Andrew Weaver is a globally recognised climate modeller at the University of Victoria (British Columbia). Weaver has worked for the UN among others. Weaver calculates that emissions from burning oil from the Alberta oil sands would not make all that much difference to global warming.
What would make a considerable difference to global warming is if global coal resources are used to produce energy. As far as I am aware from talking to some economists that burning coal is much worse than oil as far as global warming is concerned was already well-known. However, this should hardly be used as an excuse to downplay the significance of dirty oil production.
The study does not really address the greater emissions generated in the production process in the oil sands nor does it even take into account the effects of that production on local water resources and its impact on aboriginal communities that depend on that water.
The Weaver study found that if all the oil sands were mined and burned the total carbon dioxide released would raise global temperatures about .36 degrees C but if only the commercially exploitable oil was burned the rise is just .03 of a degree.
In contrast burning all the globes coal deposits would raise the global temperature by a whopping 15 degrees. Even using all natural gas resources would raise the global temperature three degrees. However natural gas is much less polluting than burning heavy oil. It is just that there is a lot more natural gas to burn. The whole study really tells one very little especially over the shorter term.
What the study will do is provide supposedly scientific support for rapid expansion of production in the oil sands. Weaver actually sees his study as making evident the need to move away from use of fossil fuels as quickly as possible. However politicians will spin the results to serve their own purposes. For more see the full article.