TORONTO - Deflecting mounting criticism over a Liberal proposal that would tax carbon emissions, party leader Stephane Dion said Thursday the country needs bold changes so it can adapt to climate change and the rising cost of fossil fuels.

While he stopped short of staking his party's next election platform on the tax, Dion told a Toronto business audience that the Conservative government has so far avoided a frank debate on the issue and is deliberately trying to confuse the public.

"I'm prepared to fight an election on a richer, greener, fairer, Canada, and I've said that for the last two years,'' Dion said.

Critics of the plan, including those in his own party, say the proposed tax, to be officially unveiled next month, is confusing, expensive and politically risky because many voters will see it as a money grab.

Finance Minister Jim Flaherty and NDP Leader Jack Layton both panned Dion's plan during question period in the Commons on Thursday.

Dion will bring in "a massive punitive increase in gasoline taxes in Canada,'' Flaherty said. "That's the last thing Canadians need.''

Layton said it would be better to properly finance public transit and to ensure that energy efficiency programs are working properly.

"Putting a tax on top of what people pay to heat their homes doesn't seem very fair,'' Layton said.

But Dion said the political establishment underestimates the Canadian public, which would support a plan to reform the country's tax system to discourage pollution.

"What can be clearer? We need to make polluters pay and put every single penny back into the hands of Canadians through the right tax cuts,'' Dion said.

"We must shift those taxes towards the things we want less of: pollution, greenhouse gas emissions, smog and waste.''

Dion said jurisdictions like British Columbia, which will bring in a carbon tax this summer, have taken the lead on a movement he hopes will "sweep the nation.''

The Liberal leader also gave accolades to Quebec, which imposed a carbon-based tax last fall that pumps revenues back into programs supporting green technology.

While Dion said shifting the burden from income and personal taxes towards pollution is something Canadians would support, he said later that convincing voters of his plan could take time.

"It's a complex issue, it's not simple, but people are not simplistic,'' he said. "They know they are in a world that needs to change.''

Dion will likely reveal the full proposal next month and spend the summer explaining it.