Do you understand that warmer liquid holds less gas? Do you understand that the estimated age of our Sun is over 4 billion years old. She might fluctuate a bit. I know that dissolved gasses release in warmer water. I've had it blow up in my face. :) You are still talking parts per million, and neglecting the Sun. You cannot be right.
Have you ever owned or had the pleasure to live around a greenhouse? The water vapor holds the heat.
Yes, warmer liquid holds less gas. The dependence shows up in the temperature dependence of the Henry constant, see
http://en.wikipedia.org/wiki/Henry%27s_Law The fluctuations from the sun explain a lot of the warming in the 80's and 90's as I explained above. There is also a steady increase due to CO2. The reason is that CO2 absorbs some wavelengths of IR that water vapor does not and increasing the CO2 causes a small increase in the temperature of the atmosphere.
The warming inside a greenhouse is partly due to trapping the warm air (preventing convection). The rest is due to the absorption of outgoing IR by the glass, just like CO2 in the atmosphere. The glass then emits about 1/2 of that heat back into the greenhouse. The water vapor inside the greenhouse helps hold some heat too but that is mostly an increase in thermal mass. It is even better to have many gallons of water in the greenhouse for thermal mass to hold the heat through the night or cloudy days.