Hans Rosling is the LeBron James of statisticians — his TED Talk on human populations has nearly 10 million views.

Early on Sunday morning, he made a call about how the world is changing.

"The biggest change of our time?" he tweeted. "Africa's increase from 1 to 4 billion people!"

The data comes from the recent United Nation's report, "World Population Prospects: The 2015 Revision, Key Findings and Advance Tables."

Four billion people before 2100, meaning that Africa will have a population on par with Asia.

"More than half of global population growth between now and 2050 is expected to occur in Africa," says the United Nations report. "Of the additional 2.4 billion people projected to be added to the global population between 2015 and 2050, 1.3 billion will be added in Africa."

After 2050, Africa is projected to be the only major area that has a continually growing population, meaning that it will house 25% of the global population in 2010 and 39% in 2100.

In 1950, only 9% of the world's population was African.

Conversely, Europe is projected to have a smaller population in 2050 than in 2015.

The UN report says that several factors contribute to Africa's continued pace:

• Lots of high fertility countries. The world has 21 countries that are "high fertility," meaning than the average woman has five or more children over her lifetime. Of those, 19 are in Africa (and the other two are in Asia). The largest is Nigeria, which according to another report will have 10% of the world's births by 2050.

• Major gains in life span. Life expectancy in Africa rose by six years in the 2000s, double the global average. Africa's average life expectancy is expected to gain about 19 years by 2100,rising to age 78.

• Major declines in child mortality. In the past decade, the rate of children under age five who died went from 142 per 1,000 to 99 per 1,000. The global fall was from 71 per 1,000 in 2000-2005 to 50 per 1,000 in 2010-15.

This means there's tremendous opportunity. And risk.

Tech graduate Titilope Oluwaseyilayo poses for a picture in front of her house in the Shomolu district of Lagos, Nigeria. Joe Penney / Reuters

The future growth of Africa is not so dissimilar from the growth of Asia, particularly China. The urbanization of China represents the greatest demographic shift of the late 20th and early 21st century, and the urbanization of Africa will be one of the largest shifts for the rest of this century.

According to the Globe and Mail, Africa had only eight people per square kilometer in 1950. By 2050, that will go up to 80 people per square kilometer.

Construction in Addis Ababa, Ethiopia. Sean Gallup / Getty That shift will be most deeply felt in the continent's megacities: Congo's Kinshasa is expected to grow to 20 million by 2030 and Nigeria's Lagos is expected to grow to 24 million by 2030, which is the population of present-day Shanghai, the largest city in the world.

Of course, it's difficult to do this kind of large-scale modeling over a long period of time with great precision. As with any continent, there's going to be variance. City Lab notes notes that while women in central Africa have kids twice as regularly as the global average, women in Southern Africa have kids about as regularly as American women today.

With 4 billion people, the stakes are high.

"We want to see African leaders make the correct and right investments in children that are needed to build a skilled, dynamic African labor force that's productive and can grow, and can add value to the economy," UNICEF's David Anthony told NPR. "The worst thing would be if this transition was just allowed to happen because what you're going to see is an unparalleled growth of the slum population."