Oil is not drilled, refined, shipped or burned equally, and climate assessments should reflect that, experts say.

Though tailpipe emissions from a gallon of gasoline remain similar whether the fuel came from shale or a deep-sea reservoir, the paths those hydrocarbons took to the tank have significant carbon footprints of their own.

These differences have big policy implications: The fight over the Keystone XL pipeline hinges on the project's carbon dioxide emissions, from the oil sands where production occurs to the energy needed to push the product more than 2,000 miles to Gulf Coast refineries to the cars and trucks that will eventually burn the oil.

President Obama said in 2013 that he would only approve the pipeline if it didn't "significantly exacerbate the problem of carbon pollution," so the numbers will play a role in deciding the ultimate fate of the project (ClimateWire, June 26, 2013).

However, making apples-to-apples comparisons between different oil streams has proved challenging, a problem experts tackled yesterday with the release of the Oil-Climate Index, a tool for comparing carbon emissions across the life cycles of different production methods.

Varying emissions from Iraq to Norway

Speaking yesterday at the Carnegie Endowment for International Peace in Washington, D.C., the institute's energy and climate program director, Deborah Gordon, explained that oil production methods have changed drastically in recent years.

"It used to be the case that a lot of crude was refined close to where it was consumed, which is why America has the biggest refining infrastructure at the moment," she said. Now, economics and geopolitics have expanded the supply chain.

"It's not unusual to have a crude start in Saudi Arabia, come to the Aramco refinery in Houston to be refined and have the product go back out to China," Gordon added. "There are greenhouse gas implications of that, but there are probably more geopolitical, strategic and environmental concerns about that."

In addition, with low oil prices, some producers are storing oil instead of selling it right away, waiting for the supply glut to dissipate, further obfuscating the emissions picture.

In an attempt to offer clarity, the Oil-Climate Index looks at 30 oils, including crude from the Zubair oil field in Iraq, the Alaska North Slope in the United States and the Ekofisk field in Norway. Researchers found that per barrel, there was an 80 percent emissions difference between the least and most carbon-intensive oils. As oil companies tap more unconventional oil reserves, this gap will likely grow.

"The biggest differentiator between the emissions of different crudes is the amount of hydrogen consumed to process these crudes, how much hydrogen you need to add in order to convert your crude oil into a lighter product like gasoline or diesel," said Joule Bergerson, an assistant professor of chemical and petroleum engineering at the University of Calgary.

The experts were cautious about using this tool to derive specific policies but suggested it could be a helpful guideline.

"What the Oil-Climate Index shows are the potential pitfalls ... of making environmental policy or climate policy on an ad-hoc basis," said David Livingston, an associate in Carnegie's Energy and Climate Program. Given oil's global span, Livingston said, the index would help lawmakers target the biggest emissions sources in the supply chain in comprehensive legislation.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500