The problems we need addressing could be happening in decades (some are manifesting already) so the rates of today do not have to be the ones in 50 years. I would rather focus on the closer dangers, than on what might happen in centuries... we are already over 8 billions, why would I worry if in centuries we are a billion less? Humanity will be still around and that looks to me like the only important gain.

The environmental problems we have today already have solutions in the lab, it's just about making them economical and scaling them up.

> why would I worry if in centuries we are a billion less?

Indeed, this is my position too. Hyperbolic discounting of the future: we don't know what's coming, let the future sort itself out and worry about the next 5 years.

25 years, we might get AI good enough for robot workforce and we can all retire instantly with no need for more kids entering the workforce to replace the pensioners, might get anti-aging and an end to old-age pensions, might get both, might get neither.

(That said, the example I gave was a reduction to, not by, 6.9%; it would be a global population of 552 million).

> The environmental problems we have today already have solutions in the lab, it's just about making them economical and scaling them up.

'just' is doing a lot of heavy lifting. Lead is still in certain common fuels, some paints, and foods to this day.

Really? So far as I can tell, only used in avgas (and being phased out), banned in paints in many countries. Food legal limits are outside my ability to judge — though I know they exist, I don't know if the legal limits are "the smallest reliability detectable level at the time the law was written" or something else.

That said, if you know how to turn any lab-only solution into an economically viable solution, please do — the world has plenty of room for improvement! :D

My point is we cannot leave it to market research and forces to solve this for us. Unwavering collective action is required to overcome the greed and apathy that allows things like lead to continue to destroy our minds and environments.

Depends on the issue.*

I think you can make a good argument that collective action helped end slavery, I don't think you can make a good argument that anything other than market forces is bringing us the transition to renewable energy.

Where's lead in that? I don't know. I don't even know if it's the same answer for each of your three uses of lead.

Ozone was easy to get an international agreement to fix, because it already had economic alternatives.

* and if you want to argue semantics over "are economic forces anything other than the de-facto collective action of the agents in the economy?", which I'm sure someone has energy for, but I'm not that someone, so I'll acknowledge it and move on.

While technically true, I think 2.4 and 1.6 present two extremely different flavors of "unsustainability", there's very little in common between these two scenarios.

2.4 actually has been sustainable for a couple of millennia by now, mostly because our technology (primarily the food production) was able to keep up with the exponential growth of population. How long this can last is a question, but even if it doesn't last -- going from 2.4 to 2.1 is not hard.

With 1.6 you don't even need to wait for millennia or even aforementioned 300 years to get into trouble. After two generations you get into the situation where working people have to share their income with too many elderly AND elderly don't only consume resources but also directly compete for them with the youth (the other class of people who consume without producing) which makes the fertility economics even worse. You can plug some holes with immigration and foreign trade but on the macro-level it's a death spiral. Very easy to get from 1.6 to 1.0, but extremely hard to return to 2.1.

Maybe I'm missing something but countries like Italy or Spain look to me like trains rushing into concrete wall. And it seems that people are mostly concerned about whether the train is running on a carbon-neutral fuel.

That number of children surviving to adulthood* has not been our experience for the last few millennia — we had far more births, but most died before they grew up and became parents themselves, leading to the estimated population of the world only doubling from 200 million in 1 AD to 400 million in 1000 AD, which would be 2.035 children per woman (assuming 25 year generational gap).

If it had been 2.4 children per woman* over that time frame, the current world population would have been 200e6 * (2.4/2)^(1000/25) = about 300 billion in 1000 AD, and 200e6 * (2.4/2)^(2024/25) = 514 trillion today.

> elderly don't only consume resources but also directly compete for them with the youth (the other class of people who consume without producing) which makes the fertility economics even worse.

Only if the elderly continue to consume pensions. If the economy collapses, pensioners protesting or voting for the other party in a democracy stops being an interesting threat, for the same reason they weren't much of a threat in 1889 when people were first taking ideas like "state pension" (in their modern usage and not e.g. medieval almshouses, and universal not e.g. what the Romans did for the military) seriously.

* I know I didn't mention "surviving to reproductive age" before, but that distinction is more of relevance to historical comparisons than future ones. I have no reason to think infant mortality will go up, after all.

> That number of children surviving to adulthood*

Agreed

> Only if the elderly continue to consume pensions.

Well no, unless you literally starve them to death. State pensions or money in general is just a redistribution mechanism which doesn't change average available resources. What really matters on a higher level is the fact that a big part of population (elderly and youth) consumes but doesn't produce. Whatever they consume is either directly produced by the working part of the population or comes from the foreign exchange of the same said produce.

So if the state pensions system collapses it just means that instead of feeding your parents through taxes you now do it directly, which on average is almost the same (difference coming from elderly who don't have kids to feed them). Which still means you have less resources to spend on your kids.

> Well no, unless you literally starve them to death. State pensions or money in general is just a redistribution mechanism which doesn't change average available resources.

The way this is currently playing out in the UK, is that pension ages are increasing.

At the extreme case, there's no more state pension: if you don't have a private pension, you're working until just before you die.

I was thinking more of heating (and, increasingly, cooling) rather than starvation: Food specifically isn't the main concern here, unlike in the 1800s, because of how few farmers we need to feed the entire population.

(And this whole thing may be inverted at short notice in a whole bunch of different ways; UBI is basically a pension age of zero, but I'm only expecting that when AI gets good enough, and IMO that's "at least five years after self driving cars, whenever that is".