# **3) Discussion and conclusion**

The preceding analysis of 37 energy forecasting studies and their 116 scenarios shows how longterm visions of the structure of the energy supply evolved over a period spanning almost 35 years. The first striking feature is that the 1970s technological optimism about our ability to switch away from fossil fuel (fossil fuels were projected to have only a 50-70% share in total primary energy at t+30) decreased significantly in the 1990s (a share of 75-90%), likely influenced by the long period of relatively low oil prices after 1985. The slight recovery of optimism in the last 5- 10 years (70-80% share of fossil fuels) seems correlated with the rise in oil prices. A potential change in worldviews after Kyoto seems very low up to 2005, a logical consequence of the Bush administration’s neglect of Kyoto (figure 13).

The decline in technological optimism is unsurprisingly correlated with a decline in modelers’ belief in the suitability of nuclear power, with projections of the share of nuclear power dropping from a high of 20-35% in the 1970s to around 5% in the last two decades (figure 14). This decline shows that modelers internalized public concerns about nuclear power and did not envisage a reversal of public opinion; furthermore, the period of low oil prices after 1985 did not offer a strong argument that the economic advantage of nuclear power outweighed the concerns.

The case of renewable is more intriguing as a trend of increasing optimism from the early 1970s to the mid 1980s (with the share rising from about 2% to 10%) was followed by a period of great uncertainty, as shown by the subsequent large range in projected shares (4-12%, figure 15). Also, a group of renewable optimists has emerged in the last decade predicting a higher share of renewables in the next 30 years. The influence of Kyoto, which was not significant for fossil fuels and nuclear, is more clearly detectable for renewables, with more optimistic studies launched in the late 1990s and published in 2001 and 2003. The rise in oil prices supported this reassessment of the role renewable energies but no study predicts a drastic acceleration of their penetration.

The apparent conservatism that emerges from this retrospective is a message to be considered in debates around climate policies. Indeed, whereas the relative stability of the structure of the energy supply over thirty years is not surprising given the inertia of energy systems, here we investigate long-term visions of the world, and technical inertia cannot explain why the projected prospects for shifting away from fossil energies have been so stable since the early 1980s. Historically, the promises of generous technical change on the supply side were not fulfilled in the case of the nuclear energy, nor in the case of new and renewable energies, for which projected shares were not upgraded during more than three decades.

This pessimism cannot obviously be extrapolated for the future but the above analysis is a reminder of the false impression of the ease of substituting for fossil fuels, an impression that emerges in long-run energy forecasting. That a large scale option can be broken by a sudden rise of public concern is not unique to nuclear energy (as we now see for carbon sequestration and for the impacts of wind energy on landscapes); in the same way efforts on new and renewable energies can be discouraged by periods of low energy prices and be made unsuccessful by too large a spectrum of options. Our concluding message is that the optimism necessary to mobilize efforts to develop low carbon energy supply should not be used to divert attention away from efforts to modify the dynamics of the energy demand nor from the enforcement of policies necessary to create stable carbon prices and encourage the taking of investment risks.