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Human Population on the 50th Earth Day

The following is from an insert to a 1994 solicitation letter from the group Zero Population Growth (renamed Population Connection in 2002).

In the seconds it takes you to read this sentence, 24 people will be added to the Earth’s population.

 Before you’ve finished this letter, that number will reach 1,000.  Within an hour ... 11,000.  By day’s end ... 260,000.

 Before you go to bed two nights from now, the net growth in human numbers will be enough to fill a city the size of San Francisco.

 It took four million years for humanity to reach the 2 billion mark.  Only 30 years to add a third billion.  And now we’re increasing by 95 million every single year.

 No wonder they call it the human race.

Answer the following questions.  Write out the calculation you made in order to get each answer.

  1. The first Earth Day was on April 22, 1970.  In what year will we celebrate the 50th Earth Day? 
  2. How old will you be on the 50th Earth Day? 
  3. Assuming that ZPG’s projection (95 million people per year) is correct, and that there were 5.64 billion people in the world on Earth Day 1994, what will be the world population on the 50th Earth Day?
  4. How many seconds did the ZPG author assume it would take an average person to read the first sentence of the insert?
  5. Each summer, the Population Reference Bureau updates its World Population Clock to reflect its best estimate for the numbers cited in the ZPG solicitation letter insert (among others). Using the latest PRB number for annual population increase, what will be the likely world population on the 50th Earth Day?
  6. Assuming the PRB's World Population Clock is correct, how many people will be added to the Earth's population in the seconds it takes an average person to read the first sentence of the ZPG insert?
  7. Assuming the Census Bureau's PopClock is correct, how many people will be added to the Earth's population in the seconds it takes an average person to read the first sentence of the ZPG insert?

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original web posting: Tuesday, November 14, 2000
last modified: Tuesday, April 14, 2015