The world's population reached an estimated 8 billion people on Tuesday, representing a gradual increase in human lifespan and global development, according to a United Nations' projection.

In a statement announcing the U.N.'s Day of 8 Billion, the world's governing body credited improvements in "public health, nutrition, personal hygiene and medicine," to the population growth while also warning of the responsibilities that come with the milestone.

The jump from 7 to 8 billion took 12 years, while the next billion-person jump is expected to take 15 years — a sign the overall growth rate of earth's population is slowing. Since 1960, the world's population has grown by a billion an average of every 12.5 years.

A look at global population increases since 1804.

Much of the population growth is centered in developing nations in Africa, such as Nigeria and Congo, and Asia, where India added almost 180 million people since 2011 and is set to surpass China as the world's most populous nation next year.

In Nigeria, the Associated Press reports that Lagos remains the second-most populous city in Africa with 15 million. Over the next three decades, the U.N. says Nigeria's population will increase from 216 million this year to 375 million.

"The population in many countries in sub-Saharan Africa is projected to double between 2022 and 2050, putting additional pressure on already strained resources and challenging policies aimed to reduce poverty and inequalities," the U.N. report said.

While population increases create obvious strains on society, as people will compete more with wildlife and each other for water, food, and space, many in the U.N. view this milestone as important to the development of humankind.

"The milestone is an occasion to celebrate diversity and advancements while considering humanity's shared responsibility for the planet," said António Guterres, the U.N. Secretary-General.

According to U.S. Census Bureau data, the U.S. population is now around 333 million. The population growth rate in 2021 was just 0.1%, the lowest since the country was founded.

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