The Environmental Protection Agency has set a timetable for regulating greenhouse gases from powerplants and oil refineries that some critics say is unrealistic. But environmental advocates say the development of the New Source Performance Standards for greenhouse gases under the Clean Air Act is long overdue and will supplement some 75 other New Source Performance Standards already in existence for the power sector and other industries.

The timetable is part of a settlement reached among EPA and several states—including California, Rhode Island and Massachusetts—and environmental groups, who had sued the agency during the Bush Administration to develop NSPS for greenhouse gases for the powerplants and oil refineries. According to EPA, powerplants and oil refineries contribute about 40% of the total greenhouse-gas emissions in the U.S.