A disputed claim by Al Gore about the carbon emissions generated by filling up two iconic cars with heavy Canadian oil sands crude has been removed from the former vice president and Nobel Prize winner's website.

Gore asserted a year ago this month, as environmentalists were gearing up to protest the Keystone XL pipeline at the White House, that the carbon dioxide generated by burning oil sands crude was significant enough to give a Toyota Prius running on the fuel "the same impact on climate" as a conventional gas-guzzling Hummer. While it remains in a column Gore cross-published at The Huffington Post, the charge is no longer present in the version of the same piece housed on his personal website.

The removal was first spotted yesterday by Michael Levi, a senior fellow in energy at the Council on Foreign Relations who challenged Gore's reasoning last year. It is unclear when the sentence, which also appears in the famed climate activist's book "Our Choice," was excised from his home page.

"It's great to see that he's come around," Levi said in an interview, noting that the former vice president's camp had defended its math as recently as November.

In end notes for "Our Choice," Gore explains his Hummer-Prius argument by citing a 2008 Energy Department study that found synthetic crude from Canada to generate about five times the carbon of conventional oil in the extraction and processing phases. Diluted bitumen, the type of oil sands crude most frequently criticized by green groups, generated slightly more than three times the carbon of conventional oil in that study.

Comparing that 5-to-1 ratio to the Hummer's 3-to-1 average fuel efficiency advantage over a Prius, Gore wrote, shows that "the greater CO2 emissions resulting from the extraction and processing of oil from tar sands overwhelm the fuel economy benefits."

But as Levi pointed out and the Congressional Research Service (CRS) reaffirmed in a report last month, comparing "well to tank" estimates for extraction and processing to "well to wheels" estimates for different autos makes for an apples-to-oranges comparison, given that the process of burning gasoline remains the primary source of carbon dioxide generated by driving a car.

"Neither the Hummer nor the Prius is moving bitumen around in northern Alberta," Levi said. "It's the emissions from burning that fuel that dominate the consequences."

CRS concluded in its analysis that well-to-wheels carbon emissions for Canadian oil sands crude were comparable to gasoline from Nigerian or Venezuelan crude and about 22 percent higher than those from U.S. domestic crude.

The oil industry, which has battled environmentalists' emissions claims about oil sands crude since Keystone XL became a political flash point in 2010, hailed the appearance of a quiet pullback from Gore.

"At some point, and maybe this is that point, you'd hope that even opponents of oil sands development would acknowledge the basic science here," Shannon Brushe, a spokeswoman for the industry-funded Oil Sands Fact Check campaign, said via email.

"Combustion is where three-quarters of emissions come from, no matter if that fuel started its life in Alberta, Texas, Nigeria or Saudi Arabia," Brushe wrote. "It's not politics, it's physics. And hopefully this change by the former vice president helps underscore that even more."