When oil and coal is burnt they emit huge amounts of carbon dioxide and other harmful gases, that have a negative effect on the environment. If temperatures are too hot it is terrible for children and elderly.
Coal and Oil also let off sulfur dioxide which mixes with the moisture and clouds in the air and forms sulfuric acid is know as acid rain as when it falls it causes forests, vegetation and crops to die.
With these effects in mind and the fact that fossil fuels are predicted to run out within the next 40-50 years it is essential that we find alternative and renewable energy sources.