Seasoned demography geeks know to anticipate the release of the UN Population Division’s World Population Prospects in the spring of odd-numbered years. An off-cycle update published last month in Science, summarizing new results and methodological changes to the projections, therefore provoked a buzz of interest and a mini-flurry of media coverage.

The United Nations and the streets of Manhattan are going into global warming saturation mode, from Sunday’s People’s Climate March through the Tuesday climate change summit convened by Secretary General Ban Ki-moon and on through an annual green-energy event called Climate Week.

An estimated 1.8 billion people today are between the ages of 10 and 24 and 85 percent of them live in developing economies and/or fragile states. Such youthful age structures can lead to a number of challenges, including increased potential for instability, and countries with large numbers of young people must find ways to address their unique needs.

Is it possible to prepare for the unexpected? Could anyone have foreseen, for instance, a nuclear meltdown triggered by an earthquake-induced tsunami? Or a brutal band of transnational militants quickly capturing Iraq’s largest dam while attempting to establish a new Islamic caliphate? Perhaps not exactly, but that shouldn’t stop us from anticipating unlikely events, says Chad Briggs, a risk assessment expert and strategy director of consulting firm GlobalInt.

As presidents, prime ministers, and other policymakers from across the continent gather in Washington, DC, this week for the first-ever U.S.-Africa Leaders Summit, what are the issues to watch?

As global environmental change accelerates, understanding how population dynamics affect the environment is more important than ever. It seems obvious that human-caused climate change has at least something to do with the quadrupling of world population over the last 100 years.

World Population Day began in 1987 after public imagination was sparked by the idea that there could be 5 billion people on Earth. Today, we’re well past 7 billion and according to the latest UN projections, headed north of 9 billion by mid-century.

“You can look into the future a couple decades and get a very good idea about where countries are going,” said Richard Cincotta during a presentation at the National Defense University last summer – at least when it comes to demography.