are climate change deniers naturally gullible?, page-109

My understanding is that water vapour is an EFFECT not a CAUSE. If you think the IPCC has ignored water vapour then you are desperately wrong. Do a search. There are mountains of research regarding the greenhouse effect of water vapour. The consensus postion is well summarised by Wikipedia:

"Although water vapour has a significant influence with regard to absorbing infrared radiation (which is the green house effect; see greenhouse gas), its GWP (Global Warming Potential) is not calculated. Its concentration in the atmosphere mainly depends on air temperature. There is no possibility to directly influence atmospheric water vapour concentration."

http://en.wikipedia.org/wiki/Global_warming_potential

Since we are talking about human induced effects, water vapour is considered to be a feedback, not a forcing. All else being equal, if the temperature goes up, water vapour concentration, on average, goes up. Why is this so difficult? Seems to be common sense to me.

Also, water vapour does have a very significant greenhouse effect, but we are not talking about this, we are talking about pumping billions of tonnes of man made greenhouse gases into the atnosphere and creating a net change to the balance which the earth has been in since the start of the Holocene.

The Holocene is the period in which human civilisation has flourished. Why has it flourished? One reason is the ideal temperate climactic conditions that allowed us to move away from hunter-gathering to farming and the development of societies. We weren't roaming with the dinosaurs or earlier and that's why comparisons with the climate of hundreds of thousands or even millions of years ago are rather bogus because we weren't around then and didn't have to endure the conditions at the time, whether hot or moderate or cold.

But don't ask me about water vapour. Do your own reading. After all you say you have a "a degree in Chemical Engineering". Water vapour concentration is a factor of temperature. As the climate warms due to more greenhouse gases, the warming will be accelerated by the extra water vapour in the atmosphere. Very simple. There is no scientific controversy but yes there is uncertainty. There will be minor variations like changes to the albedo effect and so on, but likely to be very minor.

I am also extremely perplexed when you say we don't know how much water vapour is in the atmosphere. Why do you say that? Meterologists have been measuring relative humidity for a very long time. As the temperature goes up, the atmosphere can hold more water vapour without it condensing. But water vapour is not like other gases - it does not have such a long lifespan. I am sure water can be evaporated into vapour one day and then precipitated as rain the very next day, so I there is no 'build-up' like there is with man-made GHG's. CO2, CH4 and the other man made gases last for tens to hundreds of years in the atmosphere. This is the big difference and this is why you are barking up a tree that does not exist, in my opinion.

Anyway, perhaps go and read some IPCC reports rather than asking me about it. Water vapour is discussed in all the reports. You're a chemical engineer so you will understand all the jargon.