What is the main Idea of this text? United Nations demographers, people who study populations, project the world's population will reach 9.6 billion by 2050. However, that projection has changed in recent years. In 2000, the United Nations (U. N.) predicted a global population of 8.9 billion people by 2050, which is 700 million fewer people than it is predicting now.
Meanwhile, other organizations have different 2050 projections. The United States Census Bureau projects a population of 9.4 billion. The Population Reference Bureau, a nongovernmental group that tracks U. S. demographics, has increased its projection by two million since their last estimates were published in 2010. Their number now matches the U. N. estimate. So, why do these figures evolve and why don't the estimates sync up?
Population projections are dynamic, meaning in a state of constant change. While they are often reflective of the real world, many factors that determine future trend lines are unclear and evolving.
Three Big Population Drivers
In predicting future population size, demographers first assume a no-surprise future, meaning they assume that life continues as it is now. They focus on three main drivers of population — births, deaths and migration. Life expectancy is kept on a consistent upward trend, and unpredictable events like epidemics and wars are ruled out.
"The HIV/AIDS epidemic — it was not predicted, and it substantially changed the demographics of some countries in the 1970s," said Francois Pelletier. He is head of the population estimates and projections section of the United Nations.
How Population Drivers Are Studied
When it comes to analyzing the three big population drivers, demographers draw on surveys and census data from around the world. The U. N. also takes into account progress made in achieving internationally agreed-upon initiatives. One such example was the Millennium Development Goals, which were agreed to by all the world's countries. These goals ranged from halving extreme poverty rates to providing universal primary education by 2015.
This information is used to reassess past population projections and generate a revised report. In the case of the biannual U. N. population report, World Population Prospects, three distinct population projections are created—high, medium and low variants. The middle variant — which this year is 9.6 billion people in 2050—is the one that gets the most attention.
The high variant assumes each woman, or person who could reproduce, has half a child more than the medium variant, which leads to a prediction of 10.9 billion for 2050. The low variant assumes half a child less. It would result in a 2050 population of 8.3 billion.
No Crystal Ball
Robert Engelman is president of Washington D. C.-based environmental research organization World Watch Institute. Engelman said that there is no "crystal ball" for population projections, which leaves plenty of room for error.
Changing fertility rates and birth rates have the potential to significantly impact future population levels. Fertility rates are the average number of children for every woman in a population. In 2012, the U. N. report said that global population growth has slowed overall. Still, population growth will be rapid in developing regions such as Nigeria and Malawi. There, populations are projected to increase at least five times their current numbers by 2100.
The Unknowns
And then there are the unknown unknowns. "If an asteroid hits the Earth in the right place, there may be little or no population in 2050," Engelman said, "And demographers don't think about asteroids."
Pelletier said errors in population dynamics at the global level tend to cancel themselves out. "If there's a country where you're a bit too high, and another where you're a bit too low, then the population number evens out," he said.
That helps explain why the U. N.'s projections are relatively consistent with other estimations for 2050.
Demographers say there is little reason to anticipate a population bomb or doomsday situation. In fact, the population growth rate has already started to slow, and this downward trend is projected to continue through 2050.