The recession and high fuel prices are demonstrably changing behaviour more than concerns about the environment.

BBC: Slump cuts our fuel use more than green concerns

Fuel efficiency is mainly driven by changing behaviour because of high oil prices, and by new technology that makes vehicles more efficient.

ECONOMIST: Energy and the environment

The changing consumer behaviour is closely linked to rising fuel prices, as well as to tax and insurance costs, which are higher for thirsty and powerful cars that generally emit more CO2 than smaller models.

BBC: Sales of low emission cars soar in UK

This may affect behaviour because as cars go faster they use more fuel to travel the same distance 25% more at 70mph than at 50mph, according to the Department for Transport.

ECONOMIST: Drivers are slowing down to save money

Every year the US has put certain conditions regarding North Korea's behaviour - such as allowing inspections - on budgeting for the fuel aid.

BBC: Analysis: N Korea's nuclear deal

Fuel duty has also served as a useful environmental weapon, since it accurately targets a pollutant and changes behaviour.

ECONOMIST: High petrol prices hurt, but will not throttle the economy