Carl Sagan’s predictions were really dire. Here’s a three paragraph TLDR of his specific predictions from his 1983 article that brought "Nuclear Winter" into the vocabulary:
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“Our baseline case, as in many other studies, was a 5000-megaton war with only a modest fraction of the yield (20 percent) expended on urban or industrial targets… In the baseline case, the amount of sunlight at the ground was reduced to… too dark for plants to make a living from photosynthesis.
“Land temperatures, except for narrow strips of coastline, dropped to minus 25 Celsius (minus 13 degrees Fahrenheit) and stayed below freezing for months -- even for a summer war... virtually all crops and farm animals, at least in the Northern Hemisphere, would be destroyed, as would most varieties of uncultivated or domesticated food supplies. Most of the human survivors would starve.
“But what if nuclear wars can be contained, and much less than 5000 megatons is detonated? Perhaps the greatest surprise in our work was that even small nuclear wars can have devastating climatic effects. We considered a war in which a mere 100 megatons were exploded, less than one percent of the world arsenals, and only in low-yield airbursts over cities. This scenario, we found, would ignite thousands of fires, and the smoke from these fires alone would be enough to generate an epoch of cold and dark almost as severe as in the 5000 megaton case. The threshold for what Richard Turco has called The Nuclear Winter is very low.
—
I think the reason the Carl Sagan was widely panned afterwords is that the science was just plain bad. The scale of the predictions he made were so off the charts from almost forty years of previous nuclear experience, that he was obviously was wrong. He predicted essentially the end of the humanity from a mere 100 megatons of nuclear explosions, and yet twenty years before article, the Soviet Union had tested a 50 megaton bomb with no more than the usual local effects.
Using bad science to advance a public policy goal is exactly what got us to the current "distrust of science"
To be clear, the claim was not that 100 megatons themselves would cause climate change, but that 100 firestorms in cities would, and that a 1 Mt bomb would be enough to cause a firestorm (there was one in Hiroshima).
It's not completely clear to me just how bad the science was; like the article says there is still a debate today, so it's not completely settled even now. Wikipedia has a lot of discussion.
My problem with these predictions is that volcanic eruptions at these energy scales and with plenty of ash output occur with some frequency, and the effects are still not human extinction.
5,000 megatons would be enough to destroy every major and semi-major city on the planet, literally.
There are 4,416 cities on the planet with 150k+ population. 10 100kt bombs are more than enough to destroy most cities on the planet, at least when you define "destroy" as "most everything is broken and/or on fire and most people are dead within 1 year's time".
After your 10-nukes-per-city campaign, you've still got another 5,840 100kt bombs left in your 5,000 megaton budget to divide among the largest cities (NYC, Tokyo, Hong Kong, Tehran, etc.).
I'm stating this because I don't think it's too useful to predict the secondary effects (nuclear winter, etc.) of a war so terrible that basically everyone on the planet would already be dead (from blast, fire, etc.) or dying within a year's time (radiation, starvation from infrastructure collapse, etc.).
I'm certainly not saying nuclear war wouldn't be awful - it would be!
But in judging Carl Sagan's claims, we look at what he actually wrote to the public, and it's the specific climate claims that Carl Sagan made that appear to be wildly incorrect.
The people not near the cities targeted wouldn't die from environmental results. That's the point. They might die from serious economic disruption if they can't get access to food. But there would be people who would survive it. There's quite a lot of land in flyover states and what not. A lot of that is farmland.
I'm guessing that's less than 0.01% of the actual land area. Anyway, there's mountains, forests, arctic wilderness, islands, etc. where some people live in various concentrations. Human civilization would take a massive blow from an all-out nuclear war, but human beings wouldn't go extinct, and some elements of civilization would remain. It's not like all technological capability or knowledge would be lost.
The interdependency of technology between cities, states and nation-states shouldn't be underestimated. How many books are available today that can describe how to make a semiconductor? Will these books survive? How about the process to create pure silicon? Or the lithography necessary to create CPUs? And with multiple nuclear detonations, the likelihood of EMP effects is high; this will cripple civilization as much as any explosions or fallout.
Sure, technology can survive; witness the gunsmiths in the Hindu Kush who can recreate a functioning Enfield rifle (or ak-47) from scrap metal. But the world would be set back at least 100 years or more, and much knowledge would be lost because of poor archiving, poor dissemination, and the death of experts who are invaluable.
Sure, I would almost certainly be dead, but life on Earth would continue, our species would continue, and our civilisation would continue (albeit with some major setbacks).
Besides, I don't think anyone's nuclear war plan is actually to destroy every major to semi-major city on Earth. In a realistic 1980s nuclear war, a lot of nukes would be targeted at military bases and the like. Plenty of others would destroy every major city in the US and USSR, plus each country's nuclear-armed allies. Maybe we here in Australia would get a nuke or two out of spite. But is anyone going to bother to nuke South America?
> In a realistic 1980s nuclear war, a lot of nukes would be targeted at military bases and the like
i think it's mentioned in Command and Control (book) but if I recall correctly the plan from the US perspective was not only to nuke military targets, but also all major population centers, with several thermonuclear bombs for each target, for good measure. And that was not only the USSR, but basically every ally of the USSR as well.
You can imagine that the other side was also going to do about the same thing.
Sure, some countries may have been relatively spared, but all in all the whole of Europe, US, Russia, China, would have been annihilated.
> ... is anyone going to bother to nuke South America?
Yes.
There is this tendency to assume that, because you're ("you're" in the general sense) not thinking about a place, then that place necessarily isn't important from a geopolitical point of view.
Not taking into account the geopolitical value of maintaining military bases on the US's southern flanks, it's worth noting that Brazil is the 12th largest oil producer, among its many other important economic attributes. Argentina is one of the go-to places for China to buy farm land[1]. Take those two and you're left with basically 10% of South America.
The contention was yes: cities are built primarily of loose-frame wood structures that burn easily with rapidly-spreading fires (unlike forests, which are much harder to light and sustain). So the idea is that one bomb causes the inner city and all the urban expanse surrounding it to burn within a few hours as a "firestorm" that would lift the soot into the stratosphere.
Now, that's been debunked apparently. But the hypothesis as stated is sound enough. It's not the blast itself, it's the fire.
I believe the idea is that if you explode an H-bomb over a large city an awful lot of stuff is going to catch fire resulting in huge firestorms that would (along with the effects of the explosions themselves) raise a lot of stuff into the atmosphere.
Of course, thankfully, we don't really know what would happen when a large city receives a realistic attack from multiple H-bombs.
Except we know what happens when major cities are fire bombed from World War II, and we know the effects of the much worse 1991 Kuwait oil fires which caused no such effects.
I think it's not quite so easy. There were many cities bombed in World War II (maybe 60 in Japan and additional ones in Germany), but there were only 5 or 6 firestorms. Similarly, the Kuwait oil fires created a lot of soot, but the plume is isolated to a given point, which causes it to disperse before reaching the stratosphere.
The claim is that firestorms in particular would create climate change, because a single city-sized plume could carry the soot much higher than if the city burned and released the same amount of soot in an ordinary fire.
700 oil wells along with several lakes of oil burned for months in 1991. Many of the same people who projected 'nuclear winter', advanced the same environmental winter projections for the hypothetical fires before the conflict.
I don't think we had either climate models or remote sensing capabilities during World War II adequate to assess what climate effects may have resulted from the several firestorms that occurred. The 1991 Kuwait oil fires were apparently projected by some to cause a "petroleum winter", but these models were disputed and many simulations apparently suggested that the particles would not reach the stratosphere (and evidently they did not)[0]. However, it seems that since 1998[1] it has been known that smoke from naturally occurring firestorms (resulting from wildfires) can reach the stratosphere and cause regional climate effects significant enough to alter hemispheric temperature patterns.
Except Carl Sagan himself was one of the scientists advancing the "petroleum winter effect" in 1991 in the lead up to the gulf conflict, just as he advanced his nuclear winter scenario earlier.
If your point is that Carl Sagan may not be the foremost authority on nuclear winter, I think it's already been made (though, that is an interesting catch). I have no ability to speak on that subject, I was merely pointing out that I find it misleading to suggest that firestorms have been shown not to cause climate effects when the opposite is also true in some instances.
I think celebrity scientists propounding disaster scenarios that have actual poor scientific backing, is one of the reasons why there is still so much skepticism about global warming. It is kind of like the story of the "boy that cried wolf". Scientists have been warning about impending doom so many times in the past, and in general things have never been better for humans on a global scale now. People learned to disregard dire predictions. Now, when there is a real danger, people are skeptical.
What are these "so many times" that scientists have incorrectly been warning about impending doom?
Nuclear winter might qualify, but given that it's merely the difference between "everyone dies" and "humanity survives, but civilization is wrecked and we really must ensure that this never happens," it doesn't seem huge.
Ehrlich and the whole overpopulation predictions, DDT would wipe out songbirds, the prediction we would run out of oil, a new ice age, ozone hole, the whole concept of the doomsday clock, and now the whole AI will wipe out humanity fear.
Part of this blame falls on the media. It amplifies the "gloom and doom" voices because that is what sells.
How common was Ehrlich's prediction? A doomsday scenario proposed by one guy, no matter how popular his book is, doesn't seem like it should count.
The problems with DDT and the ozone hole were averted because people took action in response to them, not because the warnings were incorrect.
The "new ice age" thing was never a mainstream prediction. The idea that scientists were warning about global cooling in the 70s is a myth.
Peak oil and the doomsday clock are both absolutely correct, they just haven't happened yet. Oil reserves are finite on human timescales, and global thermonuclear war would devastate human civilization and the chance of it happening is still disturbingly large.
AI is too early to say, but already pegging it as an incorrect warning now, when nothing even close to human-level AI exists, seems a bit premature. (One could also argue that the warning is premature, but that's different from being wrong.)
The key word in the quoted text is "scientists." The media hype was real. Unlike the current climate change hype, it wasn't based on scientific consensus.
In the context of the 70's, everything was a disaster or crisis waiting to happen. From movies that made you worry about earthquakes, burning skyscrapers, killer bees, to books Ehrlich's book, Rachel Carson's overhyped "Silent Spring" and magazines like Newsweek that touted a coming ice age. If that wasn't enough, the overwhelming sense of fear of a war with the USSR, or running out of oil due to an OPEC embargo was a real thing.
> magazines like Newsweek that touted a coming ice age
Please be a little more careful there: you are very close to shifting goalposts from "bad science" to "bad journalism"— those two are very separate things yet you don't bother to make a clear distinction.
I'm not shifting goalposts in anyway. The zeitgeist at the time was very much centered on the crisis du jour. This was in a wide array of media sources.
The ozone hole was absolutely real. We took action and fixed it. We are running low on cheaply extractable oil, but we're making progress towards replacing it with renewable sources. This is not fearmongering, this is responding to the evidence and taking action.
And the Doomsday Clock is a strange example of a false prediction, since it doesn't actually make strong predictions, just estimates the level of nuclear tension at any given time. You can hardly argue that we haven't been close to nuclear war several times in the past 50 years.
The "Spanish" flu epidemic of 1918 resulted in the deaths of 50 to 100 million. The fact that we haven't had a similar epidemic since is in large part due to the work of groups like WHO and CDC. But this preventive work is not unlike IT departments making backups -- nobody thinks it is that important until the system fails.
thaTs a pretty impressive claim to make in a pre antibiotics and pre modern medecine world when tuberculosis and rabbies were still killing a lot of people every year. we did not wait for the WHO to have better standards.
It reminds me of Bill Nye, an ME who is presented as a scientist, but isn't much more a scientist than an amateur scientist.
He's good for kids, but not someone adults should look to for science, given it's scriptwriters and producers putting forth the "science" with him as frontman.
—
“Our baseline case, as in many other studies, was a 5000-megaton war with only a modest fraction of the yield (20 percent) expended on urban or industrial targets… In the baseline case, the amount of sunlight at the ground was reduced to… too dark for plants to make a living from photosynthesis.
“Land temperatures, except for narrow strips of coastline, dropped to minus 25 Celsius (minus 13 degrees Fahrenheit) and stayed below freezing for months -- even for a summer war... virtually all crops and farm animals, at least in the Northern Hemisphere, would be destroyed, as would most varieties of uncultivated or domesticated food supplies. Most of the human survivors would starve.
“But what if nuclear wars can be contained, and much less than 5000 megatons is detonated? Perhaps the greatest surprise in our work was that even small nuclear wars can have devastating climatic effects. We considered a war in which a mere 100 megatons were exploded, less than one percent of the world arsenals, and only in low-yield airbursts over cities. This scenario, we found, would ignite thousands of fires, and the smoke from these fires alone would be enough to generate an epoch of cold and dark almost as severe as in the 5000 megaton case. The threshold for what Richard Turco has called The Nuclear Winter is very low.
—
I think the reason the Carl Sagan was widely panned afterwords is that the science was just plain bad. The scale of the predictions he made were so off the charts from almost forty years of previous nuclear experience, that he was obviously was wrong. He predicted essentially the end of the humanity from a mere 100 megatons of nuclear explosions, and yet twenty years before article, the Soviet Union had tested a 50 megaton bomb with no more than the usual local effects.
Using bad science to advance a public policy goal is exactly what got us to the current "distrust of science"