A report produced by Dr Julian Allwood and colleagues at the University of Cambridge has analysed buildings, vehicles and industry around the world to determine how much energy would be saved if "best practice" efficiency changes wre applied to them. They found that 73 per cent of global energy use could be saved by introducing such changes.

The changes to homes and buildings would range from using saucepan lids when cooking and reducing the set temperature of washing machines and dishwashers to triple-glazing windows, eliminating hot-water tanks and installing 300-millimetre-thick cavity wall insulation.

In transportation, the key change would be to limit the weight of cars to 300 kilograms. Dr Allwood admits that "300-kilogram cars would be at risk in collisions at present if they met heavier vehicles coming the other way." However, he notes that tougher emission standards and the need to reduce fuel consumption is already driving down the average weight of cars.

Dr Nick Eyre, leader of the Lower Carbon Futures group at the University of Oxford, says some of the assumptions made by the Cambridge team on how much energy could be saved by efficiency measures may even be overly conservative. Although he points out that achieving efficiency depends on people’s behaviour and not just on having appropriate technology. "A Passivhaus building will not perform to its design standard if its occupants open windows when it’s cold outside" he says.