What to eat during impact winter?

A number of possible global catastrophic risks seem like they would do their worst damage by disrupting food production. Some examples include nuclear winter, asteroid impacts, and supervolcanoes. In addition to directly laying waste to significant areas, such events would cast ash, dust, or other materials into the atmosphere. Temperatures would fall and solar radiation for primary producers would be reduced, causing agricultural failures and wreaking havoc on wilderness ecologies. It seems clear that feasible events of this sort could cost hundreds of millions or even billions of lives. But would even extreme events actually bring about would they cause human extinction or constitute an existential risk?

There are several sources of evidence we can bring to bear on the question. We can apply the "outside view" and consider the species, including hominids and primates, that have survived past volcanic and asteroid impacts. We can examine current supplies of food sources that could provide for humans during a period of impaired solar radiation. And we can look at past and present social behavior that bears on the distribution of food and recovery from period of severe famine. In the aggregate, it seems to me that humanity would survive one of these severe food disruptions, despite terrible quantities of death and misery.

This post will take a first-pass look at existing food sources that could be drawn upon during a "year without the Sun," or something close to it.

Economic growth: more costly disasters, better prevention

If you read lists of the most costly earthquakes, hurricanes, and other natural disasters, you will find that they they tend to be quite recent, with damages increasing over time. But earthquake costs have not been rising because of some geological phenomenon, i.e. earthquakes getting more frequent or higher on the Richter scale. Rather, populations and economies have been growing, so that there are more valuable things for earthquakes to destroy. This dynamic offers a powerful defense against global catastrophic risks that can be addressed by interventions with particular fixed or falling costs.

Philosophers vs economists on discounting

Temporal discounting is not about time
Economists doing cost-benefit analysis normally make use of temporal discounting, i.e. benefits further in the future count for less than those nearer to the present. In part this is done to reflect the availability of positive investment returns, but normally analysis also include an additional element of pure temporal preference.

Say that I set up a sealed habitat for some plants and cute bunny rabbits. The rabbits are placed in suspended animation, and the habitat is rocketed out of the Solar System by an automated spacecraft which will never return to interact with our world again. At a predesignated time, the rabbits will be revived and go on to live happy lives in the sealed habitat for a time and then die. With significant pure temporal preference this spacecraft is much more valuable if it is set to revive the isolated rabbits after 5 years rather than 50.

Indeed, economists typically make use of constant exponential discounting, e.g. reducing the valuation of benefits by 3% per year. At a 3% annual discount rate the value of future benefits will be cut by more than half every 23 years. After 230 years a good would be valued at less than a thousandth of an immediate counterpart.   But to most people the change in activation time does not make such an overwhelming difference. Further, constant exponential discounting makes strong distinctions between different far-future periods: benefits received in 1 million years are still more than a thousand times as valuable as benefits received in 1,000,230 years.

But real humans mostly don't care about such distinctions. A difference of a few centuries added onto a  million years is a negligible change in time: in either case they lie far beyond the current era and the proportional change is small. Favoring the earlier time for a thousandfold reduction in the goods achieved seems absurd in that context. Humans may be impatient within our own lives, care more about our children than distant descendants, and so forth, but the constant exponential discounting framework just doesn't make sense of our attitudes towards the further future.

Because of cases like this philosophers tend to reject the idea of pure temporal preference for social cost-benefit analysis, e.g. with respect to climate change, and often critique economists for persisting in making use of it. But economists are not fools, and the reasons why so many continue to do so are worth thinking about.

Utilitarianism, contractualism, and self-sacrifice

[This post is a response to cousin_it's request for counterarguments to utilitarianism.]

Saving the drowning child is not a self-sacrifice
Suppose that you live in a developed country, and earn a high income even by developed country standards. One day you are walking home from a business meeting in your best suit, worth some $1,000, and see a small child drowning in a muddy (and foul-smelling) pond off the road. No one else is around, but you could save the child, at the cost of hopelessly ruining the suit. Most people intuit that in such a case one should save the child, despite the cost of a $1,000 suit.

The utilitarian philosophers Peter Singer has often argued that since we should make a financial sacrifice for the drowning child, we should do the same to save the lives of children in poor countries, e.g. by donating to the most cost-effective public health charities identified by GiveWell. Others would generalize to saving future generations, saying that if we can reduce existential risk and avert astronomical waste to in expectation save trillions of happy lives, then that is even better than saving one life today.

However, the drowning child case is problematic as a justification for self-sacrifice in other contexts: it probably doesn't involve any self-sacrifice at all, but rather an expected selfish gain.