Ready for a bit of economics?
Under Kyoto Cap-And-Trade, Carbon Dioxide is trading for about $15 per tonne on the EU carbon markets.
A Porsche Cayenne creates about 380 grams of CO2 per kilometer. Let's assume that someone drives 100km per day that they are in London (very generous assumption). That means they generate 38kg of CO2. To create the economic incentive for someone else to offset their own Carbon - you could buy 38kg of carbon credits on the market. They would cost $0.57 or about 25 pence.
That would net out the Cayenne at Carbon Parity or Net Zero emissions.
If you do the math and just offset the difference between the CO2 limit Livingstone imposed and the Cayenne performance you would have to pay about $0.23 or about 12 pence for the offset.
Livingstone is charging people $50 for something that should fairly cost $0.57. This is about ideology and not about environment. I'm an environmentalist and this offends me.
For more info - go to the Chicago Carbon Exchange -
Chicago Climate Exchange. Note that CCX rates are lower than the EU rates because the caps are voluntary.