If we extract enough heat from the earth using geothermal energy, could we offset global warming? — Linda P., Portland Oregon
Great question. You apparently know the basics of geothermal electricity production, but let me recap for those not as familiar. To oversimplify, geothermal electricity consists of:
Locating a suitable geothermal reservoir (underground collection of hot water or steam).
Drilling a well to penetrate the hot underground water or vapor (geothermal fluid).
Extracting the hot fluid.
Using a power plant and related infrastructure to produce electricity, cool the geothermal fluid, and inject some of it back into the system for reuse.
Since we are using the heat of the earth to run the power plant, some of this energy is transformed into electricity. This means there will be a net heat loss from the reservoir, and the earth temperature must decrease (blame the laws of thermodynamics). Your question is, could we do enough of this to actually measurably cool the earth. The simple answer is no-geothermal does result in cooling, but the impact is insignificant.
Some 42 million megawatts of energy reach the surface continually and are radiated into space as the earth cools from its initial molten state more than 4 billion years ago. No feasible amount of geothermal development could make even a small dent in this process. Furthermore, the earth’s heat budget is continually replenished by the radioactive decay of naturally occurring elements, and almost all of the energy associated with each decay event is converted to heat. Plus, the heat content of the geothermal reservoir rocks is continually replenished by conduction of heat from the earth’s deeper interior.
But, if you’re thinking about global warming, using all of that heat to provide clean energy is obviously a way to go. Like the sunlight hitting the earth every day, the energy available from the heat of the earth is enormous and largely unused as a source of energy. If we could tap just a fraction of the heat reaching the surface of the earth every year, we could provide all of the heat and power needed to run our society, and avoid the potentially tragic consequences of overusing fossil fuels.