Amazon book: Empty Planet: The Shock Of Global Population Decline
Indigo/Chapters: Empty Planet: The Shock Of Global Population Decline

CPAC interview with book authors:

Short version: People in developed countries are not having enough babies. Number of babies per adult woman over her entire life is something professional scientists who study this call Fertility Rate. Scientists who study this are called geographers. Fertility rate for Canada in 2020 was 1.47. You may think that a couple must have 2 children to replace themselves, but due to children who die before reaching adulthood, it must be 2.1 just to maintain population. China, United States, and Brazil have 1.7. Russia for 2020 had 1.823. India for 2020 was 2.1: no growth or shrinkage. Only the poorest countries have a positive population growth. China's one child policy ended October 29, 2015. The reason is they don't need it, they have a shrinking population without government intervention.

Geographers estimate world population will peak at 8.0 billion in year 2060, then shrink. It's currently 7.875 billion.