Liberal Leader Stephane Dion says his controversial carbon tax proposal isn't about his personal political future, but about Canada's ecological future.

"What do we want to be, facing the worst ecological threat we can imagine?" he told CTV's Question Period on Sunday about the risk posed by dangerous climate change.

"If a country like Canada ... (doesn't) do our share, we'll fail the world. And we shouldn't do that."

On Thursday, Dion unveiled his "green shift" plan. It would involve place a carbon tax on fossil fuels (with the exception of gasoline, which is already covered by special taxes), but cut income and some other taxes.

When fully phased in after four years, the carbon tax would generate $15.5 billion per year in revenue. Dion has insisted the plan will be revenue-neutral.

This carbon tax would be the centrepiece of a Liberal effort to fight climate change.

The scientific consensus is that greenhouse gas emissions, caused by the burning of fossil fuels, must come down dramatically by mid-century to stave off dangerous climate change. Canada isn't a large total emitter, but is one of the world's highest per-capita emitters of GHGs, along with the U.S. and Australia.

Before the Liberals even announced the details of the plan, the Conservatives launched attack ads trying to label the scheme as a massive tax grab.

In recent days, Prime Minister Stephen Harper has labelled the plan as "crazy" and said Friday it would "screw everybody across the country." But he also criticized the proposal for not setting out any hard targets for emissions reductions and has likened it to the National Energy Program of the 1980s that stoked Western alienation.

Dion scolded Harper for stooping to vulgarity and repeated his challenge to debate the prime minister on this policy.

Dion said the plan would shift taxes from desirable things like income onto something undesirable, namely carbon pollution. He denied it is overly complex.

"People understand it, and I think Mr. Harper is underestimating the intelligence of Canadians, the big hearts of Canadians," he said.

Even British Conservative Leader David Cameron has spoken in favour of green taxes, he said.

"Sound familiar to you?" Dion said. "Around the world there are leaders who are not blind. They don't have their heads in the sand like Mr. Harper."

Politically risky

Many pundits have suggested if Dion fights and loses an election on this issue, he's finished as Liberal leader.

Former Liberal cabinet minister John Manley told Question Period that he thinks Dion is "perfectly aware he's taking a significant political risk."

"But I think in his judgment, when there's an election, if he loses on this, he'll have lost on something he thought was worthwhile. And if he wins on it, it will give him the opportunity to do what he believes in," he said, adding, "I don't think Canada is badly served by having politicians with convictions that they're willing to stake their careers on."

Manley described climate change as one of the great challenges facing the world.

The Liberal leader will be taking his plan on the road this summer to sell it to Canadians.

However, Dion is proposing the tax at a time when oil prices are at record-high levels and the Bank of Canada is warning about inflationary pressures in the economy.

Dion said the tax shift topic needs an extensive debate.

Energy prices are going up, he admitted, "but for that very reason, we need to learn to be less dependent on these types of fuels."

By changing the tax regime, people will be encouraged to shift away from using carbon energy, he said.

The plan will protect seniors and low-income Canadians who don't have the financial resources to adapt, he claimed.

Dion admitted that he hopes the plan will encourage green-minded voters on the Canadian left to coalesce around the Liberal party -- but also those on the right who agree with the tax shift approach.

The Green party favours a carbon tax and has proposed one of $50 per tonne. The Liberal proposal is for a tax that would rise to $40 per tonne after four years.

NDP Leader Jack Layton opposes a carbon tax and favours a "cap-and-trade" system that would make industrial polluters pay.

The Conservative government's plan requires industry to boost "energy intensity" -- meaning using progressively less energy per unit of output.

However, the government doesn't put a "hard cap" on emissions, saying one could harm industry.

Critics have argued the Tories' plan could see total emissions rise if output sufficiently increased.

However, climate activists have also said the Liberal plan, while a step in the right direction, isn't enough to reduce Canada's GHG emissions.