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It depends whom you ask, of course.
The invaluable Joe Romm, writing on the indispensible ClimateProgress.org, tells us that Confusing Climate Study Actually Makes Strong Case Against Tar Sands — If We Want To Avoid Catastrophic Global Warming | ThinkProgress

According to Time magazine, “Pipeline Politics: Are the Oil Sands ‘Game Over’ for the Climate? One Study Says No”:

The good news from the Nature Climate Change paper is that, should environmentalists lose their battle, the consequences might not be quite as bad as they’ve made it out to be.

Except that isn’t what the study finds. Indeed, the final paragraph states

If North American and international policymakers wish to limit global warming to less than 2 °C they will clearly need to put in place measures that ensure a rapid transition of global energy systems to non-greenhouse-gas-emitting sources, while avoiding commitments to new infrastructure supporting dependence on fossil fuels.

In short, if you care about the 2C (3.6F) target, building something like the tar sands pipeline is a really bad idea.

By the way, if you care about a 3C (5.4F) target, building something like the tar sands pipeline is also a really bad idea —

I offered this comment on Joe’s site:

If we posit that Time is trying to do a good job of serious journalism, what needs to happen to increase the odds of them not getting a story like this so wrong?

Oh, and then there’s this:

To have a 66% chance of limiting warming to less than the 2 °C limit put forth in the 2009 Copenhagen Accord, one carbon– climate modelling study estimated that total future global carbon emissions should be limited to less than 5.9×1017 g C (ref. 9). If this amount were to be distributed equally among the current global population, the resulting allowable per capita cumulative carbon footprint would be 85 tonnes of carbon. The eventual construction of the Keystone XL pipeline would signify a North American commitment to using the Alberta oil-sand reserve, which carries with it a corresponding carbon footprint. For comparison, by fully using only the proven reserves of the Alberta oil sands, the current populations of the United States and Canada would achieve a per capita cumulative carbon footprint of 64 tonnes of carbon.