Re: I know a Stanford egghead who thinks water is a greenhouse gas.
Your friend is correct. Water vapor (gas) is the most important green house gas in the atmosphere.
CO2 - by itself - cannot cause dangerous warming.
However, it does cause some warming.
According to theory, CO2 causes the oceans to warm. When the oceans warm, they release more H2O gas, which causes more warming.
The basic theory of man made global warming is that CO2 and H2O gas must work in concert to create highly destructive warming.
“However, it does cause some warming.”
Total BS.