By Wolfgang Lutz

May 9, 2011

The global demographic landscape is a complex one, and not surprisingly very difficult for many to comprehend. The media is alive with projections that the global population will reach seven billion people by the end of 2011, and will exceed nine billion by 2050, with much of this growth occurring in the least-developed countries, where a high rate of mortality is outweighed by an even higher rate of fertility.

The International Institute for Applied Systems Analysis (IIASA) and its partners have a somewhat different perspective on future population trends. Using the probabilistic projections developed by IIASA and the Vienna Institute for Demography of the Austrian Academy of Sciences (VID) and published in Nature, we take uncertainties about current conditions and future trends into account. According to these, the seven billion mark will only be reached by 2012-13. This is based on amore realistic estimate of fertility in China of 1.5-1.6 children per woman, 0.3 less than that published by the Chinese Family Planning Ministry and often quoted by international organisations and the press.

IIASA and others, in Nature in 2001, published their projections estimating that there was an 85 percent chance that the world population would peak by the end of the century and then start to decline. In 2100 the eighty percent uncertainty range goes from six to eleven billion, depending primarily on the future path of fertility. There is about a ten percent chance that the world population in 2100 could be less than six billion and an equal chance that it could exceed eleven billion.

While a slowing of global population growth is generally expected, the population reductions are also likely to be highly regional due to differing fertility rates. For example, there is likely to be more than a doubling of Africa's current population of around one billion, due to high fertility and low development and education rates. China, the world's most populous nation, on the other hand, is likely to see a growth over the next decades followed by almost certain decline due to reduced fertility.

IIASA studies have for a significant period shown that education, in particular female education, is a prerequisite for reducing fertility and bringing countries out of poverty. Indeed world population growth can be reversed in the longer run with a sustained decrease in fertility rates. In 2009, I published an editorial in The Journal of the Royal Statistical Society entitled 'Toward a World of 2-6 Billion Well Educated and Therefore Healthy and Wealthy People.' This paper presents extensions of demographic scenarios into the 22nd century illustrating that if the world, by the end of this century, achieved fertility rates currently found in Europe and China (about 1.5-1.7 children per woman), world population could well decline to approximately two to six billion people even with continued significant increases in life-expectancy. But such low fertility levels will likely only be achieved if the rest of the world population attains female education levels comparable to those of existing low-fertility region.

Evidence from the Demographic and Health Surveys (DHS) of the developing world also supports the view that the dominant force for limiting fertility is female education: more educated women want fewer children and tend to provide them with better opportunities in terms of health and education. More educated women tend to have better access to information and to reproductive health services that enable them to manage their fertility.

In Ethiopia, for example, the DHS shows that uneducated women have on average six children whereas those with secondary education have only two.

Education Importance

Increasing female education not only impacts fertility rate but economic development and democracy. A study by IIASA, the Vienna University of Economics and Business (WU), the Austrian Academy of Sciences, and the University of Tehran, published in 2010, indicates that there is a strong global level association between education, fertility and democracy. Applying this relationship to Iran, the study shows a high probability that Iran would move toward a more democratic political system within the next two to three decades. This prediction is based on the unprecedented recent increase in education levels, particularly among women.

Iran, one of the world's major Islamic cultures, has experienced a profound increase in education levels and dramatic changes in birth rates over recent decades. Twenty-five years ago the average Iranian woman had six to seven children; now, due to improved female education and an active and voluntary family planning program across the country, this number has been reduced to less than the replacement level, at about 1.9 in 2006. This is possibly the most rapid national level fertility decline in human history.

Previous studies have shown that a country's development, in particular its education levels, is a key determinant of the emergence and sustainability of democratic political institutions. As people become more educated, they also become more politically aware and are thus more inclined to participate in the political process. A new IIASA data set which reconstructed educational attainment distributions by gender and five year age groups for more than 120 countries could statistically establish this important relationship.

Speed Of Ageing

Another aspect of fertility decline is the resulting ageing of the population. As fewer children are born and life expectancy continues to increase, the mean age of the population rises and this has consequences in many areas, such as health and disability care and housing needs. There is a big discussion about possible effects on economic growth as the proportion of working people declines and that of pensioners increases. On the other hand, due to increasing life-spans and improved health, one could also view populations as 'ageing' more slowly than conventional measures indicate. This aspect of ageing was explored in an IIASA study published in Science, which raises many policy relevant questions about future pension systems.

The study looked at 'disability-free life expectancies,' which describe how many years of life are spent in good health. It also explored the traditional measure of old age dependency, and another measure that looks specifically at the ratio of disabilities in adults over the age of twenty in a population. The analysis showed that in Britain, for example, while the old age dependency ratio is increasing, the disability ratio is remaining constant. What that means, according to the authors, is that, "although the British population is getting older, it is also likely to be getting healthier, and these two effects offset one another."

On a global scale the population is ageing with increasing speed and this is unlikely to slow down until the mid-century. In general the peak speed of ageing depends on past patterns of fertility. In the United States and in some parts of Western Europe, timing is determined by when baby boomers start to become elderly. In China, it is determined by when the strict fertility control policies were implemented. In many countries fertility started falling in the 1960s in part because of family planning programmes and in part because of economic development. Generally the pace of ageing is expected slow down after 2050, after having reached a much higher level than today.

While globally population growth is slowing, there are sizable regions of the world where fertility levels remain high, and education levels, predominantly among women, remain low. It is in these regions where much effort must be made to increase investment in education, empowering women to implement their own informed fertility choices, become politically aware and ultimately raise the living standards and life expectancies of these populations. The combined effect on slowing population growth, increasing economic productivity and better political awareness will be an important factor in achieving global sustainable development.


Wolfgang Lutz is the leader of IIASA's World Population Program and founding Director of the Wittgenstein Centre for Demography and Global Human Capital. He is also director of the Vienna Institute of Demography (VID) of the Austrian Academy of Sciences, and Full Professor of Applied Statistics at the WU and Professorial Research Fellow at the Oxford Martin School for 21st Century Studies.


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