The United States currently relies heavily on coal, oil, and natural gas for its energy. Fossil fuels are nonrenewable, that is, they draw on finite resources that will eventually dwindle, becoming too expensive or too environmentally damaging to retrieve. In contrast, renewable energy resources are constantly replenished and will never run out. Here's a green energy infograph!
The End of Fossil Fuels: The world is moving toward a 100% renewable clean energy paradigm. There are no technological or economic barriers to replacing all energy production with wind, solar and hydro power; it is just a matter of political will, and of dismantling rigged markets.