Human population increases exponentially:
While humans may eventually define a logistic growth curve ; currently there is no evidence that this is the case. The only think that is demonstrable, as shown below, is that the rate of growth of the world's population is decreasing, but it's still exponential in nature. here is the data
In other words, the population doubling time is increasing, but there still is a characteristic doubling time. (70/n).
Its currently an open question if the whole world will also conform to the logistic growth curve that has been obtained by the developed world.
Often times exponential growth is plotted as a straight line on a semi-log plot. The Y-axis is logarithmic and the X-axis is linear.
ln (ex) = ln y
ln y = x
We can use the Statistical Graphical Tool to help understand this.
Here is some data:
Then we will try an exponential fit with 10% growth rate to see its much better.
Population Growth and Finite Resources
This depends on three factors:
|1.9||75.3||350,000||293M (2030) 285M (2050)||2.2||82.6||880,000||263(1995) 392M(2050)||2.6||87.5||1.4 million||522M(2050)|
In addition to this, the US population is undergoing a significant regional re-distribution
ZPG is only achieved in a model which limits immigration (a very
politically sensitive issue), restricts birthrates to no more than
2 per female (more politics), and makes no attempt to increase life
The fertility rate has gone up. In 1988 the rate was 1.8 per female,
now its 2.0
this increase is entirely due to teenage pregnancy.
Equilibrium is difficult to achieve because exponential growth produces
demographics such that they are substantially more people entering
their reproductive years than those which are dying of old age.
What about ZPG for the World?
The fertility rate has gone up. In 1988 the rate was 1.8 per female, now its 2.0 this increase is entirely due to teenage pregnancy.
Equilibrium is difficult to achieve because exponential growth produces demographics such that they are substantially more people entering their reproductive years than those which are dying of old age.
What about ZPG for the World?
Worst case scenario assumes 2.5 children per couple 28 billion people by 2150
Best case assumes 1.7 7.8 billion in 2050 declining to 4.3 billion by 2150
Current fertility rate is 3.3. Fertility rate in 1970 was 4.5
The above calculations, however, do not adequately factor in increases in global life expectancy.
Very Latest Projections
Population Growth Map
The above map shows the that the "industrialized" world has stabilized somewhat to population growth rates less than 1% a year. But 1% is still a doubling time of 70 years and the calculated growth rates are based, in this study, on only 5 years worth of data.
What does fertility rate depend on? Regression (to be discussed later) suggests that literacy is a key factor.
Education may be the single biggest contributor towards ZPG.
When did we know there would be a problem?
Historical Estimates of World Population (accurate to 10--20%)
So during this period of 650 years the world population was stable and fluctuated around a mean value of about 400 million.
Is this the "natural" carrying capacity of the planet?
Summary of Population Data:
Clearly in the period 1200-1600 the population of the world
was stabilized. Of course, the quality of life sucked big time.
Between 1900 and 1950 the world population rate grew at about
1% a year as shown below:
Clearly in the period 1200-1600 the population of the world was stabilized. Of course, the quality of life sucked big time.
Between 1900 and 1950 the world population rate grew at about 1% a year as shown below:
But projections based on that growth rate determined for 50 years of data would have been wrong.
Between 1950 and 1980 world population rate grew at a larger rate that 1% per year as shown below
In fact, the rate was closer to 1.8% per year which is almost a factor of 2 shorter doubling time!
Since 1980 there has been a small reduction in population growth down to about 1.65% per year.
Based on this data is fairly safe to assume, that if conditions do not change then the doubling time of the worlds population is 40--50 years.
The maximum rate ever observed, about 2.06%, occurred during the decade of the 60's. This was noticed and UN policy begin to dealt with the issue. Obviously, however, we are still growing exponentially at a significant rate.
What about other countries? Are there any that are approaching ZPG?
Growth rate: [ln (8.861/7.104)]/6 = 3.9% per decade; double = 180 years
Growth rate: [ln (95.772/28.485)]/6 = 20.2% per decade; double = 35 years
Growth rate: [ln (63.575/21.198)]/6 = 18.3% per decade; double = 38 years
Growth rate: [ln (15.609/3.495)]/6 = 25% per decade; double = 28 years
Previous Lecture Next Lecture Course Page