I know David well, and David, if you're reading this, apologies if it comes across as a bit uncharitable. But as far as I've ever been able to see, every important argument he makes in any of his papers against longtermism or the astronomical value of x-risk reduction was refuted pretty unambiguously before it was written. An unfortunate feature of an objection that comes after its own rebuttal is that sometimes people familiar with the arguments will skim it and say "weird, nothing new here" and move on, and people encountering it for the first time will think no response has been made.

For example,^[1] I think the standard response to his arguments in "The Scope of Longtermism" would just be the Greaves and MacAskill "Case for Strong Longtermism".^[2] The Case, in a nutshell, is that by giving to the Planetary Society or B612 Foundation to improve our asteroid/comet monitoring, we do more than 2x as much good in the long term, even on relatively low estimates of the value of the future, than giving to the top GiveWell charity does in the short term. So if you think GiveWell tells us the most cost-effective way to improve the short term, you have to think that, whenever your decision problem is "where to give a dollar", the overall best action does more good in the long term than in the short term.

You can certainly disagree with this argument on various grounds--e.g. you can think that non-GiveWell charities do much more good in the short term, or that the value of preventing extinction by asteroid is negative, or for that matter that the Planetary Society or B612 Foundation will just steal the money--but not with the arguments David offers in "The Scope of Longtermism".

His argument [again, in a nutshell] is that there are three common "scope-limiting phenomena", i.e. phenomena that make it the case that the overall best action does more good in the long term than in the short term in relatively few decision situations. These are

1. rapid diminution (the positive impact of the action per unit time quickly falls to 0),
2. washing out (the long-term impact of the action has positive and negative features which are hard to predict and cancel out in expectation), and
3. option unawareness (there's an action that would empirically have large long-term impact but we don't know what it is).

He grants that when Congress was deciding what to do with the money that originally went into an asteroid monitoring program called the Spaceguard Survey, longtermism seems to have held. So he's explicitly not relying on an argument that there isn't much value to trying to prevent x-risk from asteroids. Nevertheless, he never addresses the natural follow-up regarding contributing to improved asteroid monitoring today.

Re (1), he cites Kelly (2019) and Sevilla (2021) as reasons to be skeptical of claims from the "persistence" literature about various distant cultural, technological, or military developments having had long-term effects on the arc of history. Granting this doesn't affect the Case that whenever your decision problem is "where to give a dollar", the overall best action does more good in the long term than in the short term.^[3]

Re (2), he says that we often have only weak evidence about a given action's impact on the long-term future. He defends this by pointing out (a) that attempts to forecast actions' impacts on a >20 year timescale have a mixed track record, (b) that professional forecasters are often skeptical of the ability to make such forecasts, and (c) that the overall impact of an action on the value of world is typically composed of its impacts on various other variables (e.g. the number of people and how well-off they are), and since it's hard to forecast any of these components, it's typically even harder to forecast the action's impact on value itself. None of this applies to the Case. We can grant that most actions have hard-to-predict long-term consequences, and that forecasters would recognize this, without denying that in most decision-situations (including all those where the question is where to give a dollar), there is one action that has long-term benefits more than 2x as great as the short-term benefits of giving to the top GiveWell charity: namely the action of giving to the Planetary Society or B612 Foundation. There is not a mixed track record of forecasting the >20 year impact of asteroid/comet monitoring, and no evidence that professional forecasters are skeptical of making such forecasts, and he implicitly grants that the complexity of forecasting its long-term impact on value isn't an issue in this case when it comes to the Space Guard Survey.

Re (3), again, the claim the Case makes is that we have identified one such action.

1. ^{^}

   I also emailed him about an objection to his "Existential Risk Pessimism and the Time of Perils" in November and followed up in February, but he's responded only to say that he's been too busy to consider it.

2. ^{^}

   Which he cites! Note that Greaves and MacAskill defend a stronger view than the one I'm presenting here, in particular that all near-best actions do much more good in the long term than in the short term. But what David argues against is the weaker view I lay out here.

3. ^{^}

   Incidentally, he cites the fact that "Hiroshima and Nagasaki returned to their pre-war population levels by the mid-1950s" as an especially striking illustration of lack of persistence. But as I mentioned to him at the time, it's compatible with the possibility that those regions have some population path, and we "jumped back in time" on it, such that from now on the cities always have about as many people at t as they would have had at t+10. If so, bombing them could still have most of its effects in the future.

Carl Shulman's response here responds to objection 1. You can also see the tag for the time of perils hypothesis for a bit more discussion.

On 2, the structure of the objection is similar to Shulman's response on 1: we're not vanishingly unlikely to have very large (or even near maximal) population sizes. For instance, a variety of people (including longtermists) are interested in ultimately creating vast numbers of digital minds or other sources of value and there aren't clearly opposing groups which directly have preferences against this happening. I don't see a very strong analogy between current low fertility and long run cosmic resource utilization, and at a more basic level, current low fertility isn't stable: even if the status quo continues for a long time (without e.g. the creation of powerful AI resulting in much faster progress in technology), selection will likely lead to the fertility rate increasing at some point in the future unless this is actively suppressed.

We asked David about longtermists' responses to his work in the podcast episode we did with him. Here's the (rough, automatically generated) transcript, but you can listen to the relevant section here; it starts at ~33:50. 

David:  I think to contextualize that, let me use the word I'm going to use in my book, namely a strategy of shedding zeros. So, longtermists say, look, the axiological case for longtermism is 10 orders of magnitude or 15 orders of magnitude better than the case for competing short-termist interventions.

So, therefore, unless you are radically non-consequentialist, longtermism is going to win at the level. And I want to chip away a lot of zeros in those value estimates, and then maybe do some other deontic things too. And so if the longtermist is just in one swoop gonna hand me five or ten or twenty zeros, I think there's two things to say. The first is they might run out of zeros just there.

5, 10, 20 orders of magnitude is a lot. But the second is this isn't the only time I'm gonna ask them for some orders of magnitude back. And this thing that they do, which is correct, is they point at every single argument I make and they say "I can afford to pay that cost and that cost and that cost." But the question is whether they can afford to pay them all together, and I think, at least as the line of the argument in my book, that if we're really tossing orders of magnitude around that freely, we're probably going to run out of orders of magnitude quite quickly.

Leah: Got it. Okay. And, I just want to follow up on the last thing you said. So has that been the response of the people who are writing on these issues? Like, do they read your work and say, yeah, I concede that?

David: I get, well, sometimes it's concessive, sometimes it's not, but almost always, somebody raised their hand, they say, David, couldn't I believe that, and still be a longtermist? So I had to rewrite some of the demographics section in my paper. They said, look, aren't you uncertain about demographics?

Maybe there's a 10 to the 8th probability I'm right about demographics, so maybe I lose eight orders of magnitude, and the response there is, okay, maybe you do. And then they'll say about the time of perils, maybe there's a 10 to the 9th chance I'm right about the time of perils, maybe I lose nine orders of magnitude, and okay, you do.

Obviously, we have a disagreement about how many orders of magnitude are lost each time, but I think it's a response I see in isolation every time I give a paper, and I'd like people to see it as a response that works in isolation, but can't just keep being repeated.

Note that Thorstad's arguments apply more against strong longtermism, i.e. that future generations are overwhelmingly or astronomically more important than current generations, not merely that they are important or even much more important than current generations. 

Rethink Priorities did a more comprehensive survey on models of future x-risk and population sizes.

I'm going to actually disagree with your initial premise - the basic points are that the expected number of people in the future is much lower than longtermists estimate - because, at least in the Reflective Altruism blog series, I don't see that as being the main objection David has to (Strong) Longtermism. Instead, I think he instead argues That the interventions Longtermists support require additional hypotheses (the time of perils) which are probably false and that the empirical evidence longtermists give for their existential pessimism are often non-robust on further inspection.^[1] Of course my understanding is not complete, David himself might frame it differently, etc etc.

One interesting result from his earlier Existential risk pessimism and the time of perils paper is that on a simple model, though he expands the results to more complex ones, people with low x-risk should be longtermists about value, and those with high x-risk estimates should be focused on the short term, which is basically the opposite of what we see happening in real life. The best way out for the longtermist, he argues, is to believe in 'the time of perils hypothesis'. I think the main appeals to this being the case are either a) interstellar colonisation giving us existential security so we're moral value isn't tethered to one planet,^[2] or of course from b) aligned superintelligence allowing us unprecedented control over the universe and the ability to defuse any sources of existential risk. But of course, many working on Existential AI Risk are actually very pessimistic about the prospects for alignment and so, if they are longtermist,^[3] why aren't they retiring from technical AI Safety and donating to AMF? More disturbingly, are longtermists just using the 'time of perils' belief to backwards-justify their prior beliefs that interventions in things like AI are the utilitarian-optimal interventions to be supporting? I haven't seen a good longtermist case answering these questions, which is not to say that one doesn't exist.

Furthermore, in terms of responses from EA itself, what's interesting is that when you look at the top uses of the Longtermism tag on the Forum, all of the top 8 were made ~3 years ago, and only 3 of the top 20 within the last 3 years. Longtermism isn't a used a lot even amongst EA any more - the likely result of negative responses from the broader intelligensia during the 2022 soft launch, and then the incredibly toxic result of the FTX collapse shortly after the release of WWOTF. So while I find @trammell's comment below illuminating in some aspects about why there might be fewer responses than expected, I think sociologically it is wrong about the overarching reasons - I think longtermism doesn't have much momentum in academic philosophical circles right now. I'm not plugged into the GPI-Sphere though, so I could be wrong about this. 

So my answer to your initial question is "no" if you mean 'something big published post-Thorstad that responds directly or implicitly to him from a longtermist perspective'. Furthermore, were they to do so, or to point at one already done (like The Case for Strong Longtermism) I'd probably just reject many of the premises that give the case legs in the first place, such as that it's reasonable to do risk-neutral-expected-value reasoning about the very long run future in the first place as a guide to moral action. Nevertheless, other objections to Longtermism I am  sympathetic to are those from Eric Schwitzgebel (here, here) among others. I don't think this is David's perspective though, I think he believes that the empirical warrant for the claims aren't there but that he would support longtermist policies if he believed they could be supported this way.

I'm also somewhat disturbed by the implication that some proportion of the EA Brain-Trust, and/or those running major EA/AI Safety/Biorisk organisations, are actually still committed longtermists or justify their work in longtermist terms. If so they should make sure this is known publicly and not hide it. If you think your work on AI Policy is justified on strong longtermist grounds, then I'd love to see your the model used for that, and parameters used for the length of the time of perils, the marginal difference to x-risk the policy would make, and the evidence backing up those estimates. Like if 80k have shifted to be AI Safety focused because of longtermist philosophical commitments, then lets see those commitments! The inability of many longtermist organisations to do that is a sign of what Thorstad calls the regression to the inscrutable,^[4] which is I think one of his stronger critiques.

1. ^{^}

   Disagreement about future population estimates would be a special case of the latter here

2. ^{^}

   In The Epistemic Challenge to Longtermism, Tarsney notes that:

   More concretely, the case for longtermism seems to depend to a significant
   extent on the possibility of interstellar settlement

3. ^{^}

   Note these considerations don't apply to you if you're not an impartial longtermist, but then again, if many people working in this area don't count themselves as longtermists, it certainly seems like a poor sign for longtermism

^{^}

Term coined in this blog post about WWOTF

^{^}

A general good rule for life

^{^}

(I am not a time-invariant-risk-neutral-totally-impartial-utilitarian, for instance)

Show all footnotes

I think the standard response by longtermists is encapsulated in Tarsney's "The Epistemic Challenge to Longtermism": https://link.springer.com/article/10.1007/s11229-023-04153-y Tarsney concludes: "if we simply aim to
maximize expected value, and don’t mind premising our choices on minuscule
probabilities of astronomical payoffs, the case for longtermism looks robust.
But on some prima facie plausible empirical worldviews, the expectational
superiority of longtermist interventions depends heavily on these ‘Pascalian’
probabilities. So the case for longtermism may depend either on plausible but
non-obvious empirical claims or on a tolerance for Pascalian fanaticism." I don't have time to compare the two papers at the moment, but - in my memory - the main difference to Thorstad's conclusion is that Tarsney explicitly considers uncertainty about different models and model parameters regarding future population growth and our possibility to affect the probability of extinction.