Cross-posted from RH Reality Check.

“Are we going to talk about sex again?!” screamed my 12-year-old son, Nick, as he ran down the stairs, away from me. That was five years ago, and I had just sat down with him to have one of our father-son talks, this time about sex and sustainability.

Now Nick, a senior, is preparing for college at the same time that the global community is preparing for its own important landmark: The United Nations predicts that on Oct. 31, world population will reach 7 billion.

The confluence of these two events gives me reason to think about the world Nick is inheriting from my generation, and makes me consider what I can say to him as he heads off to college.

This world of 7 billion

I try to get my head around it. It’s a world of 7 billion people. With greater connectivity than I could have ever dreamed possible. A world of widening disparities and growing environmental degradation. A world with a changing climate. A world of crashing economic markets and changing debt ceilings.

It’s also a world of finite resources and growing demand.

Consider water: As the world’s population grows, the demand for water mounts, and pressure on water resources intensifies. Unfortunately, the areas where water is most scarce [PDF] are typically those with high population densities and rapid population growth. Population growth limits the amount of water available per person, and drives people into marginal regions — which are also water-stressed.

Consider forests: The top 10 countries experiencing the greatest loss of forest cover generally have large, fast-growing populations. Increased demand for fuel wood is driving a great deal of deforestation in the populous regions of East Africa and South Asia. Often, forests are cleared by migrant families that have been forced out of their crowded areas of origin.

Consider habitat loss: Global population is projected to grow to anywhere between 8 billion and 11 billion by the middle of the century, with much of that growth expected to take place in the humid tropics that harbor the planet’s richest biodiversity. Habitat loss is generally greatest where population density is highest. Urbanization also takes a toll: Sprawling cities have led to the disappearance of numerous habitats. And city-dwellers consume more, increasing pressures on ecosystems.

Consider changing climate: An analysis by the organization where I work, Population Action International, identified 26 population and climate change “hotspots.” These fast-growing countries are extremely vulnerable to climate change, in part because they face water shortages and declining agricultural production. The average number of children born to each woman in hotspot countries is five, and the average population growth rate is 2.5 percent — a rate that, if unchanged, would result in a doubling of the population in just 29 years.

Read more on population. Check out our series 7 billion: What to expect when you’re expanding.But continued population growth is not inevitable: In these hotspot countries, an average of one in four married women would like to avoid pregnancy, but is not using modern family planning. Addressing that “unmet need” for contraception would slow growth, reduce pressure on resources, and increase resilience. It is fundamental to invest in a woman’s right to decide how many children she can have and when she can have them, and to ensure that she can have them safely.

Reflections for Nick

These challenges may seem remote to my son, Nick, growing up in suburban Virginia. But they will shape the world he inhabits in profound ways. So what can I share with Nick as he launches into this world of 7 billion?

Son, as you continue to develop into a young man who will assume responsibility in the world, consider the following:

1. Understand the complexity of the world as you feel it. The starting point for your career and your contribution must be to recognize the world’s complexity and find your place within it. The United Nations projects that when you are 56 years old, in 2050, world population may have reached 9.3 billion. The size, shape, and form of that population matters to you, as it will affect your health, well-being, and security.

2. Recognize the value of women. I know that you already know the value of young women. I want you to know that the decisions these women make have a profound effect on the world. Ensuring that women can decide how many children they want, when to have their children, and the ways that they invest in those children is one of the most important moves we, as a society, can make. It is at the core of our lives. Recognize this and play your part as a man, particularly if you’re lucky enough to get married, and perhaps even be the father to a daughter.
    
3. Incorporate the needs of communities. As you think of your areas of study and learning, be sure to respond to real demands in order to add value. Don’t assume that you know what others need. Discover the genuine needs both of individuals and communities, and then respond.
    
4. Size (and scale) matter. Your world is inherently more complex and connected than I could ever have imagined when I was your age. It will only get more so. Determine where your impact can be most felt, and focus on the best way to have an impact at that scale. And, be sure to recognize how you can leverage innovation to maximize your impact.
5. Do the right thing. You know in your heart what’s right. Infuse that sensibility in your contributions to the world. Individual rights are fundamental to human well-being. Don’t confuse rights and wants. Make your contribution one that’s based in a rights approach, but make it practical and palatable. Go with your convictions. 

As I share these reflections with Nick, the world reaches the 7 billion population landmark, and my family reaches a personal landmark of launching a child out into this expanding world, I’m reminded of a question from my younger 16-year-old son, Miki. Standing at the front door as he signed for a package from the mailman, he screamed: “Dad, did you order these condoms with endangered-species slogans on them?”

The conversation continues …