Posted on behalf of Yana Balling

Population growth may have a large impact on future greenhouse gas emission patterns. A study published in Proceedings of the National Academy of Sciences finds that 16-29% of emission reductions necessary to prevent the global mean temperature from rising more than 2 degrees Celsius could be achieved by reduced population growth.

Changes in population size and in the distribution of ages have been widely neglected in past and present emission scenarios, finds Brian O’Neill of the National Center for Atmospheric Research in Boulder, Colorado, who led the study.

Neill and his colleagues used an energy-economic growth model to study how different population growth scenarios influence emission pathways by 2050 and 2100. They also considered what effect increasing urbanization might have on energy consumption and greenhouse gas emissions.

Aging reduces emissions as elderly people contribute less to economic growth. Urbanization has the opposite effect: The migration of people from the countryside to large cities boosts the supply of labour and so fuels economic growth and the demand for energy, the study finds.

Aging is likely to dominate future demographic development in most industrialised countries, the study concludes. But in China and India, which together account for more than one third of global population, urbanization is likely to be the key factor.

The analysis covered 34 countries in nine regions representing different states of economic development. The authors combined data, including household size and age, with United Nations projections on population growth. By 2100, the global population is projected to rise from around 6.5 billion to 5.5 to 14 billion.

Graphic above shows projected global totals (solid lines) and regional differences (colored bands) for population size. PNAS