Well, I have to understand you case first. So, thanks for clarifying that.
Now, what exactly is a "large greenhouse gas"?
I'll have more questions for you, but I prefer to address them one at a time.
In the
context of what I was discussing a "large green house gas" being percentage of the warming caused by the total amount of of overall warming of the total green house effect. Imagine if earth was a "black" body, like black
body temperature,,,. This is pretty much what the moon and mercury are that will be discused below. Now add a Atmosphere with green house gases and the temperature within that atmosphere will be increased and the temperature swings(On the moon there is a huge one) decreases greatly.
What is the total green house effect? Lets say that water vapor is the vast majority of such being such a big part of the green house pie. So it would cause lets say 80-90 percent of the warming effect. Imagine the moon or mercury for a second---here you have a body that has NO Atmosphere and relays purely on the solar output of the sun. This energy when it is not facing the sun go's bye, bye very quickly because it has NO green house effect to hold in the heat. Of course 02 and n2(oxygen and nitrogen) within the earth's Atmosphere are not huge green house gases, but co2, h20 within vapor form is.
Now back to total green house effect so lets say water vapor is the big boy on the block that makes up 90 something percent of the green house effect and co2 makes up most of the rest. Now you have to admit that the earth is warmer and more stable temperature regime because of it...We know for a fact that is so.
Now back to my last post above---Water vapor don't stay within the Atmosphere for a very long time, but rains out within days of going to the Atmosphere. Hell most of the planet within deserts and cold places have very little of it. So it is NOT uniform. Co2 as I stated is not totally uniformed either, I will admit it, but its ability to stay within the climate system is far longer that last for decades and clogs the natural processes to remove it. Being that the cycle is spitting it back into the system naturally within the natural process, but we add more into the system. This compounds things. Sure the oceans remove it, but they're not moving it any faster out of the system any faster then 500 years ago or 5,000 years ago. So when you think about it the shit remains for hundreds of years. It takes time to have the natural processes to work.
So yes water vapor is kind of a feed back as I said in the above post and for those reasons. Tell me where I'm wrong??? Seriously.
So yes water vapor is a huge green house gas, but it has a limited time within Atmosphere, while co2 has a long time. More heat=higher temperature=water changing state to vapor=more of that big bad green house gas.