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Class13 - Population Growth and the Need for Technologies...

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Population Growth and the Need for Technologies “Go forth and multiply” Genesis 1:28
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Joesten,”Essentials”,Saunders, 1993,324 Population Curve up to year 2000
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Cunningham/Saigo, Environmental Science, 6th, McGraw Hill, MA, 2001, 130 (Linear - straight line) Increases by constant amount: 1, 2, 3…. (Exponential - J- shaped) Increases by constant multiple: 1, 2,4,8…. Two common math models used to describe curves Two most common math models are linear and exponential (J-shaped). The preceding population curve appears to be J- shaped or exponential up to 2000.
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Population curve >2000 is expected to be s-shaped (sigmoidal) http://www.emc.maricopa.edu/faculty/farabee/biobk/expgrowth.gif *Carrying capacity - the largest number of any given species that an ecosystem can support indefinitely.
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Turk, Intro to Envir. Studies, 3rd, Saunders, NY, 1989, 85 Projection raises two questions: (1) are we likely to exceed the carrying capacity by 2100? and 2) if not, can output of current technologies be increased or are new technologies needed? Population projections are based on sigmoidal curve
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Cunningham/Saigo, Environmental Science, 6th, McGraw Hill, MA, 2001, 131 Critical number Extinction Exceeding carrying capacity has consequences *Critical number- minimum population required to sustain a species (also not known for humans). Recovery Critical number Unfortunately earth’s carrying capacity for humans is not known.
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Campbell made “estimates” of earth’s carrying capacity for humans Example problem: Annual rainfall over land portions of earth is 3 x 10 17 L/yr. The average human in a developed country consumes 10 7 L of water/yr. Estimate the maximum carrying capacity for humans at the level of a developed country with respect to water (make same assumptions as Campell) 3 x 10 17 L/yr / 10 7 L/yr/person = 3 x 10 10 persons = estimate of carrying capacity Campbell, J.A., Chemical Systems, Freeman, CA, 1970, 16
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Example problem: Photosynthesis annually produces 2.0 x 10 15 lbs of sugar by the reaction, 6CO 2 (g) + 6H 2 O(l) C 6 H 12 O 6 (aq) + 6O 2 (g). The average human in a developed country consumes 2.1 x 10 5 lbs of O 2 per year. Estimate the maximum carrying capacity of earth for humans at the level of a developed country with respect to oxygen. 2.0 x 10 15 lbs x 6CO 2 (g) + 6H 2 O(l) C 6 H 12 O 6 (aq) + 6O 2 (g) 6 MW 6 MW 1 MW 6 MW 6(44) 6(18) 1(180) 6(32) 264 lbs 108 lbs 180 lbs 192 lbs 2.0 x 10 15 lbs sugar = x lbs oxygen 180 lbs sugar 192 lbs oxygen 2.1 x 10 15 lbs oxygen = 1.0 x 10 10 persons = carrying capacity 2.1 x 10 5 lbs oxygen/person x = 2.1 x 10 15 lbs of oxygen Some estimates require chemical calculations Campbell, J.A., Chemical Systems, Freeman, CA, 1970, 16
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Campbell, J.A., Chemical Systems, Freeman, CA, 1970, 16 Based on his estimates, Campbell identified possible “limiting” factors Campbell suggested in 1970 that 1) heat will limit the carrying capacity of earth to <10 billion humans, and 2) we should develop solar technologies to replace fossil fuels to minimize heat stress as population increases.
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