EPA CONSIDERS EMISSIONS A HAZARD…. The announcement wasn’t unexpected, but it’s nevertheless encouraging.

Having received White House backing, the Environmental Protection Agency declared Friday that carbon dioxide and other greenhouse gases are a significant threat to human health and thus will be listed as pollutants under the Clean Air Act — a policy the Bush administration rejected.

The move could allow the EPA to regulate greenhouse gases, but it’s more likely that the Obama administration will use the action to prod Congress to pass regulations around a system to cap and then trade emissions so that they are gradually lowered. […]

The EPA concluded that six greenhouse gases should be considered pollutants under the 1970 Clean Air Act, which is already used to curb emissions that cause acid rain, smog and soot.

But its declaration, set for 11 a.m. EDT Friday, will not spell out how or what to regulate. Instead, the EPA and lawmakers are expected to begin that discussion.

Based on the EPA’s findings, that discussion should begin soon. The agency believes global warming will produce longer and more severe heat waves, increased smog, dangerous flooding, and the spread of diseases related to flooding and warmer weather.

The Obama administration’s move on this is the culmination of a lengthy process. Nearly two years ago, the Supreme Court surprised the Bush administration with a ruling that ordered the EPA to determine whether public health and welfare are being harmed by greenhouse gas pollution. In the wake of the decision, the Bush administration “walked a tortured policy path” to “defer compliance with the Supreme Court’s demand.”

In this sense, Obama is finishing what Bush didn’t want to start.

As for the regulatory discussion, it’s likely to be one of the most extensive rule-making debates in history. Kate Sheppard reports on what happens next:

There will be a 60-day public comment period on the EPA finding itself, after which it would be entered in the Federal Register—the government’s official publication for rules and regulations. The agency is legally required to start regulating CO2 emissions, though the EPA can decide the timing, sequence, and scope of any regulations.

The EPA could regulate a wide range of polluting entities, but the agency is likely to focus first on two main sources of pollution: cars and stationary pollution points like power plants and major industrial sources like chemical and cement manufacturers. “The EPA must go forth and regulate,” David Bookbinder, chief climate counsel at the Sierra Club, told Grist. “Those would come at the front of the regulatory train.”

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Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.