Billions of people are expected to join the earth by the year 2100: At a rate of approximately 1.5 million new people each year, the world is expected to grow by a total of 40 percent. The findings, presented by the United Nations (UN) during the 2015 Joint Statistical Meetings in Seattle on Monday, identified Africa as the main propeller of the record-breaking population.

John Wilmoth, director of the UN's population division, told the audience as he presented the findings that the projection was based on population patterns throughout human history. Currently, there are 7.3 billion humans scattered throughout the world, and in 2050, UN statisticians estimate the population will climb to 9.7 billion. By 2100, it's possible the world will reach a total of 11.2 billion.

Wilmoth and his team took a closer look at population trends to figure out what was driving the high rates of growth, finding their answer in Africa. Today, the continent’s population remains at 1.2 billion, but not for long. It’s expected to increase to 5.6 billion by the end of this century, thanks to higher rates of fertility, which have steadily improved over the last decade.

It appears declining fertility rates that have long plagued countries like Nigeria, Africa’s most populous country, have stalled. As a result, Nigeria's fertility rate is expected to grow. In a country where there are 182 million Nigerians, the UN projects the country will eventually lead to a population of 752 million in the next 85 years.

There is still a significant amount of uncertainty attached to the numbers, but Wilmoth said there is a 90 percent chance Nigeria’s population will exceed 439 million people by 2100. That’s nearly 2.5 times its current size. It’s not just Nigeria that is expected to significantly grow, but also Somalia, Niger, Gambia, and Angola among others.

A recent analysis by demographers may explain why the continent’s growing at an alarming rate. The government’s encouragement of family planning has led to a “youth bulge” of healthy, growing children. In 2010, the UN conducted a census to project worldwide population, and they incorrectly estimated fertility rates of about 17 African countries. Their fertility rates were and have since been higher since the census report.

Wilmoth warns that the rapid population growth in high-fertility countries may worsen existing problems, including scarce resources, pollution, education, maternity care, political unrest, crime, poverty, and employment. It would cost about $1.5 billion a year to provide modern contraceptives to all African women between the ages of 15 and 49 who are currently unprotected, and unless a system is put into play, the population growth is inevitable.

The UN hopes the findings can encourage countries to begin investing in areas where they’re lacking, like setting up proper health care and infrastructure to support the billions of citizens living there.

Source: Wilmoth J. Populations Projections by the United States: Better Demographic Forecasts, Better Policy Decisions. 2015 Joint Statistical Meetings.

Source: Guengant JP and May J. Global Journal of Emerging Market Economies. African Demography. 2015.