Scientific interest in understanding climate changes due to greenhouse gases began in the late nineteenth century with the Swedish chemist Svante Arrhenius, and such interest has developed considerably since that time. The history of such developments is described by the science historian Spencer R. Weart in his book The Discovery of Global Warming (Weart, 2008). Today there is no doubt that global warming, first noticed during the industrial revolution, is due to the increase of greenhouse gases, mainly CO2 from anthropogenic sources, of which electricity generation is a part. The effort now is being put into determining the relationship between CO2 in the atmosphere and the increase in air temperature at soil level.

The United Nations sponsored Intergovernmental Panel on Climate Change (IPCC), created in 1987, is currently the international organization responsible for reviewing and consolidating research on climate change and its effects. Since all nations share the atmosphere, climate change affects everyone, so control of carbon emissions is a global bonus. Any efforts made to reduce such emissions by using nuclear power instead of fossil fuels is a benefit for the whole world.

The IPCC produced major assessments on the climate change situation in 1990, 1995, 2001 and 2007. The first report underscored the seriousness of the risks associated with climate change and it was the driver for the 1992 UN Earth Summit in Rio de Janeiro, which led to the UN Framework

Convention on Climate Change (UNFCCC) and, later, in 1997, to the Kyoto Protocol. A clash between the requirements of developing and developed countries delayed the entering into force of the Protocol to 2005 and limited its validity to 2012. The Protocol established that developed countries should achieve an average 5.2% cut in CO2 emissions by 2008-2012, when compared to 1990 levels (UN, 1998). The Protocol created an emissions market and defined the so-called Clean Development Mechanism (CDM) which is non-applicable to nuclear projects. Developments expected after 2012 are not yet well defined.

One of the major worldwide advantages of nuclear power is its limited greenhouse gas emissions and its therefore corresponding contribution to a reduction in climate change (UIC, 2001). The nuclear fission reaction is anaerobic, i. e. it does not need air to generate energy, as is the case with fossil fuels. Fossil energy may be needed in the nuclear fuel cycle, for uranium mining and milling, conversion, enrichment, fuel fabrication, reprocessing and waste deposition and related transportation activities. The fabrication of components, construction and assembly of a nuclear power plant and its dismantling need fossil energy in the same way as other electricity generat­ing installations of a comparable size. The operation of a nuclear power plant is, however, generally free from carbon emissions, except for some safety and ancillary equipment such as emergency diesel generators, which have to be tested periodically, and boilers for heating sanitary and process water.

The release of CO2 from the different sources of generating electricity has received considerable attention. Up to the year 2000, it was estimated that nuclear energy could release up to 16 t CO2/GWh (Spadaro, 2000), while the release from coal and natural gas could amount to 1100 and 450 t CO2/GWh, respectively. These data are approximations that have been recently refined. First, there are differences in the type of coal and the thermal efficiency of the plant being considered: lignite can produce 1200 t CO2/GWh, while hard coal is limited to 1070 t CO2/GWh and can even go down to 974 t CO2/GWh for modern high-efficiency plants. Figures for gas combustion in conventional stations can be 650 t CO2/GWh, down to 450 t CO2/GWh for modern combined cycle plants. There are also variations in nuclear power plants mainly due to the enrichment process used: the gas diffusion process needs close to 50 times the energy needed in the gas ultracentrifugation process, and it can be as low as 5 t CO2/GWh. The data quoted here are taken from a number of different sources (NEA, 2008; Richter, 2010).

The data quoted for nuclear power include so-called plant life-cycle emis­sions, made up of the CO2 released in making the steel and concrete used in the plant, as well as that generated during dismantling and radioactive waste management, divided by the energy produced by the plant during its expected lifetime; to this is added the emissions involved in fuel cycle activities, including transportation and the limited direct emissions from operation. Longer-term operation of nuclear power plants therefore reduces their carbon footprint. This concept also applies to other carbon-free power sources, such as wind and solar power; as for nuclear power, the CO2 foot­print during operation of these sources is limited to maintenance and ancil­lary operations. Within this context, CO2 emissions from wind turbines are comparable to those of nuclear power, while those of solar power are two to three times larger.

With the basic data provided above, it is possible to determine the CO2 emissions that are avoided by using nuclear power instead of coal or gas. For one GWe nuclear plant operating with a 90% capacity factor, 7.6-9.3 million tons and 3.5-6.2 million tons of CO2 are effectively saved per year compared to that generated if the same energy were produced by coal and gas plants, respectively (depending on the technology used and the type of coal). The CO2 avoided carries a monetary value when using the Cap and Trade scheme already practised within European Union member states.

A recent report produced by the United Kingdom Committee on Climate Change states that ‘nuclear generation in particular appears likely to be the most cost-effective form of low-carbon power generation in the 2020s (i. e. before costs of other technologies have fallen), justifying significant invest­ment if safety concerns can be addressed’ (CCC, 2011). Similar results have been found by the International Energy Agency in its economic evaluation of ways to reduce the carbon content of the atmosphere to 500 ppm by 2050.