prof. r. shanthini 19 sept 2011 1 sustainable limit calculations

Prof. R. Shanthini 19 Sept 2011

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Sustainable Limit Calculations


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Calculation of Global Sustainable Limiting Rate of Carbon Dioxide Production:

1. Virgin material supply limit: To stabilize the atmospheric CO2 concentration below approximately 550 ppmv by the year 2100, global anthropogenic emissions must be limited to about 7 to 8 x 1015 g (= 7 to 8 giga metric tons) of C per year (IPCC, 1996).

Source: Graedel, T.E. and Klee, R.J., 2002. Getting serious about sustainability, Env. Sci. & Tech. 36(4): 523-9


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2. Allocation of virgin material: Each of the average 7.5 billion people on the planet over the next 50 years is allocated an equal share of carbon emissions. This translates to roughly 1 metric ton of C equivalents per person per year.




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3. Regional “re-captureable” resource base:

Recycling of carbon in the form of permanent or semi-permanent sequestration may eventually possible through controversial techniques, not at the moment.




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4. Current consumption rate vs. sustainable limiting rate: The U.S. on average produced 5.5 metric tons of C equivalents per person (including emissions from land use change) in 2000, which is well beyond the global sustainable rate of 1 metric ton of C equivalents per person per year.




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Let’s calculate the sustainable limit for some

other material, as well.



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Calculation of Global Sustainable Limiting Rate of Zinc Consumption:

1. Virgin material supply limit: The reserve base for zinc in 1999 was 430 x 1012 g (430 Tg), so the virgin material supply limit over the next 50 years is 430 Tg / 50 years = 8.6 Tg/yr.

2. Allocation of virgin material: Allocating the available zinc equally among all the world’s population gives approximately 8.6 Tg/7.5 billions people = 1.15 kg/(person.yr)



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Calculation of Global Sustainable Limiting Rate of Zinc Consumption:

3. Regional “re-captureable” resource base: Assume 30% zinc recycling rate. And, if the system is in steady state and if 30% of the 1.15 kg/(person.yr) is recycled, then each person in the region actually has (1+0.3)(1.15) = 1.5 kg/(person.yr) of zinc available.

4. Current consumption rate vs. sustainable limiting rate: In 1999, the U.S. on average consumed 1.6 Tg for a population of 260 million people, which translates to a U.S. per capita zinc consumption of 6.2 kg/(person.yr).


prof. r. shanthini 19 sept 2011 1 sustainable limit calculations

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