Examples of fossil fuels are petrol, diesel, oil and coal. They are called fossil fuels as they were created over hundreds of thousands of year from old organic material. Dead parts of plants and small animals at the bottom of the sea and in the ground were slowly turned into the fuels that we are quickly digging up and burning today.

When fossil fuels are used in vehicles, the industry or any other combustion process the greenhouse gas carbon dioxide (CO₂) is released. This carbon dioxide is an addition to the normal cycle, and by that it increases the concentration of carbon dioxide in the atmosphere – which increases the greenhouse effect and causes climate change.