Vehicle emissions are one of the major contributors to global warming, but truly environmentally friendly cars remain scarce.
Just how good are those green vehicles currently available?
There is no shortage of car lovers in the UK, but perhaps it's time more drivers considered what they did to reduce their impact on the environment.
Different cars, same destination
The thirstier cars are for petrol or diesel, the more carbon dioxide they generate and the more they contribute to global warming.
Motorists are told they should either drive less or switch to more environmentally friendly vehicles, but just how practical a solution is that?
As part of the BBC's Global Warning series motoring presenter Suzi Perry went to Dunsfold Park in Surrey - home of the Top Gear test track - to put some green cars to the test.
The majority of low carbon emitting cars currently available have diesel engines.
Among them is the Ford Focus TDCi Ghia estate, which meets
the industry's own target emissions limits set for 2008.
That's 140 grams per kilometre, for you car boffins.
With a 1.8 litre engine, it's a very respectable family car.
Like the Citroen C2, which takes pride of place in this category, it is proof that it's perfectly possible to own a vehicle that nods towards reducing CO2 emissions without compromising on size.
It's worth noting that diesel engines aren't necessarily better than petrol engines for air quality as a whole, but manufacturers are working hard on reducing the particulates.
Another solution being investigated by car manufacturers is that of hybrid engines - which run on both petrol and electricity.
Perry liked the Insight's zip
They easily beat the green credentials of the best diesels.
In this category Suzi tested the two-seater Honda Insight and the four-seater Toyota Prius, which work on broadly the same principles.
An electric motor tucked alongside the engine assists in getting the vehicle moving and provides additional power during acceleration at higher speeds.
The batteries for the motor can be recharged by the engine, or from energy absorbed during braking.
The Insight is a sports car. It's lightweight and aerodynamically styled - and has a top speed of 112 mph.
It certainly felt nippy, but it manages 83.1mpg and is the lowest CO2 emitter currently available that runs on any fossil fuel.
A close second in the carbon emission stakes, the Toyota Prius is a family car, and felt more futuristic in design.
Although it handles like a traditional automatic, the petrol engine shuts down when you come to a halt. Remaining confident it hasn't stalled takes some getting used to.
Toyota admits some owners of these cars have reported this as a fault! Then, when you get rolling again, at low speeds the car is powered purely by the electric motor.
Finally, there are those cars which take the potential of electricty that final step and run on nothing else.
One of the latest is the Reva G-Wiz.
It's a four seater - just - that runs on batteries for up to 40 miles between charges, which are just 30p for an overnight top-up.
It's certainly peppy enough in town. During a test run in London's Park Lane it was easy keep up with the traffic.
It seats four - barely
You aren't going to break any records driving one of these, but that would be missing the point.
The G-Wiz doesn't generate any CO2 at source and is exempt from road tax, town congestion charges and even from paying for parking in central London.
Suzi remarked on how quiet the G-Wiz was - and how you might take a few pedestrians by surprise if they aren't paying attention while crossing the road. Judicious horn-work might be required.
The G-Wiz's appearance could also be charitably described as an acquired taste, but it's early days and they could catch on with enlightened commuters and school-runners.
As a nation, we're buying 4x4's and multi-purpose vehicles in increasing numbers, and on average they put out more CO2 than a family saloon.
Sooner or later, we may all have to face life with cars that are smaller and don't generate carbon.
As the car industry points out, progress has been "steady" in reducing emissions, but more must be done and it'll be hard work.
Manufacturers, consumers and governments must all do their bit if we're going to take global warming seriously.
Short of giving up and walking, they may do well to consider one of these greener cars.