Running to the Gulf of Mexico from Alberta's oil fields, the pipeline would cut through the Great Plains and threaten oil spills into the Oglalla aquifer, the single largest source of fresh water in the United States. Though federal permits haven't yet been granted, landowners on the pipeline's path have been threatened with eminent domain land seizures; the federal review process has been corrupt, steered by oil company executives with insider connections and industry-hired consultants.

Despite those problems, however, Keystone XL probably wouldn't be so controversial if it carried oil from old-fashioned, stick-a-tube-in oil fields. It doesn't. Alberta's vast oil deposits are dirty and hard to reach, mixed into sand or locked deep underground. Recovering the oil is a hugely energy-intensive process, multiplying its climate footprint at a moment when extreme weather is getting worse. And if the probabilistic links between climate and weather feel fuzzy, there's nothing nebulous about the apocalyptic landscapes that Albertan oil extraction leaves behind. Primeval forests and bogs are denuded and drained, replaced by barren slopes and toxic ponds. It may take centuries for life there to recover.

"It is surreal," said Jennifer Grant, who directs the oil sands program at the Pembina Institute, an Alberta-based environmental conservation group. "It is such a vast area. From the air, you can see over 170 square kilometers" -- 65 square miles -- "of tailings ponds alone. It's astonishing to see the sheer scale."

On the following pages, Wired.com takes a tour of Pembina's tar sands photographs.

Image: Suncor's Millennium Oil Sands Mine. The yellow spots at upper right are among the largest trucks in the world. (David Dodge/Pembina Institute)