"The devil's really in the details," said Dave Martin, Greenpeace climate and energy co-ordinator. "In our view, the Dion plan really doesn't go far enough."

The Liberal plan proposes a $15.4-billion-a-year tax shift that would punish polluters and reward businesses and consumers who go green. The tax hike would be offset by such measures as income-tax cuts to lower-income Canadians.

"If it's implemented, I can see this plan making a tangible difference because it puts the machinery in place to reduce greenhouse gases," said Aaron Freeman, the policy director for Environmental Defence.

"If they combine these measures with a whole suite of other measures ... by 2020 we may have achieved the levels that we need to stem the worst effects of climate change."

Many of the environmental groups were offering such qualified support Thursday, saying a tax on carbon is a good first step but that it's only part of a complete green plan.

Under Dion's proposal, greenhouse gas emissions would be pegged at $10 per tonne, rising to $40 per tonne in the fourth year. But activists say that's far too low.

"Greenpeace and other environmental groups have been calling for virtually an immediate start at $30 per tonne of carbon dioxide equivalent, ramping up to $75 minimum within a decade," Martin said.

The lowballed price is just one of the problems Greenpeace has with the plan, Martin said.

A greenhouse gas reduction target of 20 per cent from 1990 levels by 2020 isn't high enough, the price is too low, and money directed toward tax cuts should instead be used to help Canadians conserve energy, he said.

But as many changes as Dion's plan would have to undergo to get an unqualified stamp of approval, the environmental groups said it is head and shoulders above what Prime Minister Stephen Harper's government is doing.

"There's no question that the Harper government is way behind the curve in terms of doing anything about climate change," Martin said.

Martin said the Conservative government's plan for a 20 per cent reduction in greenhouse gases from 2006 levels by 2020 falls far short of Dion's proposed reduction from 1990 levels. In fact, he said the Harper government's reduction would only amount to a less than three per cent reduction from 1990 levels by 2020.

But the thrust of the Liberal plan is a positive symbolic gesture, one that is a good first step on the road to combatting climate change, said Graham Saul, the executive director of Climate Action Network Canada.

"Pricing carbon is a necessary building block of any meaningful climate change strategy," he said.

"Putting a price on carbon will encourage conservation. So this is going to move us in the right direction in terms of sending the right signals."

Meanwhile, the Saskatchewan government, which has close ties to the Conservatives in Ottawa, called Dion's plan the start of another National Energy Program that will hurt the oil-rich West.

"This Liberal tax grab called 'Green Shift,' if it is fully implemented, Saskatchewan people will get the green shaft," said Saskatchewan Energy Minister Bill Boyd.

"We're going to see tremendous impact on the province of Saskatchewan and it will be a very, very negative impact."

Alberta Finance Minister Iris Evans said the Liberal plan would cripple Alberta, while being less punitive for central Canada where millions of vehicles also create emissions.

"Clearly, Alberta has some very large emitters in the oilsands," she said. "What it says to them is that they will be penalized."

Nova Scotia Premier Rodney MacDonald was reluctant to embrace Dion's proposal even though the notion of a carbon tax figures into his own government's climate change policy deliberations.

"Given the situation that we're in where there's a strong reliance on fossil fuels in Nova Scotia, a plan like that could have a significant impact on those on fixed incomes and seniors," he said as he emerged from cabinet on Thursday.

An executive with Canada's largest oil and gas producer said the best role the industry can play is to make sure the government knows the implications on any environmental legislation will have on operations and on capital investment plans.

"Good policy will come from an understanding of the full impacts of any proposed policy change," said Gerry Protti, EnCana's vice-president of corporate relations.

"The big issue right now on climate change with the federal and provincial governments is the harmonization question."

B.C. Energy Minister Richard Neufeld said he was wary of the proposal, expressing concerns any sweeping federal plan could encroach on provincial territory.

"I know with the Conservatives, they've told us that if they were to bring in a carbon tax or any kind of a tax on carbon they wouldn't double it in provinces that already have those kind of taxes in place," he said.

"I would hope to think, depending on elections, that the federal Liberals would be the same."

Andrew Leach, a professor at the University of Alberta, said a carbon tax is good from a businesses standpoint because of cost certainty.

"The downside are the businesses who, for whatever reason, would be maybe more favourably treated under a subjective system where the government is setting regulations on an industry-by-industry basis or a company-by-company basis."