The amount of carbon dioxide generated by any activity varies widely depending on complex factors. This website makes huge generalisations about the figures in order to make the calculations quick and easy.
The carbon dioxide generated by, for example a car, includes the manufacture, repair and disposal of the car as well as the daily fuel used. This website includes estimates of these types of whole life factors in all the calculations and so so some figures may appear to be larger than expected.
For more accurate carbon footprint calculations a web search will list several sites that use many more factors to produce a more reliable answer.
This site does not claim to be an accurate measure of your impact on global warming but rather a tool that you can use to explore some of the lifestyle decisions that are under your control.
Most of the figures here are close to those in the 2006 Carbon Trust report "The carbon emissions generated in all that we consume". (This report estimated the total carbon generated by different activites in the UK. It is possible to convert these figures to carbon dioxide generation and then divide the result by the population total giving an estimated personal contribution.)
Now use count carbon to reduce your carbon footprint.