Population & Ecological Footprints

The Ecological Footprint Quiz only shows an individual's impact. To calculate the overall impact of our species on the biosphere, we need to add up the Ecological Footprints of the Earth's entire human population. Since the size of the biosphere is finite, the greater our world family, the less nature per person.

If people have, on average, more than 2 surviving children, the population will increase. That's the mathematics of population growth. In societies with a large per capita consumption, just maintaining current population size may not be compatible with sustainability if there is no significant reduction in the average Ecological Footprint. In other words, we must address both our population size and the size of our Footprints in order to keep our planetary use of natural resources in balance.

What would happen if the factors leading to population growth changed? Below is some simplified data for the mathematically inclined, illustrating how the number of children families have affects the global population.

World Population
Year	Population (in billions)
1800	1.0
1900	1.7
2000	6.1
2100: a range of possible scenarios
a) with one-child families	1.4
b) with two-child families	8.7
c) at year 2001 growth rate	22.2
Note: 1 billion = 1,000 million = 1,000,000,000

How are the three scenarios for 2100 calculated?

The tables below provide highly simplified demographic models for calculating the implications of varying birth rates. The column for the year 2000 shows a rough age distribution of the human population today. Population values provided are gross worldwide estimates, in billions of individuals.

a) One-child families. If families were to have on average one child each, the 2.9 billion "children" will have produced 1.5 billion offspring once they become parents by 2025. The generation of 1.5 billion will in return have 0.8 billion offspring by 2050. If the population would move back to 2-child families in 2100, the population would stabilize within about 50 years at 600 million people.

	2000	2025	2050	2075	2100	2125	2150
Grandparents (51+ years)	1.1	2.1	2.9	1.5	0.8	0.4	0.2
Parents (26-50 years)	2.1	2.9	1.5	0.8	0.4	0.2	0.2
Children (0-25 years)	2.9	1.5	0.8	0.4	0.2	0.2	0.2
TOTAL (billion)	6.1	6.5	5.2	2.7	1.4	0.8	0.6

b) Two-child families: If the 2.9 billion people between 0 and 25 years were to reproduce at replacement fertility, all three age categories would eventually grow to 2.9 billion each. This would lead to a world population of 8.7 billion people by the year 2050.

	2000	2025	2050	2075	2100	2125	2150
Grandparents (51+ years)	1.1	2.1	2.9	2.9	2.9	2.9	2.9
Parents (26-50 years)	2.1	2.9	2.9	2.9	2.9	2.9	2.9
Children (0-25 years)	2.9	2.9	2.9	2.9	2.9	2.9	2.9
TOTAL (billion)	6.1	7.9	8.7	8.7	8.7	8.7	8.7

c) Maintaining current growth rate. In 2001, the growth rate (birth rate minus death rate) of the world population was 1.3 percent per year. If this rate of growth were to remain constant into the future, there would be 22.2 billion people on Earth in the year 2100.

	2000	2025	2050	2075	2100	2125	2150
Grandparents (51+ years)	1.1	2.1	2.9	3.4	5.3	7.4	9.5
Parents (26-50 years)	2.1	2.9	3.4	5.3	7.4	9.5	13.8
Children (0-25 years)	2.9	3.4	5.3	7.4	9.5	13.8	19.0
TOTAL (billion)	6.1	8.4	11.6	16.1	22.2	30.7	42.3

Data derived from: UN Population Division, http://esa.un.org/unpp, "World Population Prospects" (World population database, 2000) and Population Resources Bureau, http://www.prb.org.
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* Courtesy of Redefining Progress.Org.
See original at < http://www.myfootprint.org/ >.
For another Footprint/population essay on this website see < Sustainable Populations Using Footprint Data >.

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