Greenhouse gas signup.

Operators of oil refineries, power plants, cement kilns and other greenhouse gas generators have until Dec. 31 to sign up for the voluntary carbon emission reporting system known as the California Climate Action Registry.

Those that miss this deadline could be subject to more stringent reporting requirements under the recently signed AB 32, the landmark cap on greenhouse gas emissions.

The registry was established in 2000 as a voluntary, non-profit entity where companies can register their emissions of greenhouse gases, including carbon dioxide, methane, nitrous oxide and hydrofluorocarbons. Under AB 32, companies enrolled in the registry that have kept complete and consistent records won't have to make any major changes in the way they track carbon emissions.

Other companies, though, will face mandatory reporting requirements that have yet to be fully spelled out. It will be up to the state Air Resources Board to draft specific regulations.

To avoid what could be years of uncertainty, business groups such as the California Manufacturers and Technology Association are recommending that their members sign up with the registry before the Dec. 31 deadline. The registry's Web page is climate-registry.org.

Staff reporter Howard Fine can be reached by phone at [phone], ext. 227, or by e-mail at [e-mail].