comment by SimonBeard ·
2018-08-09T18:23:53.036Z · EA(p) · GW(p)
Thanks for prompting me on this. I was hoping to find time for a fuller reply to your but this will have to do, you only asked for the texture after all. My concerns are somewhat nebulous so please don't take this as any cast iron reason not to seek out estimates for the probability of different existential risks. However, I think they are important.
The first relates to the degree of uncertainty that surrounds any estimate of this kind and how it should be handled. There are actually several sources of this.
The first of these relates to the threshold for human extinction. We actually don't have very good models of how the human race might go extinct. Broadly speaking human beings are highly adaptable and we can of-course survive across an extremely wide range of habitats, at least with sufficient technology and planning. So roughly for human extinction to occur then a change must either be extremely profound (such as the destruction of the earth, our sun or the entire universe) very fast (such as a nuclear winter), something that can adapt to us (such as AGI or Aliens) or something that we chose not to adapt to (such as climate change). However, personally, I have a hard time even thinking about just what the limits of survivability might be. Now, it is relatively easy to cover this with a few simplifying assumptions. For instance that 10 degrees of climate change either-way would clearly represent an existential threat. However, these are only assumptions. Then there is the possibility that we will actually be more vulnerable to certain risks than it appears, for instance, that certain environmental changes might cause an irrevocable collapse in human civilization (or in the human microbiome if you are that way inclined. The Global Challenges Foundation used the concepts of 'infinite threshold' and 'infinite impact' to capture this kind of uncertainty, and I think they are useful concepts. However, they don't necaserilly speak to our concern to know about the probability of human extinction and x-risk, rather than that of potential x-risk triggers.
The other obvious source of uncertainty is the uncertainty about what will happen. This is more mundane in many ways, however when we are estimating the probability of an unprecedented event like this I think it is easy to understate the uncertainty inherent in such estimates, because there is simply so little data to contradict our main assumptions leading to overconfidence. The real issue with both of these however is not that uncertainty means that we should not put numerical values to the likelihood of anything, but that we are just incapable of dealing very well with numerical figures that are highly uncertain, especially where these are stated and debated in a public forum. Even if uncertainty ranges are presented, and they accurately reflect the degree of certainty the assessor can justifiably claim to have, they quickly get cut out with commentators preferring to focus on one simple figure, be it the mean, upper or lower bounds, to the exclusion of all else. This happens and we should not ignore the pitfalls it creates.
The second concern I have is about the context. In your post you mention the famous figure from the Stern review and this is a great example of what I mean. Stern came up with that figure for one reason, and one alone. He wanted to argue for the higher possible discount rate that he believed was ethically justified in order to give maximum credence to his conclusions (or if you are more cynical then perhaps 'he wanted to make it look like he was arguing for...'). However, he also thought that most economic arguments for discounting were not justified he was left with the conclusion that the only reason to prefer wellbeing today to wellbeing tomorrow was that there might be no tomorrow. His 0.1% chance of human extinction per year (Note that this is supposedly the 'background' rate by the way, it is definitely not the probability of a climate-induced extinction) was the highest figure he could propose that would not be taken as overly alarmest. If you think that sounds a bit off then reflect on the fact that the mortality rate in the UK at present is around 0.8%, so Stern was saying that one could expect more than 10% of human mortality in the near future to result from human extinction. I think that is not at all unreasonable, but I can see why he didn't want to put the background extinction risk any higher. Anyway, the key point here is that none of these considerations was really about producing any kind of estimate of the likelihood of human extinction, it was just a guess that he felt would be reasonably acceptable from the point of view of trying to push up the time discount rate a bit. However, of course, once it is out there it got used, and continues to get used, as if it was something quite different.
The third concern I have is that I think it can be at least somewhat problematic to break down exitential risks by threat, which people generally need to do if they are to assign probability estimates to them. To be fair, your are here interested in the probability of human extinction as a whole, which does not fact this particular problem. However many of the estimates that I have come across relate to specified threats. The issue here is that much of the damage from any particular threat comes from its systemic and cascading effects. For instance, when considering the existential threat from natural pandemics I am quite unconcerned that a naturally occurring (or even most man-made) pathogen might literally wipe out all of humanity, the selection pressures against that would be huge. I am somewhat more concerned that such a pandemic might cause a general breakdown in global order leading to massive global wars or the collapse of the global food supply. However, I am mostly concerned that a pandemic might cause a social collapse in a single state that possessed nuclear weapons leading to them becoming insecure. If I simply include this as the probability of either human extinction via pandemic or nuclear war then that seems to me to be misleading. However, if it got counted in both then this could lead to double counting later on. Of course, with great care and attention this sort of problem can be dealt with. However on the whole when people make assessments of the probability of existential risks they tend to pool together all the available information, much of which has been produced without any coordination making such double counting, or zero counting, not unlikely.
Please let me know if you would like me to try and write more about any of these issues (although to be honest I am currently quite stretched so this may have to wait a while). You may also be interested in a piece I Wrote with Peter Hurford and Catheryn Mercow (I won't lie, it was mostly they who wrote it) on how different EA organizations account for uncertainty which has had quite a bit of impact on my thinking http://effective-altruism.com/ea/193/how_do_ea_orgs_account_for_uncertainty_in_their/
Also if you haven't already seen it you might be interested in this piece by Eliezer Yudkowsky https://www.lesswrong.com/posts/AJ9dX59QXokZb35fk/when-not-to-use-probabilities [LW · GW]
PS: Obviously these concerns have not yet lead me to give up on working with these kinds of estimates, and indeed I would like them to be made better in the future. However they still trouble me.
comment by rhys_lindmark ·
2018-08-12T18:40:59.111Z · EA(p) · GW(p)
Perfect, thanks! I agree with most of your points (and just writing them here for my own understanding/others):
- Uncertainty hard (long time scale, humans adaptable, risks systemically interdependent so we get zero or double counting)
- Probabilities have incentives (e.g. Stern's discounting incentive)
- Probabilities get simplified (0-10% can turn into 5% or 0% or 10%)
I'll ping you as I get closer to a editable draft of my book, so we can ensure I'm painting an appropriate picture. Thanks again!