Carbon dioxide (CO2) geothermal technology. Illustration of using carbon capture technology to harness geothermal energy. Fossil fuel power plants (top left, using fuels such as gas, coal and oil) are a significant source of CO2 emissions. CO2 sequestration normally involves injecting and storing supercritical CO2 in deep geological formations. Here, the supercritical CO2 is captured through an injection well (blue) and pumped underground into a geothermal reservoir (lower right). The CO2 heats up as it percolates through the reservoir and the overlying aquifer, and then rises through the production wells (pink) to power a geothermal energy plant (top right).