Posted October 31, 2018
October 31 is celebrated as Halloween, more and more all over the world - and there are plenty of articles here about Halloween and its origins and the diversity of traditions accompanying this increasingly popular holiday. Just check out the articles under "Also on this date," below.
There aren't a lot of other world holidays celebrated on this day to compete with Halloween for write-ups. But I discovered that the U.N. considers October 31, 2011, to be the Day of Seven Billion - because that is the date that the human population on Earth reached 7,000,000,000!
And I was immediately struck by the question, with all the deaths and births happening every minute, all over the world...
How do we know the exact date that the human population became 7,000,000,000?
Also, I recoiled in horror. Back when I was a kid, the world population was more than three billion, and we wondered how-oh-how the world could support 1,000 or even 500 more humans. Now the population has more than doubled! And my amazed question is, how on earth does Earth support so many people???
(1) How do we know the exact date?
The answer is, we don't. Population scientists take data from censuses, surveys, and population registers, and they make estimates of the entire world population based on this information. The population of the entire world is always an estimate - although a pretty good one, based on lots of evidence - and is never an exact count.
For one thing, the evidence tells us that there are 4 or 5 people born and 1 or 2 people dying EVERY SECOND. So even if it took zero time to make a count of everyone, by the time you finished your sentence, "There are exactly ______ people in the world," you'd already be wrong.
And it takes FAR from zero time to make a count. Most nations only take a census every ten years, and although some nations do it more often - such as every five years - other nations don't have a full census very often at all. For example, Afghanistan has apparently not had a census since 1979 - and even that one was incomplete.
At any rate, October 31 is a symbolic date that tells us approximately when the human population reached seven billion.
(2) How does the Earth support seven billion people?
If you think about the world population of humans, it's shocking how quickly our population is rising in the last 200 years.
It took a long, long, long, long time - almost all of the time that humankind has lived on the Earth - to reach a population of one billion, around the year 1804. But since then, the population has grown by another billion in increasingly short intervals:
1 billion - 1804
2 billion - 1927
3 billion - 1960
4 billion - 1974
5 billion - 1987
6 billion - 1999
7 billion - 2011
To give you some perspective on that, I have been alive while the Earth housed more than 2 billion all the way up to more than 7 billion. I'm only in my 60s (old but not SUPER old), and yet the only two eras I've missed out on in humankind's 500,000-plus-year history are all the hundreds of thousands of years before the human population reached a billion and the single century of 1 billion humans!
The answer to how the planet can support so many humans is "not very well," or at least not very evenly. There is a limit to how much fresh water there is, and there is a limit to how much food can be grown on Earth. Also, there is a limit to how much waste (including carbon emissions) the planet can deal with. Assuming we would rather live in a world that has fewer famines and plagues rather than more, it behooves us to control our population growth.
Aaannnd, that's already beginning to happen:
Since 1950, most countries have had declines in their birthrates and family sizes. If this decline occurs in the rest of the nations of the world, human population may stabilize around 9 billion or possibly between 9 and 10 billion.