Of course, there is nothing factual about projecting the population. Forecasting population growth, just like predicting economic growth, is something of a guessing game. But maybe it is more accurate than most forms of forecasting. After all, armed with information about birth and death rates, and immigration policy, one can make some pretty good guesses. And the guesses/estimates published yesterday from the Population Reference Bureau are absolutely fascinating.

According to the Population Reference Bureau, the UK will be the most populous country in Europe by the midpoint of this century. And while Britain’s population surges, the European population is expected to fall from 739 million to 720 million. But globally, the population is expected to rise from 6.89 billion to 9.49 billion.

The latest population bulletin from the Population Reference Bureau makes good reading. In fact, it is hard to think of more important topics than those raised in the report. For the report’s key findings click here:

But here are some highlights.

When you are looking at population, the numbers involved are so large that it can be hard to comprehend. So let’s simplify. Right now, there are 4.4 births per second across the world. And yet in the developed world there are just 0.5 births per second. See it in these terms. The population of the developed world is around 1.2 billion; the developing world’s population is around 4.6 times bigger than that, and yet the birth rate is 8 times greater.

Worldwide in 1950, there were 12 persons of working age for every person age 65 or older. By 2010, that number had shrunk to 9. By 2050, this elderly support ratio is projected to drop to 4.

Japan has a total fertility rate of 1.4 children per woman, and an elderly support ratio of 3 – the lowest in the world, along with Germany and Italy. By 2050, Japan will have only one working-age adult for every elderly person; Germany and Italy will each have two. Meanwhile Africa’s population is projected to double to two billion by 2050, although this growth could be greater if birth rates do not decrease faster than currently. Africa’s total fertility rate is 4.7 children per woman.

In the US, as the population ages, spending on entitlement programmes such as Social Security and Medicare will rise sharply. Total spending on these two programmes is projected to increase from today’s level of 8.4 per cent of GDP to 12.5 per cent in 2030.

An interesting phenomenon is the relationship between fertility and economic growth. Economies that have a high ratio of youth to older citizens clearly have good potential for growth. If there is also an abrupt fall in the fertility rate, then there can be a spurt in wealth creation. So in the West, economies boomed as baby boomers entered the work force, while at the same time they had fewer children than the previous generation. It is called the demographic dividend. Much the same thing happened in Asia. The Population Bureau says: “the accelerated economic prosperity of East Asia over the past few decades is often attributed to this demographic dividend.”

And looking forward it seems Bangladesh and Brazil are likely to benefit from this dividend. Between the 1970s and 1990s, fertility fell from 6.9 to 3.3 births per woman in Bangladesh, and from 4.7 to 2.5 births per woman in Brazil. Conversely, in Uganda and Mali, where fertility remains persistently high – women in Mali have an average of 5.5 births each, and women in Uganda have an average of 6.4 – the number of working-age adults for each child will likely increase only slightly.

As for the UK, in 2006 there were 11.7 million youths between 10 And 24. By 2025 there are expected to be 10 .6 million. So we will see a slight decline.

The birth rate is 13 per thousand a year (the world average is 20, and the European average is 11). The population in 2009 was 61.9 million. By 2025 it is expected to have increased to 68.4 million, and by 2050 to 76.9 million. This means the population is expected to increase by 24 per cent.

Today, the world’s most populous countries, in order, are: China, India, US, Indonesia, Brazil, Pakistan, Bangladesh, Nigeria, Russia and Japan. By 2050 India is expected to be number one. Pakistan will be number 4, Nigeria number 5 and Ethiopia and the Congo Republic will join the top ten. Japan and Russia will leave the top ten.

The oldest country in the world today is Japan, followed by Germany, then Italy, Sweden, Greece, Portugal, Bulgaria, Austria, Latvia and Belgium.

In 2050, the number of working adults to support older people is expected to be 19 in Nigeria, 5 in India and 3 in China, but just 2 in France and I in Japan. For the UK, the elderly support ratio is expected to be 3. Currently the ratio in the UK is 4.  Click here for more data