Population

1900: The population of the world is 1.6 billion.

1950: The population of the world is 2.5 billion.

1975: The population of the world reaches 4 billion.

1990: The population of the world is 5.26 billion.

2000: The population of the world is just over 6 billion.

2005: The population of the world is 6.45 billion.