Fundamental restructuring of the UK's entire energy system is unavoidable if it is to meet future energy demand while reducing greenhouse gas emissions by 80% by 2050, even assuming that energy demand in all sectors can be substantially reduced, according to a report published by the Royal Academy of Engineering. To achieve this, the scale of the undertaking will require the biggest peacetime programme of investment and social change the UK has ever seen, says the Academy. 'Generating the Future: UK energy systems fit for 2050' considers four possible energy scenarios that could meet the 2050 emissions reduction target, each of which demonstrate that there is no single 'silver bullet' solution that will deliver the required 80% emissions cut. Demand reductions through a combination of increased efficiencies and behavioural change will be essential. The scale of the engineering challenge is massive � the country will need to exploit its renewable energy resources to the maximum and supplement this with other low-carbon sources including nuclear power and coal- or gas-fired generation fitted with carbon capture and storage (CCS). "There is no more time left for further consultations or detailed optimisation and no time to wait for new technical innovations. Infrastructure on this scale doesn't happen on political timescales," says Dame Sue Ion, chair of the Academy's energy scenarios working group. "It takes decades to prove and roll out large-scale major infrastructure so only those low-carbon technologies we already know of can help us to meet the 2050 targets." "The scale of the challenge is obvious when you look at DECC's UK energy flow chart for 2007," says Dr Ion. "Most of our energy is still supplied by fossil fuels. If we are to cut emissions by 80% most of the fossil fuels will have to be replaced by nuclear power and renewables such as wind, solar, marine or biomass. We compared the 2007 chart with its equivalent for 1974 and it is almost identical � remarkably little has changed in the proportion of fossil fuels we use during 33 years. We are looking at a completely different paradigm over the next 40 years and beyond. "Whatever happens in the future, we need to recognise that the changes required to the UK energy system required in order to meet the 2050 emissions reduction targets are so substantial that they will inevitably involve significant rises in energy cost to end users."