Energyrelated emission

Strictly speaking, energy-related CO2 emissions should also include transport, but to simplify things this section will deal only with 'stationary sources', such as power stations. Of the emissions arising from fossil fuel burning - a total of ~6.5 Pg C/year - nearly one-half is a result of electricity generation, either by electric utilities or through domestic energy use.

The amount of CO2 emitted as a result of the generation of a given unit of electricity varies greatly depending on the fuel used and the level of efficiency at which the power plant operates. Generally speaking, coal-fuelled power generation is the most carbon-intensive, with the emission of up to 1 kg of CO2 for every kilowatt-hour (kWh) of electricity that it provides. Oil- and gas-fuelled electricity generation tends to have a lower CO2 emission cost. Even those energy-generation strategies without apparent use of fossil fuels generally have some associated CO2 emissions. Nuclear power, for instance, relies on large amounts of energy use for fuel extraction and processing, and so indirectly results in CO2 emissions. The construction of any power station, wind turbine or other power-generation facility carries with it an emission cost through the embodied energy of the materials used in its construction. This cost must be included if the full climate benefits of any one type of energy generation are to be accurately assessed and compared with others.

Humankind's demand for, and generation of, electricity for heating, cooking, light and so on has grown at an astonishing rate during the last century. Now, as in the past, there are huge geographic disparities in energy consumption. Individuals in developed countries such as the UK and USA use much more electricity per person than in most developing countries.

The efficiency of electricity generation has increased greatly and continues to do so, although there is a large amount of energy wastage in the form of waste heat in most fossil fuel-burning power stations. The introduction of combined heat and power (CHP) systems, in which waste heat is captured and used for residential or business purposes, can raise the efficiency of coal-burning power stations from below 40% to 60%.

Such improvements in efficiency, however, have been outstripped by energy demand, and therefore energy-related emissions of CO2 continue to rise rapidly. In the longer term, some developed countries may have to accept that their level of energy consumption is unsustainable. In the shorter term, greater use of 'low carbon' energy-generation technologies, such as geothermal, wind, wave, solar and tidal power, may provide significant reductions in emissions.

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