## 1 Introduction  
The question about CO\({}_{2}\) emissions from geothermal power plants has become increasingly important as discussions on climate change have become more common. Historically, the emissions from geothermal energy utilization have been considered non-anthropogenic because they are natural source fluxes released into the atmosphere by natural surface venting. Carbon dioxide is released to the atmosphere naturally from geothermal fields through: soil flux, steam vents, fractures, steam heated mud-pools, and thermal springs. CO\({}_{2}\) can also be transported by groundwater flow, absorbing and releasing the carbon dioxide (in the geothermal reservoir) by mineral precipitation or degassing. Although soil emission of CO\({}_{2}\) can occur in many ways, the emission rate strongly depends on the characteristics of the field and, thus, may vary greatly from one field to another. The rate of natural emission can be altered by fluid extraction in the wells used for power production and district heating or, as has occurred in the past in the Larderello area, for boric acid production. In the Larderello area, natural emission from steam and gas vents progressively disappeared while the steam collection by wells grew, suggesting that the rate of natural soil emission depends on the interplay between the natural mechanism of gas emission from the soil and the utilization and extraction of steam in the geothermal field. The sources commonly recognized as possible origins of CO\({}_{2}\) in a hydrothermal system are hydrolysis of carbonate rocks, crustal magmatism, subcrustal magmatism following partial melting of mantel rocks and metamorphic processes [1]. A study by [PERSON] and [PERSON] (2002) [2] revealed that emission factors vary in a very wide range between 4 and 740 gCO\({}_{2}\)/kWh, with a weighted average of 122 gCO\({}_{2}\)/kWh. Recently, figures as high as 1300 gCO\({}_{2}\)/kWh have been reported by [PERSON] (2017) for Turkish geothermal fields [3], while the emission from fossil fuel (natural gas, coal, oil), ranges from 350 to 1100 gCO\({}_{2}\)/kWh. In other fields, such as those in the USA, the rate is reported to fluctuate with different resource management, namely the reinjection of separated fluid is found to dilute the resource and lower the emission rate from the GPP. An example from GPP Krafla in Iceland shows how the emission fluctuates according to volcanic action in the specific field, with additional utilization, and also shows how it declines and stabilizes with further operation of the GPP. It is, therefore, safe to assume that, even though the emissions of geothermal power plants originate from natural sources, the utilization of the geothermal field can affect the emission rate. According to present studies, the emission rate from GPPs can be both higher and lower than the natural rate, and, over time, utilization can further lower the emission rate. The emission factors, usually expressed as CO\({}_{2}\) emission per kWh produced by a geothermal plant, or eventually as cumulative emission including methane, defined as the Carbon Dioxide Equivalent, only partially represent the contribution of a power plant to carbon dioxide emissions in the atmosphere; this is because the contribution of surrounding soil emission must be included in the total amount of emission, taking into consideration any depletion observed pre and post geothermal development. In any case, a detailed picture of soil emission in the field is required, and even though the CO\({}_{2}\) emissions are found to be of a natural source, it is understood that it is important to measure the natural surface emissions, as well as those coming from the power plant, which is an integral part of the field being monitored. However, it must be understood that the present knowledge of the impact of geothermal utilization on the carbon cycle is not sufficient to justify a global methodology.