Following through on a pledge made by President Obama in May, the administration proposed new standards today that would cap carbon dioxide emissions from cars and light trucks in an attempt to stem society’s contribution to global warming.

The Environmental Protection Agency and the National Highway Traffic Safety Administration jointly proposed the new regulation. EPA’s part of the rule would – for the first time ever – set a limit on carbon dioxide emissions from vehicles. The average car in a manufacturer’s line of vehicles would be allowed to emit no more than 295 grams of CO2 per mile in 2012. The rule would ratchet the limit down to 250 grams per mile by 2016.

To stay within the limits, manufacturers would be forced to improve vehicle fuel efficiency. That’s where NHTSA comes in. NHTSA administers the decades-old Corporate Average Fuel Economy (CAFE) program which sets miles-per-gallon requirements on cars and trucks. NHTSA’s portion of the rule revises CAFE standards to match EPA’s proposed emissions limits. The new standards will require the average car to travel 30.1 miles on a gallon of gas in 2012 and 35.5 miles by 2016.

The CAFE standards announced today are more aggressive than those required under a law passed by Congress in 2007. Congress gave NHTSA until 2020 to set a 35 mpg standard.

The environmental gains are good but not stupendous. EPA estimates that by 2020 the standards will reduce U.S. vehicle emissions by 12.4 percent. My ’98 Toyota Camry already gets about 35 mpg, so I don’t think NHTSA is exactly shooting the moon with the new CAFE standards.

Still, this is a big deal – especially when you consider that just 9 months ago Americans were served by an administration that had trouble admitting that global warming was happening, let alone caused by man, let alone in need of a government-sponsored solution. Moreover, the Obama administration has moved quickly to propose this 600+ page (single spaced) regulation. As followers of the regulatory process know, swift progress is no small feat.