Quality not Quantity

Bridges vol. 42, December 2014 / IIASA

By: Katherine Leitzell, International Institute for Applied Systems Analysis (IIASA)          

New population projections from IIASA researchers provide a fundamentally improved view of future population structured by age, sex, and level of education, which differs from recent projections by the United Nations. 

The United Nations (UN) projects that the world population will grow to 11 billion by 2100. But according to new population projections developed by IIASA and the closely affiliated Wittgenstein Centre for Global Human Capital, that number may be off by two billion. Their new projections show that world population is likely to peak at 9.4 billion around 2070 and then decline to around 9 billion, with alternative scenarios ranging from 7 billion to almost 13 billion.

Why do IIASA’s projections differ from those of the UN? In part, because different data are being used for fertility trends, which are the main drivers of long-term population growth. But the major difference lies in the explicit consideration of education and in the assembly of massive expert knowledge to produce the new IIASA projections, published this fall in a new book, World Population and Human Capital in the 21st Century. 

Traditional demographic projection tools normally structure the population only by age and sex. The multidimensional demographic tools developed at IIASA and applied in these new projections structure the population by age, sex, and level of education. Since all demographic rates, and particularly fertility rates in developing countries, differ greatly by level of education, the future looks different when researchers explicitly consider the changing education structure of the population.

“This book presents the broadest ever synthesis of expert knowledge on drivers of fertility, mortality, migration, and education in all parts of the world,” says Wolfgang Lutz, director of IIASA’s World Population Program and founding director of the Wittgenstein Centre for Demography and Global Human Capital, a collaboration of IIASA, the Austrian Academy of Sciences, and the Vienna University of Economics (WU). Lutz led the project, which drew on more than 550 experts in a series of surveys and expert workshops held on five continents.

Beyond numbers

The potential number of people on the planet is far from the most important information contained in their new data, say Lutz and his colleagues. “What’s important is not simply the number of people, it is their capabilities, their health, and how much education they have – what we call human capital” says Lutz. A growing body of research from demographers at IIASA and elsewhere has shown clearly that education is vital in determining future population growth, future health, and many other factors including economic growth, quality of governance, and the capacity to adapt to climate change. Education has long been considered a key driver in demography but was not explicitly incorporated into models because of inadequate data and lack of familiarity with the multidimensional methods. 

“But now the data and the appropriate methods are there, and there is no reason to maintain the conventional narrow focus on just age and sex,” says Lutz. As Joel Cohen of The Rockefeller University and Columbia University wrote in a review of the book: “This monumental, pioneering volume proselytizes for a new trinity of fundamentals of demography: age, sex and education. If this book succeeds in its mission, as I hope it will, the future will look different not only for the science of demography, but also for all people’s lives.

“When we think about human behavior, it makes sense that what is in your brain is equally or even more important than your age, gender, or what is in your wallet,” says Lutz. He notes that the new approach will have far-reaching implications for research on future social and economic change.

This explicit consideration of education also has direct implications for population projections. In the case of Nigeria, the above-mentioned UN projections show an increase from 160 million in 2010 to 914 million in 2100. 

“These projections assume that fertility will remain stagnant at six children,” says Lutz. “But if we look at the education of young women today, we see that in the 20 to 24 age group, half already have secondary education, while among women aged 40 to 44 it is only a quarter. And since more educated women consistently have lower fertility, future fertility is likely to decline, as the more educated girls enter reproductive age. Disregarding this important structural change leads to higher projections of future fertility.” 

The new IIASA projections also take into account a growing body of research that redefines how people age: In the new projections, the proportion of the population considered old is based on years of remaining life expectancy, rather than on an arbitrary number of years lived.

Population, climate change, and sustainable development

Such a detailed view of future population and relevant characteristics lends itself to application in today’s ever more complex and interconnected research, and the projections were designed with this in mind. They form the “human core” of the next generation of climate scenarios, known as the five Shared Socioeconomic Pathways (SSPs), which will likely play a key role in future global change analyses including the Intergovernmental Panel on Climate Change (IPCC). The medium population and human capital projection, considered the most likely, corresponds to the middle-of-the road SSP (SSP2), which assumes that many aspects of the world will continue along their current trajectories. 

The other four SSPs represent various possible future paths, depending on differing assumptions about changes in education, economic growth, and other factors that can influence population growth. IIASA researcher Samir KC worked closely with the population side of the SSP development, and says:“Past climate scenarios only used total population size. Now, the representation of population as a driver is much richer by having the full age, sex, and education distributions.” Different scenarios based on these distributions can make a big difference to future economic growth and technology and in fields related to climate change, including energy and food demand.

A treasure trove for research

The data are now freely available for download via an online data exploration portal (see box), and researchers have begun using them to enrich their understanding of natural disaster vulnerability, impacts of aging populations, and more.

For example, one major research project at IIASA examined the links between education and vulnerability to natural disasters. The research, now published in a special issue of the journal Ecology and Society, showed that female education is strongly associated with lower levels of disaster fatalities around the world, both in developing and developed countries. Researchers found a correlation across 167 countries for which data were available, and have also conducted detailed case studies in specific countries and regions including Nepal, Thailand, and the Caribbean. In each case, researchers found a strong link between education and lower fatality rates due to natural disasters – from hurricanes to landslides – which could not be explained by differences in income or national GDP.

Lutz and colleagues have also drawn on the new projections in re-examining what should be seen as desirable fertility levels. In many developed countries, birth rates have been declining to what are now well below replacement rate, or two children per woman. The new projections assume that fertility trends are unlikely to rebound to replacement level in the foreseeable future. Is this a problem? In a recent study in the journal Demographic Research, the researchers found that it may in fact have a positive effect.

“People have this idea that replacement level fertility is the ideal,” says Lutz. “But like other questions, when we factor in education, the picture looks quite different.” A more educated workforce tends to be more productive and healthier, according to the study, which means that even with fewer people of working age, the economy does not have to go into decline and that there are more resources per child to invest in human capital formation. 

A long history of IIASA population projections

The 2014 projections build on a long history of groundbreaking population research from IIASA scientists. In the 1970s and 1980s, IIASA researchers Andrei Rogers and Nathan Keyfitz made history by developing the methods multidimensional demographic projections. IIASA also published the first global probabilistic projections and spearheaded the approach of expert‑argument-based projections.

Previous sets of projections were published in three major research papers in the journal Nature in 1997, 2001, and 2008, by Lutz and IIASA colleagues Sergei Scherbov and Warren Sanderson.

IIASA’s population projections have always been freely available for anyone to use. But with so much data on assumptions and results now available for 195 countries, by education level, age, and sex, and for sets of scenarios until 2100, the newly released population projections reach into the realm of big data – far too much information to be easily explored in a spreadsheet. So, along with the book, IIASA researchers for the first time released their data via the online Wittgenstein Centre Data Explorer. People can now delve into the details and pick out the countries or world regions, indicators about assumptions, and results that specifically interest them, at any level of detail regarding age, sex, and education categories. The data can be viewed online in maps, graphs, or tables, and easily exported for additional use.

“The initial version is still aimed at scientists, but we hope to make these data usable for policy makers, journalists, and the general public soon,” says IIASA researcher Anne Goujon, who led development of the Wittgenstein Centre Data Explorer.

Figure Caption: The medium, or most likely, scenario in IIASA’s new population projections shows world population peaking by around 2070 and then declining to approximately 9 billion (top). The new population projections explicitly include education, which is one factor leading to IIASA’s lower fertility rates and lower projections compared to those of the United Nations. In the case of Nigeria, IIASA projections also considered recent advances in women’s education in that country. Since more educated women consistently have fewer children, they project that future fertility will decline. The pyramids (left) show the projected population of Nigeria by age, sex, and education level for 2010 and 2050.


Further information

Lutz W, Butz WP, KC S (Eds) (2014). World Population & Human Capital in the 21st Century. Oxford University Press.

Lutz W, Butz WP, KC S (Eds) (2014). World Population & Human Capital in the 21st Century. Executive Summary, IIASA.

Butz WP, Lutz W, Sendzimir J (Eds) (2014). Special Feature, “Education and Differential Vulnerability to Natural Disasters.Ecology and Society

KC S, Lutz W. The human core of the shared socioeconomic pathways: Population scenarios by age, sex and level of education for all countries to 2100. Global Environmental Change (Published online 4 July 2014). [doi:10.1016/j.gloenvcha.2014.06.004].

Striessnig E, Lutz W (2014). How does education change the relationship between fertility and age dependency under environmental constraints? A long term simulation exercise. Demographic Research 30(16):465–492. [doi:10.4054/DemRes.2014.30.16].

Project Adaptive Capacity to Climate Change

Data Wittgenstein Centre Data Explorer

Wolfgang Lutz This email address is being protected from spambots. You need JavaScript enabled to view it.  

Sergei Scherbov This email address is being protected from spambots. You need JavaScript enabled to view it.  

Samir KC This email address is being protected from spambots. You need JavaScript enabled to view it. Anne Goujon This email address is being protected from spambots. You need JavaScript enabled to view it.

The International Institute for Applied Systems Analysis (IIASA) is an independent scientific institute that studies problems that are too large or too complex to be solved by a single country or academic discipline. IIASA is based in Austria and its international research covers broad areas of energy and climate, food and water, and poverty and equity. IIASA is located in Austria near Vienna and is sponsored by its National Member Organizations in Africa, Asia, Europe, and North America. To view the original article, click here.