We’ve gone—globally—from 5.3 births per woman in 1963 to 2.3 in 2022 [1]. 2.1 is replacement [2]. In the rich world, where longevity treatments will first become available, it’s 1.6 [3]. (3.3 in 1960.)
There are arguments against longer lifespans. Population growth is not one of them.
[1] https://data.worldbank.org/indicator/SP.DYN.TFRT.IN
To achieve that, I can only see a few classes of solution. We could reduce our per-capita consumption, our lifespan, or our number.
I'm assuming that the overshoot day is roughly correct. The details of exactly how much our birthrate has dropped or by how much our consumption has increased isn't important to know that there is a massive discrepancy between where we are and what is sustainable. Doing anything that increases that discrepancy is probably going to make it worse.
What is your evidence for shorter lives promoting long-term thinking? Like, look at a map of life expectancy in America [1]. Is Mississippi the bastion of ecological awareness you’re looking for?
Number and per-capita impact are the important variables. Wealth reduces the former and exponentially increases the latter. Longevity reduces the former and linearly increases the latter. (Poverty and reduction in lifespan exponentially increase the former while linearly reducing the latter; you don’t worry about efficiency when you have a short, brutish life.)
[1] https://en.m.wikipedia.org/wiki/List_of_U.S._states_and_terr...
I'm looking at it in the other direction; that long-term thinking might result in shorter lives.
Based on what? Increasing lifespan reduces fertility [1]. This is empirically and theoretically grounded. Older populations shrink [2]. Your proposal, shortening lives, is one for boosting populations and consumption.
All that said, this debate is academic. If longevity treatment is possible, we will develop it, and the population can sort itself into those who live longer and those who don’t.
https://www.forbes.com/sites/michaelshellenberger/2019/07/29...
https://www.newscientist.com/article/mg22029445-000-admit-it...
What value do you get out of believing in Earth Overshoot Day? Does it provide real, actionable utility? Does such a belief instill good feelings?
If I had to guess: it tickles the reward pathways in your brain, connected to your survival instinct to be aware of possible threats, whether real or (as I would argue is the case here) imagined. I would doubt there's anything you plan to personally do about Earth Overshoot Day, and I doubt thinking about it instills positive feelings. It's doom porn.