Geothermal energy
From Envirowiki
Geothermal energy is energy captured from the heat of the earth's core. The heat can be used to boil water and drive steam turbines for electricity, or used directly for warmth.
Geothermal energy for electricity is used by pumping water deep down (100 meters) into porous rocks, and capturing the resultant high-pressure steam and running it through turbines. Only certain geological formations are suitable, but these are readily available on most continents.
Outside of construction and maintenance, geothermal doesn't emit greenhouse gasses, but it does add heat to the atmosphere (although probably a negligible amount, which would probably be added anyway, and would dissipate immediately were it not for the greenhouse effect), but considering that we're increasing the greenhouse gasses in the atmosphere, geothermal would make us reach out new temperature equilibrium more quickly.
