Geothermal energy, when shunted properly, can save on natural gas usage. Places such as Yellowstone National Park harbor natural heat underneath the surface of the Earth. Iceland has a similar situation, as does the Big Island of Hawaii. Geothermal energy can be used to heat water and metal pipes filled with air to provide heat for colder months rather than burning fossil fuels. If done in the right areas, geothermal energy is nearly limitless in potential.
Global warming is a myth created to make money for companies who offer solutions to fight an enemy that isn't there. Yes, the temperature has fluctuated in some areas, but that happens from time to time. It doesn't mean there is this huge phenomenon which demands all of our attention.
Presently, there are too many process in motion for one single aspect (geothermal energy) to make a significant amount of difference to impact the entire process of global warming. The amount of change we as a species have inflicted upon the planet is too great to simply subside within a short amount of time. Plus we shouldn't forget that the earth is constantly orbiting closer to the sun; at the rate of a few cm every thousand years. This means the earth will continue to warm no matter what.