WASHINGTON — Capping years of work by U.S. government scientists, the Environmental Protection Agency declared Friday that the heating of the Earth's climate from fossil fuel use threatens human health and the environment.
The decision paves the way for the EPA to order the nation's first mandatory reductions of global warming emissions.
Congress is working on legislation that also would require emissions reductions. President Barack Obama and EPA Administrator Lisa Jackson said they would prefer using a new law, rather than EPA rules, to make the reductions and spur renewable energy.
The EPA's announcement on Friday, however, serves notice that if Congress doesn't take action, the EPA will.
It was the first time the federal government had said it was ready to use the Clean Air Act to require power plants, cars and trucks to curtail their release of climate-changing pollution, especially carbon dioxide from the burning of fossil fuels.
The EPA had no choice but to make a declaration on whether the science is clear that global warming poses risks. The Supreme Court ruled in 2007 that greenhouse gas emissions were pollutants under the Clean Air Act and ordered the EPA to determine whether they harmed health and welfare or whether the science was too uncertain to judge.
The EPA's response on Friday was that the scientific evidence required action to reduce risks. U.S. and international climate scientists agree that observed changes in the atmosphere, oceans and ice show the world is warming because of human actions, and that the trend carries risks of irreversible climate disruption that could persist for centuries.
Scientists have charted an increase in Earth's average temperature in recent decades, as the amount of these gases in the atmosphere has grown to levels higher than any time in human history. The EPA's statement, a proposed "endangerment finding," was based on peer-reviewed scientific analysis of the effects of an accumulation of emissions of carbon dioxide and other greenhouse gases from burning fossil fuels.
"This finding confirms that greenhouse gas pollution is a serious problem now and for future generations. Fortunately, it follows President Obama's call for a low-carbon economy and strong leadership in Congress on clean energy and climate legislation," Jackson said. "This pollution problem has a solution — one that will create millions of green jobs and end our country's dependence on foreign oil."
The Bush administration had resisted such a conclusion and said it would be costly for companies to meet new emission limits and therefore could harm the national economy.
House Republican leader John Boehner of Ohio called EPA's move toward regulation "a backdoor attempt to enact a national energy tax that will have a crushing impact on consumers, jobs and our economy."
Environmentalists called the EPA action a watershed in addressing climate change.
"It's momentous. This has enormous legal significance. It is the first time the federal government has said officially the science is real, the danger is real and in this case that pollution from cars contributes to it," said David Doniger, climate policy director for the Natural Resources Defense Council, an advocacy group.