The most famous modelled scenario illustrating an all-RE plan is the 2010 one from ECOFYS/World Wildlife Federation (WWF). The WWF model sees “green” energy types on the bottom of the graph rising up and replacing the “dirty” energy types on the top: fossil fuels as well as nuclear power. In WWF’s model, though, green energy’s replacement capacity gets a lot of help from an envisioned overall downward slope of energy demand after about 2018, presumably brought about in part by increasing energy efficiency.
Yet that hoped-for pivot is now coming up in three years, and is there not any sign of such a global demand reduction on the horizon. Rather, global energy demand looks like this now (below). The significant thickening up of the renewables lines are nowhere to be seen at the present time. Now, it's true WWF sees most of the wind, earth, and sun action happening after 2020, and it is fair to assume given cost reductions there will be inroads into fossil fuel use by that point.
According to the US’s Energy Information Administration (EIA), ongoing energy demand is starting to look more like this, broken down by region:
We can see the same contradiction played out in the three modelled scenarios presented in the recent IPCC AR5 WG3 report (2014). Each of the scenarios were devised by a different group to envision a way to limit global warming to 2 degrees by 2100. The graphs on the left reflect how the modellers see the extension of current energy use without significant policy and technological changes. The graphs on the right describe how energy generation could be adjusted to meet the 2 degree limit.
One of the scenarios, GCAM, incorporates nuclear energy and a hefty dose of Carbon Capture and Storage (CCS) into their 2 degree solution. Reductions in coal, gas, biomass, and oil without CCS, seen under the line, are what allows the target to be met despite that increasing amounts of energy are being added to the global system in an ongoing way up to 2100, as can be seen by the upward curve on the right-hand graph. To a less significant degree, GCAM also achieves the 2 degree target though gradually increasing efficiency gains, indicated by the grey bar. These efficiency gains do not, however, counteract the generalized need reflected in GCAM for an increased amount of energy in the global system.
The right-hand graph is, however, the most interesting one. MESSAGE includes a small amount of CCS but no nuclear, and as such must achieve its 2 degree solution almost entirely through efficiency and demand reductions from fossil fuels. Remarkably, solar and wind power contribute comparatively little to the envisioned climate mitigation achievement above baseline. Over time, energy is subtracted from the system at an increasingly greater rate than it is added.
Yet the IPCC models are instructive insofar as they illustrate how drastically higher the demands for efficiency and demand reduction become when we exclude nuclear power from the available palate of carbon-free energy choices. The powerful requirement of CCS seen by all modellers is another element of this story, but CCS is not yet ready for wide deployment. Nuclear power is already here, and is as such the signature thing we can work now on retaining and expanding if we don’t want to stake the fight against climate change on a bid for efficiencies and demand reductions that are likely unrealistic and, if executed on a global scale, very likely to be unjust.