In his most recent book, "Fake Invisible Catastrophes and Threats of Doom", Patrick Moore (co founder of Greenpeace) contends that if fossil fuels had not have started being burnt from the Industrial Revolution to now at some point before now, the downward trend of CO2 in the atmosphere would have become so low that plant life would not have been supported.
That would have been fun for humans. No plant life. Oh well, we'd have to only eat meat.
