You mean heat capture, right? Retention is what is kept and the CO2 will keep it.
Virtually all (99.95%) the extra heat that is captured by the extra CO2 flows to the dominant gasses. Some of that captured heat will be eventually radiated into space or flows into the ground or oceans. The rest that stays in the atmosphere, the retained heat, goes to raising the temperature of the atmosphere.
If this has all been a terminological misunderstanding about what retention means, well then that's too bad.
Not sure what you mean here, but there is none. I don't see any significant diff between 1700 and 2060 either.
The differences between 2000 and 1973 is ~1% and between 1700 and 2060 is ~21%. If I'd been off by 21% in my estimate of the ratio of retained heats, well, that might be significant depending on the application.
The Oceans are essentially saturated.
That guy was saying that the saturation level is temperature dependent. If the Earth warms, the oceans will be oversaturated and give up CO2 to the atmosphere increasing its concentration. Conversely, if the Earth cools, the oceans can take up more CO2 and the atmospheric CO2 concentration will decrease.
He is proposing this mechanism as accounting for past observed correlations between global temperature and atmospheric CO2. AGW types have latched onto this to support their theory. He is trying to debunk that argument.