Liberal leader Stephane Dion returned fire at Stephen Harper over his criticism of the Liberals' green-shift platform, challenging the prime minister to an "adult debate on the issue."

A heated Harper told a crowd in Saskatoon Friday that the Liberal carbon tax proposal would "screw everybody across the country."

On Saturday, Dion said that Harper's blunt words trivialized the climate change debate.

"I call on the prime minister to debate with me any time on TV on this issue in a respectful, meaningful and adult way,'' Dion said on Toronto's Centre Island.

CTV's chief political correspondent Craig Oliver said the prime minister's words and the Dion attack ads show that the Tories are worried about the Liberal plan.

"Dion has chosen to fight on grounds of his choosing, as all good generals do," Oliver said. "The environment is an issue that is not as comfortable or safe for the Tories."

He also said that Harper has an intense personal dislike for plans like Dion's.

"This is more than just a green plan. It's really a federal program, involving economics, income redistribution . . . the kind of thing Harper has always hated," Oliver said. "He's always warned against Trudeau-like national policies."

"This could become the centre of the next election campaign."

Dion was in Toronto for the Toronto International Dragon Boat Race, but despite the fun atmosphere, he pushed back against Harper comments.

"It was vulgar and I don't think Canadians are impressed by that,'' Dion said. "They want the prime minister to act as a prime minister.''

Dion unveiled his plan this week, which would put a $15.4 billion tax on carbon emissions. This increase in taxes would be offset by cuts in income and corporate taxes.

The Liberals say the tax will be revenue neutral and punish big polluters.

Critics have called it a tax grab and say it won't help the fight against climate change. They say also it will raise the prices of goods related to energy.

However, notable environmentalists, including David Suzuki, have spoken out in favour of the plan.

With files from The Canadian Press