That's a little vague and probably wrong. The rise from 260 or 280 up to the present 395 ppm is from fossil fuels. If mankind were not in the picture there would have been a rise anyway, but only to perhaps 300 ppm at the most. The reason is simple: oceans warming naturally (as a result of the end of the Little Ice Age) were outgassing CO2. Now they are ingassing and that is measurable and factual. So the rise in CO2 in the atmosphere is not from the oceans, it is from fossil fuels and land use changes.
You've bought into the dogma when your accepting that the number spouted is all man-made.
The last ice age was accomplished with 2000+ CO2.
2000+ man-made? That is what you'd be suggesting.