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Earth’s Changing EnvironmentLecture 11
GrowthGrowthGrowth
Growth Rate
Growth Rate = % change/year
World population increased from 6.079 billion in 2000 to 6.154 billion in 2001.
This corresponds to a Growth Rate equal to 1.2%.
US Population Growth
Current US Population:
293 millionGrowth Rate = 0.87%Population Growth
= 0.0087x 293 million
= 2.5 million2050 Population: 403 million
Global Population Growth
Current Global Population:
6.3 billionGrowth Rate = 1.15 %Population Growth
= 0.0115x 6.3 billion
= 73 million2050 Population: 9.1 billion
Global Population GrowthMore/Less Developed Countries
Now World: 6.3 billion MDC: 1.20 LDC: 5.10
2050 World: 9.1 billion MDC: 1.25 billion LDC: 7.84 billion
Growth in Energy ConsumptionMDCs & LDCs
Now World: 400 QBtu MDC: 270 QBtu LDC: 130 QBtu
2050* World: 800 QBtu MDC: 320 QBtu LDC: 480 QBtu
* A mid-range prediction
What is the carrying capacity of the Earth?
Population growth increases environmental impacts
Increasing population and increasing energy consumption will accelerate:
depletion of fossil fuel resources
increasing pollutiondeclining biodiversity
US Energy ConsumptionUS Primary Energy Consumption 1949-2002
20
30
40
50
60
70
80
90
100
1940 1950 1960 1970 1980 1990 2000 2010
Year
En
erg
y (Q
btu
)
?
Arab Oil Embargo of 1973
Exponential Growth Models
US Primary Energy Consumption 1949-2002
20
30
40
50
60
70
80
90
100
1940 1950 1960 1970 1980 1990 2000 2010
Year
En
erg
y (Q
btu
)
Exponential Growth
Constant Growth Rate
Doubling Time
DT, the doubling time, is the time for something (population, energy consumption, pollution) to double.
DT (years) = 70 / Growth Rate (%)
If Growth Rate = 3.5%, DT = 70/3.5 = 20 years.
Growth in Energy ConsumptionUS Primary Energy Consumption 1949-1972
20
30
40
50
60
70
80
1945 1950 1955 1960 1965 1970 1975
Year
En
erg
y (Q
btu
)
Growth rate = 3.4% What’s the doubling time?
Exponential Growth ModelsUS Primary Energy Consumption 1949-2002
20
30
40
50
60
70
80
90
100
1940 1950 1960 1970 1980 1990 2000 2010
Year
En
erg
y (Q
btu
)
Growth in Energy Consumption
Growth rate = 1.6% What’s the doubling time now?
US Primary Energy Consumption 1983 - 2002
70
75
80
85
90
95
100
105
110
1980 1985 1990 1995 2000 2005
Year
En
erg
y (Q
btu
)
Per Capita graph shows the effect of population growth
US Per Capita Primary Energy Consumption
200
250
300
350
400
1940 1950 1960 1970 1980 1990 2000 2010
Year
Per
Cap
ita
(Mil
lio
n B
tu)
Global Energy Consumption
Growth rate = 1.76% What’s the doubling time?
Global Primary Energy Consumption
250
300
350
400
450
1975 1980 1985 1990 1995 2000 2005
Year
En
erg
y (
QB
tu)
Global Energy Consumption
Growth rate = 0.2 % What’s the doubling time?
Global per Capita Primary Energy Consumption
0
20
40
60
80
1975 1985 1995 2005
Year
Pe
r C
ap
ita
En
erg
y
(Mill
ion
Btu
)
Another Calculation
During 2003, India consumed
13 QBtu of primary energy.Suppose the growth of Indian
energy consumption equals 5%.What will be India’s consumption
level in 2059?DT = 70 / 5 = 14 years56 y / 14 y = 4Doubles 4 times: 2x2x2x2 = 16 In 2059: 16 x 13 = 208 QBtu
Lifetime of a Non-Renewable
Lifetime (L) of a non-renewable Resource (R) with current consumption (C) increasing with a fixed growth rate (G):
L = [Ln(G R/C + 1)]/G
Example: Oil
R = 2000 Gbo C = 28 Gbo/year G = 5% L = 30 years
R = 4000 Gbo L = 42 years
G = -1 % L = 125 years
A note of caution The doubling time
calculation is very useful for estimating the effects of exponential growth, but it does not always lead to realistic predictions. If the growth rate is not constant, then growth will not be exponential.
