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 The more Hydropower, the less coal and oil. Coal and oil are non-renewable which is good because they release one of the worst greenhouse gases, carbon dioxide. Carbon dioxide increases the warmth of the earth; this is called Global Warming. Global Warming can melt the polar ice caps which will first extinct the endangered polar bears and flood a lot of the world. The good thing is that there are 80,000 dams and 20% of all electricity is produced by them! The only thing that turns things around is that coal and oil are cheap.