Twenty prominent scientists have sent a letter to President Barack Obama urging him to reject an application for a 1661-mile pipeline that would transport tar-sands oil from Alberta, Canada, to the Texas Gulf Coast.

A fifth of U.S. crude oil imports come from Canada. Close to half of those are in the form of tar-sands crude. By 2030, the tar-sands figure could be as high as 36 percent. The problem: tar-sands crude is an environmental disaster from the time forests are cut down to extract the viscous bitumen right up through the burning of the product. Estimates of the extra greenhouse gas emissions from these processes compared with normal crude oil extraction, refining and burning run as high as 82 percent.

The State Department is involved in the decision about whether to allow TransCanada to build the Keystone XL pipeline because it crosses an international boundary. Two environmental impact statements have been completed and a final one will be published this month. A decision by Secretary Hillary Clinton was already expected by the end of the year, but Big Energy fans in Congress passed legislation last month demanding a quicker decision.

Pipeline advocates say it would be good to have a friendly source for more U.S. oil imports and that this would lower prices. But while the United States is already refining and burning considerable amounts of tar-sands oil, the pipeline oil would be exported to other countries from the Gulf Coast. The Department of Energy says the impact on oil prices would be minimal.

Environmental advocates oppose the pipeline because they oppose tar-sand mining in the first place. The litany of effects is vast: destruction of arboreal forests, toxic holding ponds, inordinate water consumption, pollution of watersheds and huge additions of greenhouse gases into an atmosphere already choking on them.

As for the pipeline itself, there would be inevitable spills of the stuff, which would be more hazardous than from conventional crude spills, as well as threats to aquifers, including the Ogallala Aquifer, the nation's largest, which feeds agriculture in the nation's bread basket and provides drinking water for 2 million Americans. Contaminating that with a tar-sands spill could be catastrophic. Last year alone, TransCanada had nine spills from a bitumen pipeline.

Hence, the letter. Here's the text:

The Honorable Barack Obama

President of the United States

The White House

1600 Pennsylvania Avenue, N.W.

Washington, D.C. 20050 August 3, 2011 President Obama: We are researchers at work on the science of climate change and allied fields. We are writing to add our voices to the indigenous leaders, religious leaders, and environmentalists calling on you to block the proposed Keystone XL Pipeline from Canada’s tar sands. The tar sands are a huge pool of carbon, but one that does not make sense to exploit. It takes a lot of energy to extract and refine this resource into useable fuel, and the mining is environmentally destructive. Adding this on top of conventional fossil fuels will leave our children and grandchildren a climate system with consequences that are out of their control. It makes no sense to build a pipeline system that would practically guarantee extensive exploitation of this resource. When other huge oil fields or coal mines were opened in the past, we knew much less about the damage that the carbon they contained would do to the Earth’s climate system and to its oceans. Now that we do know, it’s imperative that we move quickly to alternate forms of energy—and that we leave the tar sands in the ground. We hope those so inclined will join protests scheduled for August and described at tarsandsaction.org. If the pipeline is to be built, you as president have to declare that it is “in the national interest.” As scientists, speaking for ourselves and not for any of our institutions, we can say categorically that it’s not only not in the national interest, it’s also not in the planet’s best interest. Sincerely, James Hansen

Research Scientist

The International Research Institute for Climate and Society

The Earth Institute, Columbia University Ralph Keeling

Director, Scripps CO2 Program

Scripps Institution of Oceanography

...and 18 others. Complete list after the squiggle.

[Patriot Daily News Clearinghouse's diary taking an extensive look at tar sands and the Keystone XL pipeline will appear Sunday afternoon.]