For the first time in its history, the U.S. Supreme Court has waded into the political debate on global warming.
Under the Bush administration, the Environmental Protection Agency or EPA has argued that carbon dioxide and the like aren't pollutants under the Clean Air Act, and therefore, the agency has no power to regulate them.
In a sweeping 5-4 decision released Monday, the Supreme Court rejected that position, declaring that Clean Air Act gives the Environmental Protection Agency the authority to regulate the emissions of carbon dioxide and other greenhouse gases from cars.
Supreme Court Justice John Paul Stevens wrote the majority opinion, and was joined by Justices Anthony Kennedy, David Souter, Ruth Bader Ginsburg and Stephen Breyer.
The Supreme Court majority decided US motor-vehicle emissions make a "meaningful contribution to greenhouse gas concentrations" and hence, to global warming.
"A well-documented rise in global temperatures has coincided with a significant increase in the concentration of carbon dioxide in the atmosphere. Respected scientists believe the two trends are related," Justice Stevens wrote.
Environmental groups applauded the Court's decision.
"It's an important signal that the Bush administration cannot continue to ignore the problem of global warming for political reasons when the science is so clear and there's such clear pressure from the public to move forward," said Josh Dorner, spokesperson for the Sierra Club in Washington D.C.
"An enormous victory for the fight against global warming," declared Doug Kendall, whose group Community Rights Counsel filed an amicus brief in the case on behalf of the U.S. Conference of Mayors.
"The Supreme Court has recognized both the importance of the problem and the need for the federal government to act on the solution," Kendall said, arguing the decision is a major victory for states who want to rely on the congressional Clean Air Act.
"The Supreme Court's decision, in Massachusetts v. EPA, repudiates the Bush administration's do-nothing policy on global warming," said David Doniger, Natural Resources Defense Council's attorney in the case.
Greenpeace, the well-known environmental group, viewed the decision today as a political victory against the Bush administration's policy on climate change.
"What this ruling shows is the degree to which the Bush administration just continues to be out of step, not only with the science, but with congress and public opinion," said Chris Miller, director of global climate change at Greenpeace.
"All of these years that the Bush administration has been in office, instead of trying to find out ways that they can combat global warming, they've been denying the science, they've been fighting lawsuits ... so this is a big defeat for them, and it's also a big defeat for the automotive industry that spent a lot of time energy and effort trying to beat this back," said Miller.
The automotive industry, which stands to be affected the most by any change in government regulation, reacted favorably today, arguing the ruling may be good for automakers in the long run.
"The Alliance of Automobile Manufacturers believes that there needs to be a national, federal, economy-wide approach to addressing greenhouse gases," said Dave McCurdy, president and CEO of the Alliance of Automobile Manufacturers.
Many U.S. vehicle manufacturers have said they would like to see a national standard for emissions, instead of the current system of different standards in every state.
Today the EPA responded to the Supreme Court decision with a defense of the Bush administration's climate change policy.
"EPA is reviewing the Court's decision to determine the appropriate course of action," said Jennifer Wood, press secretary for the EPA.
"The Bush Administration has an unparalleled financial, international and domestic commitment to reducing greenhouse gas emissions," Wood said, arguing the administration has a goal to reduce greenhouse gas intensity 18 percent by 2012.
"The president's policy achieves near-term reductions, while investing in long-term solutions," she said.
During a White House press briefing today, deputy press secretary Dana Perino argued the administration has already tried to reduce carbon dioxide emissions by increasing mileage standards for light trucks and SUVs through the Department of Transportation's CAFE program.
"The way to get cars to be more efficient is to burn less gas and to go more miles and that's what we've been working to do," said Perino.
When asked why the administration has declined to mandate that businesses cap their greenhouse gas emissions, Perino said, "we did not move forward with a full, mandatory cap because we believe that it would have been harmful to United States businesses."
"Everyone is emitting up into the air," said Perino, "and if there are no actions taken by the major developing countries, like China and India ... you're going to put the American economy at a great disadvantage, push American businesses overseas, and then do nothing for the environment," she said.
Dissenters of the Supreme Court decision included some of the more conservative justices, including Justices Scalia, Clarence Thomas, Samuel Alito and Chief Justice John Roberts.
The dissenting Justices questioned whether concern over global warming is warranted.
"The Court's alarm over global warming may or may not be justified, but it ought not distort the outcome of this litigation," wrote Justice Scalia in his dissension.
"No matter how important the underlying policy issues at stake, this Court has no business substituting its own desired outcome for the reasoned judgment of the responsible agency," wrote Scalia.
Eleven states joined Massachusetts in bringing the suit against the EPA, including California, Connecticut, Illinois, Maine, Massachusetts, New Jersey, New Mexico, New York, Oregon, Rhode Island, Vermont and Washington State, along with numerous other environmental groups and nonprofit organizations.
Fourteen "friend of the court" briefs were also filed from independent scientists, former EPA administrators, former Secretary of State Madeleine Albright, electric power companies, state and local governments, and others.
However, some of those same groups say it may be years before any real change is taken by the EPA.
"It puts a process into motion that essentially compels the EPA to at some point issue regulations on carbon dioxide," said Dorner. "I think, obviously, that process will be a slow one and we might see some action in Congress before that process comes to full fruition. It just moves things down the field one more step."
The Supreme Court had three questions before it: Do states have the right to sue the EPA to challenge its decision? Does the Clean Air Act give EPA the authority to regulate tailpipe emissions of greenhouse gases? Does EPA have the discretion not to regulate those emissions?
The Court said 'yes' to the first two questions and, on the third, it ordered EPA to re-evaluate its contention it has the discretion not to regulate tailpipe emissions.
The Court said the agency has so far provided a "laundry list'" of reasons that include foreign policy considerations and added that the EPA must tie its rationale more closely to the Clean Air Act.
The political climate has changed dramatically over the issue of global warming since the court agreed last year to hear the case -- the Supreme Court's first on the subject.
In November of 2006, Democrats took control of Congress and pledged to make global warming a national issue.
In February, the world's leading climate scientists reported global warming is "very likely" caused by man and is so severe that it will "continue for centuries."
An interesting development in the politics of climate change is how the issue of global warming is playing out in the 2008 presidential campaign.
"Virtually all of the frontrunners for the 2008 presidential bid are significantly stronger on this issue (than the Bush administration)," said Chris Miller of Greenpeace, pointing to '08 candidates Sen. Hillary Clinton, D-N.Y., Sen. Barack Obama, D-Ill., and Sen, John McCain, R.Ariz., who all advocate capping greenhouse gas emissions.
But perhaps one of the biggest political players in the climate change arena is former Vice President Al Gore.
His Academy Award-winning documentary, "An Inconvenient Truth", which makes the case for prompt action on climate change, has gained widespread attention and applause, not to mention giving Gore a microphone to the world during the Oscars.
Standing alongside David Guggenheim, director of the Gore-inspired documentary, on stage, Gore proclaimed, "My fellow Americans, people all over the world -- we need to solve the climate crisis. It's not a political issue. It's a moral issue. We have everything we need to get started with the possible exception of the will to act. That's a renewable resource. Let's renew it."
The former Vice President turned environmental activist also recently testified before both the House and Senate on the issue of global climate change, spurring rumors of another presidential bid, all of which have been downplayed but not entirely rejected by Gore.
ABC News' Jan Crawford Greenburg, Ariane DeVogue, and Dennis Powell contributed to this report.