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.

As the largest-ever generation of young people enters adulthood, armed conflict is having a profound effect on their future. People under the age of 24 comprise nearly half the world’s population but are the primary participants in conflict today. Conflict is more prevalent in younger societies, and half of all forcibly displaced people are children.

“Saving the planet depends on women achieving full human rights, and that begins with reproductive rights,” writes the Natural Resources Defense Council’s Frances Beinecke in a new set of essays on reproductive health published by the United Nations Foundation and the Aspen Institute.

In 2013 the United Nations Population Division revised its population projections to show that population could grow even faster than previously anticipated, especially in Africa. Planning ahead for feeding a hot, hungry, teeming planet is both a numbers game and social venture. Calories, climate change, and acres of land are some of the factors on one side of the equation. The 7 billion people in the world, projected to grow to 9.6 billion by 2050, are on the other.

Years ago, when I was a diplomatic correspondent at a large national magazine, if I encountered what I thought of as “science stuff,” I sent it to the science desk. I was busy covering foreign policy, wars, and ethnic and religious conflicts – not science. It was only when I took a new job focused on educating the U.S. media on a wide range of international issues that I began to discover the rich world I had overlooked, and see new links and connections.

Many recurring problems in natural resource management are the result of missing a key point: ecosystems and human systems are inextricably linked and dynamic, changing constantly. We are part of a socio-ecological system, not external to it, as many previously thought. In the “age of man” – the Anthropocene, as some scientists call the current era – cross-sectoral collaboration is needed to make substantial headway in tackling complex challenges, such as natural resource-related conflict and climate change.

This past December, Bangladesh turned 42, bringing the country Henry Kissinger once predicted would become a “basket case” into comfortable middle age (though perhaps this analogy breaks down for countries like Switzerland, age 722).