ExxonMobil has had a horrible four-week run in the aftermath of its Pegasus pipeline break in Arkansas, but a just-published greenhouse gas emissions study by the company's research arm could provide a bit of a bright spot amidst the gloom. The new ExxonMobil study looks at the total lifecycle of natural gas from drilling to power generation, and concludes that its carbon footprint can be significantly lower than coal.
Lifecycle emissions are a huge issue for ExxonMobil and the natural gas industry. Natural gas emits far less greenhouse gases than coal when burned at power plants, but evidence has been emerging that this benefit could be completely wiped out by methane leakage at gas drilling fields and other earlier points in the lifecycle. So, before the cheering starts around the water coolers over at ExxonMobil or anywhere else, let's take a closer look at the new study.
Basically, the study (just published in the American Chemical Society's Environmental Science and Technology journal) found that the carbon footprint of the overall lifecycle of natural gas was 53 percent lower than coal. That finding is based on CO2eq, which is a standard unit of comparison among different greenhouse gases, including methane.
The main thing to note is that the study is specific to natural gas from the Marcellus shale region in the Northeastern U.S., which has become notorious due to its reliance on the natural gas drilling method known as fracking. That's significant because at the drilling stage of the natural gas lifecycle, rates of methane leakage can vary significantly from one gas field to another.
For example, while the ExxonMobil study indicates that methane leakage from gas fields in the Marcellus is relatively insignificant compared to overall lifecycle emissions from Marcellus gas, earlier this year the National Oceanic and Atmospheric Administration confirmed previous findings for a field located in Colorado that suggest the potential for far greater rates of methane leakage elsewhere.
Since the study compares Marcellus gas to "U.S. coal," that makes it pretty difficult to draw general conclusions about its usefulness for power plant owners who are seeking ways to reduce greenhouse gas emissions. The only real takeaway is that, so long as both coal and gas remain key players in the U.S. energy landscape, choosing one over the other in terms of reducing greenhouse gas emissions is an extremely complex proposition that calls for energy managers to delve deeply into comparative lifecycle emissions on a field-by-field, mine-by-mine basis rather than simply looking at power plant emissions.
Add to that the other risks involved in fracking, including water contamination and earthquakes related to wastewater disposal, and you've got an even cloudier idea about which fossil fuel is more sustainable than the other.
In recent years, Exxon has taken a more relaxed approach to promoting climate change denial, though possibly that is due less to a change of heart and more to the realization that climate change can work in its favor by enabling it to grow its natural gas operations at the expense of coal.
In that regard, it's also worth noting that that another notorious climate change denial voice, that of the Koch brothers, was one of the funders behind last year's Berkeley Earth Surface Temperature study (BEST). The study basically re-confirmed previous climate science findings, but that's not to say that the Koch brothers were dismayed at seeing their favored position blown to bits, since they also have a significant stake in the natural gas market.
[Image: Refinery flare by Kristian Dela Cour]
Tina writes frequently for TriplePundit and other websites, with a focus on military, government and corporate sustainability, clean tech research and emerging energy technologies. She is a former Deputy Director of Public Affairs of the New York City Department of Environmental Protection, and author of books and articles on recycling and other conservation themes. She is currently Deputy Director of Public Information for the County of Union, New Jersey. Views expressed here are her own and do not necessarily reflect agency policy.