President Obama today issued the toughest emission and mileage standards in history for new cars sold in the United States, a move environmentalists hail as the first step ever by the U.S. government to curb global warming.

Obama says ending the dependency on oil will take time and an historic effort."In the past, an agreement such as this would have been considered impossible," Obama said. "That is why this announcement is so important, for it represents not only a change in policy in Washington, but the harbinger of a change in the way business is done in Washington."

Obama said the rule will provide "the clear certainty that will allow these companies to plan for a future in which they are building the cars of the 21st century."

The changes will likely mean higher price tags on new cars for consumers, but the administration says the increase in mileage standards will negate that initial expense by lowering fuel costs.

"It will clearly be more expensive to meet these tighter standards," said Paul R. Portney, dean of the Eller College of Management at the University of Arizona.

The new energy-efficient cars will cost on average about $1,300 more per car by 2016, according to a senior Obama administration official. But the Environmental Protection Agency says Americans will make that money back in fewer trips to the pump over three years.

In the sweeping changes, the White House ordered automakers to significantly increase the gas mileage of the cars they make and significantly reduce the amount of pollution they emit. Car companies will also be forced to cut the amount of greenhouse gas emissions in new cars by about 25 percent.

The average current fuel-efficiency standard for cars and light trucks is 25 miles per gallon. With the president's announcement today, that standard will go up to 35.5 miles per gallon by 2016.

This is four years earlier than what the current law requires, and is an average 5 percent per year increase in fuel efficiency from 2012 through 2016.

The changes will likely mean higher price tags on new cars for consumers, but the administration says the increase in mileage standards will negate that initial expense by lowering fuel costs.

"It will clearly be more expensive to meet these tighter standards," said Paul R. Portney, dean of the Eller College of Management at the University of Arizona.

The new energy-efficient cars will cost on average about $1,300 more per car by 2016, according to a senior Obama administration official. But the Environmental Protection Agency says Americans will make that money back in fewer trips to the pump over three years.

"There are immediate savings, obviously, to the consumer because of the fuel savings. For people who buy their cars on time, over a 60-month loan, which is about 70 percent of the American people, on a month-to-basis it may end up being a wash in terms of the slight increase in the price of the car, but that is offset by the lower gasoline used," a senior Obama administration official said.

Experts compare the new cars to energy-efficient lightbulbs. A regular bulb costs $2.99, and the energy-efficient one is $12.99. But in the long run, the product that is more energy efficient will not just save energy but save money in the long run.

"Citizens in the United States will get better mileage on their cars. They will spend less on gasoline each year," said Portnoy.

White House energy and climate director Carol Browner said U.S. automakers expressed their desire to the administration to make more fuel-efficient cars and wanted the government to give them the predictability and certainty of a national standard so they could make investments toward cleaner vehicles.

Browner refused to comment on whether the Obama administration may consider a tax on gasoline, which some say could also reduce the United States' dependency on foreign oil.

"We work, obviously, within the laws on the books," Browner said on "Good Morning America" today. "And what we're using is the president's executive authority to propose these standards, and it is the first-ever time that EPA and DOT [Department of Transportation] have taken their existing individual authorities and woven them together so that we can give the American public and the car companies what they want."