Why is the world's population growing faster than expected?

crowds in China
© JOHANNES EISELE/AFP/Getty Images/ tourists in China

If the latest projections prove to be accurate, we need to plan for about a 10% increase in the needed supply of food, drinking water, and energy, and in carbon dioxide emissions by 2050, as compared to the projections for the same year from 2002.

Population growth is one of the most controversial subjects on any environmental website, and always keeps our community manager busy. Many people believed a) that we have more of a consumption problem than a population problem, and b) things are looking up; Fred Pearce actually predicted a population crash as we are seeing in Japan, as did Carl Sagan, who noted that when grinding poverty goes down, do does the birthrate. He called it the demographic transition.

But this may have been overly optimistic. Michael Sivak, known to TreeHugger readers for his work on Sustainable Worldwide Transportation at the University of Michigan and now managing director of Sivak Applied Research, sends us his latest research which we reprint in full here:

United Nations’ accelerating population forecasts: A cause for alarm?

Every two or three years, in a series of publications entitled World Population Prospects, the United Nations issues a forecast for the future growth of the world population. The eight latest median forecasts for 2050 are shown in the table below. In the course of the 15 years of the examined prospects—from 2002 to 2017—the forecast world population for 2050 increased by about 10%, or a staggering 0.9 billion.

data from article© Sivak Applied Research

What are the reasons for the increase in these projections? Because the projections for the world depend on the projections for the individual countries, the full answer would be complex. Nevertheless, there are two key reasons for the large increases in the forecast world population: general increases in both the assumed fertility rates and the assumed life expectancies—both being critical factors in the forecasting process.

As an example of the increased assumed fertility rates, in the 2002 projections, the overall fertility rate for the world during 2020-2025 was assumed to be 2.33 live births per woman, while in the 2017 projections, the fertility for the same period was assumed to be 2.43 births. Similarly, the assumed world fertility rate during 2035-2040 was 2.12 births in the 2002 projections, but 2.31 births in the 2017 projections.

As an example of the increased assumed life expectancies, in the 2002 projections, the overall life expectancy at birth for the world during 2020-2025 was assumed to be 69.1 years, while in the 2017 projections, the life expectancy for the same period was assumed to be 72.9 years. Similarly, the life expectancy during 2035-2040 was 72.4 years in the 2002 projections, but 75.5 years in the 2017 projections.

If the latest projections prove to be accurate, we need to plan for about a 10% increase in the needed supply of food, drinking water, and energy, and in carbon dioxide emissions by 2050, compared to a projection from just 15 years earlier.

Furthermore, given the continuously increasing projections for 2050, we also need to be prepared for the possibility that the actual future fertility rates and life expectancies would be even higher than those assumed in the latest projections. That would result in even larger future world population than in the latest United Nations projections, with the consequent additional strain on the world resources and climate.

Why is the world's population growing faster than expected?
If the latest projections prove to be accurate, we need to plan for about a 10% increase in the needed supply of food, drinking water, and energy, and in carbon dioxide emissions by 2050.

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