Brainstorming some possibilities, not taking myself too seriously:
--2020 will be remembered as a year of death and disruption; the economy will suffer massively, perhaps enough to count as a recession.
--Many old people will die (something like 10%?) this is a big higher than the current fatality rates but I predict they will rise once hospital systems are overwhelmed. This will have a few knock-on effects: 1. Health care expenditures will drop for the next few years, since old and sick people are the biggest source of such expenditures and the population of old and sick people will be substantially smaller. 2. There will be a noticeable increase in average spending money available to younger people due to inheritances. 3. Politics in the USA at least will shift noticeably (though not dramatically) to the left, since the dead people will be disproportionately right-leaning. 4. Politics worldwide will generally shift in a more radical direction, since the proportion of young people to old people will increase. 5. One of the contenders for the US presidency might die before the election. (This is unlikely even if 50% of the world gets infected, but it is likely enough to deserve mention I think.)
--China's dramatic and draconian measures to contain the virus will come to be seen as a success story, something that would have worked if only other nations had behaved similarly (and perhaps, if China keeps its border closed, it actually will work for China at least?). This leads to an increase in authoritarianism in general around the world, made substantially stronger by the general tendency of authoritarianism to rise during crises.
--The world will, in general, take pandemic risks much more seriously from now on, making it substantially harder for something like this (or worse) to happen again.
Just for the record, I think that this estimate is pretty high and I'd be pretty surprised if it were true; I've talked to a few biosecurity friends about this and they thought it was too high. I'm worried that this answer has been highly upvoted but there are lots of people who think it's wrong. I'd be excited for more commenters giving their bottom line predictions about this, so that it's easier to see the spread.
Wei_Dai, are you open to betting about this? It seems really important for us to have well-calibrated beliefs about this.
Yeah, I kind of wrote that in a hurry to highlight the implications of one particular update that I made (namely that if hospitals are overwhelmed the CFR will become much higher), and didn't mean to sound very confident or have it be taken as the LW consensus. (Maybe some people also upvoted it for the update rather than for the bottom line prediction?)
I do still stand by it in the sense that I think there's >50% chance that global death rate will be >2.5%. Instead of betting about it though, maybe you could try to convince me otherwise? E.g., what's the weakest part of my argument/model, or what's your prediction and how did you arrive at it?
Epistemic status: I don't really know what I'm talking about. I am not at all an expert here (though I have been talking to some of my more expert friends about this).
EDIT: I now have a Guesstimate model here, but its results don't really make sense. I encourage others to make their own.
Here's my model: To get such a large death toll, there would need to be lots of people who need oxygen all at once and who can't get it. So we need to multiply the proportion of people who might have be infected all at once by the fatality rate for such people. I'm going to use point estimates here and note that they look way lower than yours; this should probably be a Guesstimate model.
This comment suggests maybe 85% fatality of confirmed cases if they don't have a ventilator, and 75% without oxygen. EDIT: This is totally wrong, see replies. I will fix it later. Idk what it does to the bottom line.
But there are plausibly way more mild cases than confirmed cases. In places with aggressive testing, like Diamond Princess and South Korea, you see much lower fatality rates, which suggests that lots of cases are mild and therefore don't get confirmed. So plausibly there are 4x as many mild c... (read more)
With South Korea, I think most cases have not had enough time to progress to fatality yet. With Diamond Princess, there are 7 deaths out of 707 detected cases so far, with more than half of the cases still active. I'm not sure how you concluded from this "that lots of cases are mild". Please explain more? That page does say only 35 serious or critical cases, but I suspect this is probably because the passengers are now spread all over the world and updates on them (e.g. progressing to serious or critical) are no longer being provided (unless someone dies).
Also don't understand this part. "4x as many mild cases as severe cases" is compatible with what I assumed (10%-20% of all cases end up severe or critical) but where does 3% come from?
Update on Diamond Princess: as of now, Wikipedia says that the death toll is 14, or 2% of the passengers who tested positive within the first month. However, the dead all seem to have been elderly (there were many elderly passengers, as expected for a cruise liner). More specifically, 11 of them were over 70, another was over 60, and two others were of undisclosed age due to family wishes.
I don't know how to adjust those results for demographics, and of course you can't use them to predict what would happen without hospital care. But it's a promising sign (relative to Wei'd predictions) that we've made it this far without anything obviously worse than what happened in Italy and Spain, and even those have seen far less than 0.1% of their population die. NYC is estimated to have a 20% rate of infection, and it too has had less than 0.1% of its population die (though this may rise somewhat, as their wave of cases crested fairly recently).