The graph above shows population projections based on three different fertility assumptions. The medium-fertility variant is the median of thousands of projections that the United Nations Population Division calculates in their biannual revisions. The high-fertility variant assumes a fertility rate of 0.5 children more for each country; the low-fertility variant assumes a fertility rate of 0.5 fewer for each country.
As you can see, the difference of only half a child (on average, of course) now can mean a difference on the order of billions in the future.
We are facing a world that could have anywhere from 8.7 billion to 10.8 billion people in 2050. Currently at 7.3 billion, we are already facing myriad global challenges. How will we improve the quality of life for billions when population growth continues rapidly in the poorest places on earth—the very places least able to cope? This is a challenge that must be met, primarily, with universal access to voluntary family planning.
If you would like to look closer at the 2015 UN population estimates and projections, please click here.