1 Lecture #5 Efficiencies and Growth Patterns

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3 Population with Respect to Time

4 Population Growth Constant rate of increase leads to exponential growth Exponential growth has a portion that increases very quickly → This is referred to as the knee of the graph The knee of the population graph appears to be around 1900 Zooming in on that portion of the graph…

5 Population Growth (cont’d) 1830 = 1 billion 1930 (100 years) = 2 billion 1960 (30 years) = 3 billion 1975 (15 years) = 4 billion 1987 (12 years) = 5 billion 1998 (11 years) = 6 billion

6 Population Growth (cont’d) Every time there is a breakthrough (improved farming, clothing, medicine, technology) there is a jump in population This initial jump decreases until another breakthrough It is unknown when these jumps will occur

7 Population Growth (cont’d)

8 Energy Growth

9 Energy Growth (cont’d) As people became more advanced they had the freedom to use energy more and have a better lifestyle The energy used to produce food has slightly increased The energy for houses & commerce, industry, and transportation has significantly increased The forms of energy used have also changed

10 Energy Growth (cont’d)

11 Energy Growth (cont’d) As different forms of energy were found, society adapted and used the newer forms The newer forms usually had advantages of: →Cheaper at first, more efficient, more versatile, easier to obtain, more abundant Total energy on a logarithmic scale (next graph)

12 Energy Growth (cont)

13 Demand 20% ROI 10% ROI Energy (Quads) Time (years) Energy Growth (cont’d) U.S. Energy Demand Versus Possible Supply from Solar Energy

14 Energy Growth (cont’d) Even if the energy obtained from solar collectors grows by 10% it does not significantly increase (has not reached the knee of the curve) If solar energy obtained grows by 20% it becomes noticeable but does not account for the increase in energy needed

15 Energy Growth (cont’d) Doubling time of U.S. energy use has been about 38 years Average ROI = 1.84% →1750 = 1 quad →1788 = 21 quad = 1,000,000,000,000,000 BTU →1826 = 4 →1864 = 8 →1902 = 16 →1940 = 32 →1978 = 64 →2016 = 128 →2054 = 256

16 Growth Rates Growth rates are usually expressed as “Rate of Increase” (ROI) By knowing the ROI the “Doubling Period” can be determined, which is the amount of time needed for the value to double In Economics ROI = “Return on Investment” which means the same thing

17 Growth Rates (cont) An approximate equation for Doubling Period is: →Doubling Period = 70 * years / (% growth rate) For example: →What is the doubling period if the world’s population is increasing at 1.3%? →Doubling Period = 70 years / 1.3 = 53.8 years * Actually closer to 72

18 Growth Rates (cont’d) Doubling with small numbers does not lead to a significant increase Doubling at large numbers grows extremely fast For example: →Beginning with 1 lily in a pond, and the number of lilies doubles every day →The pond can sustain 14,000 lilies →How many days until there are 14,000 lilies?

19 Lilies in Pond Lilies in a Pond (limit = 14,000 lilies) DayLilies ,384

20 Lilies in Pond - Graphical

21 Growth Rates What are the limiting agents that affect the growth of organisms? →Food Supply →Energy Supply →Space →Pollution

22 Growth Rates (cont’d) What happens when organism growth becomes limited? →Expansion to new territories →War →Disease →Death

23 Growth Rates (cont’d) Hopefully technology breakthroughs will reduce or remove the limitations →Better food production techniques →New energy sources →Improved ways for using current energy sources →Improved medical procedures Uncertain when these will occur and in what areas (energy, food, medicine)

24 Growth Rates (cont’d) What are the signs that an energy resource is starting to limit growth? →Total “cost-of-use” becomes unacceptable (too expensive) →Government places restrictions on use