"100 litres of nonrenewable fossil fuel per vehicle"

So you could deduce we had 3 vehicles.

I'm assuming about a 50/50 weight split in the main combustion products,
i.e. CO2 and H2O.

Mark

He may be correct, Rainbow, as the mass (rather than density) of the
combustion products is always greater than the mass of fuel burnt as the
weight of combining oxygen has to be taken into account.
eg for CO2 , carbon (Atomic Weight 12) is combined with oxygen (AW 16) in
the ratio of  12 carbon to 32 oxygen. This means that for every 12 grams of
carbon from the fuel used, 32 grams of oxygen from the air is combined  to
make 44 gms of CO2.
Bristan

Ah, the joys of selective quoting.

The writer went on to say, after the bit quoted above:

"Your return flight to Melbourne for the weekend used a similar amount
of fuel per head. Every time you put on the air con rather than a jumper
you become part of the problem. In your 30 square eveless heated
towel-rail downlight-constellation ducted-air McMansion.

"Take a drive (no, a bus) to the 2600 megawatt Bayswater Power Station,
and boggle at the mountain of coal conveyor-fed direct from mine to
furnace. Every time you flick a switch another kilogram of carbon goes
up into the atmosphere.

"There’s a disconnect between our lifestyle and its consequences. Assume
for the moment that they’re right: the 97% of scientists who say that
global warming heading towards catastrophic climate change is real, and
greenhouse gas emissions from burning coal, oil, and gas are the primary
cause. Decades hence our children’s children, living with this, will
incredulously ask their grandparents, What were you thinking…? The
epithet 'future eaters' would be apt."

And he could cetainly start by protesting other motor sports first, and
don't forget how many tree's are sacrificed for football fields, schools,
shopping centres & golf courses every year. :P