Changes in population growth and composition, including aging and urbanization, could significantly affect global emissions of carbon dioxide over the next 40 years. The research, appearing in Proceedings of the National Academy of Sciences (PNAS), was conducted by an international team of scientists from the National Center for Atmospheric Research (NCAR), the International Institute for Applied Systems Analysis (IIASA), and the National Oceanographic and Atmospheric Administration. By mid-century it is estimated that global population could rise by more than three billion people, with most of that increase occurring in urban areas. The study showed that a slowing of population growth, following one of the slower growth paths considered plausible by demographers at the United Nations, could contribute to significantly reducing greenhouse gas emissions. The researchers found that such slow growth paths by 2050 could account for 16 to 29 percent of the emissions reductions thought necessary to keep global temperatures from causing serious impacts.