The atmosphere is a plexiglass enclosure. The land is something that will absorb some warmth but hold it for only a short time. The Sun is cycled on and off to see both day and night activity. During the day, the water captures joules and releases some of them. It increases humidity levels. Joules movement is from Land to Water during the day as the Water lags the Land. During night the joules move from Water to Land warming it. At night the sources of joules are the Water warmed during the day plus any warmth remaining from the prior day plus a small contribution from the cooling Land. The Land is a minor source for Water warming. Water being better able to absorb and store joules is the major source for the system.
Now add CO2.
The Land joules have their old path, into the Water. The land can punch more into the Water as less is lost to the TOA. The Water will lose less to the Atmosphere during sunny days. The water has now warmed because of the CO2. Its SW absorption is the same. At first it emits less because of the CO2, but then it has more to emit which does it, while having greater storage. The water has more joules than before and will emit those to the Land for a longer time each night. CO2 has lowered TOA loss until the new warmer equilibrium is reached. Each night the Water tries to reach equilbrium with the Land which has little storage so it’s a waypoint on the way to the TOA. It is the Water warming the Land more than before with the help of CO2.