The Sierra Club of Canada gave top marks to the Green party and a failing grade to the Conservatives in its ranking of parties' climate change platforms on Friday, just days before an expected election call.

The Green party's A- mark reflects a plan that "is very ambitious," national campaigns director Jean Langlois said at an Ottawa news conference.

"It's more ambitious than the minimum as defined by the science."

The Liberals, who have made their environmental plan, dubbed the Green Shift, the centrepiece of their platform, received a B+. Their aim is to balance a carbon tax with income-tax cuts.

While Langlois congratulated the Liberals for putting together a credible plan, he said the party lost marks for an "ambiguous" target for reducing greenhouse gases.

The party plan calls for reductions of 20 per cent below 1990 levels by 2020, and that could rise to 25 per cent if other countries take on comparable targets.

Both the Bloc Québécois and the New Democratic Party received Bs.

"The Bloc have a target that reflects what needs to be done based on science. However, their plan is not very detailed," said Langlois. For instance, the party doesn't specify a price for carbon emissions.

Canada 'so far behind'

The NDP also has science-based reduction targets, said Langlois, but it lost marks for relying only on cap and trade for reducing emissions and forgoing a carbon tax.

Under cap and trade, government limits how much greenhouse gas polluters are allowed to emit. Those who reduce their emissions below the cap receive pollution permits they can sell to companies that go over their cap.

A carbon tax involves government charging polluters for each tonne of greenhouse gas they produce.

"Canada is so far behind, we need both," said Langlois.

The Conservative party received an F+ because the Sierra Club said it has chosen a "completely inadequate" target for reducing greenhouse gases and because it is relying on intensity targets to meet its goals.

Emissions can be limited by an absolute cap or by a maximum allowable intensity measured relative to economic output. An intensity target allows overall emissions to grow as long as the greenhouse gas producer is using energy more efficiently.

The Sierra Club's report card rates parties based on information published as of August.

Executive director Stephen Hazell said the group would be publishing another report card closer to election day to reflect potential changes during the campaign.

On Friday afternoon, Prime Minister Stephen Harper confirmed he will meet with Gov. Gen. Michaëlle Jean on Sunday morning and ask her to dissolve the government, triggering an election campaign.

Canadians would go to the polls Oct. 14.