If this slump in fertility is generational (i.e., late X'er/Millennial families choosing to delay marriage/childbirth) couldn't this all sort itself out with higher birthrates among the 35-45 age cohort sometime in the near future? Basically, the median age at first-marriage has been moving later faster than older couples are popping out kids?
There is a reason women over 35 don't tend to have very many kids.
Anyway, this whole thing is only a problem within an economic system that demands perpetual expansion. Meanwhile, unending population growth causes ecological devastation. Socialism would solve this.
Socialism is the last thing that would solve this.
Why?
The record in the USSR and Eastern Europe is that the environment has no value in socialist decisionmaking.