But those are not identified by any scientists mentioned in the piece. Nor have they suggested volcanoes or massive past warming causing more off gassing from warming of the deep ocean. That warming would have to be well over 12C over the past 1000 years.
In short, there's never any explanation of where the rise in CO2 is coming from if it is natural as they allege. They also didn't explain the other proxies like fossil leaf stomata see "Reading a CO2 signal from fossil stomata" by Beerling and Royer.
But the claim that CO2 is increasing in the atmosphere can only date from 1930.
The machine for measuring CO2 in the air was not perfected and put into service until 1930.
So if you claim an increase in CO2 from 1930 to 2019, how meaningful is that?