In the original WORLD-2 model, the natural resources are not specified and it is assumed that the total quantity of natural resources will last for 250 years at the rate of resource usage in 1970. In this study, fossil fuels (oil: NRO, coal: NRC and natural gas: NRG) are adopted as natural resources (NR) on Earth for comparison with energy from space. Their quantity is calculated in the natural resource unit equivalent to about 10 barrels of oil in the same way as in the original WORLD-2 model. Other energy resources on Earth, such as electricity generated by water, wind, nuclear fission, etc., are not considered in this study, because energy produced from them is one order of magnitude smaller than that from fossil fuels at present. In the original WORLD-2 model, the pollution is also not specified, but it is assumed that the quantity of pollution is one pollution unit per person in 1970. In this study, the CO2 level in the air (which is closely related to the consumption of fossil fuels) is adopted as pollution (POL). The CO2 level is determined by CO2 production with the consumption of fossil fuels, and CO2 absorption by oceans and forests. The absorption rate of CO2 is given as a parameter in this study.
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