With 267 people being born every minute and 108 dying, the world’s population will top seven billion next year, a research group projects, while the ratio of working-age adults to support the elderly in developed countries declines precipitously because of lower birthrates and longer life spans.

In a sobering assessment of those two trends, William P. Butz, president of the Population Reference Bureau, said that “chronically low birthrates in developed countries are beginning to challenge the health and financial security of the elderly” at the same time that “developing countries are adding over 80 million to the population each year and the poorest of those countries are adding 20 million, exacerbating poverty and threatening the environment.”

Projections, especially over decades, are vulnerable to changes in immigration, retirement ages, birthrates, health care and other variables, but in releasing the bureau’s 2010 population data sheet, Carl Haub, its senior demographer, estimated this week that by 2050 the planet will be home to more than nine billion people.

Even with a decline in birthrates in less developed countries from 6 children per woman in 1950 to 2.5 today (and to 2 children or less in Brazil, Chile, Cuba, Iran, Thailand and Turkey), the population of Africa is projected to at least double by midcentury to 2.1 billion. Asia will add an additional 1.3 billion.