Water vapour is also a greenhouse gas. Rising temperatures as a result of increased CO2 emissions are amplified by the increased ability of the atmosphere to hold water vapour. Fortunately, the atmosphere naturally removes excess water vapour in the form of rain. That is why CO2 is the problem gas, and why the climate skeptics' argument about water vapour is wrong.

Nevertheless, the abundance of water vapour serves very well to demonstrate the greenhouse effect. To do this from home, you need to step outside early in the morning and record the state of cloud cover (dense cover, medium cover or clear skies) for a period of 2 to 4 weeks. Take a sheet of writing paper and divide it into 4 columns, as illustrated below. Use the first column for the date, and one column for each state of cloud cover. You will also need to note the overnight minimum temperatures from the TV weather report.

Date	Clear Skies (0-1)	Medium Cover (3-5)	Dense Cover (6-8)
01/08/2010			13.9
02/08/2010	12.5
03/08/2010	10.2
04/08/2010	9.2
05/08/2010			8.8
06/08/2010		12.7
07/08/2010	8.1
08/08/2010	6.6
09/08/2010			9.6
10/08/2010			14.1
11/08/2010			16.1
12/08/2010	12.5
13/08/2010	10.4
14/08/2010	6.1
15/08/2010	7.8
16/08/2010	7.6
17/08/2010	10.2
18/08/2010	9.5
19/08/2010	11.7
20/08/2010			17.5
21/08/2010	6.9
22/08/2010	8.1
23/08/2010			11.6
Mean	9.2		13.1

If you prefer, you can obtain this information from the Bureau of Meteorology. To ensure objectivity, the above example uses data for Brisbane from the bureau's web site. Click here to see the raw data.

Each day, enter the date in column 1, and the minimum temperature in the appropriate column for the observed cloud cover. Although their are various factors that affect temperature, including wind direction, at the end of the period you should see a clear trend. The overnight minimum temperatures in the dense cover column should be between 2 and 4 degrees C higher in the clear skies column. The explanation is that the higher concentration of water vapour on nights with dense cloud cover traps the heat that is radiated from the Earth. CO2 traps heat in exactly the same way, and as explained earlier, this has been accurately measured by scientific instruments.

The basic principle of climate change, the greenhouse effect, is so simple a child can understand it. Greenhouse gases simply form a blanket around the Earth which traps heat. Don't let the nonsense peddled by those with a vested interest in ignoring climate change shift your attention from this simple truth.

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