Geothermal fluids often contain carbon dioxide, which is a very effective growth stimulant for plants in greenhouses. Studies have shown that as CO2 concentration is increased from a normal level of 300 ppm (mmol/kmol) to levels of approximately 1000 ppm crop yields may increase by up to 15%. It is suggested that geothermal greenhouse heating offers a further opportunity for utilization of the carbon dioxide present in the fluid