On September 22, 2009, EPA issued final greenhouse gas reporting regulations. The text of the regulations, and some explanatory materials are available here.
In general, the regulations apply to certain industry categories and to generators of more than 25,000 metric tons of CO2 equivalent GHGs. Reporting is, for the most part, based on emissions from a specific facility (not an entire company) but there are exceptions, for example for automobile manufacturers. Certain industry categories (petroleum refineries, cement manufacturing) are required to report regardless of the threshold; other industries that were proposed for inclusion in draft regulations have been exempted (e.g., electronics manufacturing), and agricultural emissions are mostly exempt. Most building owners will not be required to report emissions from boilers and facility equipment because those sources, even for a large building, are unlikely to meet the 25,000 metric ton threshhold. Similarly, virtually all state and local government facilities are likely to fall below the reporting threshhold. EPA estimates that the reporting regulations will cover 85 percent of greenhouse gas emissions from the United States.
Reporting will be required starting January 1, 2010, with the first report due March 31, 2011.
EPA's website has a list of frequently asked questions that help to answer some of the questions about applicability of the regulations, but this rule is just the beginning in what will likely be a more comprehensive set of reporting regulations.