Flecc's right when he mentions population. Our environmental impact as nations and as a species in general is the product of the way we way and the number of us. If population keeps rising, our use of resources must fall. If use of resources (whether that's oil, gas, phosphorous, etc.) is forced to fall due to scarcity then war and famine become more serious risks.
Remember that all artificial nitrogen fertiliser is made from natural gas, and the price of that is rocketing...
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