Please excuse my ignorance but I have two questions that you may be able to help with.

1) If the % of co2 in the atmospere is 0.03% and of that 95% is natural in origin, that means that human produced CO2 is 0.0015% of the total. Is reducing our CO2 emissions going to have any effect ?

2) Is water vapour considered to be a greenhouse gas and if so what is its effect ? (I have read that H2o vapour % of the atmosphere can vary between 1 and 4%)

Very simple answers (if possible)!

Many thanks

[QUOTE]Originally posted by spooky060:
Please excuse my ignorance but I have two questions that you may be able to help with.

To save people repeating themselves this is a link to another discussion on this board - what % of world CO2 emissions do humans contribute? – that went over much the same ground.
http://community.channel4.com/eve/forums/a/tpc/f/9250037634/m/3530071557

Water vapour is a greenhouse gas and was covered in depth in a recent discussion here:
http://community.channel4.com/eve/forums/a/tpc/f/9250037634/m/8680017957

A quick intro to why GHG do matter when it comes to atmospheric temperature:

Greenhouse gasses and their roles; H20, CO2, CH4 etc.
Though only a tiny amount of GHG are in the atmosphere they keep earth’s temperature habitable.
Not all Greenhouse Gasses are the same; they interact with different wavelengths of infrared (their absorption bands) in different ways. The more infrared is absorbed the warmer the atmosphere becomes.

Water vapour absorbs infrared at 0.6 Microns, 0.72 Microns, 0.82 Microns, 0.94 Microns, 1.10 Microns, 1.38 Microns, 1.87 Microns, 2.70 Microns, 3.20 Microns, and 6.30 Microns.
Carbon dioxide absorbs infrared radiation at wavelengths of 2.69 micrometers (Microns) & 2.76 Microns, 4.25 Microns, 14 Microns, and 15 Microns.
Methane absorbs infrared at 3.4 Microns, 7.4 Microns, 7.58 Microns, and 7.87 Microns.
Carbon monoxide absorbs infrared at 2.3 Microns, and 4.7 Microns.
Nitrous oxide absorbs infrared at 7.83 Microns, 16.98 Microns, and 44.9 Microns.
Ozone absorbs infrared at 9.0 Microns, 9.6 Microns, and 14.2 Microns.

For example, the 8-18 micron band is where water vapour is a weak absorber of infrared radiation and where the Earth's thermal radiation is greatest. Part of this "window" (12.5-18 micron) is largely blocked by carbon dioxide absorption, even at the low levels originally existing in the atmosphere.
The remainder of the "window" coincides with the absorption proclivities of the other radiative gases: methane, tropospheric ozone, CFCs and nitrous oxide. It also appears that increased levels of carbon dioxide will increase the capture of heat in its absorption band to some extent.

More also here on absorption bands etc:

http://www.astronomy.ohio-state.edu/~pogge/Ast161/Unit5/atmos.html

Of greater concern is the release of Methane into the atmosphere as the atmosphere warms, as there is greater room in the absorptions bands for them to be blocked by rising levels of CH4.
(CH4 = a simple molecule consisting of one carbon atom bonded to four hydrogen atoms. Part of the carbon family if you like.)

quote:

1) If the % of co2 in the atmospere is 0.03% and of that 95% is natural in origin, that means that human produced CO2 is 0.0015% of the total. Is reducing our CO2 emissions going to have any effect ?

Humans have increased CO2 from 280 parts per million (ppm) to about 380 ppm over the last couple of hundred years - so it's a 1/3 increase (those figures approximately match your percentage figure). Reducing our emissions will have some effect in slowing down the warming. Though really over the next 100 years we need to stabilise levels (which means virtually no net emissions).

quote:

2) Is water vapour considered to be a greenhouse gas and if so what is its effect ? (I have read that H2o vapour % of the atmosphere can vary between 1 and 4%)

Water vapour is a greenhouse gas. It varies regionally, but on average it stays the same level so it doesn't cause additional warming by itself. If CO2 warms the earth, then water vapour will increase slightly as a response to the warmth, and add to the warming caused by the CO2.