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# How Many Humans Are On Earth?

By
Jason Marshall, PhD,
November 9, 2011

As you may have heard, humanity reached a milestone last week. Well, actually, it might not have occurred last week—it could've happened a few weeks ago, or it might still be a few weeks away from happening, but the inevitable fact is that it's going to happen.

What exactly? For the first time in Earth's history 7 billion human hearts simultaneously beat out their songs of life upon its surface. Of course, many more than 7 billion people have lived in history, but this is the first time that 7 billion people have been alive at the same time.

Yippee, right? Isn't this like a weird "Happy Birthday" kind of thing that we should all be celebrating? Well…it's complicated. To start with, take a look at how Earth's population has grown over the past few centuries:

• In 1800, there were around 1 billion people
• In 1927, there were around 2 billion people (127 years later)
• In 1960, there were around 3 billion people (33 years later)
• In 1974, there were around 4 billion people (14 years later)
• In 1987, there were around 5 billion people (13 years later)
• In 1999, there were around 6 billion people (12 years later)
• In 2011, there are around 7 billion people (12 years later)

If you prefer to ingest your data graphically, here's an expanded look at this trend starting way back many thousands of years ago:

Population of the world from 10,000 BCE to 2000 CE (from Wikipedia)

What's the big deal here? Well, for a while the human population grew pretty slowly. But then around 1800 it started growing at an insane rate. After taking thousands of years to finally reach 1 billion people in 1800, it took only 127 more years for the population to double to 2 billion. And then it took only 47 more years for the population to double again to 4 billion.

Clearly, you can't keep growing a population like this without running into problems. That's just math. Eventually we'd literally run out of room to live, we'd deplete every last precious naturally occurring resource, we'd exhaust our capability to deal with all the byproducts of our existence, and problems would arise. Actually, they already have.

But, fortunately, it's not all doom and gloom. Assuming it takes another 12 years for the human population to rise from 7 to 8 billion, it will have taken a total of 49 years to double the population from 4 to 8 billion people. If you compare that to the 47 years it took to go from 2 to 4 billion people, you'll see that the rate of growth has been slowing recently. And, as the following graph shows, the growth rate is expected to continue declining in the future.

Growth rate of world population (1950-2000) (from Wikipedia)

Which is good news for the Earth and its inhabitants (humans and non-humans alike) since, as with everything, you can have too much of a good thing!

Image courtesy of Shutterstock

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