This afternoon, EPA is holding a press conference "to discuss the release of" its long-awaited Advanced Notice of Proposed Rulemaking (ANPR) on regulations to control greenhouse gas (GHG) emissions in the United States. Rather than proposing a specific set of regulations, the ANPR is intended to frame public comment and EPA deliberations about an appropriate way to regulate GHG emissions under the Clean Air Act.

The genesis of this regulatory process began in April 2007, when the United States Supreme Court in Massachusetts v. EPA held for the first time that EPA had the authority under the Act to regulate GHGs emitted by motor vehicles as "air pollutants." The Court further held that the agency is required to regulate such emissions if the EPA Administrator finds that they are "reasonably be anticipated to endanger public health or welfare."

Although EPA has not yet issued such an "endangerment finding”—and, indeed, has been sued (unsuccessfully) for failing to do so in a timely manner—it is expected that EPA will address this question in the ANPR at the same time it proposes GHG regulations. EPA officials have indicated that the proposed rules will go well beyond motor vehicle emissions, and will encompass mobile and stationary sources of GHG in multiple sectors of the economy.

In May 2008, EPA issued a draft ANPR for review by the White House and Agency political leaders. It is unclear whether EPA actually plans to release the final ANPR at this time, or whether it will simply announce that the release will be delayed. (It is clear that the ANPR will not be released today, as it does not appear in today's edition of the Federal Register.)