well, everyone knows that the most major one is pollution of the air. Burning of fossil fuels is a long, dangerous and complicating process. For starters, people get cancers because they work all day in mining the fossil fuels, because they literally breath and inhale it, therefore get terrible health issues. One, burning the fossils cause the air to become polluted, and thus literally changes our planet in horrible unimaginable ways. The burning of the fossils cause global warming and climate change because the burning releases carbon dioxide and other toxic greenhouse gases into our atmosphere, and thus trap heat in the atmosphere, literally burning us alive.