Ignorance is bliss
Ignorance is bliss, isn't it ?
Even a rudimentary search on the effect of water vapour would show you that it has a residence time in the atmosphere of about 5 days - at which point it turns into rain somewhere. So adding more water vapour to the atmosphere is literally pissing in the wind - and has as just as little effect.
In contrast, CO2 stays in the atmosphere and biosphere for several tens of thousand of years :(
And a slightly bigger search would show you that decline in the ratio of atmospheric CO2 13C:12C is due to the burning of (13C depleted) fossil fuels. Yes folks, that's our CO2 piling up there!
And what did Arrhenius work out 100 years ago? CO2 absorbs infra-red radiation (heat), so adding more CO2 to the atmosphere causes it to heat up, by absorbing more of the the infra-red radiated by the earth's surface.
And that's what's been seen in the three surface temperature data sets (GISSTemp, HadCRUt and NCDC), and the satellite data.
This isn't rocket science. The only complicated part is calculating exactly what the temperature rise will be, and how fast, for a given CO2 concentration. And guess what: the calculations (models) match up very well with the observed temperature changes, even after events like volcanic eruptions.
In particular, the "smoking gun" for many scientists is that models successfully predicted both the rise in surface air temperature and the *decline* in stratospheric air temperatures. No other proposed cause of global warming leads to a *decline* in stratosphere temperatures.
ps: the emissions from a hydrogen "fuel" cell (water vapour) are in fact harmless - but the emissions from making the hydrogen in the first place are not !