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

Emissions from tar sands mining, such as this pit in Alberta, were left out of Canada's carbon emissions reporting. (Photograph: Jiri Rezac/eyevine) 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.

It's not entirely clear what motivated the decision to obscure the data. The government reported GHG from the tar sands last year. But here are some possibilities:

International image. The tar sands are becoming increasingly high profile and are a growing source of embarrassment to Canada in the international arena. No matter how popular the industry in Harper's native Alberta, it is probably not pleasant being called a climate villain or a carbon bully several times a year at Bonn and the other fixtures of the UN climate change negotiations.

Timing. The government may have been concerned about jeopardising an important pipeline deal. Canadian firms are awaiting final approval from the State Department for a pipeline that would carry up to barrels of a oil a day from Alberta to the refineries of Texas. Opposition from landowners along the 1,700-mile route has already delayed the project til later this year. Last week, a group of legislators from Nebraska asked Hillary Clinton, who has final say, to delay a decision until 2012 to give them time to put environmental safeguards in place. Members of Congress are said to be preparing a similar protest letter.

The PR consultant told them to. Mike De Souza, the same reporter who broke the story on the GHG reporting, has written another story suggesting that the Canadian government last year considered hiring a PR firm to help promote the tar sands. It also weighed the benefits of tar sands tourism: paid-for trips for European journalists and elected officials.

"Consideration should be given to hiring a professional PR firm to help the Pan European Oil Sands Team further develop and implement a serious public advocacy strategy," the report was quoted as saying.

That's my current favourite theory. The provincial and federal governments have made an enormous effort to lobby US officials on the tar sands. So what's the big deal then in burying a little factoid or two even deeper in a 567-page technical report to a bunch of UN bureaucrats?

Except of course that those kind of dodges reek strongly of the faith-based/anti-reality views of the George Bush presidency, when political considerations repeatedly took precedence over evidence-based standards.

As environmental groups and others have regularly noted, Harper has been too focused on the tar sands as an image problem, rather than an environmental one. Now it seems as if that approach has infected government institutions, with Environment Canada aiding the effort to obscure irksome figures and facts

"It's a consistent pattern that we have seen on the part of the Harper government to really attempt to spin the tar sands," said Andrea Harden-Donahue, energy campaigner at the Council of Canadians, the country's biggest citizens' group.