It's the obvious but forbidden truth: on a finite and already swollen planet, we can't expand indefinitely.

Some time in the next few months, the world's population clock will tick over 7 billion people. Global population has tripled in my lifetime, and is continuing to rise. The United Nations has just predicted we face a world of 10 billion in 2100. This has immense implications for all of us, and Australia will not be immune from the impacts.

Illustration: Andrew Dyson

No one can confidently predict where we will find the food, energy, water and resources needed to supply even the basic needs of so many people. On a finite planet, we are already using up far more than we can replenish, literally exhausting the environment on which we rely for our survival.

For decades, overpopulation has been off the international agenda. It is barely mentioned in the media, and is rarely discussed in relation to, say, climate change or the looming global refugee crisis. Yet it is the common factor that links all our global problems, and ignoring it condemns billions of people to lives of poverty and injustice.