Although human activities have no direct effect on water vapour levels, temperature rises caused by human activity, do have an indirect effect in increasing quantities of water vapour in the atmosphere, thereby increasing global warming.

The increase in water vapor is cause by solar radiance warming the oceans. It will decline when solar radiance declines. Your supposition is way off.
In fact, human activity has the same effect on global warming as it does on water vapor.

My reasoning was that by warming the atmosphere with CO2 etc, people will be causing more water vapour to evaporate into the atmosphere. That according to this research adds to the greenhouse gas effect, does it not? Compared with the variations in solar energy, this extra side-effect may, or may not be significant. So is my reasoning right? And how important are solar energy fluctuations, compared to extra water vapour caused by human activity?

I understand your reasoning. To understand mine you need to understand that I do not think people are warming the Earth with CO2, period.

That according to this research adds to the greenhouse gas effect, does it not?

It does indeed. But to say man increases water vapor is like saying man increases the volume of water in Lake Michigan by emptying a bottle of Dasani into it. Especially when you consider all the feedback loops that render any anthropogenic influence as insignificant.

As I'm sure you know, water vapor is not the only factor in the greenhouse effect, just the most abundant gas. The greenhouse gases stay in the atmosphere an average of twelve years., but that is not to say that ALL the greenhouse gases stay for twelve years. That's just the average.
The water vapor is not really an issue. Carbon dioxide, on the other hand, stays in our atmosphere 50 - 200 years. About 3/4 of our atmospheric CO2 comes from the burning of fossil fuels. The reason for this is , in part, due to the fact that it sticks around for such a long time. It's a cumulative effect. Thus, most of the CO2 emitted from gasoline engines since the the days of Henry Ford are likely still hanging around.

That is not true Hugdal, The Earth is one great big CO2 sink. The Oceans being the largest and most absorbent. If you look at the chart I provided you on one of our last discussions you will see CO2 increases follow warming, they do not precede warming. The CO2 will be absorbed eventually and the CO2 "hanging around" will not hang around forever. The effectiveness of the ocean as a co2 sink is diminished by the water vapor being released by the oceans. This will reverse itself and the ppm ration of CO2 will decrease as this happens. There is no static norm.

Actually it is true, according to the National Geographic article I clipped today.

Here is an excerpt:
Human activities, burning fossil fuels and clearing forests, have greatly increased concentrations by producing these gases faster than plants and oceans can soak them up. The gases linger in the atmosphere for years, meaning that even a complete halt in emissions would not immediately stop the warming trend they promote.

I never said they would 'hang around' forever. I said 50 - 200 years. It is due to the fact mentioned in the article. We're simply producing them faster than they can be absorbed, thus causing a net increase.

by producing these gases faster than plants and oceans can soak them up.

this was my point. Your article does not dismiss my previous statement which was perfectly aligned to this quote. However, where I part ways is the assertion that the insignificant contribution man makes causes the increase. The increase in ppm greenhouse gases is due precisely to what I said and as the quote from your article suggests.

We're simply producing them faster than they can be absorbed, thus causing a net increase.

We are not producing them. As I have stated repeatedly (and I have provided you a chart), CO2 increases FOLLOW warming.

Then you're denying the fact that there is CO2 in factory emissions and automobile exhaust? CO2 is a product of burning fossil fuels. I think very few would agree with that position.

Too, CFCs are ENTIRELY man-made. .

You're half right about CO2 increases following warming. I don't have the graph in front of me, but I'm pretty sure it's the exact one I provided from the EPA. You seem to have omitted the text that went with it, however.

Here it is:
The heating or cooling of the Earth's surface can cause changes in greenhouse gas concentrations. For example, when global temperatures become warmer, carbon dioxide is released from the oceans. When changes in the Earth's orbit trigger a warm (or interglacial) period, increasing concentrations of carbon dioxide may amplify the warming by enhancing the greenhouse effect.

Thus, it's a cycle, not a simple case of cause and effect.