Green Diesel Cars
Lean, mean, but not totally clean
Diesels are becoming a more and more popular choice: 40% of the cars sold in the UK in 2007 were diesels. They burn less fuel than petrol cars over a given distance, which means fewer CO2emissions and lower fuel costs. Diesels driven on motorways are actually more fuel efficient than hybrid cars. In addition, they can save on road tax.
Too good to be true? Maybe. In cities, hybrids are a better deal all round in terms of emissions and financial savings. Diesel is less refined than petrol and produces soot when burned, with mixed environmental impacts.
How will it make a difference?
The average UK driver could save 580kg of CO2 a year by swapping to the equivalent diesel model - 15% of the average Brit's direct carbon footprint.
Traditionally a smart move for the cash conscious, recent fuel price hikes mean diesels only overcome their extra purchase cost if driven very long distances. According to the AA a diesel car, costing about £1,400 more than its petrol equivalent, can take more than 45,000 miles before fuel efficiency savings recoup the extra cost of purchase.
To take the edge off the costs, choose a diesel with extremely low emissions and you could save £50 a year on car tax from the DVLA.
What's the debate?
Diesel cars' claims to environmental friendliness need to be qualified slightly. For one thing, estimates of how much diesels reduce emissions vary quite widely: from 15 to 25%. For another, whatever the CO2 savings, diesel gives us some other emissions to worry about.
Diesel also causes more smog-forming mono-oxides of nitrogen (NOx) emissions, which are implicated in the formation of ozone and acid rain. Ozone near the ground damages plants, reducing their ability to mop up carbon dioxide (CO2) from the atmosphere and has significant impacts on human health.
Diesels produce more soot (known as particulates) than petrol engines. While soot is categorically bad for human lungs, the jury's still out on its climate impact. Scientists claim they can both contribute to climate change (see BBC News: 'Soot 'influences arctic climate'') and slow it down (see BBC News: 'Why the Sun seems to be 'dimming'') - but research so far suggests the warming impact outweighs the cooling effect.
However, many diesel cars now come with a diesel particulate filter (DPF) either as standard or as an option. This filter removes nearly all of the particulates from the exhaust and goes a long way to improving air quality in our cities. In 2009, the new Euro V emissions regulations will require all new diesel cars to be fitted with a DPF.
Some environmentalists also argue there's no substitute for driving less, and that cheaper long distance motoring can act as an incentive to drive more. Climate consultant Chris Goodall unearthed a study in France suggesting that drivers who switched to diesel cars from petrol drove an average 17% further.
So petrol or diesel car?
Show me other fuel types: