According to speculation and study, what will happen to the global birth rate in about 40 years?

Birth rate will increase

Birth rate will decrease

Birth rate will stay the same

Birth rates also vary in a geographic area among demographic groups. Some increases and some decreases. In 2012 the average global birth rate was 19.15 births per 1,000 total population, compared to 20.09 per 1,000 total population in 2007. Again, the average global birth rate has shrunk to 18.6 births per 1,000 total population in 2016. There is a possiblity is will decrease