I obtained a probability of human extinction given insufficient calorie production of 10^-6 (= 1/10^6), considering 1 M years is the typical lifespan of a mammal species
This is a central input to your low estimate but it seems like a non-sequitur to me? 1 million years is the unconditional lifespan. The number you want is the lifespan conditional on insufficient calorie production, which is potentially a very different number.
Put another way, you could also reason that there is zero risk from nuclear war:
Humans are a mammal species, therefore the baseline probability of extinction is 1e-6.
Based on the reasoning in OP, the probability of extinction conditional on nuclear war is 1e-6.
These numbers are exactly the same.
Therefore, there is zero chance of extinction from nuclear war.
Thanks for the comment, Michael! I agree 1 M years refers to the unconditional lifespan of a mammal species. However, I think humans would only be in a situation similar to that of a random mammal species conditional on insufficient calorie production, which I defined as “less than 1.91 k kcal/person/d” in the worst year. From Fig. 5a of Xia et al. (2022), humans produced around 3.5 k kcal/person/d in 2010.
This is a central input to your low estimate but it seems like a non-sequitur to me? 1 million years is the unconditional lifespan. The number you want is the lifespan conditional on insufficient calorie production, which is potentially a very different number.
Put another way, you could also reason that there is zero risk from nuclear war:
Humans are a mammal species, therefore the baseline probability of extinction is 1e-6.
Based on the reasoning in OP, the probability of extinction conditional on nuclear war is 1e-6.
These numbers are exactly the same.
Therefore, there is zero chance of extinction from nuclear war.
Thanks for the comment, Michael! I agree 1 M years refers to the unconditional lifespan of a mammal species. However, I think humans would only be in a situation similar to that of a random mammal species conditional on insufficient calorie production, which I defined as “less than 1.91 k kcal/person/d” in the worst year. From Fig. 5a of Xia et al. (2022), humans produced around 3.5 k kcal/person/d in 2010.