Via NPR:
It was just over two centuries ago that the global population was 1 billion — in 1804. But better medicine and improved agriculture resulted in higher life expectancy for children, dramatically increasing the world population, especially in the West. U.N. forecasts suggest the world population could hit a peak of 10.1 billion by 2100 before beginning to decline. But exact numbers are hard to come by — just small variations in fertility rates could mean a population of 15 billion by the end of the century.
