Greenhouse Gas Emissions and Climate Impacts

For the last century, human activities have been altering the global climate. Climatic warming is a fact; it endangers the environmental living conditions as well as global economy [8]. The global average surface temperature increased from 1900 to 2006 by at least 1.0°C; during the same time period the CO2 content of the atmosphere doubled [4]. It is widely recognized that the most probable cause of climatic warming is the increasing content of greenhouse gases in the atmosphere. Observations show that the Earth's surface has warmed by approximately 0.6°C during the twentieth

Fig. 4.2 Installed capacity in 2010 worldwide (total 10.7 GW) [14]
Fig. 4.3 Forecasting up to year 2050 [14]

century [16]. Atmospheric abundances of the major, human-generated greenhouse gases, i.e. CO2, CH4, and nitrous oxides (NOx), reached their highest recorded levels in modern history by the year 2000 and are continuing to rise. About 37% of incremental atmospheric CO2 accumulation is caused by electric power generation, mainly from coal combustion power plant [17].

When compared to other energy source of power generation, geothermal power plants have much lower CO2 emissions. The results show that geothermal power production has a significant environmental advantage over burning fossil fuels for electrical power production. Electrical production from geothermal fluids results in an order of magnitude less CO2 per kilowatt-hour of electricity produced compared to burning fossil fuels (Fig. 4.4).

A highly respected source (World Energy Assessment - a collaborative effort between UNDP, UNDESA and the World Energy Council) attests the largest potential value to geothermal energy among all forms of renewable energy sources. The comparison is given in Fig. 4.5. The values are given in capacity units, i.e. energy per unit time. It is obvious that geothermal energy has the largest capacity, although the accuracy of the reported number is limited [7].

1000

800-

Geothermal Natural Gas Oil Coal

Fig. 4.4 Comparison of CO2 emission from electricity generation from different energy sources [15]

5000

sooo 4ooo 3000

2ooo 1000 o

1575

e276

Geothermal Solar

Wind

Biomass

Hydro

Fig. 4.5 Potential of renewable energy sources [18]

CO2 emission from geothermal power plants in high temperature fields is about 120 g/kWh (weighted average of 85% of the world power plant capacity). With the present engineering solutions, it could be possible to increase geothermal power from the expected value of 11 GW for year 2010 up to a maximum of 70 GW in 2050; the gradual introduction of the new developments (binary plants, EGS systems) may boost the growth rate with exponential increments, thus reaching the global world capacity of 140 GW in 2050. The corresponding electricity production of about 1,000 TWh/year in 2050 will mitigate (depending on what is substituted) hundreds of million tons CO2/year. Future technology including reinjection will result in negligible emissions (10 g CO2/kWh). The extrapolations to year 2050 are given in Figs. 4.6 and 4.7 [7, 8].

1990 2000 2010 2020 2030 2040 2050

Fig. 4.6 Installed global geothermal capacity and electricity production 1995-2005 and forecasts for 2010-2050 (From Fridleifsson et al. [8, 19])

1990 2000 2010 2020 2030 2040 2050

Fig. 4.6 Installed global geothermal capacity and electricity production 1995-2005 and forecasts for 2010-2050 (From Fridleifsson et al. [8, 19])

Fig. 4.7 Mitigation potential of geothermal power plants in the world and assumptions for emission of 120 CO2/kWh for today and 10 g CO2/kWh for future technology (From Fridleifsson et al. [7, 19])

Geothermal technologies for power generation or direct use operate with little or no greenhouse gas emissions. Since no burning processes are involved they are low in CO2 emissions. Geothermal energy development has thus great CO2 emission reduction potential when substituting fossil sources of energy. Further development - depending on future growth rates - could reduce CO2 emissions even more significantly. The current and future potential contributions to reduce CO2 emission by geothermal power generation and direct use have been assessed in a study carried out for the Intergovernmental Panel on Climate Change [8, 19].

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