OTTAWA — NDP Leader Jack Layton is hoping to reclaim his party's title as Canada's environmental champion with a carbon pricing plan aimed at punishing big polluters rather than consumers.

Layton unveiled his plan Wednesday in the wake of some scathing -- and, for the NDP, rare -- criticism from environmentalists over his refusal to consider endorsing a carbon tax.

New Democrats have traditionally won high praise from environmentalists for their eco-friendly policies. But last week, Layton was slammed for his denunciation of Liberal Leader Stephane Dion's emerging plan to impose a carbon tax.

Layton had said a carbon tax would punish consumers, particularly seniors and the poor, for buying essentials such as gas, home heating fuel and electricity.

Famed environmentalist David Suzuki said he was "shocked'' by Layton's criticism and called the NDP's opposition to a carbon tax "nonsense.''

Layton's alternative "cap and trade'' plan would force big polluters -- which account for half of Canada's greenhouse gas emissions -- to pay $35 per ton of carbon emitted.

Layton said his plan would generate about $2.5 billion a year that would be invested in developing green technologies and helping make them affordable for average Canadians.

"It will ensure that the big polluters begin to pay their share. It's about time,'' Layton told a partisan crowd.

Flanked by NDP candidates with impressive environmental credentials, Layton emphasized his party's long history of championing green causes.

"The struggle for a sustainable future has helped to define the New Democratic Party of Canada. It's the cornerstone of why I sought to serve in the House of Commons.''

Layton's announcement seemed to go some way toward soothing environmentalists.

Clare Demerse of the Pembina Institute said Layton's initial criticism of Dion's carbon tax left the impression that the NDP is opposed to putting a price on carbon. She was pleased to learn that Layton is simply choosing a different mechanism.

Demerse said there's not enough detail available yet on either Layton's or Dion's proposals to judge which might be most effective. But in principle she said, either cap and trade or a carbon tax, or some combination of the two, are equally feasible methods for pricing carbon.

"It's really not an either-or situation.''

Demerse said it's "an artificial distinction'' to suggest, as Layton has done, that the NDP route would punish polluters while the Liberals' would punish consumers. She noted that a carbon price charged to big emitters will eventually end up being passed on to consumers.

For his part, Dion said cap and trade "makes a lot of sense.'' He said the Liberal plan will include both a carbon charge for big emitters and a carbon tax.

Still, Dion said it will take years to develop a cap-and-trade system. In the meantime, he said, a carbon tax could be imposed relatively quickly and the revenue could be immediately shifted into income tax cuts or other measures aimed at helping the most vulnerable cope with skyrocketing fuel costs.