By Roger Harrabin
BBC Environment Analyst
California has led the way in the battle to regulate CO2
As the Terminator said in the Rose Garden - they have turned a crisis over car manufacturing into an opportunity for cleaner cars using less of that foreign fuel.
Arnie Schwarzenegger has been at war with the auto giants since he tried to use California's special powers over air pollution to regulate the greenhouse gas CO2 in the face of President George W Bush's refusal to enact federal laws.
Thirteen other states wanted to follow the Californian lead but the car-makers blocked them in court.
Then came that dual crisis of the oil shock and the recession that left the car-makers - particularly those heavy on gas-guzzlers - begging for US government help.
President Barack Obama extracted a price - an agreement to a federal standard on emissions by 2016 and an acceleration by four years of a previous Bush plan to improve energy efficiency by about a third.
'We're in the race'
The car-makers put a brave face on it, saying that they welcomed the "regulatory certainty" of national rules, even though they had been campaigning against them.
In fact the "compromise" is effectively a victory for Mr Schwarzenegger. It will mean the average new US car gets 35.5 miles per American gallon,the equivalent of 42 per UK gallon. By then, European laws will mandate about 45 mpg.
UK AND US GALLONS
The UK measurement of a gallon is slightly larger than that for a US gallon.
UK gallon: 4.546 litres
US gallon: 3.785 litres
1 US gallon = 0.833 UK gallons
The head of the US Environmental Protection Agency, Lisa Jackson, told BBC News: "We are lagging. We have some work to do. But today is a reason to be happy about the progress made. You know, we have a road to drive down - but we're firmly on it and now we're in this race."
The problem from a global perspective is the timing.
Although more efficient cars will be mandated by 2016, the car fleet will not be fully modernised for many years after that. So the new policies will not do much to help America's 2020 greenhouse gas targets, which have been criticised by poor nations for being much less ambitious than climate science demands.
But the American government has had to compromise with its own car-makers who are perceived to have neglected fuel efficiency since they managed to create a loophole in previous efficiency standards that allowed thirsty SUVs to dominate the market.
Unless the ailing American giants move quickly, they will be left with more unsellable models as imports dominate the US market.
Significantly, even though today's move will put up the price of some cars, it was welcomed by the drivers' association, the AAA, because it will reduce drivers' fuel costs and lower dependence on oil imports.
The White House claimed that the average car owner would ultimately save $2,800 through improved mileage.
Perhaps more significant is the fact that CO2 has been regulated at the federal level at all. This rule is a harbinger of emissions caps across other sectors of the economy.
But the opponents are massing against the president's plans and not all concessions will be as easily secured as the one obtained when the car-makers were on their knees.