Population growth isn't the only demographic issue.
Dependency ratios are important.
Rich countries are better at tolerating rising dependency ratios.
Poor countries will tend to lose their young, productive workers to rich countries if dependency ratios rise too quickly.
Russia (and China) will grow old before they grow rich.
This will drive desperate actions.
http://esa.un.org/unpd/ppp/Figures-O...ency-Ratio.htm