Right now, the US EPA is involved in a huge effort to get more accurate information about quantities of greenhouse gases emitted by US industries. Congress and EPA have both declared that companies can't claim that their greenhouse gas emissions are trade secrets — but EPA's upcoming rulings on confidentiality for data going into the companies' GHG calculations will be important. Those determinations may impact whether companies' reporting is accurate — and whether they can ever be held accountable for their emissions.
EPA's collection of emissions data is a key precursor to actual regulation of greenhouse emissions — something many industries have fought tooth and nail for years. The Supreme Court has ruled that EPA has the authority, or even the obligation, to regulate GHG emissions under the Clean Air Act.
The EPA had compiled a Greenhouse Gas Inventory  since 1990, but it was based only on sector-by-sector estimates, rather than reporting by individual facilities and companies. In October 2009, the Obama administration's EPA launched a regulatory proposal for mandatory reporting of GHG emissions from large sources in the US. The threshold above which facilities would have to report is 25,000 metric tons of carbon dioxide equivalent per year. An estimated 85 percent of total US emissions from some 13,000 facilities are covered by the proposed reporting rule.
Many companies have been loath to share such emissions information, even before the GHG reporting rule proposal. They say it can reveal information about their production rates or production efficiency which competitors can use against them. But the Clean Air Act and other environmental laws have established for decades the legal principle that the public have a right to know about pollution that may harm their health and property as well as the environment.
EPA has already done some major rulemaking about what information is and is not required to be reported and made public. That began with a major rulemaking proposal for the GHG reporting program issued on October 30, 2009, and another issued July 7, 2010, setting the broad outlines of what would and wouldn't be allowable as confidential business information (CBI) under it. In subsequent rulemakings, EPA revised and refined what could be CBI, and the process is not finished yet. EPA's web site has a detailed timeline of this process. 
EPA has already ruled that companies' annual emissions of carbon dioxide and other GHGs should be public. But after that, it gets complex and technical fast. The latest and current phase involves which data elements going into companies' emission calculations could be claimed as CBI.
The period for public comment on EPA's CBI determination has been extended. It now closes April 9, 2012.
This rulemaking matters a lot because it affects whether local reporters can do good stories about GHG emissions from local facilities.