How large? Some say really large, for peat's sake.
Canadian oil sands are back in the news. President Obama announced last week that he would "fast-track" development of the southern portion of the Keystone XL pipeline, the proposed avenue that would bring bitumen from Canadian oil sands to refineries in Texas. But there was another aspect of the oil-sands debate that might have missed the headlines but remains a hot topic in the scientific community: is the carbon footprint of oil sands larger than that of conventional oil? And if so, by how much?
Oil Sands: A Short Primer
The oil sands under discussion underlay a vast region of Alberta. To extract "oil" from these oil sands (also called tar sands, especially in the United States, because of the stuff's sticky-goo quality) typically requires mining the heavy, viscous, tar-like hydrocarbon locked up in these deposits à la coal. Once extracted, the oil sands go through a separation process to get rid of the sand and clay and extract the bitumen, which is then "upgraded" into a synthetic blend or diluted so it can "flow" like oil. Once flowable, it can be sent off to a refinery for final processing.
It is also possible to extract the bitumen without mining; such in-situ methods are expected to become more common once those deposits accessible by surface mines are exhausted. (To see what in-situ mining looks like, check out the Pembina Institute's photos.)
Going Well-to-Wheels in Search of a Carbon Footprint
Because of all the energy required to first extract oil-sands bitumen and then convert it to a standard crude, the accepted wisdom has been that the carbon dioxide (CO2) emissions from oil sands are larger than those of conventional oil. How much larger?
The answer to that question is typically found using something called a well-to-wheels life-cycle analysis, a thorough examination that accounts for all the greenhouse gases emitted over the entire life cycle of the fuel, from the initial well or mining development to the final stage of the fuel's combustion.
(It turns out that not all well-to-wheels analyses are created equal, so to speak. Some consider more of the processes related to the production of a product; others consider fewer. In the case of oil sands, this is especially true of so-called indirect emissions, such as those that might arise from land-use changes or vented emissions.)
For years, I (and many of my colleagues) most often turned to work by Alexander Farrell and Adam Brandt (then both of the University of California at Berkeley) that was published in 2006 in the journal Environmental Research Letters. Their estimate: oil sands, like heavy oil, emitted about 40 percent more CO2 than conventional oil (see figure). (In a 2011 report, Brandt estimated the carbon footprint for a likely oil-sands blend to be about 20-percent larger than that of a conventional oil blend used in Europe.)
|These estimates suggest that oil-sands crude has a significantly larger carbon footprint than conventional oil but are not the worst of the liquid fuels potentially available. By far, the worst is oil shale -- dirty stuff but available in plentiful supplies in Colorado, Utah, and Wyoming. (Source: A E Farrell and A R Brandt, "Risks of the Oil Transition," Environmental Research Letters, 30 October 2006. Used with permission.)|
But now there's another analysis out there suggesting that oil sands' carbon footprint is quite a bit smaller.
Authored by the energy consulting firm IHS CERA, it estimates that oil sands' well-to-wheels emissions are only 5- to 15-percent higher than those from conventional oil burned in the United States, and that "the average oil sands import to the United States has well-to-wheels life-cycle [greenhouse gas] GHG emissions about 6 percent higher than the average crude oil refined in the United States." (Note that the lower carbon footprint is in part due to the fact that what flows through the pipeline from Canada is not just bitumen but a mix of synthetic crude oil and bitumen diluted with condensates.)
Why such different numbers between analyses? The main reason is that well-to-wheels studies vary considerably and have yet to become standardized. Writing in the journal Environmental Science and Technology last December, Brandt (now at Stanford University) found that the top five life-cycle models differed by as much as 40 percent in estimating upstream emissions for oil-sands oil.
For some folks like New York Times columnist Joe Nocera, who accepts IHS CERA's estimates, a 6-percent carbon-footprint penalty is not enough to fuss over -- certainly not enough to "doom the planet," and so we may as well get down with the Keystone pipeline.
But Then There's the Peat Forsaking
Is 6 percent enough to worry about when you're trying to find a pathway to reverse the world's trend toward ever-increasing greenhouse gas emissions? I suspect we're not going to get a unanimous answer on that one. But I don't think that's the question we should be asking ourselves here.
The right question is: Are we counting all the carbon in the oil-sands footprint? The answer to that question is almost surely no.
Extraction of oil sands often means the destruction of peat bogs -- ecosystems that are among the world's richest depositories of carbon. When those bogs are destroyed, the carbon stored in them eventually ends up as CO2 in the atmosphere. If you want a total accounting of CO2 emissions from oil-sands exploitation, a well-to-wheels analysis that does not include land-use change won't cut it -- you must include the effect of the land-use disturbance from mining, and most do not. Of the five models reviewed by Brandt last December, only one included the carbon from land-use changes. Is that significant?
A paper by Rebecca Rooney of the University of Alberta and colleagues published last week in the Proceedings of the National Academy of Sciences suggests that it can be quite significant. To get an estimate of just how large, the authors compared pre- and (planned) post-mining landscapes for four representative mines within Canada's oil-sands region, and then scaled up their results to evaluate the impact that the landscape changes would have on carbon storage over the entire region.
The authors found that after mining, the peatlands that currently dominate the region would be reduced by 65 percent. That loss would be a double whammy, because not only would a significant slug of carbon be emitted (on the order of 40 to 175 million metric tons of CO2, or as much as seven years' worth of tar-sands emissions at 2010 production levels), but less carbon would be sequestered in the future. An independent 2010 study by Sonia Yeh of the University of California (Davis) and colleagues estimated that the carbon footprint of the land-use component of mining peatlands would be double those without peat.
As the presidential election season swings into high gear, it appears that President Obama has decided to answer the Republican "drill, baby, drill" refrain with one that's not all that different: "all of the above." Take your pick. Either one may mean "warm, baby, warm."
This post originally appeared on TheGreenGrok.
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