In the first major move by the federal government to address climate change, the U.S. Environmental Protection Agency (EPA) has declared heat-trapping greenhouse gas emissions a threat to public health and welfare, setting the stage for potentially major regulations.

According to a notice released April 17, EPA Administrator Lisa Jackson believes "the total body of scientific evidence compellingly supports" the finding that greenhouse gases endanger public health and welfare. Jackson also says cars and trucks contribute to greenhouse gas pollution.

While the so-called endangerment finding does not represent regulatory action in and of itself, it will obligate EPA to limit greenhouse gases in the future. The finding lumps greenhouse gases in with other air pollutants that require regulation under the Clean Air Act.

EPA is already working on regulations and expects to propose them for public comment "several months from now," according to the notice. The initial regulations will target vehicle emissions, but the endangerment finding will eventually require EPA to regulate stationary sources such as power plants or other industrial facilities.

Congressional Democrats pushing legislation to address climate change welcomed EPA's announcement and hope to gain added leverage during the debate over a pending cap-and-trade proposal. Rep. Edward Markey (D-MA), one of the principal authors of the cap-and-trade bill, called EPA's notice a "game-changer."

Markey and other Democrats are betting that industry lobbyists and some Republicans will throw their support behind the cap-and-trade bill, viewing it as less onerous than EPA regulations.

The National Association of Manufacturers (NAM), an industry trade group, urged the Obama administration to "defer to Congress," signaling that the Democratic strategy may have some merit.

House Minority Leader John Boehner (R-OH), calling EPA's decision an "energy tax," said, "The Administration is abusing the regulatory process to establish this tax because it knows there are not enough votes in Congress to force Americans to pay it."

The cap-and-trade bill, sponsored by Markey and Rep. Henry Waxman (D-CA), attempts to prevent duplication or contradiction between EPA regulations and the proposed legislative solution by forbidding the agency from moving forward with any efforts to regulate greenhouse gas emissions under the Clean Air Act.

Instead, an economy-wide cap-and-trade program in which polluters haggle for emissions allowances would prevail. The program would set maximum emission levels for the entire U.S. and ratchet the cap down over time. By 2050, the program would reduce emissions 83 percent below 2005 levels, according to the bill.

However, until and unless the bill becomes law, EPA must continue plodding down a regulatory path. The U.S. Supreme Court ruled in April 2007 that EPA must determine whether greenhouse gases warrant regulation, though it did not set a deadline for the agency.

The Bush administration began that process shortly after the Court's ruling but later backed away from any aggressive action. In July 2008, EPA issued an advanced notice of proposed rulemaking, which only solicited comments on the issue of climate change and greenhouse gas regulation. The notice was criticized as a masquerade for real action.

Before publishing the advanced notice, Bush's EPA had prepared an endangerment finding, but White House officials blocked the agency from moving forward. Officials at the Office of Management and Budget (OMB) refused to open an e-mail sent by EPA with the finding attached, leaving the notice in bureaucratic limbo.

The finding prepared under Bush's EPA likely served as the basis for Jackson's finding, allowing the Obama administration to move quickly on the issue.

EPA backed up its finding by saying that the higher temperatures that greenhouse gases cause lead to a higher risk of heat-related deaths and increase the spread of food and water-borne illnesses. EPA says that the U.S. is already experiencing climate change's effects and that those effects "are expected to mount over time."

EPA also noted the negative effects on public welfare, including increases in wildfires, heavy rain, and flooding, as well as risks to crops and wildlife.

Jackson made the endangerment finding under a section of the Clean Air Act that deals expressly with vehicle emissions; the notice does not address stationary sources. However, the Clean Air Act requires EPA to regulate pollutants from stationary sources if the emissions endanger public health and welfare.

"EPA also will soon have to address whether power plants' CO2 emissions 'contribute' in the same way to dangerous global warming pollution," according to David Doniger, a climate change policy expert at the Natural Resources Defense Council.

Limits on stationary sources could have a major impact on the electricity industry. Electricity generation is responsible for 34 percent of U.S. greenhouse gas emissions, according to EPA. Transportation-related emissions account for 28 percent. The remainder is produced mostly by industrial sources, commercial sources, and residential sources, all of which could also be encompassed by stationary source regulations.

The endangerment finding is currently available on EPA's website. Once published in the Federal Register, EPA will accept public comment for 60 days. Jackson will likely formally announce her determination shortly thereafter.