Calgary is rated as the cleanest city in the world. Second, the forests are reconstituted when the mines are shut. The oil sands mines are no different from the mines in Ontario, BC or anywhere else in the country.

And it is the cars built in Ontario, or government subsidized jets built in Quebec, that generate the most CO2. As for forests, hydropower dams destroy more forests than mines (because the trees are permanently cut, unlike the mines).