NDP Leader Jack Layton's opposition to a carbon tax shows he's more interested in hurting the Liberals than helping the environment, says Green Party Leader Elizabeth May.

"We need to act on the climate crisis, and a carbon tax is a litmus test of whether a party is serious about it or not," May told CTV's Question Period on Sunday.

Layton's opposition to a carbon tax "is not part of the global social democratic approach," she said, adding his political rivalry with the Liberals may be driving policy.

The Green Party also advocates a carbon tax. The Liberals will soon unveil a proposal that would shift taxes off income and onto carbon, with the overall tax burden remaining unchanged. By putting a price on carbon, people will theoretically use less, thus helping reduce the greenhouse gas emissions that are driving climate change.

Layton has taken some blows from environmentalists for his party's stance, including David Suzuki, perhaps the most prominent environmentalist in Canada.

"I'm really shocked with the NDP with this. I thought that they had a very progressive environmental outlook," Suzuki told Question Period on May 18.

Layton told Question Period that his party supports the pricing of carbon and that his party's policies are in line with many of those promoted by the David Suzuki Foundation.

The solution promoted by Layton involves "cap and trade" -- putting a strict limit on greenhouse gas emissions by what he called the "big polluters." Those polluters would pay if they exceed, and the revenues would be directed by the government to climate-friendly initiatives, he said.

"Things like helping weatherize homes right across the country, creating thousands and thousands of jobs for Canadians and reducing their bills and greenhouse gas emissions," he said.

The NDP would see more green cars built in Canada and invest in public transit and renewable energy, Layton said.

A cap-and-trade system would move more quickly than a carbon tax. Big oil and gas supports a carbon tax, while U.S. Democrat Barack Obama supports cap-and-trade, he said.

But environmentalist Stephen Hazell of the Sierra Club has said cap-and-trade systems take a long time to develop.

Tories oppose carbon tax

Conservative Environment Minister John Baird told Question Period on May 18 that his government will "force the big polluters, big corporate polluters" to pay for their emissions.

"(Liberal Leader Stephane) Dion wants to give some sort of unlimited licence to pollute and just simply allow big business to buy their way out of this problem," he said.

Layton said his party's policies were nothing like those of the Harper government. Prime Minister Stephen Harper "has his head stuck in the tar sands," he said.

May called cap-and-trade a "right-wing, free-market approach" -- although she conceded her party supported it on a sectoral basis.

Some have said a carbon tax could drive up home heating costs and adversely affect those least able to bear the additional cost.

Properly implemented, a carbon tax would protect the vulnerable by shifting taxes and providing income supplements to low-income households, May said.

High taxes on income and payroll don't give Canadians the financial flexibility to do things like increase the energy efficiency of their homes, she said.

"It needs to be explained, but I think Canadians are smart enough to understand the idea that we need to ensure that we reduce our use of fossil fuels, that the climate crisis is upon us, and this is not the only thing we need to do, but it is the foundation for a successful climate policy," May said.

Oil prices are high and likely to stay there in the near term. Some analysts think introducing a carbon tax now would be a politically risky move.

"Canadians are sick of politicians who don't tell them the truth," May said.

Some politicians "want to pander to prices at the pump while ignoring disappearing glaciers, persistent droughts and increased storm events," she said.

"We need to act on the climate crisis, and I'm disappointed that Mr. Layton is on the wrong side of this one."