Published: March 10, 2013 | NY Times

The State Department’s latest environmental assessment of the controversial Keystone XL oil pipeline makes no recommendation about whether President Obama should approve it. Here is ours. He should say no, and for one overriding reason: A president who has repeatedly identified climate change as one of humanity’s most pressing dangers cannot in good conscience approve a project that — even by the State Department’s most cautious calculations — can only add to the problem.

The 875-mile pipeline avoids the route of an earlier proposal that traversed the ecologically sensitive Sand Hills of Nebraska and threatened an important aquifer. It would carry 830,000 barrels a day of crude oil from the tar sands of Alberta to pipelines in the United States and then onward to refineries on the Gulf Coast. From there, most of the fuel would be sent abroad.

To its credit, the State Department acknowledges that extracting, refining and burning the oil from the tar-laden sands is a dirtier process than it had previously stated, yielding annual greenhouse gas emissions roughly 17 percent higher than the average crude oil used in the United States. But its dry language understates the environmental damage involved: the destruction of the forests that lie atop the sands and are themselves an important storehouse for carbon, and the streams that flow through them. And by focusing on the annual figure, it fails to consider the cumulative year-after-year effect of steadily increasing production from a deposit that is estimated to hold 170 billion barrels of oil that can be recovered with today’s technology and may hold 10 times that amount altogether.

It is these long-term consequences that Mr. Obama should focus on. Mainstream scientists are virtually unanimous in stating that the one sure way to avert the worst consequences of climate change is to decarbonize the world economy by finding cleaner sources of energy while leaving more fossil fuels in the ground. Given its carbon content, tar sands oil should be among the first fossil fuels we decide to leave alone.

Supporters of the pipeline have argued that this is oil from a friendly country and that Canada will sell it anyway. We hope Mr. Obama will see the flaw in this argument. Saying no to the pipeline will not stop Canada from developing the tar sands, but it will force the construction of new pipelines through Canada itself. And that will require Canadians to play a larger role in deciding whether a massive expansion of tar sands development is prudent. At the very least, saying no to the Keystone XL will slow down plans to triple tar sands production from just under two million barrels a day now to six million barrels a day by 2030.

The State Department will release a fuller review in early summer, and at some point after that the White House will decide. That decision will say a lot about whether Mr. Obama and his secretary of state, John Kerry, are willing to exert global leadership on the climate change issue. Speaking of global warming in his State of the Union address, Mr. Obama pledged that “if Congress won’t act soon to protect future generations, I will.” Mr. Kerry has since spoken of the need to safeguard for coming generations a world that is not ravaged by rising seas, deadly superstorms, devastating droughts and other destructive forces created by a changing climate.

In itself, the Keystone pipeline will not push the world into a climate apocalypse. But it will continue to fuel our appetite for oil and add to the carbon load in the atmosphere. There is no need to accept it.

>> Tell Pres. Obama to reject Keystone XL