Sep 23, 2014 | Demography
By: Wolfgang Lutz, Bill Butz, Samir KC, Warren Sanderson, and Sergei Scherbov: IIASA World Population Program
Demographers from the United Nations Population Division and several universities published a paper in Science last week that argues the world population is unlikely to stop growing this century. They calculate that there is an 80% probability that world population, now 7.2 billion, will increase to between 9.6 and 12.3 billion in 2100, with the median at 10.9 billion.
Different projections for future fertility rates in countries such as China and Nigeria are one major reason for the difference in projections between IIASA and the UN. Photo Credit: Evgeni Zotov via Flickr
Next month, we will announce the results of our newest assessment at the launch of a new book entitled: “World Population and Global Human Capital in the 21st Century” (Lutz, Butz and KC, Oxford University Press 2014). Contrary to the UN projections, the IIASA medium (most likely) scenario indicates that world population will increase to 9.2 billion by 2050, peak at 9.4 billion around 2070 and start a slow decline to 9.0 billion by the end of the century.
The new UN paper uses a probabilistic approach to global population projections providing quantitative uncertainty ranges. Such an approach was first developed at IIASA. In a 1997 Nature article, IIASA used probabilistic methods to indicate that the doubling of world population was unlikely. And in a 2001 Nature article, IIASA demographers projected that there was an 85% chance that the world’s population would stop growing this century.
The UN and IIASA population projections use very different approaches for defining the assumptions underlying future fertility and mortality trajectories. The new IIASA projections are based on the substantive input of more than 550 experts worldwide who were invited to evaluate in a peer review manner a set of alternative scientific arguments bearing directly on the future demographic trajectories. This was done through an online survey as well as a series of meetings on five continents. The resulting state of our knowledge and substantive reasoning is documented in over 500 pages in the OUP book.
Alternatively, the UN population projections have recently moved away from their earlier expert-based assumptions to the other extreme: Their new probabilistic population projections reflect expert judgment only in the design of a specific statistical model which then is applied to national time series of 60 years (1950-2010) to extrapolate 90 years (2010-2100) into the future. There is no room for country-specific expert knowledge or for substantive considerations.
IIASA population projections explicitly include education, which is one factor that leads to lower fertility rates and lower projections by IIASA compared to the UN. Source: Wittgenstein Centre Data Explorer
There are two other factors explaining the difference: One is that IIASA now systematically adds a differentiation by level of education in addition to the conventional age and sex to its population projections, as education significantly influences fertility rates (Policy Brief: Rethinking population policies). Once this important source of population heterogeneity is explicitly taken into account the future looks different. In the example of Nigeria, the UN projects an increase from 160 million in 2010 to 914 million in 2100 while IIASA projects only 576 million. The IIASA projections do consider the fact that recently Nigeria has made significant progress in girls education, such that today half of the women aged 20-24 already have secondary education, while among women aged 40-44 the percentage is only 25 percent. 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.
Another difference lies in the reading of the current fertility levels in Africa as well as in China. The UN assumes that fertility in Nigeria has been stagnant at 6 children per woman for the past decade and for this reason their purely statistical model results in very slow future decline. However, the most recent Demographic and Health Survey (DHS 2013) for Nigeria shows that fertility has already declined to 5.5—a level the UN assumes would only be reached by 2020-25.
The same is true for other African countries such as Mali where the DHS shows fertility has already fallen to 6.1 a value that according to the UN projections would only be reached in 2025-30. For China, currently still the world’s biggest country, the UN assumes that fertility stands at 1.66 and will not decline further but rather increase in the future. Based on expert reasoning the IIASA projections assume that fertility in 2010 was around 1.5 and will decline to 1.4 in the coming decades, following the patterns of Japan, South Korea, Taiwan and Hong Kong which are currently in the 1.0 – 1.4 range.
Population pyramids for Nigeria show IIASA’s projected population and education levels for 2010 and 2050. Source: Wittgenstein Centre Data Explorer
References:
Lutz W, Butz W, and KC S, eds. 2014 World Population and Global Human Capital in the 21st Century, Oxford University Press 2014.
Patrick Gerland, Adrian E. Raftery, Hana Ševčíková, Nan Li, Danan Gu, Thomas Spoorenberg, Leontine Alkema, Bailey K. Fosdick, Jennifer Chunn, Nevena Lalic, Guiomar Bay, Thomas Buettner, Gerhard K. Heilig, and John Wilmoth. 2014. World population stabilization unlikely this century. Science 1257469 [DOI:10.1126/science.1257469]
Lutz W, Sanderson WC, Scherbov S. 1997. Doubling of world population unlikely. Nature, 387(6635):803-805 (19 June 1997) www.nature.com/nature/journal/v387/n6635/full/387803a0.html
Lutz W, Sanderson WC, Scherbov S. 2001. The end of world population growth. Nature, 412(6846):543-545 (2 August 2001) http://dx.doi.org/10.1038/35087589
Wolfgang Lutz. 2014. A Population Policy Rationale for the Twenty-First Century. Population and Development Review. doi:10.1111/j.1728-4457.2014.00696.x
Sep 11, 2014 | Poverty & Equity
Tarja Halonen was the 11th President of the Republic of Finland and Finland’s first female head of state from 2000 to 2012. She currently serves as the Co-Chair of the UN High-level Panel on Global Sustainability, and the Chair of the Council of Women World Leaders. She is also a member of the high-level reflection group, the Alpbach-Laxenburg Group.
“Being poor does not mean that you are stupid; it sometimes demands a lot of intelligence to survive if you are poor. It is very important to take these issues seriously and our primary focus should be the empowerment of people.” – Tarja Halonen at the 2014 Alpbach Forum
IIASA: How have you been involved in the formation of the Sustainable Development Goals? Why is this process important?
TH: I have been involved in this process since the development of the Millennium Development Goals, and I consider that it is very important that we continue to work for these principles after the implementation of the millennium goals has ended in 2015.
In spite of all of their weaknesses the Millennium Development Goals were important goals, informing the knowledge and expectations that we have regarding sustainable development and a global climate agreement or commitment. To me, the post-2015 Agenda and the Sustainable Development Goals, are perhaps the most important guarantee for the future of the world.
What is different about the approach of the Alpbach-Laxenburg Group?
We have said many times—and many world leaders agreed at Rio+20—that it is time to stop working in silos. We need a multidimensional approach, where academia, politicians, business, civil society, and also NGOs are involved. This is where the Alpbach-Laxenburg Group is so important. I think that this group is an effort to address that need, and I hope that by bringing together the various areas of society we can address the great social injustices in the world. It is not only the business of scientists what happens in the world. It is not just someone else’s problem: everyone needs to be involved in the process.
How do you hope to see the issues of gender inequality reflected in the group?
In 2012 I was co-chair of a report entitled “Resilient People, Resilient Planet: A Future Worth Choosing” for the UN Secretary General, as part of my role on the High-level Panel on Global Sustainability. While compiling this report we noticed that there are a lot of resources that are overused and which cause problems. However, what is underused is human capital.
There are three categories we should focus on: the poor, youth and women. Of course all of these groups are very important to include. But for women, inequality is a lifelong story that you cannot get rid of.
It is very important to take these issues seriously and implement measures to change the status quo. I have already tried in many ways, and of course the Council of Women World Leaders has already done a lot of work which I am very thankful for. I am also very proud of Michelle Bachelet, current President of Chile, and the first Under-Secretary General and Executive Director of UN Women, who has led work on the empowerment of women at all levels. We need to make an effort to strengthen gender and women’s rights as part of the post-2015 goals. There are many similar attempts to raise this issue but I hope this group can make it a stronger voice.
-Interview by Philippa Brooks, IIASA Communications Manager, during the 2014 European Forum Alpbach
Alpbach, Austria
Note: This article gives the views of the interviewee, and not the position of the Nexus blog, nor of the International Institute for Applied Systems Analysis.
Sep 4, 2014 | Systems Analysis
At IIASA in Laxenburg this week, renowned mathematician Don Saari laid out a challenge for the Institute’s scientists: to better understand complex systems, he said, researchers must find better ways to model the interactions between different factors.
“In a large number of models, we use climate change or other factors as a variable. What we’re doing is throwing in these variables, rather than representing interactions—like how does energy affect population?” said Saari, a longtime IIASA collaborator and council member, and newly elected IIASA Council Chair, a position he will take up in November. “The great challenge of systems analysis is figuring out how to connect all the parts.”
“Whenever you take any type of system and look at parts and how you combine parts, you’re looking at a reductionist philosophy. We all do that in this room,” said Saari. “It is the obvious way to address a complex problem: to break it down into solvable parts.”
The danger of reductionism, Saari said, is that it can turn out completely incorrect solutions—without any indication that they are incorrect. He said, “The whole may be completely different than the sum of its parts.”
Take a Rubik’s cube as an example: Saari said “If you try to solve it by first doing the red side, then the green, then the blue, you will end up with a mess. What happens on one side is influenced by what’s happening on all the other sides.”
In the same way, the world’s great systems of energy, water, climate all influence each other. During the discussions, IIASA Deputy Director Nebojsa Nakicenovic noted that current work to extend the findings of the Global Energy Assessment to include water resources could narrow the potential number of sustainable scenarios identified for energy futures by more than half.
Saari pointed out that many of the world’s great scientists—including Nobel Prize winner Tom Schelling and Kyoto prize winner Simon Levin, both IIASA alumni—reached their groundbreaking ideas by elucidating the connections between two different fields.
It may sound like a simple solution to a methodological challenge. However, understanding the connections and influences between complex systems is far from simple. As researcher Tatjana Ermoliova pointed out in the discussion, “In physical systems you can hope to observe and discover the linkages.” But between human, economic, and global environmental systems those linkages are elusive and fraught with uncertainty.
At the end of the lecture, IIASA Director & CEO Prof. Dr. Pavel Kabat turned the challenge towards IIASA scientists, and we now extend it also to our readers: How can scientists better model the connections between systems, and what needs to change in our thinking in order to do so?
You must be logged in to post a comment.