Why should we use fossil fuels only when absolutely necessary?

Burning of fossil fuels affects the environment due to the release carbon dioxide and other harmful gases such as Sulphur dioxide, nitrogen oxides and carbon monoxides. These gases trap heat in the earth’s atmosphere and causes global warming which contributes to global climate change. It is therefore necessary that we use these fuels only when absolutely necessary. It took millions of years for the dead organisms to get converted into these fuels. On the other hand, the known reserves of these fuels will last only a few hundred years. It is therefore, necessary to conserve these natural resources. This will also result in better environment, smaller risk of global warming and their availability for a longer period of time.