By announcing the proposed finding, the Environmental Protection Agency is setting in motion new government actions to limit carbon dioxide and other greenhouse gases, which would have widespread economic and social impact on how the United States produces and consumes energy, from requiring better fuel efficiency for automobiles to requiring power plants and other industrial sources to reduce emissions of pollutants that contribute to climate change.
EPA Administrator Lisa Jackson said the EPA analysis "confirms that greenhouse gas pollution is a serious problem now and for future generations" and warrants steps to curtail it.
Environmentalists hailed the policy shift.
"The importance is that the federal government will now begin setting limits for the first time on carbon dioxide and other greenhouse gas pollutants something the Bush Administration refused for 8 years to do as the problem grew worse and worse," the Sierra Club's David Bookbinder told CBS News correspondent Bob Orr.
But any new pollution caps targeting climate change won't be in place any time soon. Regulations by the EPA's own admission could take years, and face likely court challenges.
And they wouldn't be cheap. A crackdown on auto exhaust and new requirements reining in factory emissions could cost untold billions at a time manufacturers and businesses are fighting just to survive a recession, Orr reports.
The Obama Administration would prefer to hold off on regulations and let Democrats on Capitol Hill pass actual laws curbing carbon emissions, Orr reports. But Republicans, calling that idea a new energy tax, are already promising a fight.
Friday's action by the EPA triggered a 60-day comment period before the agency issues a final endangerment ruling. That would be followed by a proposal on how to regulate the emissions.
The agency said in its finding that "in both magnitude and probability, climate change is an enormous problem" and that carbon dioxide and five other gases "that are responsible for it endanger public health and welfare within the meaning of the Clean Air Act."
The EPA concluded that the science pointing to man-made pollution as a cause of global warming is "compelling and overwhelming." It also said tailpipe emissions from motor vehicles contribute to climate change.
The action was prompted by a Supreme Court ruling from two years ago that said greenhouse gases are pollutants under the Clean Air Act and must be regulated if found to be a danger to human health or public welfare.
In addition to carbon dioxide, a product of burning fossil fuels, the EPA finding covers five other emissions that scientists believe are warming the earth when they concentrate in the atmosphere: Methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6).
The court case, brought by Massachusetts, focused only on emissions from automobiles. But it is widely assumed that if the EPA must regulate emissions from cars and trucks, it will have no choice but to control identical pollution from power plants and industrial sources.
However, the Bush administration strongly opposed using the Clean Air Act to address climate change and stalled on producing the so-called "endangerment finding" demanded by the High Court in its April 2007 ruling.
Last year, claiming that doing so was the "wrong way" to address the pollutants contributing to climate change.
Jackson said while the agency is prepared to move forward with regulations under the Clean Air Act, the Obama administration would prefer that Congress addressed the climate issue through "cap-and-trade" legislation limiting pollution that can contribute to global warming.
While EPA officials said the agency may still be many months from actually issuing such regulation, the threat of dealing with climate change by regulation could spur some hesitant members of Congress to find another way to address the problem.
Congress is considering imposing an economy-wide cap on greenhouse gas emissions along with giving industry the ability to trade emission allowances to mitigate costs. Legislation could be considered by the House before the August congressional recess.
"The (EPA) decision is a game changer. It now changes the playing field with respect to legislation," said Rep. Ed Markey, a Democrat whose Energy and Commerce subcommittee is drafting broad limits on greenhouse emissions. "It's now no longer doing a bill or doing nothing. It is now a choice between regulation and legislation."
Sen. Barbara Boxer, a Democrat who heads the Environment and Public Works Committee responsible for climate legislation, said EPA's action is "a wake-up call for Congress" - deal with it directly through legislation or let the EPA regulate.
Warning that global warming threatens "our health, our economy, and our children's prosperity," Environmental Defense Fund attorney Vickie Patton commended the EPA's move, saying, "The U.S. is taking its first steps as a nation to confront climate change."
U.N. Secretary-General Ban Ki-moon urged world leaders to respond with the same urgency to climate change as they did to the global financial crisis. He said in a speech at Princeton University that climate change could have even more dire effects than a recession.