The Diet passed a bill Friday to revise the current antiglobal-warming promotion law so that about 8,000 firms will have to report emissions of six greenhouse gases.
As of next April 1, companies will be legally required to report their emissions of carbon dioxide, methane, nitrous oxide and three alternatives to chlorofluorocarbon, which will be made public.
More than 10,000 offices and facilities, whose emissions account for about half of Japan's total, will be affected by the revisions, according to government officials.
The government hopes making the information public will force firms to take stronger measures to slash emissions.
But the revised law exempts the release of data that would reveal business secrets.