Should we be more concerned about H2O than CO2 in the atmosphere?

[Michaelangelica]

Water vapor is the number one greenhouse gas by a county mile.

 

Could we be helping water into the air by providing more surfaces for it to evaporate from, such as dams and swimming pools? Also by our uses of water and our technology? (irrigation, steam power).

 

Certainly a warming planet will have warmer air which in turn will hold a LOT more water.

 

In the last 100 years we have built thousands of dams.

Produced billions of sweaty people.

Irrigated all over the place.

Built millions of swimming pools.

Pumped up an ocean or two of ground, mineral and spring water.

Boiled billions of jugs and pots of water.

Built thousands of de-salination plants.

Warmed the ocean.

Made a million steam sterilisers.

Warmed the air.

Made heaps of methane producing Tips (Oxidation of anthropogenic methane is a major source of stratospheric water).

Made a trillion plane flights.

Invented air conditioning (including out-door misting air conditioning)

and

while normal air conditioning de-humidifies it usually dribbles harvested water onto a hot, black road or footpath.

 

So do we have any historical record or ways of finding out what was the average of Earth's humidity 100 years ago?

 

Not much on my brief look on the web, but this was interesting

RealClimate » Water vapour: feedback or forcing?

Whenever three or more contrarians are gathered together, one will inevitably claim that water vapour is being unjustly neglected by 'IPCC' scientists.

"Why isn't water vapour acknowledged as a greenhouse gas?", "Why does anyone even care about the other greenhouse gases since water vapour is 98% of the effect?",

. . .

First some basics. Long-wave (or thermal) radiation is emitted from the surface of the planet and is largely absorbed in the atmosphere.

Water vapour is the principle absorber of this radiation (and acknowledged as such by everybody). But exactly how important is it?

. . .

it's clear that water vapour is the single most important absorber (between 36% and 66% of the greenhouse effect), and together with clouds makes up between 66% and 85%. CO2 alone makes up between 9 and 26%, while the O3 and the other minor GHG absorbers consist of up to 7 and 8% of the effect, respectively.

. .

Oxidation of anthropogenic methane (which is a major source of stratospheric water)

and,

conceviably, direct deposition of water from increases in aircraft in the lower stratosphere, can increase stratospheric water and since that gives a radiative forcing effect,

 

Here is some historical data but it is very recent

Water Vapor Trends

 

There have been several estimates of longer-term changes in tropospheric water vapor. The most recent global estimate shows an increase in precipitable water during the period 1973-1990, with the largest trends in the tropics, where increases as large as 13% per decade were found.

 

A recent study of water vapor trends above North America based on radiosonde measurements from 1973 to 1993 finds increases in precipitable water over all regions except northern and eastern Canada, where it fell slightly.

The regions of moisture increase are associated with regions of rising temperatures over the same period, and the regions of decreased moisture are associated with falling temperatures.

AGU Web Site: Water Vapor in the Climate System. A Special Report.

[Pyrotex]

I don't think so.

The reason is that water so easily changes state to liquid or solid and falls out of the atmosphere as rain, snow, ice, etc. This puts a maximum limit on how much water vapor can remain in the atmosphere, as a function of air pressure and temperature.

 

CO2, on the other hand, can increase as a percentage without bounds.