All stabilization scenarios indicate that a huge share of emissions reductions, in the range of 60-80 per cent, would come from changes in energy systems. It has been found that this will require different sets of mitigation options across regions, with varying shares of renewable energy, nuclear energy, carbon capture and sequestration (CCS), biomass and hydrogen and other advanced energy carriers. In a way, it is a prerequisite for increasing shares of zero-carbon energy systems. However, it would be wrong to overestimate its contribution, even in advanced economies (Barker, Dagoumas and Rubin, 2009).