I've seen a few commentors and bloggers cite this study from Nature Food to explain why they think nuclear war may lead to the collapse of civilization in event of a full nuclear exchange between the US and Russia. I read it and updated towards Nature Food being a publication with bad terrible editorial standards more than anything else.
The Apocalypse is Bad at Math
Wow, 5 Billion people dead. That's pretty bad. It actually projects 99% population reduction in China, the US, and Russia due to a 90% reduction in global farm yields. But let's break down those numbers. Firstly, how did they even get those crop yield numbers? Well, it turns out they assumed a 10 degrees C decrease in temperatures in the northern hemisphere, and then assumed no change in the crop selection and area under cultivation.
This isn't just bad statistics. It's intentionally misleading. Of course, if temperatures drop 10 degrees and people do literally nothing in response crop yields will decrease massively. But that's not how human beings work. They will increase land under cultivation in the tropics, clear-cut the Amazon, and do whatever it takes to get food production going again. Obviously, they will switch to more cold-resistant crops rather than lose 100% of their harvest to frost. These assumptions are terrible. Garbage in, garbage out.
This is a bad paper. Other scientists in the field know it's a bad paper, which is why almost no one has cited it. It's a scaremongering piece designed to push a denuclearization agenda and is used as clickbait by journalists. Its bad assumptions make it basically useless. Please don't take any apocalyptic nuclear starvation scenarios based on it seriously. I am utterly astounded that a journal like Nature let this one through. I will definitely try to publish in Nature Food in the future.
I don't know that we would have the political will to clearcut the Amazon and switch out our crop supply, even in the face of >70% death by starvation. Political polarization is very high right now. When either side proposes anything, the other will oppose it, even if it's saving humanity.
You might rightly say "but starvation is a powerful motivator!" and it is, but the people doing the starving won't be the people who could move the crops - the farmers and the world's lumber industry, who would be foiled by politics at every turn. The starving people will be too hungry to really do anything.
So maybe not 5 billion dead, but I wouldn't be surprised at about 3 billion.
Upvoted because this is a good comment, but strong disagree with the underlying premise. Actual global nuclear war would render existing partisan divides irrelevant almost instantly; typical partisan culture-war divides would be readily ignored in favor of staying alive.
I could imagine more relevant international divides of this type, such as wealthier and militarily powerful first-world nations hoarding their own resources at the expense of poorer nations, but I don't think that partisanship within single nations would overwhelm the survival instinct.
In your subsequent post, "Actually, All Nuclear Famine Papers are Bunk", you talk about the impressive, year-plus grain stores that farmers rack up each fall. How much does this vary throughout the year? Presumably a nuclear war that struck at the worst possible time (perhaps that May 1 that the Nature paper strategically chose?) would leave us with much reduced food stores.
The Nature paper seems to imply that protein would be the toughest thing to scrounge up in a nuclear winter scenario, rather than raw calories. This is probably less storable than other macronutrients like carbohydrates and fat?
I totally agree that it's ridiculous to think that people would just plant the same foods over again despite the obviously colder weather. On the other hand, in a post-nuclear-exchange scenario, I would be worried that farmers might not be able to access the normal distribution networks for purchasing new seeds, or that it would be more difficult to repair / replace crucial planting equipment, or that farmers (especially in the third world) wouldn't have the information/education/experience needed to switch crop varieties successfully. I'd love to read a paper or blog post where someone tried to game out how the negative effects of the war (on equipment, trade networks, etc) and positive effects (of adaptation to colder temperatures by planting different crops) would change the Nature paper's conclusion, either for worse or better.
These sorts of assumptions are the default in the climate change literature. Few agricultural impacts studies account for crop migration or for the prospect that we might introduce new cultivars. I imagine the authors are following the lead of the climate literature there, though it obviously massively overstates the impact of cooling or warming
I also think this highlights a wider problem with the nuclear winter literature. The scholars in the field are very obviously biased. Robock and his collaborators write almost all of the papers but clearly have an agenda. Just take a look at Alan Robock's website - flashing nuclear bomb gifs and pictures with Fidel Castro.
I followed Robock's work in solar geoengineering and it was also clearly biased. He claimed that solar geoengineering would knock out the monsoons, but his paper actually showed that solar geo would reduce disruption to the monsoon. Researchers in the field expressed frustration about Robock's meme, which he spread because he doesn't like solar geo.
If you look at the nuclear winter literature in the 1980s, all of the scientists say "this is bullshit". The only thing that changed with the second round of nuclear winter papers starting with Robock was that he used modern climate models. But the criticism was never about the climate model, it was about how much particulate matter would get into the atmosphere and how long it would stay there. So, the idea that modern science validated nuclear winter is just wrong.
A very prominent climate physicist told me that the assumptions in the Robock papers are turned up to maximise damage rather than to actually be plausible, and that people are scared to point this out because of the politicised nature of the debate on nuclear war
The smoke estimates in the Robock papers didn't change despite a massive decline in the nuclear arsenal.