Today in Copenhagen, the Harper government will walk into the UN climate summit not with the intention of transitioning Canada into a clean energy economy, but instead with the agenda of prolonging the oil industry frenzy in the tar sands in northern Alberta.

It is crunch time to stabilize the climate so that our children inherit a safe world. Scientists tell us there is no more room in the atmosphere for the heat-trapping gasses that result from our burning of fossil fuels, and that we must in fact reduce the concentrations of those gasses if we want some measure of security.

Into this historic moment steps the tar-sands industry, on the one hand breathless when describing the hundreds of billions of barrels of oil it could potentially get out of the ground, while on the other pleading to be seen as a minor global warming villain. But you cannot have it both ways.

The current estimate of recoverable oil from the tar sands is 175 billion barrels, which if processed and burned amounts to over 110 billion tonnes of carbon dioxide in the atmosphere. This alone, if it happened quickly, is enough to increase global concentrations of heat-trapping gasses to levels that scientists consider more than dangerous.

Even the growing emissions from just producing rather than burning tar-sands oil will compromise Canada's climate efforts and stress our federation. Currently, the tar-sands industry produces 40 million tonnes of emissions, about the same as the entire country of Norway. But, according to Canadian government figures, expansion plans could increase these emissions to almost 110 million tonnes by 2020 – about the same as adding in New Zealand and Switzerland too.

If Canada is serious about reducing national emissions at the same time the tar sands expand, then the proportion of Canada's emissions from the tar sands could quickly rise from 5 per cent to more than a quarter. Moreover, under a national cap-and-trade system, this growth in tar-sands emissions could squeeze out other industries that compete with the tar sands for finite pollution permits, which is why Ontario Premier McGuinty is calling on Ottawa to design a fair system that does not let this happen.

But won't carbon capture and storage (CCS) let us have our tarry cake and eat it too? A recent WWF/Co-operative Bank report on CCS in the tar sands showed that even the most optimistic projections for implementation of CCS would still result in the tar sands taking up all of Canada's allowed emissions by 2050 if the country as a whole makes science-based emission reductions. CCS won't even bring tar-sands oil down to the "life-cycle" emissions profile of regular oil – accounting for emissions created both producing and consuming the oil.

Given the sobering context of climate science, the debate about life-cycle emissions of tar-sands oil is bizarre. Industry likes to cite one study that says tar-sands oil is just a bit worse than the worst oil on the market, like crude from Nigeria where flaring is rampant. But at this point in history we have no choice but to rapidly switch to the best of the best of transportation fuels, like powering our cars and buses with electricity from renewable energy.

The production phase of tar-sands oil produces on average three times the emissions as producing regular oil, but this average threatens to get worse as the vast majority of the deposit is too deep to strip mine, and requires more energy to access. None of the experimental methods of extraction that could reduce emissions is required by law, and in the meantime the Alberta government has issued draft guidelines to let the industry burn the tar itself for energy, which is dirtier still.

Nor should Canadians be taken in by one-sided industry arguments about the economic benefits of the tar sands. Consider this: tar-sands growth means we now have a "petro-loonie" that rises when the price of oil rises, as it will inevitably do again, causing trouble for our manufacturers as their products get priced out of international markets. The Ontario government estimates that a 5-cent change in our dollar impacts $6 billion of Ontario's GDP.

The Harper government has refused to table a climate plan in advance of Copenhagen because it knows that Canadians will see that a growing tar-sands industry is incompatible with doing our part to stabilize the atmosphere for our children. So, it will walk into international climate negotiations today playing for time, seeking loopholes for tar-sands polluters, and generally trying to get away with doing as little as possible.