More than 100 leading US and Canadian scientists called for a halt on future mining of the tar sands, saying extraction of the carbon-heavy fuel was incompatible with fighting climate change.



In a letter published on Wednesday, the researchers said tar sands crude should be relegated to a fuel of last resort, because it causes so much more carbon pollution than conventional oil.

The letter, released two days after G7 countries committed to get off fossil fuels by the end of the century, added to growing international pressure on the Canadian government, which has championed the tar sands and is failing to meet its earlier climate goals.

“If Canada wants to participate constructively in the global effort to stop climate change, we should first stop expanding the oil sands. More growth simply shows Canada has gone rogue,” Thomas Homer-Dixon, professor of governance innovation at the University of Waterloo, said in a statement.

The researchers included a Nobel prize winner, five holders of Canada’s highest national honour, and 34 researchers honoured by Canadian and US scientific societies.

The researchers said it was the first time that scientists had come out as professionals in opposition to the tar sands. The letter offered 10 reasons for the moratorium call, ranging from extraction’s impact on local First Nations communities to destruction of boreal forests and climate change, and argued that foregoing tar sands production would not hurt the economy.

They said they hoped to present those findings to Canada’s prime minister, Stephen Harper, who has lobbied hard in Washington and European capitals for the tar sands.

“We offer a unified voice calling for a moratorium on new oil sands projects,” the scientists said in the letter.

“No new oil sands or related infrastructure projects should proceed unless consistent with an implemented plan to rapidly reduce carbon pollution, safeguard biodiversity, protect human health, and respect treaty rights.”

They said the decisions made by Canada and the US would set an important example for the international community, when it comes to fighting climate change. “The choices we make about the oil sands will reverberate globally, as other countries decide whether or how to develop their own large unconventional oil deposits,” the scientists said.

Since 2000, Canada has doubled tar sands production, and Harper has lobbied Barack Obama to approve the controversial Keystone XL pipeline, which would open up new routes to market for Alberta oil.

The crash of oil prices will likely put some future projects on hold, but are unlikely to affect current production, analysts said.

The organisers of the letter said all future projects should be shelved unless Canada put in place safeguards to protect local people and environment and prevent climate change.

“The oil sands should be one of the first fuels we decide not to develop because of its carbon intensity,” said Thomas Sisk, professor of environmental science at Northern Arizona University, and one of the organisers of the letter.

“It is among the highest emitting fuels in terms of greenhouse gas emissions … If we are trying to address the climate crisis this high carbon intensive fuel should be among the first we forego as we move to an economy based around cleaner fuels.”

Researchers including Sisk first outlined reasons for opposition to the tar sands in Nature last year.

Wednesday’s intervention deepens an emerging political and economic distinction around coal and tar sands among climate campaigners.

As a fossil fuel divestment movement moves from college campuses to financial institutions, a number of prominent supporters, such as Rockefeller Brothers Fund, moved swiftly to ditch coal and tar sands holdings, but plan more gradual moves away from oil and gas.

Scientists agree that two-thirds of known fossil fuel reserves will need to stay in the ground to avoid warming above 2C, the internationally agreed threshold on catastrophic climate change.

The Guardian supports the fossil fuel divestment campaign, and has called on two of the world’s largest health charities, The Bill and Melinda Gates Foundation and the Wellcome Trust, to rid its holdings of coal, oil, and gas.