When burned, fossil fuels produce heat energy as well as a number of waste products and gas emissions. Fossil fuels are burned to produce the heat used in the generation of electrical power. Oil and natural gas are often refined to produce fuels used in heating and transportation.
Fossil fuels were formed from the remains of plants and animals that lived millions of years ago. These remains were eventually covered by layers of rock. Different types of fossil fuels are formed from organic matter depending on the temperature and pressure they were subject to as well as a number of other factors. Coal, oil and natural gas are considered a non-renewable resource, meaning that there is a limited supply of these fuels.
The combustion of fossil fuels produces a wide range of waste products such as ash, slag and other particulates. Burning fossil fuels also produces carbon dioxide, a greenhouse gas that contributes to global warming. Coal and oil also produce sulfur dioxide when burned, a gas that causes breathing problems for many living creatures and contributes to acid rain. Fossil fuels are a widely-used fuel source that have been responsible for three-quarters of human-caused greenhouse gas emissions over the past two decades.