Even where gas prices are higher than in the U.S., CO2 emissions will not decline by market forces alone, according to a recent report [PDF] commissioned by the European Union: The report argues that “meeting climate change mitigation objectives will require a combination of approaches aimed at tripling fuel efficiency, reducing carbon contents of fuels and reducing total transport volumes. The researchers suggest that 20-30 per cent reductions in carbon emissions could be achieved through improvements in fuel efficiency by reducing vehicle power and weight and applying existing technologies, such as hybridised powertrains. However, the researchers say many customers will be unwilling to choose smaller cars unless they are required by law, or unless incentives exist.”