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Global Population Growth

“At first there is only one lily pad in the pond, but the next day it doubles, and thereafter each of its descendants doubles. The pond completely fills up with lily pads in 30 days. When is the pond exactly half full?

Answer: on the 29th day.”

—Old French riddle

INTRODUCTION

Since 1800, human population has grown from one billion to six billion people. Over the next half century, that number is projected to rise to nine billion. In this activity you will investigate different populations growth rates as well as how long it takes the populations of different countries and territories to double.

The meaning of a growth rate is the increase in a country’s population during a period of time expressed as a percentage of the population at the start of that time (think back to the dice lab). For example, if a town had 75 people in 1980 and 100 people in 1981, the growth rate for the year would be 33 percent.

GROWTH RATES

Using the equation for growth rate to the right, complete the following questions. Show all work.

  1. Use the equation below to double check in information in the introduction. The initial population was 75, and after 1 year, the population was 100 people.
  1. If a population started at 50 people, and ended with 500 people after 5 years had passed. What would the population growth rate be?
  1. Use the data to calculate the growth rate (r) for the time periods below

Human Population, 1920 - 1940

Date / Population
(millions) / Date / Population
(millions) / Date / Population
(millions)
1920 / 1800 / 1930 / 2070 / 1940 / 2300
  1. What was the growth rate from 1920 to 1930?
  1. What was the growth rate from 1920 to 1940?

GLOBAL POPULATION GROWTH

As we have discussed, not all countries are growing at the same rate. So, certain parts of the world’s population are doubling faster than others. In this activity,will be using 10-year compounded growth rates to determine when each country’s population will double. The 10- year growth rate is based on annual growth rates for 2003 from the U.S. Bureau of Census International Database. The starting population for each country will be 50 individuals, and for this activity the growth rate will be assumed to be constant.

Directions:

  1. Your team will be assigned four to six countries.
  2. Your assigned countries will be circled. Find each country’s 10-year growth rates on the “Growth Rates Worldwide” handout. (The 10-year growth rate tells you the rate at which the population of the country increases every 10 years.)
  3. Based on each country’s growth rate, make a prediction as to how many decades (10-year periods) it might take for each country’s population to double in size.
  4. Record your predictions in the appropriate place on the predictions data table for each country below.

Predictions Table:

Country / Growth rate / Prediction (number of decades for the population to double)

Procedures continued:

  1. Use an initial population of 50 individuals for each country. Follow the steps listed below in the “Calculating Population Growth” section on the following page to calculate how large each country’s population will be after 10 years.
  2. On a separate piece of paper, copying the data table in the example on the next page, create a data table for each of your countries. Record the new population size for each decade in those tables.
  3. Repeat the process until each country’s population size doubles (meaning it surpasses 100).
  4. Staple you data table sheet to this packet.
  5. Use your results to make a bar graph that shows how many years the populations of each of your countries took to double.

Calculating Population Growth

  1. Multiply the initial population (50) by the growth rate. This will give you the number of individuals that are added to the population in a 10-year period. (This number should be rounded up, since partial individuals do not exist in the real world.)
  2. Add the result from Step 1 to the initial population to get the new population after 10 years.
  3. For the next 10-year period, the new population size becomes the starting population value. Multiply the new population size by the growth rate. As before, add the resulting number of individuals to the starting population to calculate the new population size after 20 years.
  4. Repeat the process until each country’s population has doubled. Note that because you are looking a 10-year periods, the population may not be exactly double in size at the end of a period. For instance, in the example given, you would stop after 30 years, when the population reaches 124.

Sample Problem:

For a country with a 10-year growth rate of .25. If the initial population was 50, how many years before it doubles?

Sample Data Table:

Starting Population / 10- year growth rate / Number of new individuals / New population size
Initial / 50 / .25 / 12.5 (round to 13) / 63
After 10 years / 63 / .25 / 15.75 (16) / 79
After 20 years / 79 / .25 / 19.75 (20) / 99
After 30 years / 99 / .25 / 24.75 (25) / 124

Sample Answer:

If the initial population was 50, then the country’s population doubles to 100 sometime after 20 years.

YOU NEED TO MAKE DATA TABLES THAT LOOK LIKE THIS FOR EACH COUNTRY! REMEMBER TO STAPLE IT ON!

Graph:

ANALYSIS SECTION

1.Compare your results with your original predictions. How do they compare?

2.How doesincreasing or decreasing thegrowth rate affect how quicklythe population size increases ordecreases?

3.Use your “Growth RatesWorldwide” handouts to findthe country or territory with thelowest growth rate and thecountry or territory with thehighest growth rate. Use yourformula to calculate how long itwould take each one to double.

4.How do they compare to the countries in your original data set? If you were a leader of either of those countries, what would be your concerns about your country’s growth rate?

5.The world population is currently estimated at roughly over seven billion people. If the projected 10- year growth rate is 0.123, how long will it take for the world population to double?

DOUBLING RATES

Currently, the human population is growing at an exponential rate as we saw in the “Human Populations Growth worksheet.” Populations that grow exponentially grow at a constant “doubling rate.” You have been using the 10-year compounded growth rate to see about how long it takes populations to double. There is however, an equation that shows how long it will take a population to double.

The rate of national growth is expressed as a percentage for each country, commonly between about 0.1% and 3% annually (r). For example, in the year 2000, Canada's annual growth rate was 1% and in the United States the annual growth rate was. 9%. The growth rate can be used to determine a country or region or even the planet's "doubling time," which tells us how long it will take for a country's current population to double. This length of time is determined by dividing the growth rate into 70. This is seen in the equation to the right.

Sample Problem:

Given Canada's overall growth of 1% in the year 2000, we divide 70 by 1 (from the 1%) and yield a value of 70 years. Thus, in 2070, if the current rate of growth remains constant, Canada's population will double from its current 31 million to 62 million.

Doubling Rate Problems:

  1. In 2013, the estimated population size of Kenya was 22,262,501, and the growth rate was 2.27%. Calculate the population size of Kenya if it were to double. Then calculate how many years this would take if the growth rate remained constant. Show work

Initial population / Doubled population / How many years to double?
  1. In 2013, the estimated population size of Denmark was 5,556,452 and the growth rate was 0.23. Calculate the population size of Denmark if it were to double. Then calculate how many years this would take if the growth rate remained constant.

Initial population / Doubled population / How many years to double?
  1. In 2013, the world population was estimated to be 7,095,217,980 and the growth rate was 1.095%. Calculate the population size of the world if it were to double. Then calculate how many years this would take if the growth rate remained constant.

Initial population / Doubled population / How many years to double?
  1. Are these numbers guaranteed? Why or why not?

Data for growth rates and population size:

2