Earth globe illuminated for Christmas, Montepellier.

According to the UN, the world's population reached eight billion on November 15. There is a photo of Jean-Marc Zaorski and Gamma-Rapho.

Less than a century after the planet supported just 2 billion people, the UN predicts that the world's population will reach 8 billion.

The long-term projection for the UN population has been revised down from 11 billion to 10 billion by the end of the century.

People of the world: Line chart showing global population since 1950, which is expected to reach 10.4 billion by 2100.

The UN Population Division is the source of this information.

The UN has named 15 November the Day of Eight Billion, but demographers don't know if it really was. Earth's population will start to shrink within a few decades due to the slowing growth of the human population.

Patrick Gerland is the leader of demographic work at the UN Population Division in New York City. It is around this time that humanity is reaching 8 billion.

Will global population increase? The researchers can't agree.

This could be the most reliable estimate that the UN has come up with. The organization switched from five years to annual intervals for analyzing data. Many countries have been able to collect statistics in recent decades.

There are still significant blind spots for countries that are experiencing humanitarian crises. Gerland says that the accuracy of the underlying data varies greatly around the world.

Differing estimates

The rapid rise in population was caused by advances in public health and medicine, which allowed more children to live to adulthood. The fertility rate stayed high in lower-income countries.

Demographers are interested in fertility rates and how they are expected to change, because these factors help to drive what will happen to the global population in the future A notable diversion in what various models had previously forecast for the world's population is due to differences in assumed fertility rates. The results suggested a spread between 8 billion and 11 billion by the century's end.

China's population will peak eventually. Depending on who you ask.

Tom Sobotka is a researcher at the Vienna Institute of Demography.

According to the International Institute for Applied Systems Analysis, the world's population will be about 9 billion by the year 2200. An update from the institute will increase the estimate to between 10 billion and 10 billion. The change is due to higher observed and expected survival rates in lower income countries. There are higher estimates of fertility rates in Pakistan.

More reliable data

Since the end of China's one-child policy in 2015, data from China has been more reliable.

There was always a mismatch between the different sources of data from China. If they had a girl, they wouldn't register an initial birth. Many children don't appear in official statistics until they start school. Education statistics were used for more accurate information.

The UN predicts that China's population will shrink every year until the end of the century.

Gerland says that the population in China will decline in the future due to the fact that there are more deaths than births in the country.