"If you take a look at the marketplace today, we have different fuel economy and environmental standards in California versus the federal government, and if you're a car company, that makes it hugely complicated, because you have to build different versions of the same vehicle, depending on where you plan to market," Anwyl said.
But one critical open question for automakers -- will these cars be as safe as the ones they are currently manufacturing, because of the timeline to produce them?
In the late 1970s, the United States pushed for better fuel efficiency very quickly, and the result was lemon cars like Chevrolet's Vega and Ford's Pinto.
"We don't want another episode of cars that were quickly engineered and manufactured and turned out to not to be very good cars for the car-buying public," Portnoy said.
Patrick Michaels, senior fellow in Environmental Studies at the Cato Institute, says car companies that are critical of the White House's move are not in much of a position to object, after the federal bailout of Chrysler and General Motors.
"U.S. automakers used to be U.S. automakers. Now they're owned in part by the government. So the government can tell them pretty much what they want them to produce," Michaels said.
Also onboard are California Gov. Arnold Schwarzenegger and auto-friendly Michigan Gov. Jennifer Granholm, who were at the White House today for Obama's announcement. Schwarzenegger has been leading the push for more environmentally friendly cars, by imposing tough standards on all new cars sold in California.
"California's relentless push for greenhouse gas reductions from automobiles is paying off not just for our state, but for all Americans, for our environment, for automakers and our economy," said Gov. Schwarzenegger in a statement. "This historic agreement to reduce greenhouse gases will mean cleaner air for our children and grandchildren, greater economic security as we rely less on foreign oil, and a chance at renewal for our auto industry. Today, we're seeing what happens when California leads on energy and the environment and doesn't waiver, doesn't get bogged down, doesn't let obstacles get in the way."
At the White House for the announcement were officials from the Department of Transportation, which is tasked with handling the new CAFE standards, and from the Environmental Protection Agency, which will handle the new greenhouse gas emission standards.
Environmentalists say the technology is already there to make cars to meet the new requirements. As evidence, they point to Japanese cars that already exceed these standards.
"The American manufactures know how to do it. They can and they will. This is going to force them to do it," Becker said.
Consumers will still be able to choose what kind of car they want to drive -- but those cars will just be fuel efficient.
"All companies will be required to make more efficient and cleaner cars," a senior administration official told ABC News. "We did that my proposing individual standards for each class size of vehicles. This has the affect of preserving consumer choice, you can continue to buy any particular car you'd like."
ABC News' Kristina Wong contributed to this report.