Global Demographic Trends and Future Carbon Emissions
Brian C. O’Neill et al., “Global Demographic Trends and Future Carbon Emissions,” Proceedings of the National Academy of Sciences, vol. 107, no. 41 (12 October 2010), pp. 17521–17526. DOI: 10.1073/pnas.1004581107. URL (full paper): www.pnas.org/content/107/41/17521.full.pdf?with-ds=yes.
This paper was collaboratively assessed.
Perhaps the most widely cited peer-reviewed paper in the past decade on population-environment connections
Perhaps the most widely cited peer-reviewed paper in the past decade on population-environment connections, this study projects that a low trajectory of world population growth could contribute between 16 and 29 percent of the carbon dioxide (CO2) emissions savings needed by 2050 to avoid a 2-degree Celsius warming of the global climate, in comparison to a projected middle path of growth. This emissions savings is broadly equivalent to what would be saved by ending all deforestation by the same year. By 2100, the low-growth trajectory would reduce global CO2 emissions from 37 to 41 percent. The estimates were based on a model that integrated population, economic, and technological trends.
The authors also considered the impacts of urbanization and population aging on changes in greenhouse gas emissions. Neither of these factors influenced emissions changes to the extent that feasible variation in population growth did. The authors cite a 1995 U.S. government estimate that fully meeting the unmet need for family planning in the United States would reduce fertility in the country by 0.2 children per woman. The authors independently estimate that meeting this need would reduce fertility by 0.6 to 0.7 children per woman in developing countries. Although the average person in developing countries contributes much less to CO2 emissions than the average person in developed ones, both regions would contribute far less emissions in this century on the lower population-growth trajectory.
“Family planning would have a substantial environmental benefit.”
Key quote: “Family planning would have a substantial environmental benefit.”
FPESA assessments (three total) found the article to be scientifically strong and compelling, although two assessments expressed concern that the model was not fully explained or easily comprehensible, making the calculations and the paper hard to follow for the lay public. One assessment noted that the United Nations population projections that were the basis for the paper have since been superseded by later projections that would likely affect the emissions calculations—a common problem in scientific literature based on population data that are in a state of constant change.
Overall assessment: From its ambitious conception to its careful modeling and quantification of demographic impacts on emissions, this paper deserves the fame it has garnered. Its communications value could have been improved by clearer, more accessible writing and explanation, although the concepts and findings are not simple ones to convey. By virtue of its mathematical sophistication, the results obtained, and the articulation of its implications for family planning policy, this paper is in the top tier among papers assessed in the FPESA project that support the hypothesis that family planning promotes environmental sustainability. It would be especially valuable to refresh the paper’s basic model in the near future with newer data, comparing the results to the original paper.
The following annotation and assessment is excerpted from the forthcoming report of the Family Planning and Environmental Sustainability Assessment (FPESA) project. The report will contain selected annotations from more than 930 peer-reviewed articles reviewed for potential relevance to the hypothesis that family planning supports environmental sustainability. The annotations are written by project director Robert Engelman with input from members of the project team and, where indicated, members of the project’s international network of research assessors.