UNITED NATIONS — Eight billion humans are living on planet Earth — a huge milestone officially projected for and being recognized Tuesday by the United Nations.

After a big surge in the second half of the 20th century, population growth may now begin to slow. It could take 15 years to reach nine billion and the UN doesn't expect to reach 10 billion until 2080.

People are living longer, with generally better access to health care, food, clean water and sanitation than in past generations. A smaller share of humans live in extreme poverty.

There are still challenges — ongoing ramifications from the pandemic, a record number of forcibly displaced people and worsening climate change.

“It is a momentous milestone for humanity," Natalia Kanem, executive director of the UN Population Fund (UNFPA), told reporters last month.

"Some express concerns that our world is overpopulated with far too many people and insufficient resources to sustain their lives. I am here to say clearly, that the sheer number of human lives is not a cause for fear."

Earth's population has doubled since 1974.

Population growth has slowed: It took 12 years for the global population to climb from 7 billion to 8 billion, according to the UN. We will not reach 9 billion for about 15 years.

Half of the population still lives in just 7 countries: China, India, the US, Indonesia, Pakistan, Nigeria and Brazil. India's population could surpass China's any day.

"Last century was one of exponential population growth," Jennifer Sciubba, Wilson Center scholar and author of 8 Billion and Counting, told Axios. She said this century is characterized more by diverging demographic trends.

"We see wide gulfs in birth, death and even migration around the world."

In many ways, demographic trends globally indicate that life is improving. We're living longer, thanks to declining child and maternal mortality, cures for deadly diseases, improved health care and other factors.

Extreme poverty has declined and income inequality between countries has largely lessened over the past 25 years, according to the UN.

The share of people living in extreme poverty — less than $2 a day — has fallen from 44% in 1974 to 10%, according to data from GapMinder.

But there are populations facing serious challenges, and the pandemic undid some progress on education, health care and poverty.

Climate change continues to pose one of the biggest threats to humanity, according to the UN, and advancements in lower-income parts of the world could complicate global efforts to reduce its impact.

A record 100 million people have been forcibly displaced from their homes, made worst by the Taliban takeover of Afghanistan and Russia war with Ukraine.

Severe famine is threatening the Horn of Africa. International aid agencies have recently been struggling to find enough resources to deal with multiple conflicts and crises at once.

"The big picture is that things are getting much better," Sciubba told Axios. Even so, there are countries with high fertility rates "marked by famine and conflict, mass displacement... We have to hold multiple truths in our heads," she added. — Agencies