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The doubling time is the time it takes for a population to double in size/value. It is applied to population growth , inflation , resource extraction , consumption of goods, compound interest , the volume of malignant tumours , and many other things that tend to grow over time.
The doubling time (t d) of a population is the time required for the population to grow to twice its size. [24] We can calculate the doubling time of a geometric population using the equation: N t = λ t N 0 by exploiting our knowledge of the fact that the population (N) is twice its size (2N) after the doubling time. [20]
Population growth is the increase in the number of people in a population or dispersed group. The global population has grown from 1 billion in 1800 to 8.2 billion in 2025. [ 2 ] Actual global human population growth amounts to around 70 million annually, or 0.85% per year.
A popular approximated method for calculating the doubling time from the growth rate is the rule of 70, that is, /. Graphs comparing doubling times and half lives of exponential growths (bold lines) and decay (faint lines), and their 70/ t and 72/ t approximations.
P 0 = P(0) is the initial population size, r = the population growth rate, which Ronald Fisher called the Malthusian parameter of population growth in The Genetical Theory of Natural Selection, [2] and Alfred J. Lotka called the intrinsic rate of increase, [3] [4] t = time. The model can also be written in the form of a differential equation:
When calculating or discussing relative growth rate, it is important to pay attention to the units of time being considered. [ 2 ] For example, if an initial population of S 0 bacteria doubles every twenty minutes, then at time interval t {\displaystyle t} it is given by solving the equation:
The global population could peak to an all-time high just below nine billion people in 2050 and then start falling, a new analysis suggests.. Researchers from the Earth4All initiative for the ...
The UN Population Division report of 2022 projects world population to continue growing after 2050, although at a steadily decreasing rate, to peak at 10.4 billion in 2086, and then to start a slow decline to about 10.3 billion in 2100 with a growth rate at that time of -0.1%.