 Although fossil fuels are continually formed by natural processes, they are generally classified as non-renewable resources because they take millions of years to form and known viable reserves are being depleted much faster than new ones are generated.Most air pollution deaths are due to fossil fuel combustion products, it is estimated to cost over 3% of global GDP, and fossil fuel phase-out would save 3.6 million lives each year.The use of fossil fuels raises serious environmental concerns.