A speedy transition to low or zero carbon energy systems is necessary to stabilise concentrations of greenhouse gases at levels consistent with a 2 C target. It requires global cuts in emissions by at least 50 percent by mid-century and essentially zero emissions in industrialised countries. Such transitions appear feasible based on resource availability, existing and projected technologies, and associated costs, but require purposeful steering by states and other key actors in society.

Scenarios on low-carbon futures and energy transition pathways have in recent years recurred as a strategic element in climate and energy policy. The overall message from various scenarios and analyses is that radical emission reductions are urgently needed and technically feasible to achieve at reasonable economic costs to society. In other words, there is relatively broad consensus on what needs to be done. However, low-carbon scenarios are seldom explicit on how to make the transitions towards low-carbon futures happen. Alas, the policy, governance and institutional challenges implied are largely underestimated or not addressed.

Long-term stabilization scenarios indicate that the concentration of greenhouse gases needs to be stabilized at levels below 450 ppm in order to have a 50 percent chance of staying below the 2 ºC temperature target. For this target, global emissions need to be at least halved by the mid-century, while emissions in advanced industrialized countries (i.e. OECD) are cut by 80-100% in 2050.

Transition pathways, or ‘emission envelopes,’ indicate the relative importance of various technologies and mitigation options that are available. In general, four types of energy-related mitigation options are emphasized; energy efficiency improvements; renewable energy sources; carbon capture and storage (CCS); and nuclear power. For the purpose of this report, we have decided not to address nuclear power as it is not part of the international climate negotiations.

In the IEA BLUE scenario energy efficiency accounts for 36 %, renewable energy for 21 %, CCS for 19% and nuclear power for 6% of the emissions reduction, while fossil fuel switching and efficiency improvements in power generation account for the remaining 18%.