Exponential Growth
When a quantity increases by a constant amount per unit time e.g.1, 3, 5, 7, etc. it is called linear growth. But, when it increases by a fixed percentage it is known as exponential growth e.g. 10, 102, 103, 104,………….., or 2, 4, 8, 16, 32 etc. Population growth increase in exponential rate and that explains the dramatic increase in global population in the past 150 years.
Doubling Time
The time needed for a population to double its size at a constant annual rate is known as doubling time. It is calculated as follows:
Td = 70/ r
where Td = doubling time in years
r = annual growth rate
If a nation has 2% annual growth rate, its population will double in 35 years.
Total Fertility Rate
It is one of the key measures of a nation’s population growth. TFR is defined as the average number of children that would be born to a woman in her lifetime if the age specific birth rate remains constant.
Infant Mortality Rate
It is an important parameter affecting future growth of population. It is the percentage of infant died out of those born in a year. Although this rate has declined in the last 50 years, but the pattern differs widely in developed and developing countries.
Life Expectancy
It is the average age that a newborn infant is expected to attain in a given country. The average life expectancy, over the globe, has risen from 40 to 65.5 years over the past century. In India life expectancy of males and females was only 22.6 & 23.3 years, respectively in 1900. In the last 100 years improved medical facility and technological advancement has increased the life expectancy to 60.3 & 60.5 years, respectively for the Indian males and females. In Japan and Sweden life expectancy is quite higher, being 82.1-84.2 for females and 77-77.4 for males, respectively.
Q. Demographic Transition.
Ans. Population growth is usually related to economic development. There occurs a typical fall in death rates and birth rates due to improved living conditions leading to low population growth, a phenomenon called demographic transition.
It is associated with urbanization and growth and occurs in four phases:
i. Pre-Industrial Phase characterized by high growth and death rates and net population growth is low
ii. Transitional Phase that occurs with the advent of industrialization providing better hygiene and medical facilities and adequate food, thereby reducing deaths. Birth rates, however, remain high and the population shows 2.5-3% growth rates
iii. Industrial Phase while there is a fall in birth rates thereby lowering growth rate.
iv. Post Industrial Phase during which zero population growth is achieved.
Demographic Transition is already observed in most developing nations. As a result of demographic transition the developed nations are now growing at a rate of about 0.5% with a doubling time of 118 years. However, the matter of concern is that more than 90% of the global population is concentrated in developing nations which have a growth rate a little more than 2%, and a doubling time of less than 35 yers.
Source: Perspectives in Environmental Studies, by Kaushik & Kaushik
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