The world population could reach 11 billion people by the year 2100, according to new reports from the United Nations and other organizations.

The human population in the world today is roughly 7.2 billion people, and researchers estimate there is an 80 percent chance of that number reaching 11 billion by the end of the century. At that time, investigators believe between 9.6 and 12.3 billion people will be living on Earth.

This is largely driven by population growth in sub-Saharan Africa, which is increasing at rates faster than most experts expected. Roughly one billion people live on the continent today. That number could be between 3.5 and 5.1 billion by the end of the century. Population growth there was greatest in the nations of Nigeria, Tanzania and the Democratic Republic of the Congo, which have large populations and high rates of birth.

During the early 19th Century, the world's population reached one billion people for the first time in history. That number doubled in the 1920s, and reached six billion in 1990s. In 2011, the number of humans on the planet reached seven billion people.

Increasingly large population could put a strain on food supplies and natural resources, according to some researchers.

Investigators examined birthrates around the world, along with pregnancy rates, migrations and mortality rates.

"Previous forecasts did indeed forecast a leveling off of the world population around 2050, and in some cases a decline," Adrian Raftery, a sociologist who helped lead the population study, said.

Earlier estimates assumed birthrates in sub-Saharan Africa would decline over time, helping to reduce the world population. That did not happen, and the population of the continent continues to climb. Investigators on the study believe better education and easier access to contraceptives in Africa could help nations on the continent reduce population growth.

In 2013, the United Nations released a study predicting world population would rise to around 10.9 billion people by the year 2100. Wolfgang Lutz, a demographer from Austria, predicted the global population would peak between eight and 10 billion people around the year 2050, before leveling out.

North America, Latin America, and Europe will each have one billion people or fewer by the end of the century, according to researchers. Asia is expected to reach a population of five billion people by the year 2050, before that number begins to decline, the report details.

Prediction of world population by the end of the century was profiled in the journal Science.