To what extent do CO2 emissions from motor vehicles vary?

Question

Do the CO2 emissions from petrol / gas vehicles vary depending on driving style? Are emissions a function of the engine type or the fuel efficiency?

If a motor car is rated at 105 g/km, but it is driven particularly aggressively would it actually generate 150 g/km or just 106 g/km?

If the same car is rated as getting 45 mpg, but a particular driving style, like long gentle motorway journeys, result in an efficiency of 60 mpg would the CO2 emissions be around 75 g/km or better?

If the CO2 is from the fuel, does a car idling generate more CO2 than a car moving but using the same amount of fuel?

Answer 1

CO2 is produced by burning the carbon in the fuel, so if your driving style causes you to use twice as much fuel, you will produce twice as much CO2. Driving aggressively can have a big impact on fuel consumption. It's hard to quantify, but a 50% increase in fuel consumption and CO2 emissions is certainly possible. Conversely, the CO2 emissions will be lower when driving on a "long gentle motorway journey".

A car that's idling while burning the same amount of fuel as a moving car produces the same CO2 emissions, if measured as grams of CO2. If measured as grams per kilometer though, the idling car produces much more CO2, because the emissions didn't help get you anywhere.