[Nasrudith]

Blaming nitrogen fixing or industrial agriculture for global warming is objectively wrong. The Romans were causing significant rise in atmospheric carbon levels just through the sheer scale of many small fires and deforestation. About the only sources of fossil fuels released were methane ignorantly released from mining and maybe Greek fire if the theory that it really was surface deposits of crude petrochemicals is correct.

Population capacities and thus overpopulation aren't fixed things meaning overpopulation is relative to conditions. It would be absurd to call algae overpopulated if they thrive just fine at concentrations in one epoch with different population conditions just because it would cause red tide in another epoch.