Energy is not just about electricity and heating. Another use of energy is transport – cars, buses, trains, boats, planes, motorbikes etc all need some sort of fuel to make them go. At the moment most run on petrol or diesel, which are derived from oil, one of the main fossil fuels.

Transporting goods and people by land, water and air is responsible for 25% of the world?s greenhouse emissions, and this is increasing all the time.

Plants, such as sugar cane, corn, sunflowers and soy beans can be used to power cars. They are turned into fuel and put into cars with specially designed engines.Ethanol and biodiesel are types of biofuel.

25% of car fuel in Brazil is ethanol made from sugar cane.

So why use plants instead of fossil fuels?

* Any crops used as fuel can be replanted. So long as they grow fast enough and enough are planted, the fuel won?t run out.

* Any CO2 given off when used in the cars will be re-absorbed by the replacement crops. It could be carbon neutral.

* Biofuels are not too expensive to produce – they do not need to be mined like fossil fuels.

There are, of course, drawbacks:

* They still produce Carbon Dioxide and other greenhouse gases when used in the cars so they are not totally green.

* If all the vehicles in the world converted to using biofuels, a huge amount of land would be needed to grow the crops on. Vast areas of valuable rainforest habitat have already been destroyed in Brazil to make way for biofuel crops.

* If forests are cut down and replaced with biofuel crops, less CO2 is absorbed from the atmosphere than if it remained as a forest.

* The production and application of fertilisers etc for the crops uses energy and gives off greenhouse gases. It is estimated that 74 units of fossil fuel energy are used to produce 100 ethanol units.