By Michael D. Lemonick
Talk to people who care about the environment and you'll hear plenty about pollution, deforestation, sustainability and climate change. What you won't hear is the word "population," unless it refers to populations of endangered species.
But if you think about it, the Earth's booming human population is at the root of just about every environmental crisis that threatens the natural world. Last October 31, Earth's population reached 7 billion people (unofficially, because there's no way to pinpoint the actual day, but it was in the ballpark). Every last one of them taps into the planet's resources as they eat, work and create waste in a myriad of different forms. By 2027 we'll be up to 8 billion, and the U.N. predicts we'll hit 9 billion in 2047.
Even now, however, the pressure on Earth's resources is already extreme, and more people will only make it worse. Deforestation and other forms of habitat destruction, for example, are mostly the result of all those billions of people clearing land for places to live and grow food.
Destroy natural habitats and you throw ecosystems out of whack, to say nothing of wiping species off the planet at such an alarming rate that scientists believe we may be seeing Earth's sixth mass extinction (the previous five were caused by things like asteroid impacts or gigantic volcanic eruptions). All those billions of people burning wood and coal and oil, for heating, transportation, electricity and manufacturing, moreover, generate air pollution, including heat-trapping greenhouse gases.