330 plus or minus 10 ppm is in my 1959 meteorology text for CO2.
I don’t recall being shocked at this number compared to pre industrial revolution. Of course 1959 was a naive period.
parts per million, people!!
“parts per million, people!!”
To paraphrase another FReeper;
It’s as if you rented a 10,000 seat arena for a concert, and 4 people came and sat down.
Population is now about 7 Billion.