The Limits to Growth model was based on the assumption of exponential growth. Exponential growth increases surprisingly rapidly compared with linear growth. Arithmetic or Linear versus Exponential Growth An example of arithmetic growth is 1, 2, 3, 4, 5, and so on. Exponential growth means a quantity increases by doubling: 2, 4, 8,16, 32, and so on. A Riddle "A French riddle for children illustrates another aspect of exponential growth&emdash;the apparent suddenness with which it approaches a fixed limit. Suppose you own a pond on which a water lily is growing. The lily plant doubles in size each day. If the lily were allowed to grow unchecked, it would completely cover the pond in 30 days, choking off the other forms of life in the water. For a long time the lily plant seems small, and so you decide not to worry about cutting it back until it covers half the pond. On what day will that be? On the twenty-ninth day, of course. You have one day to save your pond." Source: Donella H. Meadows et al., The Limits to Growth, Pan Books Ltd, London and Sydney, 1972, p. 29. Back to top...