Let’s take a look at the math. It is estimated that the human population is growing at a relatively low rate: 1.14% per year. But as long as the population is growing, it doesn’t matter how low the rate is. The math tells us that a growing population will eventually double. At the current growth rate, a doubling will take about 61 years.
Is there anyone who believes that 15 billion is a good number for our population? What would it take to feed that many people? Even from among those who argue that through technology it will eventually become possible to feed 15 billion people, I’ve yet to hear someone hope for a population that size.
It's hard to think of a problem we face that isn't rooted in overpopulation. Take climate change: we recently learned that rising atmospheric concentrations of CO2 over the last 100 years trend perfectly with the rising human population. A reasonable interpretation of that correlation is that population growth is driving climate change. The graphic to the right illustrates the correlation between the two.
The shocking rate of extinction in other species is also driven by population growth. So is deforestation, the depletion of our fisheries and the Great Pacific garbage patch. Pollution is driven by population growth. So are water shortages, food shortages, urban sprawl and traffic.
Environmental concerns are often championed by the left. But I'd also argue that the right has a lot to be concerned about. 100 years ago when there were only about 76 million Americans one person's pursuit of their happiness infringed less on another's. There are four times as many Americans today, 325 million and growing. That type of exponential growth has a compounding effect on the loss of liberty. If you're concerned about liberty, about excessive regulation, then you ought to pay attention to the real-world effect a growing population has on those two concerns. There is more regulation today than there was 100 years ago because there are more people. I'm not intelligent enough to know what the optimum population is for our country, but we're all intelligent enough to know that the more people you put in a finite space, the more each individual infringes on the freedom of the others.
National security is also a population concern. 100 years ago you didn't need electricity to feed the population. The "pre-electrical" carrying capacity of the planet was less than 2 billion people. Our electrical infrastructure has increased the planet's carrying capacity to 7.5 billion. The reliable, widespread availability of electrical power has brought several key technologies online that have allowed us to increase the carrying capacity of the planet. Those technologies include fertilizers, pesticides, mechanical irrigation, refined fuels for farm machinery and transportation, food factories and refrigeration.
The loss of the grid wasn't an existential threat 100 years ago because our grandparents were more self-reliant. They had more agricultural area per capita around their urban centers to meet their needs. It's just not possible for today's population to live as close to the land (as locally) as our grandparents did 100 years ago.
It is a statement of fact to say that our major metropolitan centers have outstripped their local carrying capacities. To meet the human need we now outsource the production of food and basic goods over very long supply lines. Those supply lines are dependent on reliable electrical power, which means that a disruption to grid could cause mass starvation, posing an existential threat the the country.
It doesn't matter whether you're conservative or progressive, population growth makes it harder to create the world you want to see.
It is true that the growth rate of the human population is declining in some parts of Europe. Some people cite that fact as a dismissal of the overall problem. But it’s the overall problem that we have to face. In other words, it’s the planet-wide growth rate that matters–not a localized rate.
The human population was half what it is now when I was born. It was half that when my grandfather was born. I have a hard time wrapping my mind around those numbers. What gets me is that the growth rates seemed low during the last century. For example, the growth rate peaked in the 1960s at 2.2%.
Although recent rates of growth seem low, they took us from 1.6 to 7.5 billion people quite quickly. And it's not difficult to calculate where growth will take us next.