The libertarian conservative Koch brothers and the progressive liberal Tom Steyer are in a billionaire's showdown in the current election cycle, spending heavily in Congressional races across the country on their favorite candidates.

In an odd twist, the counterpunching last week was over culpability for carbon pollution.

The Koch brothers got to watch Steyer take an uppercut from an unexpected source—the New York Times. The paper took aim at Steyer—climate champion and Keystone XL pipeline foe—for having profited handsomely in the not-too-distant past from financing coal plants.

It was a bitter irony for Steyer's climate activist supporters that he emerged from the ring bruised as a carbon polluter. They blamed the Times for delivering the Kochs' sucker punch.

Tom Steyer/Credit: Fortune Brainstorm Green 2013

A blog called Powerline with ties to Charles and David, the activists said, was the source of the Times story, and they faulted the paper for doing a hit piece on a man who has repented his history with coal and has since made tackling climate change his life's goal.

Steyer's turnaround took moral courage, they argued, and asked: What about the Koch brothers? What is their history with global warming emissions?

It turns out the Koch brothers built their first fortune on the particularly dirty form of oil mined in Alberta's tar sands, where they have been major players for 50 years, and remain deeply invested.

The key moment came in 1969, when Charles Koch secured full ownership of a heavy oil refinery in Minnesota that his father had a stake in.

In his 2007 book Charles Koch called that acquisition "one of the most significant events in the evolution of our company." The refinery was a doorway that permitted Koch Industries "to enter chemicals and, more recently, fibers and polymers," he said.

Today the refinery processes about 320,000 barrels of tar sands oil every day, and accounts for a substantial but unknown fraction of the greenhouse gas emissions of the sprawling Koch Industries conglomerate.

Below is an interactive timeline that tells the story of the Kochs' 50 years in the tar sands. It updates an in-depth story InsideClimate News published in 2012.