What are fossil fuels and why are they a problem?

Fossil fuels are a natural fuel such as coal or gas, formed in the geological past from the remains of living organisms. The burning of fossil fuels is bad because it causes carbon dioxide levels to rise in the atmosphere. This extra carbon dioxide adds to the enhanced greenhouse effect causing global warming. This is why burning fossil fuels is bad. If we use more fuels then we should, the planet and mankind itself suffers in the long term.