Here is one attempt to compare apples to apples. According to the Metaculus’ community, the probability of global population decreasing by at least 95 % by 2100 is:
Due to nuclear war, 0.608 % (= 38 % * 32 % * 5 %). This is the product between:
38 % probability of population decreasing at least 10 %.
32 % probability of population decreasing at least 10 % due to nuclear war if population decreases at least 10 %.
5 % probability of population decreasing at least 95 % due to nuclear war if population decreases at least 10 % due to nuclear war.
Due to climate change, lower than 0.0228 % (= 38 % * 6 % * 1 %). I say lower because Metaculus’ probabilistic predictions have to be between 1 % and 99 %, which means 1 % can be anything from 0 to 1.5 %.
In agreement with these, I set the reduction in the value of the future for a median global warming in 2100 relative to 1880 of 2.4 ºC due to:
Climate change to a value 6.20 (= 2.28/0.365) times as high.
These resulted in an optimal median global warming in 2100 of 2.3 ºC[1], so Metaculus’ predictions suggest decreasing emissions is not much better/worse than neutral. This conclusion is not resilient, but is some evidence that comparing apples to apples does not lead to a median global warming in 2100 much different from the one we are heading towards.
It is unclear to me whether Metaculus’ community is overestimating/underestimating the risk of nuclear war relative to that of climate change. However, I think comparing the risk from climate change and nuclear war based on the probability of a reduction of at least 95 % of the global population will tend to underestimate the risk from nuclear war, because:
I believe the probability of a population loss greater than 95 % (e.g. 99.9 % or extinction) would be a better proxy for the reduction in the value of the future.
Metaculus’ community predictions suggest nuclear war is more likely relative to climate change for greater population loss. The probability of global population decreasing by 2100 by at least:
10 % due to nuclear war is 5.33 (= 32⁄6) times that due to climate change.
95 % due to nuclear war is 26.7 (= (32 * 5)/(6 * 1)) times that due to climate change.
Note this is likely an overestimate, since the 3rd factor I used to calculate the risk from climate change based on Metaculus’ predictions is artificially limited to 1 %.
This moves me somewhat, though I would still really love to see a serious examination of nuclear winter to get better estimates, getting to 5% of 95% population loss conditional on nuclear war seems really high esp given it does not seem to condition on great power war alone.
I say lower because Metaculus’ probabilistic predictions have to be between 1 % and 99 %, which means 1 % can be anything from 0 to 1.5 %.
I have recently noticed Metaculus allows for predictions as low as 0.1 %. I do not know when this was introduced, but, if long ago and forecasters are aware of it, 0.0228 % chance for a 95 % population loss due to climate change may not be an overestimate.
Thanks! In that case, 92.5 % (= 160⁄173) of the predictions for a population loss of 95 % due to climate change given a 10 % loss due to climate change were made with the 1 % lower limit. So I assume 0.0228 % chance for a 95 % population loss due to climate change is still an overestimate.
Here is one attempt to compare apples to apples. According to the Metaculus’ community, the probability of global population decreasing by at least 95 % by 2100 is:
Due to nuclear war, 0.608 % (= 38 % * 32 % * 5 %). This is the product between:
38 % probability of population decreasing at least 10 %.
32 % probability of population decreasing at least 10 % due to nuclear war if population decreases at least 10 %.
5 % probability of population decreasing at least 95 % due to nuclear war if population decreases at least 10 % due to nuclear war.
Due to climate change, lower than 0.0228 % (= 38 % * 6 % * 1 %). I say lower because Metaculus’ probabilistic predictions have to be between 1 % and 99 %, which means 1 % can be anything from 0 to 1.5 %.
In agreement with these, I set the reduction in the value of the future for a median global warming in 2100 relative to 1880 of 2.4 ºC due to:
ASRSs to a value 1.74 (60.8/34.9) times as high.
Climate change to a value 6.20 (= 2.28/0.365) times as high.
These resulted in an optimal median global warming in 2100 of 2.3 ºC[1], so Metaculus’ predictions suggest decreasing emissions is not much better/worse than neutral. This conclusion is not resilient, but is some evidence that comparing apples to apples does not lead to a median global warming in 2100 much different from the one we are heading towards.
It is unclear to me whether Metaculus’ community is overestimating/underestimating the risk of nuclear war relative to that of climate change. However, I think comparing the risk from climate change and nuclear war based on the probability of a reduction of at least 95 % of the global population will tend to underestimate the risk from nuclear war, because:
I believe the probability of a population loss greater than 95 % (e.g. 99.9 % or extinction) would be a better proxy for the reduction in the value of the future.
Metaculus’ community predictions suggest nuclear war is more likely relative to climate change for greater population loss. The probability of global population decreasing by 2100 by at least:
10 % due to nuclear war is 5.33 (= 32⁄6) times that due to climate change.
95 % due to nuclear war is 26.7 (= (32 * 5)/(6 * 1)) times that due to climate change.
Note this is likely an overestimate, since the 3rd factor I used to calculate the risk from climate change based on Metaculus’ predictions is artificially limited to 1 %.
Thanks for doing this (upvoted!).
This moves me somewhat, though I would still really love to see a serious examination of nuclear winter to get better estimates, getting to 5% of 95% population loss conditional on nuclear war seems really high esp given it does not seem to condition on great power war alone.
Agreed!
I have clarified above the 5 % is conditional on a nuclear war causing a population loss of at least 10 % (not just a nuclear war).
Thanks, this makes a lot of sense then!
I have recently noticed Metaculus allows for predictions as low as 0.1 %. I do not know when this was introduced, but, if long ago and forecasters are aware of it, 0.0228 % chance for a 95 % population loss due to climate change may not be an overestimate.
It was less than 1 year ago, I would guess around 6 months ago.
Thanks! In that case, 92.5 % (= 160⁄173) of the predictions for a population loss of 95 % due to climate change given a 10 % loss due to climate change were made with the 1 % lower limit. So I assume 0.0228 % chance for a 95 % population loss due to climate change is still an overestimate.