OK..to be clear, when you say..
"I mean a system that is closed" I ask..What is this "system"?
"Effectively, I mean at a global level"... Can you help me understand what you mean by a global system?
"We cannot currently grow away from this planet".....eh?
"The amount of energy available to us is limited to what the sun provides"... I have to ask, and what about wind, wave, nuclear, carbon-based etc etc?
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