Most of our energy comes from fossil fuels—coal, oil, and natural gas supply about 85 percent of US primary energy consumption. Although the supplies of these fossil fuels are vast, they are not unlimited. And more important, the earth's atmosphere and biosphere may not survive the environmental impact of burning such enormous amounts of these fuels. Carbon stored over millions of years is being released in a matter of decades, disrupting the earth's carbon cycle in unpredictable ways
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