No the lowball figure comes from comparing natural biological CO2 sources with manmade sources. In that case the biological sources are about 20 times manmade. But the biosphere is also a sink and, not coincidentally about the same as the bio source. IOW, man's is all source, very little sink, biological is 50 50. The net annual rise therefore is 100% manmade.
Volcanoes are an asterisk. Pinatubo was equal to a day or two of manmade CO2.
The net annual rise therefore is 100% manmade.Horse hockey. This is an opinion and not proven fact.
Besides there is no such thing as man made - the stored hydrocarbons were once biologic creatures, so it is all natural. Unless you believe in abiogenic petroleum which has not been disproven IMO. I consider it a a viable theory.