As the number of humans already on Earth has resources bursting at the seams, researchers are now finding it's not just population size that impacts the planet's health. The composition of that population and where they live also play huge roles in the release of greenhouse gases.

Aging and urbanization, in particular, could significantly affect global emissions of carbon dioxide over the next 40 years, according to new research published this week in the journal Proceedings of the National Academy of Sciences.

"By examining the relationship between population dynamics and greenhouse gas emissions, this groundbreaking research increases our understanding of how human behaviors, decisions and lifestyles will determine the path of future climate change," said Sarah Ruth, program director in the National Science Foundation (NSF), which funded the study, along with a European Young Investigator's Award, and the Hewlett Foundation.

By mid-century it is estimated that the global population could rise by more than 3 billion people, with most of that increase occurring in urban areas, the researchers say.

To figure out how these changing demographics might impact climate change, the researchers developed scenarios for energy use, emissions and economic growth using a computer model (Population- Environment-Technology model, or PET).

They also analyzed data from national surveys covering 34 countries and representative of 61 percent of the global population to estimate key economic characteristics of household types over time, including labor supply and demand for consumer goods.

Overall, they found that if population follows one of the slower growth paths foreseen by demographers at the United Nations, by 2050 it could account for 16 to 29 percent of the emission reductions thought necessary to keep global temperatures from causing serious impacts, the researchers found.

"If global population growth slows down, it is not going to solve the climate problem, but it can make a contribution, especially in the long term," said study researcher Brian O'Neill, of the National Center for Atmospheric Research (NCAR) in Boulder, Colo.

The team found that growth in urban populations could lead to as much as a 25-percent rise in projected carbon dioxide emissions in some developing countries. The increased economic growth associated with city-dwellers was directly correlated with increased emissions, largely due to the higher productivity and consumption preferences of an urban population.

On the other hand, aging could reduce emissions levels by up to 20 percent in some industrialized countries, a finding that also had to do with productivity – older people are less likely to participate in the labor force or have lower labor productivity, and are associated with slower economic growth, the researchers say.

"Demography will matter to greenhouse gas emissions over the next 40 years," O'Neill said. "Urbanization will be particularly important in many developing countries, especially China and India, and aging will be important in industrialized countries."

The authors suggest that developers of future emissions scenarios give greater consideration to the implications of urbanization and aging, particularly in the United States, European Union, China and India.

"Further analysis of these trends would improve our understanding of the potential range of future energy demand and emissions," O'Neill said.

The research was conducted by scientists at NCAR, the International Institute for Applied Systems Analysis (IIASA), and the National Oceanographic and Atmospheric Administration (NOAA).

This article was reprinted with permission from LiveScience.
Related on LiveScience.com: