unsustainable increases in population always end badly: famine, warfare, pandemics......"be fruitful and multiply" is what will do us in as a species. That in and of itself would not be a problem, but we have mostly stopped killing each other and we keep saving the lives of people that might die.
one thing for sure...humans wont be around when that happens,,,we will have been extinct for hundreds of thousands of years....Over millions of years all plastic will settle to the ocean floor either as free micro plastics or within the bodies of living organisms. It will eventually be taken down into the earths mantle via subduction at the plate boundaries. Subjected to the tremendous heat and pressure within the earths mantle what it will emerge as, via volcano's etc., is anyone's guess but the earth will recycle it as something.
just another failed trial in evolution.... in the meanwhile I think I will go fishing,,,,,,