Class notes 26

Physics and Society
Global Issues
#2
Global issues:
Biological diversity ⇒ Biodiversity
 Population issues

Population Issues
• How fast is the world’s population increasing?
• Why has the population been growing so fast?
• Projections (extrapolations)
• TFR
• How many people can the Earth support?
Population Growth: Numbers
Check
http://www.census.gov/cgi-bin/ipc/popclockw
for current estimate of world population
Check
http://www.census.gov/cgi-bin/popclock
for current estimate of population in the US
Data illustrating population growth from 1950 until present :
http://www.census.gov/ipc/www/idb/
Year
Population
Average
Annual
Growth
Rate (%)
Average
Annual
Population
Change
1950
1951
1952
1953
1954
2,556,000,053
2,593,766,843
2,635,808,441
2,681,128,483
2,728,970,894
1.47
1.61
1.70
1.77
1.86
37,766,790
42,041,598
45,320,042
47,842,411
51,338,406
1955
1956
1957
1958
1959
2,780,309,300
2,833,163,500
2,888,883,431
2,945,278,983
2,997,498,840
1.88
1.95
1.93
1.76
1.39
52,854,200
55,719,931
56,395,552
52,219,857
41,952,183
1960
1961
1962
1963
1964
3,039,451,023
3,080,074,578
3,136,085,194
3,205,482,213
3,276,488,697
1.33
1.80
2.19
2.19
2.08
40,623,555
56,010,616
69,397,019
71,006,484
68,914,399
1965
1966
1967
1968
1969
3,345,403,096
3,415,530,879
3,485,173,833
3,556,919,849
3,631,445,161
2.07
2.02
2.04
2.07
2.05
70,127,783
69,642,954
71,746,016
74,525,312
75,116,177
1970
1971
1972
1973
1974
3,706,561,338
3,783,950,269
3,860,726,782
3,937,095,195
4,012,815,398
2.07
2.01
1.96
1.90
1.81
77,388,931
76,776,513
76,368,413
75,720,203
73,475,831
1975
1976
1977
1978
1979
4,086,291,229
4,158,335,383
4,230,668,361
4,302,946,157
4,378,136,381
1.75
1.72
1.69
1.73
1.71
72,044,154
72,332,978
72,277,796
75,190,224
75,641,253
Again the numbers
for world population
More
39 yrs
1980
1981
1982
1983
1984
4,453,777,634
4,529,901,004
4,610,154,133
4,690,496,401
4,769,914,078
1.69
1.76
1.73
1.68
1.68
76,123,370
80,253,129
80,342,268
79,417,677
80,660,545
1985
1986
1987
1988
1989
4,850,574,623
4,932,980,829
5,018,492,004
5,104,569,514
5,190,303,832
1.68
1.72
1.70
1.67
1.66
82,406,206
85,511,175
86,077,510
85,734,318
86,688,377
1990
1991
1992
1993
1994
5,276,992,209
5,359,443,166
5,441,767,654
5,522,887,616
5,602,585,704
1.55
1.52
1.48
1.43
1.41
82,450,957
82,324,488
81,119,962
79,698,088
79,779,384
1995
1996
1997
1998
1999
5,682,365,088
5,760,931,648
5,840,445,216
5,918,624,368
5,996,215,340
1.37
1.37
1.33
1.30
1.27
78,566,560
79,513,568
78,179,152
77,590,972
76,883,461
2000
2001
2002
6,073,098,801
6,149,416,885
6,225,517,558
1.25
1.23
1.21
76,318,084
76,100,673
75,881,416
6B-day on
10/12/99
according to UN
Graphs are easier to “read”
Extrapolations start here
Annual addition in millions
Annual growth rate
Scale of plot
is important
From: “God’s Last Offer”
Ed Ayres, Editor of
World Watch magazine
Related spike ...
Another one ...
And ...
Why has population been growing so fast?
Why do you think?
• improved medicine
• improved sanitation
• improved nutrition
⇒ major decline in death rates
and corresponding increase in life expectancy
Decline in death rates started in Europe and North America in 1800s
During last century this decline also took place in developing countries
Life expectancy
1930
1960
1990
Numbers
US : http://www.cdc.gov/nchs/fastats/lifexpec.htm
Demographic transition
Birth rates have also been falling, but not as quickly!
Relevant concept :
demographic transition
Two meanings according to Joel Cohen (theoretical biologist)
Idealized historical pattern of changes in birth, death, and
population growth rates involving schematically four stages
1)
high average birth & death rates nearly equal
⇒ no growth
2)
death rates fall, birth rates high ⇒ growth
3)
low death rates, birth rates declining ⇒ still growth
4)
low death & birth rates ⇒ no growth
Resulting in a stable but much larger population
Demographic ...
Other meaning of demographic transition
Hypothesis about the mechanisms of these changes
industrialization
urbanization
education
general modernization first leading to falling death rates and
then to a fall in birth rates
according to this hypothesis, social and economic
development causes the transition
However, this is not borne out by experience in the world’s
poor countries since World War II
Example: Kerala “Despite low income and productivity growth since 1970,
Kerala’s citizens enjoy a life expectancy on a par with Hungary and
literacy rates comparable with those in Norway. ...
… fertility rate of 1.8 per woman …” from: “World Resources 1998-99”
Projections
Relation between relative change per year and doubling time
Quick reminder: compound interest
After one year
⇒
original amount x ( 1+ percent interest / 100)1
After two years
...
⇒
original amount x ( 1+ percent interest / 100)2
After 50 years
⇒
original amount x ( 1+ percent interest / 100)50
1% fifty years : (1 + 1 / 100 )50 = 1.64
so 64% increase
Doubling time : growth rate given ask for doubling time Td
(1 + growth rate (in percent) / 100 ) Td = 2
For 1 % solve 1.01 Td = 2
so Td = ln 2 / ln 1.01 = 69.7 yr
For 1.8 % solve 1.018 Td = 2 so Td = ln 2 / ln 1.018 = 38.9 yr
For 4 % solve 1.04 Td = 2
so Td = ln 2 / ln 1.04 = 17.7 yr
TFR
Projections of future population levels involve TFR
TFR = total fertility rate = average # of children born per woman in
reproductive lifetime (at current birth rates)
age15-50: use numbers of the present year
Region
1990 TFR
World
3.3
Europe
Northern America
Oceania
USSR
1.8
1.8
3.2
2.4
Region
1990 TFR
Africa
China
India
Latin America
Other Asia
6.5
2.5
4.4
4.1
5.0
Source: UN 1992
Projections
UN estimates
Innocent?
- constant fertility : area TFR fixed at 1990
levels plus continued slow decline in
death rates
How many people in 2150?
Can’t go this path ...
continued
• Instant replacement (also unrealistic)
life expectancy of 87.5 for women and 82.5 for men
plus immediate rise in some and drop in other areas
of TFR to replacement level ⇒ 2.06
2150 ⇒ 8.4B
• More realistic ones : somewhere in between
UN
Worldbank
low
medium high
2025
7.6
8.5
9.4
8.4
2050
7.8
10.0
12.5
10.0
2100
6.0
11.2
19.2
11.3
2150
4.3
11.5
28.0
11.5
Picture
Some countries
Country
1950
1990
2030
China
India
United States
Indonesia
Nigeria
Pakistan
Brazil
Bangladesh
Russia
Mexico
563
369
152
83
32
40
53
46
114
28
1,134
853
250
189
87
118
153
114
148
85
1,624
1,443
345
307
278
260
252
243
161
150
What lowers TFR?
• reduce child mortality rates through better health care
• increase per-capita income by economic development
• increase female secondary enrollment (postponing marriage)
• increase use of contraceptives by making it affordable
Sci Am December 1993 p 60
Example
Similar results for
- child mortality
- per-capita income
- female secondary
enrollment
How many people can the Earth support?
• Growth in developed nations also a problem
• Why?
G7 nations (10% of global population)
consume 40% of fossil fuels, most commodities
and forest products
Even small increases in population can have
a significant impact (bigger “footprint”)
Human carrying capacity ⇒ requires more specificity
- what kind of life?
- with what technology?
- for how long?
- leaving what kind of earth for the future?
Carrying capacity
Estimate must include
- diet (how many calories per person)
- productivity of available cropland
- critically important water needs
- energy use (related to climate)
- sustainability
Estimates have had an enormous range
Probably the earth is overextended; hopefully not irreversibly
I hope you will consider info
from this course as an
encouragement to think globally
and in the long term.
Thanks for taking this course!
WimD