Prof. Martin O. Saar, Department of Geology and Geophysics at the University of Minnesota. Abstract: Geothermal energy offers clean, consistent, reliable electric power with no need for grid-scale energy storage, unlike most renewable power alternatives. Here, I discuss a new method with the potential to permit expansion of geothermal energy utilization while supporting rapid implementation through the use of existing technologies. Carbon dioxide (CO2) sequestration in deep saline aquifers and exhausted oil and natural gas fields has been widely considered as a means for reducing CO2 emissions to the atmosphere as a counter-measure to global warming. However, rather than treating CO2 merely as a waste fluid in need of permanent disposal, I propose that it could also be used as a working fluid in geothermal energy capture, as its thermodynamic and fluid mechanical properties suggest it transfers geothermal heat more efficiently than water. Therefore, using CO2 as the working fluid in geothermal power systems may permit utilization of lower temperature geologic formations than those that are currently deemed economically viable. Hence, CO2-based geothermal systems may lead to more widespread utilization of geothermal energy, whether regional geothermal temperatures and heat flow rates are low, intermediate, or high. In addition, the proposed system reduces CO2 emissions from electricity production through both geologic CO2 sequestration and displacement of hydrocarbon fuels via use of renewable geothermal energy. Furthermore, geothermal power plants are quite scalable and can provide both on-demand peak as well as base-load power.