5 Things to Know about Population and Heat-trapping Emissions

, senior climate scientist | May 9, 2012, 14:03 pm EST
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[Co-written with Peter Frumhoff, Director of Science & Policy/Chief Scientist, Climate]

In public talks about climate science, my colleague, Peter Frumhoff and I often show images of the projected rapid increase in global emissions of carbon dioxide, the most important heat-trapping gas.

Two American mothers separated by a century

A century separates these two mothers with their young children. Left photo by G.M. Ekwurzel, right photo source www.mass.gov.

Industrialized nations have been responsible for the lion’s share of heat-trapping emissions to the atmosphere. Now, most of the projected growth in emissions is in countries with emerging economies, with fastest rates of growth expected in India, Brazil and China. And when we talk about the options for reducing emissions, we’re often asked, “If we want to solve the climate problem, shouldn’t we really be focusing on reducing population growth?” We want to share with you some of our thoughts about this.

EIA projections CO2 Emissions OECD vs non-OECD countries

Growth in carbon dioxide emissions are projected to be much higher in new regions compared to countries that contributed the most historically. The OECD is the Organization for Economic Cooperation and Development. Its members include Australia, Austria, Belgium, Canada, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Japan, Luxembourg, Mexico, the Netherlands, New Zealand, Norway, Poland, Portugal, South Korea, Spain, Sweden, Switzerland, Turkey, the U.K., and the U.S. Figure source: Energy Information Agency at the U.S. Department of Energy.

The images juxtaposed above convey one aspect of this topic. On the left is my great grandmother with my grandfather in a stroller near the start of the twentieth century, on the right an image of a mother adjusting her child’s  car seat in the twenty-first century. These are both American images. The lifestyles of these two mothers and their children are poles apart with very different consequences for emissions (see figure below for carbon dioxide emissions over time in the U.S.).

Today, the per capita heat-trapping emissions of Americans have grown to one of the highest in the world. Much of the opportunity for reducing emissions comes from changing the way we power U.S. and other industrial economies, so that emissions per person in developed countries becomes lower, even as we further improve quality of life.

Let’s take a quick look at 5 things to know about the links between population growth and heat-trapping emissions that warm our planet.

Number of People and Growth Rate

According to the United Nations Population Division, the world population has continued to grow, but the growth rate peaked back between 1965 and 1970. Image source: Association for the Advancement of Science (atlas.aaas.org).

1. World Population is Still Growing, But at a Declining Rate.

There are more than 7 billion people on the planet today. By mid-century, population is projected to grow by another 1 to 3 billion people. By 2100, mid-range projections of fertility are around 10 billion people with significant uncertainty depending primarily on future fertility rates. These are oft-cited, well-known statistics and projections. What is often surprising to many is that the rate of population growth is declining from a peak of around 2.1 percent per year between 1965 and 1970. Global average growth rates have dropped ever since. Not all locations or nations follow this average trend (more on that later).

China vs US carbon dioxide emissions per person over time

Emissions of carbon dioxide per person in the United States and China over time. Data source is Carbon Dioxide Information Analysis Center (CDIAC) of the U.S. Department of Energy (DOE). Visualization from Gapminder World, powered by Trendalyzer from www.gapminder.org.

2.  When it Comes to Reducing Future Heat-Trapping Emissions, Population Composition and Size Both Matter

It is not just a matter of how many births but where those births are occurring and where people are moving to live with consequent implications for future emissions of heat-trapping gases. Compared to 1970 when most people lived in rural settings, more of us are living in cities and that trend is only expected to continue.  Urbanization has been long recognized by demographers and has implications for how people use energy, but until recently has not been fully incorporated into climate projections.

Recent research by Brian O’Neill and colleagues incorporates into model projections the influence that urbanization, as well the number of people per household and the age of household members  have on future heat-trapping emissions. Urbanization tends to increase emissions and emerging economies experiencing rapid urbanization with a highly productive work force is a growing regional driver of emissions. Older or smaller households have characteristically different consumption patterns than do younger or larger ones, for example, and these in turn affect the overall emissions of an ageing population. Especially in historically industrialized nations, the ageing population reduces the proportion of the population in the labor force  and tends to decrease emissions in these countries. On a global scale urbanization and age structure tend to offset each other, but locally these are important drivers in the changing share of emissions among countries. Taking account of these factors, and incorporating assumptions of economic growth used by the IPCC in their scenarios of future emissions, O’Neill and colleagues looked carefully at what reductions in emissions might result from different population growth scenarios and from a more detailed assessment of changes in population composition.

Urbanization Increased between 1950-2010

Over half the world’s population lives in an urban setting today compared with around 30 percent in 1950. Data Source: Population Division of the Department of Economic and Social Affairs of the United Nations Secretariat, World Population Prospects: The 2006 Revision and World Urbanization Prospects: The 2007 Revision, http://esa.un.org/unup. Photo by B. Ekwurzel

The bottom line: Under medium IPCC emissions path known as “B2,” emissions could be reduced by about 1.4 gigatons of carbon per year by 2050 under a “low” rather than “medium” population growth scenario. And population composition factors are projected to have a significant effect regionally: for example, when properly accounting for urbanization trends in the developing world, emissions tend to be higher than previous models have indicated (this is due mostly to shifts in labor force to more energy intensive activities); for the industrialized world, population aging tends to dampen emissions, as a greater proportion of the population exits the labor force. 1.4 gigatons carbon per year is a lot – roughly equivalent to net annual tropical forest emissions (based on 2011 estimates for tropical deforestation and degradation and uptake).

The climate and societal consequences of slowing population growth depends on how population growth reduces. Fertility rates often decline with economic growth – people with higher incomes tend to have fewer kids – but per capita emissions tend to increase with higher incomes in our current fossil energy intensive economies. So absent the transition to a low carbon economy, higher than projected economic growth as a driver of decreased fertility would not necessarily provide the carbon benefits O’Neill et al suggest.

We surely need to transition to low carbon economic development. But there’s ample evidence that fertility rates drop when women have access to voluntary family planning and educational opportunities.

Country comparison of number of births per woman 1950 to 2010

Countries with dramatic drops in total fertility rates are linked to increased access to family planning and other reproductive rights, usually, but not always, along with improvements in mother and child health and female education. In contrast, countries in the same region which did not make similar efforts have higher fertility rates. Original country comparisons source: Association for the Advancement of Science (atlas.aaas.org). Updated data based on United Nations, Department of Economic and Social Affairs, Population Division (2011). World Population Prospects: The 2010 Revision.

3. Women with Access to Effective Voluntary Family Planning, Education and Economic Opportunities Are Having Fewer Children

Many studies look at population drivers identified in Cairo during the 1994 International Conference on Population and Development. This famous conference highlighted the influence on population trends when women have access to effective voluntary family planning so they can decide when and how many children they have, as well as the impact of girls’ education and women’s access to economic opportunities.

Fertility rates Brazil 1940 to 2008

Dramatic drop in number of children born per woman in Brazil. Data Source: Cavenaghi, S. and J.E.D. Alves. 2011. Diversity of childbearing behaviour in the context of below-replacement fertility in Brazil, United Nations Population Division- No. 2011/8.

Income and Rates of Fertility in Brazil

Income makes a larger difference in fertility rates among women who had less than 8 years of education in Brazil (Italy is also shown for comparison). Source: Cavenaghi, S. and J.E.D. Alves. 2011. Diversity of childbearing behaviour in the context of below-replacement fertility in Brazil, United Nations Population Division- No. 2011/8.

Education and fertility rates in Brazil

Education beyond 9 years of school outstrips income disparities with regard to fertility rates among women in Brazil (Italy is also shown for comparison).

Despite increases in a woman’s ability to plan births in many countries, there remains a substantial “unmet need” in much of the world for access to voluntary family planning (a woman is said to have an unmet need if she does not want to have children in the near future, but is not using an effective method of family planning). Scott Moreland and colleagues report that there remains an estimated unmet need between 5 and 33 percent in the countries of Asia, 6 and 40 percent for Latin America and the Caribbean, and between 13 and 38 percent in sub-Saharan Africa. Meeting this unmet need would help on many economic, quality of life as well as emissions fronts.

Let’s examine Brazil to illustrate the interplay among these factors. In Brazil, fertility  rates have dropped from a high of 6.3 births per woman in 1960 to less than 1.9 births per woman  – below “replacement-level fertility” of about 2.1 children per woman in 2008. “Replacement-level fertility” is the level that, if sustained over time, population size would remain flat absent migration. Increased access for girls and women to education, economic opportunity, and voluntary family planning make a difference as well as the more difficult to measure cultural shifts over this time period.

As country by country reports on education indicate, there are still challenges around the world in giving girls access to quality education.  Again, let us return to Brazil as an example of the interplay among level of education and economic well-being that links with fertility rates (see figures to the right).

In many countries fertility rates remain high. It is instructive to compare similar countries in a region that differ in their fertility rates. These within region contrasts highlighted in the AAAS population atlas demonstrate for example, that in South Asia, Bangladesh reduced fertility rates faster than Pakistan. In the Caribbean, the Dominican Republic experienced greater drop in fertility rates compared to Haiti.

4.  Population Investments are a Complement, Not a Substitute, for Building a Low-Carbon Energy Future.

Investments in “unmet need,” education, and economic opportunities can reduce fertility rates and hence population growth. Work by O’Neill and colleagues show that such reductions in population growth can provide real reductions in heat-trapping emissions. As noted above, these reductions can be part of the solution to climate change.  But smaller populations don’t necessarily produce fewer emissions. How we power our economies and live our lives truly matters.

With roughly 20 percent of the world’s population, the U.S. and other industrialized countries have produced about 80 percent of the world’s carbon dioxide emissions from energy use since the dawn of the Industrial Revolution. Today, each American generates on average more than four times the carbon dioxide emissions than our counterparts in China, fifteen times that of individuals in India. We have both a responsibility and an economic opportunity to drive global progress by combining deep reductions in our emissions with investments in the development and adoption of clean energy technologies and reduced deforestation abroad.

And we can help support universal access to voluntary family planning and education for women and girls—goals that are critical in their own right and embodied within the Millennium Development Goals—which can also support further reductions in population growth, enhance quality of life, and, when coupled with expanded adoption of clean energy technologies, help all countries limit their emissions as they further develop their economies. The pace of funding on these important international programs have fluctuated over time and still there is more progress to be made to achieve some of the goals set out in Cairo in 1994.

5.  Here are some places you can go to get more information on population and climate change.

UCS doesn’t work directly on population science and policy issues, but we recognize that this is an area that is hugely important and insufficiently discussed in the climate policy arena. In addition to the hyperlinks above, here are some places you can go for more information.

Send a comment and let us know about any additional resources on this topic that you would like to share.


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  • Kathleen Mogelgaard

    Thank you for this thoughtful post. Since meeting women’s needs for family planning can have important, positive outcomes for both climate change mitigation and adaptation, it would be terrific to see these factors assessed in climate change planning.

    Unmet need for family planning remains quite high among women in many countries that are highly vulnerable to climate change impacts, like declining agricultural productivity. You can see an interactive map of these “population and climate change hotspots” at Population Action International’s website here: http://populationaction.org/Publications2/Data_and_Maps/Mapping_Population_and_Climate_Change/Summary.php

    While population dynamics, reproductive health needs, and women’s empowerment are frequently left out of discussions of our climate future (I wrote about the absence of population in assessments of food security in a climate-altered future here: http://www.newsecuritybeat.org/2012/03/food-security-in-climate-altered-future.html), I am hopeful that more voices from more sectors will help to mobilize the political will and resources needed to close remaining gap in access to family planning worldwide.

    Assessing these issues in the context of climate planning (National Adaptation Plans, for example) and global discussions of sustainable development (like the upoming Rio+20 talks) would be a great place to start.

    • http://www.ucsusa.org/news/experts/brenda-ekwurzel.html Brenda Ekwurzel

      Kathleen, thank you for pointing out those resources. I was especially surprised to see the very high numbers of people projected for the Niger River Delta and the Nile River Delta regions in 2035 and 2090 in the interactive map feature of hot spots.

  • http://www.popjustice.org Laurie Mazur

    Thank you for this excellent, thoughtful analysis. It’s great to see women’s empowerment and reproductive health getting some well-deserved attention as one of many means to address the climate crisis — and as an important end in itself. I have also written about the benefits of this strategy, for example:
    Also, it’s worth noting that women’s empowerment and reproductive health will also nurture individual and social resilience, which is essential for coping with the climatic changes that are already in the pipeline:

  • Wiliam J. Chopak

    As a former electronic technician, engineer, program manager, inventor, and author, now a 66 yo, honorably discharged disabled American veteran of both militaty and civilian service, I find it totally unacceptable that our nation can’t or won’t build a 2 passenger, no frills, safe, 100 miles on a charge, 85 mph top speed, carbon fiber body, less than $10K electric automobile. It would be America’s VW bug of the 50’s with a bigger positive impact than the bug. This would be the perfect “stimulous” package for our nation. I am very disappointed that the best we can do is the Volt @ $35K, after all their “research”.