China has gained access to Canada's giant tar sands reserves this week, some of the most carbon-intensive fuels on the planet.

 

US regulators approved the US$15 billion takeover of Canadian oil and gas company Nexen Inc by China's state-owned CNOOC – China's largest-ever foreign takeover. It needed US approval because of Nexen's holdings in the US.

 

The state-owned energy giant now has access to offshore production in the North Sea, the Gulf of Mexico and western Africa, as well as the Middle East and now Canada.

 

But it's Canadian tar sands that have been causing most concern to environmental activists.

 

Tar sands are deposits of oil mixed with clay and sand and embedded in rocks, often beneath the surface. 

 

Extracting the oil has been estimated to be three times more carbon-intensive than conventional oil sources, according to Global Forest Watch Canada.

 

It also requires vast open mines and has been linked to the pollution of local waterways with toxic chemicals.

 

A two-year study of the Athabasca River by ecologists at the University of Alberta found levels of arsenic, copper, cadmium, lead, mercury, nickel, silver and zinc far in excess of national guidelines downstream from industrial oil sands sites in the Canadian province.
 

Some scientists say exploiting tar sands would produce enough carbon emissions to push the world towards dangerous levels of climate change.