One of the most common questions about the American Clean Energy and Security Act is, "Who will it cover?" The bill will apply to firms that emit more than 25,000 metric tons per year of carbon dioxide or its equivalent in other greenhouse gases.

Supporters have always said that meant the bill would only regulate big polluters. Opponents claimed that small businesses, schools, churches – even individuals – could be subject to new government rules.

Now, a new study from Duke University gives us the answer.

Turns out that the 25,000-ton threshhold includes only 1.3 percent of all U.S. manufacturing facilities – a fraction of America's more than 350,000 sites. However, those few companies are responsible for 82.5 percent of  the manufacturing sector's greenhouse gas emissions. According to Duke's David Cooley:

Large-scale polluters are responsible for a supermajority of U.S. greenhouse gas emissions, so we can get enormous environmental benefits while regulating a small percentage of firms.

The bill will also apply to about half of the country's electric power plants, but almost no farms or commercial buildings.

Who's not on the list? No schools. No churches. No individuals. If you don't own your own smokestack, you can pretty much count on being exempt.

EDF is proud to have provided funding for the study, which you can download from the Duke site [PDF].