Dr. David Denkenberger received his B.S. from Penn State in Engineering Science, his masters from Princeton in Mechanical and Aerospace Engineering, and his Ph.D. from the University of Colorado at Boulder in the Building Systems Program. His dissertation was on his patented expanded microchannel heat exchanger. He is an assistant professor at University of Alaska Fairbanks in joint in mechanical engineering and Alaska Center for Energy and Power. He co-founded and directs the Alliance to Feed the Earth in Disasters ( and donates half his income to it. He received the National Merit Scholarship, the Barry Goldwater Scholarship, the National Science Foundation Graduate Research Fellowship, is a Penn State distinguished alumnus, and is a registered professional engineer. He has authored or co-authored 104 publications (>2000 citations, >50,000 downloads, h-index = 23, third most prolific author in the existential/global catastrophic risk field (, including the book Feeding Everyone no Matter What: Managing Food Security after Global Catastrophe. His food work has been featured in over 25 countries, over 200 articles, including Science, Vox, Business Insider, Wikipedia, Deutchlandfunk (German Public Radio online), Discovery Channel Online News, Gizmodo,, and Science Daily. He has given interviews on 80,000 Hours podcast and Estonian Public Radio, WGBH Radio, Boston, and WCAI Radio on Cape Cod, USA. He has given over 80 external presentations, including ones on food at Harvard University, MIT, Princeton University, University of Cambridge, University of Oxford, Cornell University, University of California Los Angeles, Lawrence Berkeley National Lab, Sandia National Labs, Los Alamos National Lab, Imperial College, and University College London.


International Cooperation Against Existential Risks: Insights from International Relations Theory

I agree that IR is important for EA. I would be particularly interested to hear your opinion on collapse of civilization scenarios here.

EA and the Possible Decline of the US: Very Rough Thoughts

I was surprised you did not mention nuclear war as a cause of the decline of the US. If you take Luisa Rodriguez's average estimate of US-Russia nuclear war, 0.38% per year, that's about 20% chance in 50 years. And that does not take into account possible US-China nuclear war. I think even if nuclear winter did not happen, just the war would cause a significant decline in the US. So would that meet your definition?

Is Earth Running Out of Resources?

More concerning than jet engines might be the high efficiency natural gas turbines for generating electricity. However, it looks like Ruthenium is even better than Rhenium for these applications. And in general, you can avoid rare earth metals and just accept slightly lower performance for combustion turbines, wind turbines, electric car motors, LED lights, solar cells, etc.

Everyday Longtermism

I believe the framing in the 80,000 Hours podcast was something like when we run out of targeted things to do. But if we include global warming, depending on your temperature increase limit, we could easily spend $1 trillion per year. If people in developed countries make around $30,000 a year and they donate 10% of that, that would require about 300 million people. And of course there are many other global catastrophic risks. So I think it's going to be a long time before we run out of targeted things to do. But it could be good to do some combination of everyday longtermism and targeted interventions.

What is the likelihood that civilizational collapse would directly lead to human extinction (within decades)?

I was glad to see some discussion of potential irrational behavior. As was mentioned recently on the EA forum, I think there is a tendency for rational people to assume that other people will behave more rationally than they actually will. I think we have seen a lot of irrationality in the handling of COVID. And I think it would be far worse in the case of larger catastrophes. I think I remember reading that if something like half or three quarters of one's close family and friends died, there was a high chance of one becoming schizophrenic.

I think the fact that so many thoughtful people think collapse of civilization is likely from slow climate change (e.g. 50/50 chance for 4°C temperature rise according to Mark Lynas in his 80,000 Hours podcast), which is far less extreme than 50% of people dying, should give us pause. I tend to be more optimistic, but I do recognize the possibility that stressors could be handled poorly.

Big List of Cause Candidates

Great list! It reminds me of Peter McClusky's "Future of Earning to Give" post showing that there is plenty of room for more funding of high impact projects.

What is the likelihood that civilizational collapse would directly lead to human extinction (within decades)?

Here, food stocks is defined in the source paper as a group of “92 products” used “to reconstruct 50 years of aggregated food reserves, expressed in caloric equivalent (kcal), at the regional and global scales.” (Laio et al. 2016)

This is a great reference in that it does more than just look at stocks of grain. It does it for the end of each year, which is a pretty favorable case. The stocks of food would be considerably less right before harvest in the northern hemisphere, I would estimate ~3 months of food instead of 6. Also, their number is assuming 2880 kcal per day per person, which is appropriate to account for waste, but would not account for edible food fed to animals. But I agree with your rationing vegan number of approximately seven months if the catastrophe happened at the end of the year (but about half that for the worst timing scenario).

What is the likelihood that civilizational collapse would directly lead to human extinction (within decades)?

I am also excited to see work on such an important, neglected topic.

While I haven’t looked into this much, I feel fairly convinced that hundreds of thousands or millions of people could survive using traditional approaches to agriculture in parts of the world with more moderate climate effects (and basic mitigation strategies, like switching to crop types that are more resilient to temperature and precipitation fluctuations).

ALLFED has indeed found a number of cool tolerant crops that could likely grow in nuclear winter conditions in the tropics. However, they are generally planted far away from the tropics, so if there were not long distance cooperation, the situation would be bad. Even without long distance cooperation, artifacts have moved thousands of kilometers, but I think it takes thousands of years. One possibility would be relocating crops from nearby mountains, but that would only work in specific circumstances.

On the other hand, there could be long distance movement of people, perhaps with remaining above ground fossil fuel and current ships. But then places where agriculture is easier in nuclear winter such as Oceania could be overwhelmed with migrants.

The carrying capacity of the Earth for hunter-gatherers is thought to be around 10 million if the survivors regress to pre-paleolithic levels of technology (if they lose, for example, flakes, handaxes, controlled use of fire, and wooden spears) (Taiz, 2013). 

It appears that this is not the correct reference for that quote. Taiz says that the global population was 10 million in 8,000 BC and another one of your references said that by then the hunter gatherers had covered the globe and had 10 million population (some say only 1 million) and they would generally have had those pre-paleolithic technologies. Ellis says 100 million hunter gatherers would be possible with prehistoric technology, which is much higher than the actual population in 8,000 BC (though it would be consistent with your statement).

Several experts, including ALLFED director David Denkenberger, have affirmed this conclusion — they do not expect humanity to dip below the minimum viable population even in relatively extreme sun-blocking scenarios.

To be clear, I don’t expect it, but I think extinction is a non-negligible probability.

Before getting into the likelihood that society would recover from civilizational collapse under these starting conditions, I’ll briefly discuss whether we should expect human civilization to actually collapse in my sense in this scenario.

Doesn’t appear to be public?

What is the likelihood that civilizational collapse would directly lead to human extinction (within decades)?

Regarding case 1, with a pandemic leaving 50% of the population dead but no major infrastructure damage, I think you can make much stronger claims about there not being 'civilization collapse' meaning near-total failure of industrial food, water, and power systems. Indeed, collapse so defined from that stimulus seems nonsensical to me for rich quantitative reasons.


If there were a pandemic heading toward 50% population fatality, I think that it is likely that workers would not show up to critical industries and there would be a collapse of industrial civilization. I looked into whether the military could replace those workers, and it did not look feasible. Whether there would be further collapse of large-scale cooperation is less certain. If that cooperation is maintained, I agree it would be possible to have agricultural productivity similar to preindustrial Europe. However, it would mean a very rapid scale up of hand/animal farming equipment, and hand powered wells, carts that could be drawn by animals, etc (which ALLFED is planning on investigating). Some people say that modern crop varieties would actually do worse than traditional crop varieties if there were no artificial fertilizers and pesticides. If that were true or if scaling of tools were difficult, then we could have much worse agricultural productivity than preindustrial Europe.

Loss of rapid communication would likely imply fragmentation of large countries, if it is true that empires can only be maintained with I think a ~14 day communication radius (I thought the reference was here, but maybe it was something cited there). Furthermore, it is possible that cooperation outside of 100% groups is lost, particularly because of fear of the disease. In this case, I think it is likely with current preparation to only be able to do hunting and gathering. In addition, the hunting and gathering population density could be much less than historic, because the overshoot in population density could mean that plants and animals that are good to eat could be driven to extinction by desperate humans. 

Though it is possible that current food storage could be protected well, it is not clear to me that there would be a strong defense advantage. The desperate attackers would have weapons as well. If we go significantly above the carrying capacity and food is distributed fairly equally, then everyone would starve.

Books / book reviews on nuclear risk, WMDs, great power war?
  • Feeding Everyone No Matter What
    • I believe this is mostly focused on interventions to mitigate how bad nuclear winter would be, if it happened.

Yes, there is more detail on the nuclear risk in this paper. And this paper on a fault tree model of the chance of nuclear war.

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