In the far north latitudes, buried within a seemingly endless expanse of evergreen forests, the authorities in Canada are building up one of the world's best natural defences against global warming.

In a series of initiatives, Canadian provincial governments and aboriginal leaders have set aside vast tracts of coniferous woods, wetlands, and peat. The conservation drive bans logging, mining, and oil drilling on some 250m acres – an area more than twice the size of California.

The sheer scale of the forest conservation drive is somewhat of an anomaly for Canada, whose government has been accused of sabotaging the global climate change talks by its development of the Alberta tar sands and its refusal to make deep cuts in its greenhouse gas emissions.

Last week, a former adviser to Barack Obama urged Canada to do more to keep up with America's moves towards a cleaner energy economy.

In the latest addition to the carbon storehouse, the provincial premier of Manitoba, Gary Doer, this month announced a $10m (£5.6m) Canadian fund to protect a 10.8m acre expanse of boreal or evergreen forest. It was one of Doer's last acts as premier; he took over as Canada's ambassador to Washington this month.

The $10m will go towards efforts by indigenous leaders to designate boreal forest lands in eastern Manitoba as a Unesco world heritage site. The Pimachiowin Aki world heritage project, which straddles the Manitoba-Ontario border, extends efforts by Canadian provincial leaders to protect the wide swaths of pristine forests in the north. It also ensures the survival of one of the best natural defences against global warming after the world's oceans, environmentalists say.

A report by the International Boreal Conservation Campaign said the forests, with their rich mix of trees, wetlands, peat and tundra, were a far bigger carbon store than scientists had realised, soaking up 22% of the total carbon stored on the earth's land surface.

"If you look across Canada one of [the boreal forest's] great values to us globally is its carbon storage value," said Steve Kallick, director of the Pew Environment Group's International Boreal Conservation Campaign. "There is so much carbon sequestered in it already that if it escaped it would pose a whole new, very grave threat."

Canada's cold temperatures slow decomposition, allowing the build-up of organic soil and peat. The forest floors beneath its evergreens hold twice as much carbon per acre as tropical forests, such as the Amazon.

It is unclear how long Canada's forests can continue to serve as carbon vaults. "As the climate warms, the place is going to dry up. There will be a problem with insect infestation. There is going to be increased natural carbon release due to fire or wetlands drying up," said Sue Libenson, a spokeswoman for the International Boreal Conservation Campaign.

But she added: "The general premise is that there is still a hell of a lot of carbon in there." Its release would be a climate catastrophe.

Canada's 1.3bn acres of boreal forest store the equivalent of 27 years' worth of current global greenhouse gas emissions, a Greenpeace study found. The destruction of those forests, scientists warn, would be like setting off a massive "carbon bomb" because of the sudden release of emissions.

That threat appears to have concentrated the official mindset in Canada, which otherwise has a poor record on action on climate change. On a per capita basis, the country is one of the worst polluters on the planet, producing about 2% of the world's emissions even though it has just 33m people. It holds one of the worst track records among industrialised states for living up to its commitment under the Kyoto accords. By 2007, greenhouse gas emissions were 34% above the target Canada agreed at Kyoto.

Canada's prime minister, Stephen Harper, is resisting doing much more, committing to just a 6% cut over 1990 levels of greenhouse gas emissions by 2020. "I see Harper's policy as a continuation of the Bush agenda," said David Martin, climate director for Greenpeace Canada.

A key advisor to Obama made a similar point last week, comparing Canada's current climate change policy to the inaction in America under George Bush. "The Canadians would be well served by keeping up with what's going on in the United States with respect to this push towards clean technology," John Podesta, who oversaw Obama's transition team, told a conference in Ottawa.

Environmentalists also fear that Harper intends to exclude the Alberta tar sands – the heavy crude deposits that have fuelled the rise in emissions – from any future greenhouse gas emissions regime.

But the Harper government did relent on forest protection, working with the Sahtu and Deh Cho First Nations to set aside 40m acres in the Northwest Territories.

Canadian provincial leaders have moved even more aggressively in recent years, with Ontario committed to protecting 55m acres, or about half of its forest, and Quebec committed to protecting 150m acres. "Canada is torn between wanting to promote the tar sands and make money off it now, and wanting to live up to its promises under the Kyoto accord. But as far as protecting carbon rich ecosystems, particularly the boreal forest, Canada is a world leader," said Kallick.