Although nuclear energy is a low CO2 energy system, it is not a very efficient tool for rapidly reducing carbon emissions. Global climate change does not justify a considerably increased global nuclear programme for the next two to three decades. Even if for other political or socioeconomic reasons such an intensive global nuclear programme were initiated, its impact on CO2 emissions would be only marginal. This is true irrespective of the costs and feasibilities of alternative emission reduction strategies, such as energy efficiency measures, or the availability of other low CO2 energy supplies.