Barely a day goes by it seems when someone from Stephen Harper's government is not touting the benefits of the Alberta tar sands.

But when it came to counting up the carbon emissions produced by the tar sands - big and growing bigger - a strange amnesia seems to have taken hold.

The Canadian government admitted this week that it deliberately left out data indicating a 20% rise in emissions from the Alberta tar sands when it submitted its annual inventory to the United Nations.

The deliberate exclusion does not amount to an attempt to deceive the UN about Canada's total emissions. Emissions from the tar sands were incorporated in the overall tally in the report. But it does suggest that the government is anxious to obscure the source of its fastest-growing source of climate pollution: the Alberta tar sands.

Greenhouse gases from the tar sands grew by 21% in the last year reported, despite the economic receission. Even more troubling, the tar sands is becoming even more carbon intensive, with emissions per barrel of oil rising 14.5% in 2009. And overall production is set to triple by 2020, according to some projections.

So that's an increasingly significant share of Canada's greenhouse gas emissions - 6.5% now and rising.

"It is not as if they were left out of the total, but no matter where you looked in the report you couldn't find out what sector the emissions were from," said Clare Demerse, director of climate change at the Pembina Institute, an environmental think tank.

Environment Canada told reporters it was just fulfilling UNFCC reporting requirements.