# Which global fertility rate would allow the human population to adjust to Earth's carrying capacity while maintaining an acceptable dependency ratio?

Humans currently consume the ecological resources of 1.75 Earths (https://www.footprintnetwork.org/).
Assuming that global average consumption remains stable (less in the global North and more in the global South) this would imply that the human population would have to be 43% lower and that a fertility rate of 2.1 is unsustainable. But at the same time fertility rates under 1.0 seem to lead to socio-economic dislocations including potentially unsustainable dependency ratios as larger older generations have to be supported by smaller younger generations. Which fertility rate would allow the human population to adjust to Earth's carrying capacity as soon as possible while minimising socio-economic dislocations?

• Wealth leads to a decline in reproduction rates, visible e.g. in the demographic pyramids of e.g. Germany or the UK. So the question should rather be "how much do we need to reduce our consumption rate".
– Erik
May 6, 2020 at 8:50
• @Erik: I’m trying to understand what the basic global aggregate fertility rate would need to be primarily to get a sense of magnitude. I think the dynamics of how to get to this rate would be a separate question, probably centred on the problem of decoupling: how to increase (or maintain) well-being sufficiently for birth rates to decrease (or remain low) while simultaneously lowering the consumption of natural resources. May 7, 2020 at 12:14
• You need to population to drop to about 60 %, so when you know the time frame, you can calculate this quite easily. Within one generation it'd be a fertility rate of 0.6, the longer you stretch you time frame, the higher the rate may be. Still, it'd couldn't be 1.0 or above.
– Erik
May 7, 2020 at 12:30
• If consumption is held stable I understand that the global fertility rate would have to drop to 1 / 1.75 (EF) = 0.57 x 2 (the fertility rate measures number of children per woman) = 1.14 for the population to shrink into the ecological footprint within a generation. Only a few industrialised territories are at or below this level but it is generally not considered sustainable socio-economically and it is usually compensated with immigration of working age people to increase the dependency ratio. On a global aggregate level immigration would of course not be possible. May 7, 2020 at 14:42