I find out that the explosion of several volcanoes, Tamboro I believe is one, have dwarved the energy of every nuclear weapon in the height of the cold war. This has lead me to think that the entire concept of nuclear winter is bunk although I don't know what effects radiation would have. What are others opinions on this?
Stuart wrote:Bunk is a pretty fair description. The "nuclear winter" theory was predicated on a series of hypothetical models that had been constructed by a group of "concerned scientists" lead by Carl Sagan who constructed a computerized model of earth, cranked in a series of hypothetical statistics on the effects of nuclear weapons and then claimed that the results from that model constituted "facts".
There were a number of serious problems with this process. One of them was that, when the hypothetical effects of nuclear initiations were cranked into other models of earth, they didn't produce the results Sagan had reported. In fact, the results reported by Sagan's group were only achieved when his particular model of the earth was used. This was a remarkable thing so people looked at Sagan's model to see how it differed from the rest. The answer turned out to be quite simple. The model Sagan had shown to the world press to “prove” the danger of “nuclear winter,” depicted the earth as being a barren ball of rock with no mountains and no oceans. Oceans, as Sagan well knew, act as gigantic energy flywheels that moderate temperature, helping cool adjacent continents in summer and warm them in winter.
Sagan, in other words, knowingly committed deliberate scientific fraud. He cooked up a phony computer model to concoct the phony “nuclear winter” results he wanted for political reasons. It subsequently became apparent that he had avoided using the already-available NCAR computer climate model precisely because he knew it would not produce the “nuclear winter” he wanted to sell to gullible journalists and an ignorant public.
Once that point had been realized, Sagan's assumptions were examined in greater depth. It turned out that none of the people in his group of "concerned scientists" were nuclear weapons experts. What they'd done was taken some generalist public sources, cherry-picked the ones that suited them and used them without examining how the various nuclear weapons effects interacted. Again, there was a healthy dollop of deliberate scientific fraud here. Where effects didn't give the results required, they were exagerrated or morphed until they did. By the time the critique was over, "nuclear winter" as a concept was totally discredited; today its a touchstone. If somebody starts to spout forth on the dangers of "nuclear winter" they're nutcases. Sagan's credibility never recovered; he never got another hearing from the serious nuclear weapons and policy community.
However, one useful thing did come out of all this. In order to examine the probability of Sagan's fairy stories, people cranked real data on nuclear weapons into real atmospheric models. The results were actually quite interesting (there is a novel currently being posted in HPCA called "Anvil of Necessity" which draws on that work).
For those who like grim details, the following was the nuclear exchange used as a basis for these studies. The US was presumed to have been hit by 5,800 warheads witha total yield of 3,900 megatons. Nuclear devices initiated in Europe totalled 3,300 with a total yield of 1,200 megatons The USSR was deemed to have been hit by 6,100 devices having a total yield of 1,900 megatons. China got hit by 900 devices witha total yield of 1,300 megatons. By way of comparison in TBO, Germany got hit by 232 devices totalling 8.6 megatons.
Other areas receiving at least a dozen warheads include Canada, North and South Korea, Japan, Taiwan, Greenland, Puerto Rico, India, Israel, Australia, Guam, Cuba, Syria, and Egypt. Other countries got single devices, mostly on their capitals. Nobody didn't get hit by something. This massive exchange used about half the global strategic and theater nuclear arsenal; about 10% was launched but did not reach a target and 30% was destroyed on the ground. By the time we finished there were 10,000 nuclear weapons left in the arsenals out of the 67,000 that we started with. Initial casualties were 400 million dead; by the time things had worked out, this increased to 1.2 billion. Welcome to my world.
The smoke clouds from the fires etc peak three days after the exchange. Essentially, they would spread to form a doughnut shaped band around the world that would essentially cover North America, Europe and the USSR. This smoke (actually, its particulates rather than smoke) cloud consisted of 1,500 million tons of dust, 25 million tons of smoke from vegetation, and 80 million tons of smoke from cities and other manmade sources. It is very important to note that the last type of smoke has the greatest impact: smoke from petroleum and petroleum products is particularly effective at absorbing sunlight. Altogether, about 0.4 cubic km (0.1 cu. mi.) of dust and smoke is in the stratosphere. The general effect (and this is the peak remember) would be to reduce sunlight intensity and temperature by a degree comparable to an overcast day. That's a general comment, if the observer is downwind of a stricken target, the intense plume from the smoke generated by large continuing fires will reduced mid-day light levels to that of twilight. The average peak temperature will be reduced by around 13 degrees F. However, there is a peculiar effect here; average trough temperatures will be increased by roughly the same amount (for exactly the same reason that a cloudy night is warmer than a clear one; the smoke clouds also tend to hold warm air in. That was an effect that Sagan and his crew deliberately suppressed.
Within ten days, the smoke/particulate concentration would decline rapidly although smoke in the upper atmosphere still absorbs much sunlight. The primary effect ceased to become temperature and the gross temperature changes would already be a thing of the past. Instead, the patchyness of the initiation effects would cause unusual weather conditions including strong winds in some coastal areas (in effect we've dumped huge amounts of energy into the climatoscene and that starts to work its way out). A curious predictable phenomena is that dense fogs would develop over the oceans and along waterways. Another interesting effect is that the ozone layer would be reduced by nearly half yet nearly all of the Earth's surface would receive less solar ultraviolet radiation than before the war. The reason is curious; although smoke levels would be dropping rapidly, there would now be a thin veil of very fine high altitude particulates that effectively act as a block to UV radiation. The sunsets will be incredibly beautiful.
Twenty days after the nuclear exchange climatic effects would have peaked. By this time, areas alongside seas, oceans and other large bodies of water would have effectively returned to their pre-exchange temperature sets. High-altitude areas woudl actually be warmer than before the exchange, sometimes dramatically so. At an altitude of 40,000 feet, the air termperature would be no less than 70 degrees F higher than normal (!!!) Surface temperatures far inland will drop by around 20 degrees F but this is a transient phenomena. The critical thing is light level; although the veil of fine high-altitude dust doesn't have a critical temperature effect, it cuts light levels by around 25 percent, ensuring that crops fail.
Within three months, temperature effects are virtually over. Worldwide, peak temperatures will have been reduced by, at most, 2 degrees F while trough will be increased by the same amount. This will shorten crop growing seasons a bit but since the crops are failing anyway it won't make much difference. This temperature change will persist for two or three years. by which time the atmosphere will have been purged of dust and smoke.
The best way to describe the real climate change would be that a state of "nuclear autumn" would become widespread. In other words both the high and low ends of the temperature spectrum would be shaved so that things tend to the "median" situation.
