World population has increased from an estimated 3 million people in pre-agricultural times to approximately 7.2 billion people in 2015. The population continues to grow at a rate of around 1.1 percent per year, and this growth is estimated to continue throughout the 21st century.
World population increased slowly until the modern era. It was not until around 1800 that it reached 1 billion people. At the beginning of the 20th century, there were approximately 1.6 billion people on Earth. The total population increased by nearly 4.5 billion people during the next 100 years.
The future rate of population growth is a source of dispute among sociologists. Estimates as to when world population might peak and what level it might reach depend upon a number of assumptions. The population in the year 2050 is likely to be between 9 and 11 billion, with most of this growth occurring in less-developed areas of the world.
By the end of the 21st century, world population could be anywhere from a low estimate of 6 billion to a high estimate of 16 billion. The future trajectory depends on how quickly fertility rates drop in highly-populated regions. If they drop sharply, world population could peak in the middle of the century and then begin to decrease. If they drop slowly or not at all, the total population could continue to grow indefinitely.