For this example, the initial population size is estimated to be 10, Next, you must calculate or estimate the growth rate. This is typically a growth rate per year in percent, but it can be any period length the problem calls for. Next, you must determine the total number of years or periods that the growth occurs for. In this example, the growth occurs for 5 consecutive years. Plugging in the information from the steps above, the final population is calculated to be Sometimes these numbers are rounded to the closest integer because you can have half a person.
Therefore it is appropriate to reference the time in which these countries will double their population. Doubling time is perhaps the most illuminating manner of presenting population growth to the lay person.
However, it should be noted that the explanations below refer to a constant rate of growth, which as we note, is not as applicable to countries now as it was in the past.
A quantity grows exponentially when its increase is proportional to what is already there. Exponential growth has surprising consequences. Significant gains can be made by simply relying on exponential growth over time. One way of saying this is that the longer you wait on your investment, the faster your returns come in. In the following graph, you can see that over time, returns increase dramatically. There are also clear disadvantages to exponential growth.
When populations continue to grow, the impact of growth becomes increasingly significant over time. Because of the nature of exponential growth, "when things get bad, they get bad in a hurry". In 10 years, the population will double to , people, in another 10 years it will double again to , people, and ten years after that it will double again to , people. The following graph shows this exponential population growth. Again it is possible to switch this chart to any other country or world region in the world.
How do we expect this to change in the coming decades? What does this mean for population growth? Population projections show that the yearly number of births will remain at around million per year over the coming decades. It is then expected to slowly decline in the second-half of the century.
As the world population ages , the annual number of deaths is expected to continue to increase in the coming decades until it reaches a similar annual number as global births towards the end of the century. As the number of births is expected to slowly fall and the number of deaths to rise the global population growth rate will continue to fall. This is when the world population will stop to increase in the future.
Population growth is determined by births and deaths and every country has seen very substantial changes in both: In our overview on how health has changed over the long run you find the data on the dramatic decline of child mortality that has been achieved in all parts of the world. And in our coverage of fertility you find the data and research on how modern socio-economic changes — most importantly structural changes to the economy and a rise of the status and opportunities for women — contributed to a very substantial reduction of the number of children that couples have.
But declining mortality rates and declining fertility rates alone would not explain why the population increases. If they happened at the same time the growth rate of the population would not change in this transition. What is crucial here is the timing at which mortality and fertility changes. It is shown in the schematic figure. It is a beautifully simple model that describes the observed pattern in countries around the world and is one of the great insights of demography.
If fertility fell in lockstep with mortality we would not have seen an increase in the population at all. The demographic transition works through the asynchronous timing of the two fundamental demographic changes: The decline of the death rate is followed by the decline of birth rates. This decline of the death rate followed by a decline of the birth rate is something we observe with great regularity and independent of the culture or religion of the population.
The chart presents the empirical evidence for the demographic transition for five very different countries in Europe, Latin America, Africa, and Asia. In all countries we observed the pattern of the demographic transition, first a decline of mortality that starts the population boom and then a decline of fertility which brings the population boom to an end.
The population boom is a temporary event. In the past the size of the population was stagnant because of high mortality, now country after country is moving into a world in which the population is stagnant because of low fertility. Perhaps the longest available view of the demographic transition comes from data for England and Wales.
In , Anthony Wrigley and Roger Schofield 11 published a major research project analyzing English parish registers—a unique source that allowed them to trace demographic changes for the three centuries prior to state records. As far as we know, there is no comparable data for any other country up until the mid-eighteenth century see the following section for Sweden , where recordkeeping began in The chart shows the birth and death rates in England and Wales over the span of nearly years.
As we can see, a growing gap opens up between the birth and death rate after , creating a population explosion. Statistics Sweden, the successor of the Tabellverket, publishes data on both deaths and births since recordkeeping began more than years ago. These records suggest that around the year , the Swedish death rate started falling, mainly due to improvements in health and living standards, especially for children.
Yet while death rates were falling, birth rates remained at a constant pre-modern level until the s. During this period and up until the first half of the 20th century, there was a sustained gap between the frequency of deaths and the frequency of births.
It was because of this gap that the Swedish population increased. The following visualization supports these observations. The visualization presents the birth and death rate for all countries of the world over the last 5 decades. Countries per continent can also be highlighted by hovering and clicking on them in the legend on the right side of the chart.
By visualising this change we see how in country after country the death rate fell and the birth rate followed — countries moved to left-hand-side first and then fell to the bottom left corner.
Today, different countries straddle different stages of the model. Most developed countries have reached stage four and have low birth and death rates, while developing countries continue to make their way through the stages. There are two important relationships that help explain how the level of development of a country affects its population growth rates:. Combining these two relationships, we would expect that as a country develops, population growth rates decline.
Generally, this is true. Over the last two decades we have seen declining population growth rates in countries at all stages of development. In the average woman on the planet had 5 children.
The first panel in this chart shows this fundamental change. The total fertility rate at which a population replaces itself from one generation to the next is called the replacement fertility rate. If no children died before they grew up to have children themselves the replacement fertility rate would be 2.
Because some children die , the global replacement fertility rate is currently 2. Why then is global population growth not coming to an end yet? The number of births per woman in the reproductive age bracket is only one of two drivers that matter here. The second one is the number of women in the reproductive age bracket. If there were few women in the reproductive age bracket the number of births will be low even when the fertility rate is high.
At times when an increasing share of women enter the reproductive age bracket the population can keep growing even if the fertility rate is falling. The second chart in this panel shows that the population growth over the last decades resulted in increasingly larger cohorts of women in the reproductive age bracket. As a result, the number of births will stay high even as the number of births per woman is falling. This is what the bottom panel in the chart shows. According to the UN projections, the two drivers will cancel each other out so that the number of births will stay close to the current level for many decades.
The number of births is projected to change little over the course of this century. In the middle of the 21st century the number of births is projected to reach a peak at million and then to decline slowly to million births by The coming decades will be very different from the last. How close we are to peak child we looked at in a more detailed post. Population momentum is one important driver for high population growth.
But it of course also matters that all of us today live much longer than our ancestors just a few generations ago. Life expectancy is now twice as long in all world regions. In all of this it is important to keep in mind that these are projections and how the future will actually play out will depend on what we are doing today. Population momentum is driven by the increasingly large cohorts of women in the reproductive age bracket.
And this is when global population growth will come to an end. Hans Rosling explained it better than anyone , with the help of toilet rolls. At the global level, population changes are determined by the balance of only two variables: the number of people born each year, and the number who die. How large of an impact does migration have on population changes across the world? In the United States we see that since the early s, migration into the USA has exceeded emigration out of the country.
This means net migration has been positive, and resulted in a higher population growth rate than would have occurred in the scenario with zero migration. In , for example, the actual population growth rate was 0. With zero migration, this would have been 0. This is also true for most countries across Europe. In fact, population growth would have been negative i. In , the European population increased by 0.
The opposite is of course true for countries where emigration out of the country is higher than immigration. Take Nepal as an example: in the mids its actual population growth rate has been lower than it would have been in the absence of migration.
In , its growth rate was 0. With zero migration it would have been 1. This article previously covered aspects of population age structure; you now find this material in our entry on Age Structure. We evaluate the track record of the UN projections in the entry on future population growth.
But historic and current population estimates between sources are also not identical. How do these sources compare? In the chart we see the comparison between the UN shown in red and US Census Bureau in blue estimates globally and by region. Global estimates have varied by around 0.
The largest variation comes from estimates of Asia, Africa and Latin America — where census data and underlying data sources will be less complete and lower quality. This means some interpretation and judgement is necessary from expert demographers within each organization. Matt Rosenberg. Geography Expert. Updated March 24, Cite this Article Format. Rosenberg, Matt. Understanding Population Growth Rates. Current World Population and Future Projections.
Interesting Facts and Information About the U. Indigenous Population. Interesting Facts about Diverse Groups in America. Population Growth and Movement in the Industrial Revolution.
Overview of the Second Industrial Revolution. Current Population of the United States. Population of Cuba: Data and Analysis. Your Privacy Rights. To change or withdraw your consent choices for ThoughtCo.
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