20 Mar 07
The owners - us - determine the greatest portion of CO2 a car emits in its total lifecycle. Every study done into a car's environmental impact has concluded that fuel burnt is by far the biggest emitter of CO2. More than building it, more than transporting it and more than (properly) getting rid of it. The exact amount is anywhere between 70-90% of all the carbon emissions a car is responsible for.
That figure is for fuel used to power the car, but another chunk of a car's total CO2 bill comes from the production of that fuel. Extraction, refining and transport of petrol and diesel accounts for 10% of CO2 output, according to the Camden study.
This is where alternative fuels can fall down. The production of bioethanol in particular is much more energy-hungry than regular petrol, and the Camden study makes that point: 'For some US corn-derived ethanol, the fossil fuel energy required to produce the ethanol is greater than the energy value of the final product.'
biodiesel is much better, but hydrogen is another energy sucker in its production phase.
The petrol and diesel advantage is expected to be hacked back in the next years as dwindling underground oil reserves force companies to look to more energy-intensive sources, such as oil sands (a combination of clay, sand, water and bitumen).
With production out of the equation, a car emitting the UK average of 169g/km of CO2 will still produce 28 tonnes of the gas over 100,000 miles. That's enough to fill four hot air balloons.
