The person-affecting value of existential risk reduction


The standard motivation for the far future cause area in general, and existential risk reduction in particular, is to point to the vast future that is possible providing we do not go extinct (see Astronomical Waste). One crucial assumption made is a ‘total’ or ‘no-difference’ view of population ethics: in sketch, it is just as good to bring a person into existence with a happy life for 50 years as it is to add fifty years of happy life to someone who already exists. Thus the 10lots of potential people give profound moral weight to the cause of x-risk reduction.

Population ethics is infamously recondite, and so disagreement with this assumption commonplace; many find at least some form of person affecting/asymmetrical view plausible: that the value of ‘making happy people’ is either zero, or at least much lower than the value of making people happy. Such a view would remove a lot of the upside of x-risk reduction, as most of its value (by the lights of the total view) is ensuring a great host of happy potential people exist.

Yet even if we discount the (forgive me) person-effecting benefit, extinction would still entail vast person-affecting harm. There are 7.6 billion people alive today, and 7.6 billion premature deaths would be deemed a considerable harm by most. Even fairly small (albeit non-pascalian) reductions in the likelihood of extinction could prove highly cost-effective.

To my knowledge, no one has ‘crunched the numbers’ on the expected value of x-risk reduction by the lights of person affecting views. So I’ve thrown together a guestimate as a first-pass estimate.

An estimate

The (forward) model goes like this:

  1. There are currently 7.6 billion people alive on earth. The worldwide mean age is 38, and worldwide life expectancy is 70.5.
  2. Thus, very naively, if ‘everyone died tomorrow’, the average number of life years lost per person is 32.5, and the total loss is 247 Billion life years.
  3. Assume the extinction risk is 1% over this century, uniform by year (i.e. the risk this year is 0.0001, ditto the next one, and so on.)
  4. Also assume the tractability of x-risk reduction is something like (borrowing from Millett and Snyder-Beattie) this: ‘There’s a project X that is expected to cost 1 billion dollars each year, and would reduce the risk (proportionately) by 1% (i.e. if we spent a billion each year this century, xrisk over this century declines from 1% to 0.99%).
  5. This gives a risk-reduction per year of around 1.3 * 10-6 , and so an expected value of around 330 000 years of life saved.

Given all these things, the model spits out a mean ‘cost per life year’ of $1500-$26000 (mean $9200).

Caveats and elaborations

The limitations of this are nigh-innumerable, but I list a few of the most important below an approximately ascending order.

Zeroth: The model has a wide range of uncertainty, and reasonable sensitivity to distributional assumptions: you can modulate mean estimate and range by a factor of 2 or so by whether the distributions used are Beta, log normal, or tweaking their variance.

First: Adjustment to give ‘cost per DALY/QALY’ would be somewhat downward, although not dramatically (a factor of 2 would imply everyone who continues to live does so with a disability weight of 0.5, in the same ballpark as those used for major depression or blindness).

Second, trends may have a large impact, although their importance is modulated by which person-affecting view is assumed. I deliberately set up the estimate to work in a ‘one shot’ single year case (i.e. the figure applies to a ‘spend 1B to reduce extinction risk in 2018 from 0.0001 to 0.000099’ scenario).

By the lights of a person-affecting view which considers only people who exist now, making the same investment 10 years from now (i.e. spent 1B to reduce extinction risk in 2028 from 0.0001 to 0.000099) is less attractive, as some of these people would have died, and the new people who have replaced them have little moral relevance. These views thus imply a fairly short time horizon, and are particularly sensitive to x-risk in the near future. Given the ‘1%’ per century is probably not uniform by year, and plausibly lower now but higher later, this would imply a further penalty to cost-effectiveness.

Other person affecting views consider people who will necessarily exist (however cashed out) rather than whether they happen to exist now (planting a bomb with a timer of 1000 years is still accrues person-affecting harm). In a ‘extinction in 100 years’ scenario, this view would still count the harm of everyone alive then who dies, although still discount the foregone benefit of people who ‘could have been’ subsequently in the moral calculus.

Thus the trends in factual basis become more salient. One example is the ongoing demographic transition, and the consequently older population give smaller values of life-years saved if protected from extinction in the future. This would probably make the expected cost-effectiveness somewhat (but not dramatically) worse.

A lot turns on the estimate for marginal ‘x-risk reduction’. I think the numbers offered in terms of base rate, and how much it can be reduced for now much lean on the conservative side of the consensus of far-future EAs. Confidence in (implied) scale or tractability an order of magnitude ‘worse’ impose commensurate increases on the risk estimate. Yet in such circumstances the bulk of disagreement is explained by empirical disagreement rather than a different take on the population ethics.

Finally, this only accounts for something like the (welfare) ‘face value’ of existential risk reduction. There would be some further benefits by the light of the person-affecting view itself, or ethical views which those holding a person affecting view are likely sympathetic to: extinction might impose other harms beyond years of life lost; there could be person affecting benefits if some of those who survive can enjoy extremely long and happy lives; and there could be non-welfare goods on an objective list which rely on non-extinction (among others). On the other side, those with non-deprivationists accounts of the badness of death may still discount the proposed benefits.


Notwithstanding these challenges, I think the model, and the result that the ‘face value’ cost-effectiveness of x-risk reduction is still pretty good, is instructive.

First, there is a common pattern of thought along the lines of, “X-risk reduction only matters if the total view is true, and if one holds a different view one should basically discount it”. Although rough, this cost-effectiveness guestimate suggests this is mistaken. Although it seems unlikely x-risk reduction is the best buy from the lights of a person-affecting view (we should be suspicious if it were), given ~$10000 per life year compares unfavourably to best global health interventions, it is still a good buy: it compares favourably to marginal cost effectiveness for rich country healthcare spending, for example.

Second, although it seems unlikely that x-risk reduction would be the best buy by the lights of a person affecting view, this would not be wildly outlandish. Those with a person-affecting view who think x-risk is particularly likely, or that the cause area has easier wins available than implied in the model, might find the best opportunities to make a difference. It may therefore supply reason for those with such views to investigate the factual matters in greater depth, rather than ruling it out based on their moral commitments.

Finally, most should be morally uncertain in matters as recondite as population ethics. Unfortunately, how to address moral uncertainty is similarly recondite. If x-risk reduction is ‘good but not the best’ rather than ‘worthless’ by the lights of person affecting views, this likely implies x-risk reduction looks more valuable whatever the size of the ‘person affecting party’ in one’s moral parliament.

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