He’s only been in office a few days, but President Obama has already triggered an earthquake under the global car industry.

His green light for new fuel economy rules was expected. Obama has ordered the Transportation Department to come up with new guidelines by this March.

These will probably demand that the average 2016 model-year car sold in the US is good for nearly 40 (imperial) mpg. Demanding, perhaps, but not onerous.

However, the real shock is his decision to allow the Environmental Protection Agency to consider California’s request to set its own fuel economy standards.

California has long led the world in demanding cleaner engines. Over 40 years ago, it established the Clean Air Act, which forced car makers selling in the state to produce engines that emitted progressively lower levels of the pollutants that contribute to health-damaging smog.

Indeed, California effectively banned diesel engines in 1990 and today all the buses in LA run on clean-burning compressed natural gas.

However, because CO2 emissions do not directly affect human health, the gas was not considered under the Clean Air Act. In 2003, however, California wanted to change this, and bring CO2 emissions under the remit of the Clean Air Act. The US government prevented the move.