The International Panel on Climate Change (IPCC) reviews periodically the evidence for climate change and, depending on the rate of greenhouse gas emissions, makes predictions on future evolutions. Because the future of nuclear energy cannot be discussed without reference to these aspects, we summarize the main conclusions reached by the IPCC as well as by organi­zations such as the World Energy Council (WEC) and the International Institute for Applied Systems Analysis (IIASA) who focus on the prediction of future energy consumption.

Evidence for anthropically induced climate change

Figure 2.1 shows how the concentration of three important greenhouse gases in the atmosphere follows the world population increase.

The correlation between the four curves is striking with an especially fast increase of greenhouse gas concentrations after 1950. Although the greenhouse efficiency of methane and other gases is much larger than that of CO2, its much larger abundance gives it the dominant contribution. Typically, CO2 accounts for 62% of the additional radiative forcing due to anthropic emissions, methane for 20% and other gases for the rest. Water has an amplifying role but is not a driving factor.

Although the increase of greenhouse gas concentrations is unquestion­able, its effects on temperature are more difficult to establish. Figure 2.2 shows a clear rise of the temperature during the last century. However, this increase is not attributable solely to increased concentration of green­house gases. Climatic models indicate that only the temperature increase observed between 1960 and the present can be attributed to greenhouse gas emissions.