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Regulating carbon dioxide has been a hard slog for environmentalists, and some energy analysts say that the Waxman-Markey bill and parallel efforts by the Obama administration constitute a multifaceted attempt to achieve the goal by regulation if legislative attempts fail.

The “citizen suit” would allow people to force government action on climate change, seemingly a redundancy in a bill that would achieve that goal if passed. But environmentalists have been cautious in their tack, arguing that many environmental protections on the books were not vigorously enforced under the Bush administration.

Environmental lawyers played down the significance of the provision.

The measure would not guarantee payouts from the government or successful lawsuits, Mr. Doniger said, but would set the bar for people seeking to force the government to act on climate change.

He likened the measure to tort laws regarding cigarette smoke or cancer-causing chemicals, in which the harmful effects are not seen for decades.

“If this pollution isn't curbed, it isn't just today or tomorrow you have problems, it's also 20 to 30 years from now,” Mr. Doniger said.

Expansion of the Clean Air Act to allow “citizen suits” on climate change has been a goal among environmental groups and moderate to liberal Democrats for many years - although the measure has never succeeded.

But amending the Clean Air Act is “potentially a big gamble” because it opens other sections of the act to modification during the bill-drafting process, said a Democratic energy lobbyist, who spoke on the condition of anonymity because of ties to committee members.