http://thinkprogress.org/romm/2011/0...sands-climate/
The Canadian tar sands are substantially dirtier than conventional oil as the chart above shows (longer analysis here).
They may contain enough carbon-intensive fuel to make stabilizing atmospheric concentrations of carbon dioxide at non-catastrophic levels
all but impossible.
The environmental impacts of tar sands development include:
irreversible effects on biodiversity and the natural environment
reduced water quality
destruction of fragile pristine Boreal Forest
destruction of associated wetlands, aquatic and watershed mismanagement
habitat fragmentation
habitat loss
disruption to life cycles of endemic wildlife particularly bird and Caribou migration
fish deformities
negative impacts on the human health in downstream communities
An overwhelming objection is that exploitation of tar sands would make it
implausible to stabilize climate and avoid disastrous global climate impacts.
The tar sands are estimated (e.g., see IPCC Fourth Assessment Report) to contain at least 400 GtC (equivalent to about 200 ppm CO2). Easily available reserves of conventional oil and gas are enough to take atmospheric CO2 well above 400 ppm, which is unsafe for life on earth.
However, if emissions from coal are phased out over the next few decades and if unconventional fossil fuels including tar sands are left in the ground, it is conceivable to stabilize earth’s climate.
Phase out of emissions from coal is itself an enormous challenge.
However, if the tar sands are thrown into the mix, it is essentially game over.
There is no practical way to capture the CO2 emitted while burning oil, which is used principally in vehicles.
Governments are acting as if they are oblivious to the fact that there is a limit on how much fossil fuel carbon we can put into the air. Fossil fuel carbon injected into the atmosphere will stay in surface reservoirs for millennia. We can extract a fraction of the excess CO2 via improved agricultural and forestry practices, but we cannot get back to a safe CO2 level if all coal is used without carbon capture or if unconventional fossil fuels, like tar sands are exploited.