Quantifying the Invisible: Getting a Handle on Methane's Climate Impact
- Robin Beckwith (Staff Writer JPT/JPT Online)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- November 2011
- Document Type
- Journal Paper
- 54 - 57
- 2011. Copyright is held partially by SPE. Contact SPE for permission to use material from this document.
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Earlier this year, a Cornell University professor made quite a splash publishing a paper asserting that emissions from shale gas rivaled those from coal. A July 2011 study issued by the Post Carbon Institute underscored this conclusion. Not so, say five separate recent reports—from Carnegie Mellon University, IHS Cambridge Energy Research Associates (CERA), the US National Energy Technology Lab-oratory (NETL), Argonne Laboratory, and Deutsche Bank Climate Change Advisors (coauthored by individuals from Worldwatch Institute and ICF International). At heart are issues related to measuring and quantifying emissions of an odorless, colorless gas—methane (CH4)—considered the second-most prevalent long-lived greenhouse gas after carbon dioxide (CO2).
The conventional wisdom is that natural gas is “cleaner” than coal. This is indisputable when considering its combustion. For an equivalent amount of heat, natural gas combustion produces about 30% less CO2 than petroleum combustion and about 45% less CO2 than coal combustion. However, the contention these studies wrestle with is that the release of methane during the life cycle associated with natural gas extraction—including drilling, hydraulic fracturing, completions, production, processing, and transport—could be great enough to outweigh this benefit.
Why Atmospheric Methane Matters
According to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), issued in 2007, “over the last 650,000 years, ice core records indicate that the abundance of CH4 in the Earth’s atmosphere has varied from lows of about 400 ppb during glacial periods to highs of about 700 ppb during interglacials.” In 2005, the report states, the global average abundance of CH4, measured at a network of 40 surface air flask sampling sites in both hemispheres, was 1,774.62 ±1.22 ppb. It would thus appear that present atmospheric levels of CH4 are unprecedented in at least the last 650,000 years. According to figures released by the US National Oceanic & Atmospheric Administration, CH4 is responsible for 18% of global warming since the beginning of the Industrial Revolution, while CO2 is responsible for 64%.
According to Martin Heimann in Enigma of the Recent Methane Budget, published in the 11 August 2011 issue of Nature, “About 60% of global methane stems from human activities. This includes emissions associated with energy production and usage—such as coal mining, incomplete combustion of fossil fuels, and gas leaks. These fossil-fuel-derived emissions, together with methane from landfills, organic waste, cattle raising, rice agriculture, and bio-mass burning, were probably the main cause of the increasing concentrations after pre-industrial times.”
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