1) There is a total of approximately 12.4 billion acres of agricultural land (cropland, rangeland, irrigated land) on the major continents. Given that the average Net Primary Productivity (NPP) of agricultural land is approximately 2900 kcal m-2 y-1 calculate the annual global NPP associated with these lands (your answer should be reported in SI units, i.e. Joules)

Question

1) There is a total of approximately 12.4 billion acres of agricultural land (cropland, rangeland, irrigated land) on the major continents. Given that the average Net Primary Productivity (NPP) of agricultural land is approximately 2900 kcal m-2 y-1 calculate the annual global NPP associated with these lands (your answer should be reported in SI units, i.e. Joules)

2)
Assume that animals (humans and domesticated animals) have a 10% energy conversion efficiency and that we need approximately 2800 kcal d-1 to survive. How many i) Human Vegetarians and ii) Human Omnivores could the planet presently support (for simplicity assume that 50% of the energy content of the omnivore diet comes from meat or meat products). Comment on the implication of this calculation.

UNITS YOU MAY WANT TO USE:
1 ha = 2.47 acres; 1 ton = 1017 kg (1.017 tonne); 1 ly (langley) = 1 cal cm-2; 1 cal = 4.184 J
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Answer 1

There is really nothing here except unit changes: The idea is to multiply area*NPP to get Joules/(m^2 y). YOu will have to change acres to ha to m^2, and kilo cal to Joules.